Highway Material Testing Manual Dr. PVSN Pavan Kumar

HIGHWAY MATERIAL TESTING MANUAL

Dr. PVSN PAVAN KUMAR Professor, Guru Nanak Institutions Technical Campus 1

INDEX

INDEX .......................................................................................................................................2 LIQUID LIMIT..........................................................................................................................4 PLASTIC LIMIT .......................................................................................................................7 FIELD DRY DENSITY BY CORE CUTTER METHOD........................................................9 FIELD DRY DENSITY BY SAND REPLACEMENT METHOD ........................................12 HYDROMETER ANALYSIS .................................................................................................16 SIEVE ANALYSIS .................................................................................................................22 PERMEABILITY TEST – CONSTANT HEAD METHOD ..................................................26 PERMEABILITY TEST – VARIABLE HEAD METHOD ...................................................30 STANDARD PROCTOR COMPACTION TEST ..................................................................33 MODIFIED PROCTOR COMPACTION TEST.....................................................................37 CALIFORNIA BEARING RATIO TEST (HEAVY COMPACTION)..................................40 CALIFORNIA BEARING RATIO TEST – LIGHT COMPACTION ...................................44 CONSOLIDATION TEST ......................................................................................................48 UNCONFINED COMPRESSION TEST ................................................................................53 TRIAXIAL COMPRESSION TEST .......................................................................................58 DIRECT SHEAR TEST ..........................................................................................................66 VANE SHEAR TEST..............................................................................................................72 SHRINKAGE LIMIT ..............................................................................................................76 SPECIFIC GRAVITY OF SOIL .............................................................................................79 AGGREGATE CRUSHING VALUE .....................................................................................82 AGGREGATE IMPACT VALUE ..........................................................................................85 SPECIFIC GRAVITY AND WATER ABSORPTION ..........................................................88 AGGREGATE ABRASION TEST (DEVAL MACHINE) ....................................................91

2

AGGREGATE ABRASION TEST (Los Angeles Machine) ..................................................94 FLAKINESS INDEX...............................................................................................................98 ELONGATION INDEX ........................................................................................................102 BITUMEN PENETRATION TEST ......................................................................................106 DUCTILITY TEST................................................................................................................109 SOFTENING POINT TEST ..................................................................................................112 FLASH AND FIRE POINT TEST ........................................................................................115 NORMAL CONSISTENCY OF CEMENT ..........................................................................117 FINENESS OF CEMENT .....................................................................................................120 INITIAL SETTING AND FINAL SETTING TIME OF CEMENT.....................................122 SOUNDNESS OF CEMENT ................................................................................................125 COMPRESSIVE STRENGTH OF CEMENT ......................................................................127 WORKABILITY OF CONCRETE BY COMPACTION FACTOR ....................................130 WORKABILITY OF CONCRETE BY SLUMP TEST........................................................133 WORKABILITY OF CONCRETE BY VEE - BEE CONSISTOMETER METHOD.........136 COMPRESSIVE STRENGTH OF CONCRETE..................................................................138 BULKING OF SAND............................................................................................................141 FLEXURE STRENGTH OF CONCRETE ...........................................................................143

3

LIQUID LIMIT (IS 2720 Part V - 1985) Aim: To determine the liquid limit of the given soil sample (-425 micron sieve) Equipment & Accessories: Casagrande Liquid limit device, grooving tool, porcelain dish, 425 micron sieve, spatula, balance (0.01 gm sensitivity), water content cans, oven, distilled water.

Fig.1 Casagrande apparatus Theory: Liquid limit is the water content at which the soil passes from zero strength to an infinitesimal strength; hence the true value of liquid limit cannot be determined. For determination purpose liquid limit may be defined as the water content at which a part of soil, cut by a groove of standard dimensions, will flow together for a distance of 1.25 cm under an impact of 25 blows in a standard liquid limit apparatus. Procedure: 

Adjust the cup of the liquid limit apparatus with the help of tool gauge and adjustment plate to give a drop of exactly 1cm on the point of contact on base. 4



Take about 120gms of air-dried sample passing 425μ sieve.



Mix it thoroughly with known quantity of distilled water to form a uniform taste.



Place a portion of the paste in the cup. Smooth the surface with spatula to a maximum depth of 1cm. Draw grooving tool through the sample along the symmetrical axis of the cup, holding tool perpendicular to the cup.



Turn the handle at a rate of 2 revolutions per second and count blows until the two parts of the sample come in contact at the bottom of the groove along a length of 1.25cm.



Determine the moisture content of portion of soil where two parts come in contact.



Transfer the remaining soil in the cup to the main soil sample and mix thoroughly after adding a small amount of water.



Repeat the steps 4, 5 and 6. Obtain at least five sets of readings in the range of 10 to 50 blows.

Fig.2 Liquid limit test Observations & Calculations: Table. 1 Observations of Liquid limit Container No.

Empty wt. of container

24 42 36 13

34.15 33.86 31.29 35.42

Empty wt. of container + weight of wet soil 46.17 44.52 47.24 48.31

Empty wt. of container + weight of dry soil 41.90 41.06 42.60 44.97

Moisture content (%)

No. of blows

55 48 41 35

12 18 26 35

5

Graph: Plot a straight line graph between number of blows (Log scale) and water content (ordinary scale). Water content corresponding to 25 blows is the liquid limit.

Moisture Content (%)

60

50

40

30 25 20 10

100

Fig.3 Model Graph Result: Liquid limit of the given soil sample = 42%

6

PLASTIC LIMIT Aim: To determine the plastic limit of the given soil fraction passing through 425 micron sieve. Equipment & Accessories: 3mm diameter rod, balance, glass plate, distilled water, oven, water content cans.

Fig.1 Plastic limit test Theory: The moisture content at which soil has the smallest plasticity is called the plastic limit. For the determination purpose, the plastic limit is defined as the water content at which a soil will just begin to crumble when rolled into a thread of 3mm diameter. The difference in moisture contents between the liquid limit and plastic limit is termed as plasticity index. Knowing the liquid limit and plasticity index, soil may be classified with the help of plasticity chart according to Indian standard soil classification (IS 1498-1970).

Procedure: 

Take about 30gm, of air dried sample passing through 425 micron sieve.



Mix thoroughly with distilled water on the glass plate until it is plastic enough to be shaped into a small ball.



Take about 10gm of the plastic soil mass and roll it between the hand and the glass plate to form the soil mass into a thread. If the diameter of thread becomes less than 3mm without cracks, it shows that water added is more than plastic limit; hence the soil is kneaded further and rolled into thread again. 7



Repeat this rolling and remolding process until the thread starts just crumbling at a diameter of 3mm.



If crumbling starts before 3mm diameter thread, it shows that water added is less than the plastic limit of the soil, hence some more water should be added and mixed to a form mass and rolled again, until the thread starts crumbling at a diameter of 3mm.



Collect the pieces of crumbled soil thread at 3mm diameter in an air tight container and determine the moisture content.



Repeat this procedure for two more samples

Observations & Calculations:

Trial No. Container No. 1 32 2 44 3 52

Table.1 Observations of Plastic limit Wt. of Wt. of wet soil Wt. of dry soil container + container + container 34.15 46.17 38.14 33.86 44.52 37.46 31.29 47.24 36.64

Plastic limit = Moisture content 33.20 33.78 33.54

Result: Average plastic limit of the given soil = 33.51% Plasticity Index of the given soil = Liquid Limit – Plastic limit QUESTIONS 1. 2. 3. 4. 5. 6. 7.

How is the plastic limit defined to determine it in the laboratory? What is the degree of saturation at liquid limit and plastic limit? How does oven dry soil sample affect the value of plastic limit? If a thread of 5mm is made instead of 3mm what is the effect on plastic limit? What is the shear strength of soil at liquid limit? What is A – line? Explain its significance What type of soil sample is used for determination liquid and plastic limits?

8

FIELD DRY DENSITY BY CORE CUTTER METHOD IS 2720 (Part 29) : 1975 Aim: To determine the in-situ density by core cutter method. Equipment & Accessories: Cylindrical core cutter, steel rammer, steel dolly, balances (0.01gm, 1gm), steel rule, spade, straight edge, knife, water content cans, oven.

Core cutter Mould

Rammer

Dolley

Fig.1 Core cutter apparatus Theory: Density is defined as the mass per unit volume of soil and can be expressed g/cm 3 or t/m3 or kg/m3. When the density is defined as the ratio of weight of total soil mass to the total volume, it is called wet density or bulk density. It can be denoted by γ. When the density of a soil is defined as the ratio of weight of soil grains to the total volume, it is termed as dry density and is denoted by γd. The following is the relation between dry density, bulk density and moisture contents:

d 

 1 w

Density is used in calculating the stress in the soil due to it’s over burden pressure. It is needed in estimating the bearing capacity of soil foundation system, settlement of footings, earth pressures behind the retaining walls and embankments, stability of slopes, dams etc. Permeability of a soil depends on its density and it is by knowing the dry density, relative density of a cohesionless soil can be determined. 9

Procedure: 

Measure the height of and internal diameter of the core cutter and calculate its volume.



Weigh the clean core cutter.



Clean and level the place where the density is to be determined.



Apply grease inside and outside the core cutter and place the dolly on the top of the cutter.



Ram the core cutter into ground to its full depth with the help of steel rammer.



Remove the soil round the cutter by spade or pick axe.



Lift the core cutter, trim the top and bottom surfaces of the sample carefully and clean the outside surface of the cutter.



Weigh the core cutter with soil.



Remove the soil core from the cutter and take a representative sample to determine moisture content and hence dry density.

Observations & Calculations: Dia. of the core cutter

= 10 cm

Height of core cutter

= 13 cm

Volume of core cutter Weight of core cutter Weight of core cutter + Soil

= V = 1021 cm3 = W1 = 1130 g = W2 = 3120 g

Weight of soil

= W2 – W1 = W = 1990 g

Bulk density

= 

Can No. : Weight of empty can Weight of can + wet soil

24 = 20.12 g = 44.32 g

Weight of can + dry soil

= 41.38 g

Moisture content

= w = 14.91%

Dry Density

= γd =

W = V

= 1.95 g/cc

 = 1.95/(1+.149) = 1.70 g/cc 1 w

Bulk density of the soil

= 1.95 g/cc

Moisture content Dry Density of the soil

= 14.91% = 1.70 g/cc QUESTIONS 10

1.

What is the difference between the air dried and oven dried sample?

2.

Why the soil samples are dried at 105 to 110ºC? Why not less or more than this range?

3.

What are the practical applications of moisture content in the field problems?

4.

Why does the quantity of soil taken for determination of moisture content depend on the size of the soil particles? (more quantity for large size particles and less for smaller or fine particle soils)

5.

What are free pore water and water of hydration? Which one is determined in this test? Explain

6.

What is the difference between the specific gravity of soil grains and soil?

7.

What are dry, wet, saturated and submerged unit weights of soil?

8.

Out of different densities which is maximum and which is minimum?

9.

What is the degree of saturation in oven dry soils?

10. In fully saturated soils, what is the degree of saturation? 11. In which type of soil, core cutter test of field density is preferred, Why?

11

FIELD DRY DENSITY BY SAND REPLACEMENT METHOD IS 2720 (Part 28) : 1974 Aim: To determine the in – situ density by sand replacement method Equipment/Accessories: Sand Pouring Cylinder, trowel, cylindrical calibrating container, metal tray with hole at center, sand (clean, oven dried, passing 600 micron sieve), balances ( 1gm, 0.01gm), oven, moisture content cans, scraper tools.

Fig.1 Sand replacement apparatus Theory: Density is defined as the mass per unit volume of soil and can be expressed g/cm3 or t/m3 or kg/m3. When the density is defined as the ratio of weight of total soil mass to the total volume, it is called wet density or bulk density. It can be denoted by γ. When the density of a soil is defined as the ratio of weight of soil grains to the volume, it is termed as dry density and is denoted by γd. The following is the relation between dry density, bulk density and moisture content:

d 

 1 w

Density is used in calculating the stress in the soil due to it’s over burden pressure. It is needed in estimating the bearing capacity of soil foundation system, settlements of footings, earth pressures behind the retaining walls and embankments, stability of slopes, dams etc. Permeability of a soil depends on its density and it is by knowing the dry density, relative density of a cohesionless soil can be determined. Procedure: A. Calibration of apparatus 

Measure the internal volume of calibrating container from the volume of the water required to fill the container.



Fill the pouring cylinder with sand about 1 cm from top and weigh it. 12



Place the pouring cylinder on a plane surface, open the shutter and allow the sand to run out. When there is no movement of sand in the cylinder, close the shutter and weigh it with remaining sand.



Place the pouring cylinder with remaining sand concentrically on the top of the calibrating container.



Open the shutter to allow the sand to run out and fill the calibrating cylinder.



When there is no further movement of sand in the cylinder, close the shutter.



Weigh the pouring cylinder to nearest gram.

B. Measurement of soil density 

Clean and level the ground where the field density is required.



Fill the pouring cylinder with dry sand with in about 1.0cm of the top and weigh it.



Place the metal tray with central hole over the portion of the soil to be tested.



Excavate the soil approximately 10cm, diameter and 15cm, deep with chisel, bend spoon etc. The hole in the tray will guide the diameter of the hole to be made in the soil.



Collect the excavated soil in metal tray and weigh it to nearest gram.



Determine the moisture content of the excavated soil.



Place the pouring cylinder over the hole so that base of the cylinder covers the hole concentrically.



Open the shutter and allow the sand to run out into the hole. When there is no movement of sand, close the shutter.



Remove the cylinder and weigh it.

13

Fig. 2 Sand replacement test

Observations & Calculations:

A. Calibration of apparatus Wt. of pouring cylinder + sand = W1

11040 g

Wt. of pouring cylinder + sand after filling the conical bottom = W2

10590 g

Wt. of sand in conical bottom = W1 – W2 = W3

450 g

Wt. of pouring cylinder + sand after filling the calibrating cylinder = W4

9570 g

Wt. of sand in calibrating cylinder = W1 – W4 = W5

1470 g

Volume of calibrating cylinder = V =

980 cc

Density of sand (γsand) = W5/V = 1470/980

1.5 g/cc

B. Measurement of soil density Wt. of pouring cylinder + sand = W6 =

11040g

Wt. of pouring cylinder + sand after filling the hole and cone= W7

8823g

Wt. of sand in hole = W8 = W6 – W7 – W3

1767g

14

Wt. of excavated soil = W9

2415g

W 9  Bulk density of soil =    sand W8 

2.05 g/cc

Moisture content determination Can no. = Wt. of empty can =

26

Wt. of can + wet soil =

43.22g

Wt. of can + dry soil =

42.46g

Moisture content =

9.2%

Dry density of the soil =

1.88 g/cc

Bulk density of soil =

2.05 g/cc

Water content = Dry density of soil =

9.2% 1.88 g/cc

34.15g

Result: Field bulk density = 2.05 g/cc Water content = 9.2% Field dry density = 1.88 g/cc QUESTIONS 1.

Why it is preferred to keep the depth of hole equal to the height of calibrating cylinder?

2.

What happens if conical portion is not there at the bottom of pouring cylinder?

3.

In what type of soils is this method of determination of field density preferred?

4.

What is the inclination of conical portion approximately equal to?

5.

In field densities, why do we give importance to dry density than wet density?

15

HYDROMETER ANALYSIS IS 2720 (Part 4) - 1985 Aim: To determine the percentages of various soil grains (finer than 75μ ) by hydrometer analysis Equipment & Accessories: Hydrometer (Calibrated at 27ºC, range 0.995 to 1.03) graduated cylinders (1000ml), dispersing agent (containing 33 gm of sodium hexameta-phosphate and 7gm of sodium carbonate in distilled water to make one liter of solution), mechanical stirrer (high speed 75000rpm), balance, stop watch, scale and distilled water.

Fig.1 Hydrometer Theory: Hydrometer analysis is based on stokes law which defines the velocity of a freely falling sphere through a liquid.

v

2  s  l  2  r 9   

γs = density of sphere, r = radius of sphere γl = density of liquid, η = viscosity of liquid v= velocity of sphere or terminal velocity 16

By applying the above law to a soil particle suspended in distilled water, the terminal velocity of the soil particle will be given by

gD 2 G  1ρw v 18η If v 

He where He = height of fall of particle in cm, t = time in minutes 60t

We get D 

0.3 He He . M g (G  1)  w t t

Where M 

0.3 g (G  1)  w

Eqn. 1

The percentage finer N based on the weight Wd is calculated from the following equation  G  R N   100   G 1 M s

Eqn.2

where G = Average specific gravity of soil grains Ms = Weight of dry soil sample taken from the soil passing 75μ sieve R = (ρ -1) 1000 ρ = Hydrometer reading Procedure: 

Soil containing considerable amount of organic matter, or calcium compounds, pretreatment of the soil with hydrogen peroxide or hydrochloric acid may be necessary. If the soil consists of less than 20% of the above substances pre-treatment is avoided.



Take 50gm of dry pre treated soil (passing through 75 micron sieve) and add 100ml of dispersing agent and mix it thoroughly.



Transfer the sample to the cup of mechanical stirrer using distilled water until the cup is ¾ th full and operate the mixer for about 15 minutes.



After stirring, wash the suspension into 1000cc. graduated jar and add enough water to bring the level to 1000 cc mark.



Mix thoroughly the suspension in the jar by placing the palm of the hand in the open end and turning the jar upside down and back. 17



Place the jar on the table and insert the hydrometer. Start the stop watch simultaneously.



Read the top of the meniscus at 1/2, 1, 2, 4, 9, 15, 30 minutes and after one hour, tabulate the values as shown below.



Note the length of the bulb (h). Note the distance between the stem of the hydrometer to the graduations of the hydrometer (H).



Weigh the hydrometer and note the distance two graduations on the measuring jar.

Fig.2 Principle of hydrometer method Observations & Calculation: Ave. specific gravity of soil grains = G = 2.67 C/s area of the jar = A =

Volume between two graduations = 29.94 cm2 Dis tan ce between two graduations

V = Volume of hydrometer in cc (weight of hydrometer in grams) = 90 cc Constant factor = M = 0.00136 Height of bulb = h = 17 cm Calibration of hydrometer

18

He = H +

V  1 h  H  2 A  Table. 1 Calculation of effective height, He

Sl No.

Hydrometer reading, 

1 2 3 4 5 6 7 8

R = (ρ-1) x1000

1.030 1.025 1.020 1.015 1.010 1.005 1.000 0.995

30 25 20 15 10 5 0 -5

Distance between the stem of the hydrometer to the graduations of the hydrometer, H, cm 7.07 8.85 10.63 12.41 14.18 15.96 17.74 19.52

Calibration Chart

Effective depth, He cm

22 20 18 16 14 12 10 8 6 4 2 0 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Hydrometer Reading

Fig. 3 Calibration chart Table. 2 Calculation of particle size and percent finer Time in minutes t

Hydrometer reading ρ

R = (ρ-1) x1000

He (obtained from calibration chart)

0.5 1 2

1.0295 1.0265 1.0235

29.5 26.5 23.5

7.25 8.32 9.38

Particle size D, from Eqn.1 in mm 0.052 0.039 0.029

Percentage finer, N Eqn. 2 98.26 88.27 78.27 19

4 8 15 30 60 120 240 480 1440

1.0205 1.017 1.014 1.011 1.0085 1.0065 1.0045 1.0035 1.0035

20.5 17 14 11 8.5 6.5 4.5 3.5 3.5

10.45 11.70 12.76 13.83 14.72 15.43 16.14 16.49 16.49

0.022 0.016 0.013 0.009 0.007 0.005 0.004 0.003 0.001

68.28 56.62 46.63 36.64 28.31 21.65 14.99 11.66 11.66

Graph:

Percent Finer By Weight

Plot the calibration chart between the hydrometer on x-axis and effective height ‘He’ along yaxis. Plot the grain size distribution curve. Read the diameters corresponding to 60%, 30% and 10% finer and calculate coefficient of curvature and uniformity coefficient.

100 90 80 70 60 50 40 30 20 10 0 0.001

D30 = 0.007 mm D60 = 0.002 mm

0.010

D60 = 0.018 mm

0.100

Diameter in mm

Fig.4 Grain size curve Coefficient of curvature = D60/D10 = 9 Uniformity coefficient = D302/(D60 x D10) = 0.0022/(0.018*0.002) = 0.11 Result: Classification: Fine grained silty soil QUESTIONS 1.

What is hydrometer?

2.

What is stroke’s law? How does it helps in hydrometer analysis?

3.

What is hydrometer calibration? Where it is used? 20

4.

What does hydrometer measure?

5.

What is meniscus correction? How do you determine it? What is its use?

6.

What is the effect of the size of soil particles on their velocity in soil water suspension?

7.

When do you go for hydrometer analysis?

21

SIEVE ANALYSIS IS : 2720 (Part 4) - 1985 Aim: To determine grain size distribution of coarse grained soils passing through I.S. 4.75 mm sieve and retained on 75μ sieve. Equipment & Accessories: Set of I.S. Sieves: 4.75mm, 2.0mm, 1.0mm, 600μ, 425μ, 300μ, 150μ, 75μ, balances accurate to g. and 0.1gm, sieve brushes, sieve shaker.

Fig.1 Stacking of sieves

Theory: The percentage of various sizes of particles in a given dry soil sample is found by particle size analysis or mechanical analysis. The following analysis is performed in two stages. i) Sieve analysis

ii) Sedimentation analysis

Sieve analysis is meant for coarse grained soils only, with sedimentation analysis is performed for fine grained soils (-75μ) The sieve analysis is the true representative of grain size distribution as the test is not affected by temperature etc. In the Indian standard (IS 460 – 1962), the sieves are designated by the size of the aperture in mm. Application: The grain size distribution curve gives an idea regarding the gradation of the soil i.e., it is possible to identify whether a soil is well graded or poorly graded. In mechanical soil stabilization, the main principle is to mix a few selected soils in such proportion that a 22

desired grain size distribution is obtained for the design mix. Hence for proportioning the selected soils, the grain size distribution of each soil is to be first known. Procedure: 

Weigh 500g of oven dry representative soil sample.



Wash the sample with addition of water on 75μ sieve, transfer the retained material into a tray and keep the tray in oven for 24 hours at 105ºC to dry it completely



Set the sieves in the decreasing order, keeping 4.75mm sieve at top and collecting pan at bottom.



Place the entire assembly in a sieve shaker and sieve the sample for about 15 minutes.



Take the weight of material retained on each sieve and tabulate the values as follows:

Observations and Calculations: Table. 1 Calculation of percentage finer Sieve Size

Weight retained

% retained

4.75mm 2.00mm 1.00mm 600μ 425μ 300μ 150μ 75μ Pan

72 69 52 94 74 54 42 23 20

14.4 13.8 10.4 18.8 14.8 10.8 8.4 4.6 4

Cumulative % retained 14.4 28.2 38.6 57.4 72.2 83 91.4 96 100

% finer 85.6 71.8 61.4 42.6 27.8 17 8.6 4 0

Graph: Plot the grain size distribution curve by taking grain size (mm) on log scale and % finer on ordinary scale.

23

% finer

Grain size distribution 100 90 80 70 60 50 40 30 20 10 0 0.01

D10 = 0.18 mm

0.1

D30 = 0.45 mm

Particle size

D60 = 1 mm

1

10

Fig. 1 Particle size distribution curve Read the diameters corresponding to 60%, 30% and 10% finer. Calculate the co-efficient of curvature (Cc) and uniformity coefficient (Cu) by using the relations. Cu =

D302 D 60 and Cc = D60  D10 D10

Where D60 = Diameter at 60% finer = 1 mm D30 = Diameter at 30% finer = 0.45 mm D10 = Diameter at 10% finer = 0.18 mm Uniformity coefficient = 5.55 Co-efficient of curvature = 1.12 Result: Soil classification: Well graded sand (SW) QUESTIONS 1.

What is the purpose of sieve analysis?

2.

What is the advantage of soil classification?

3.

What are the coarse grained and fine grained soils as per Indian standard (IS) classification of soils?

4.

Whether all the soils can be classified based on sieve analysis? 24

5.

What are well graded and uniformly graded soils?

6.

Why a semi – log graph paper is necessary for plotting the grain size distribution curve?

7.

Draw the grain size distribution curves for poorly graded, well graded and uniformly graded soils

8.

What is the meaning of GW, GP, GM, GC, SW, SP, SM, SC in soil classification?

9.

What is meant by gap graded soil?

10. What is A-line and what is its significance?

25

PERMEABILITY TEST – CONSTANT HEAD METHOD IS : 2720 (Part 36) - 1987 Aim: To determine the co-efficient of permeability of the given soil sample at desired density by constant head method. Equipment & Accessories: Permeameter with all accessories, filter papers, compaction device, measuring jars, stop watch etc. Theory: The property of the soils which permit water (fluids) to percolate through continuously connected voids is called its permeability. In all the cases, flow is taken as laminar and it is assumed that Darcy’s law is valid. q = discharge per unit time = KiA K = Co-efficient of permeability i = hydraulic gradient A = c/s area of the soil The co-efficient of permeability expresses the degree of permeability and has the velocity dimensions. The value of K depends on viscosity and unit weight of fluids, shape and arrangement of soil grains, void ratio and the climatic conditions. It may be determined directly in the laboratory by conducting the following tests: i. Constant head method-suitable for coarse grained soils. ii. Variable head method-suitable for fine grained soils.

26

Fig.1 Constant head permeameter

1. Constant head filter tank 3. Inlet valve 5. Porous disc or screen 7. Spring 9. Manometer tubes 11. Manometer Outlet 13. Tap water valve Gravel filter

2. Filter tank valve 4. Top plate 6. Screened manometer groove 8. Manometer valve 10. Metal or transparent acrylic plastic cylinder 12. Screen 14. Outlet valve

Procedure: 

Remove the cover of the mould and apply a little grease on the sides of the mould.



Measure the internal diameter and effective height of the mould and then attach the collar, base plate to the mould. Place brass dummy plate in the base plate for compaction.

27

Fig. 2 Constant head method 

Disturbed sample is prepared by compacting 3 kg of air dried soil added with sufficient water to achieve required density (Instead Undisturbed sample may also be used).



Remove the collar and base plate, trim off the excess soil and level with top of the mould.



Put the porous plate in the mould and a filter paper above which the soil sample is kept. On this sample another filter paper is placed.



Over this assembly washer and cover are placed.



Connect the reservoir with water to the inlet at the top of the mould and allow the water to flow in till the sample gets saturated.



Allow the water to flow through the soil and establish a steady flow by observing the quantity of flow for given time interval.



Collect the water in a measuring jar for a convenient time interval ‘t’ sec.



Repeat step (9) for five times and tabulate the results as follows:

Observations and Calculations 28

Length of soil sample, L = 12.73 cm Diameter of the mould/ sample = 10 cm C/S area of the sample A = 78.53 cm2

1.

Quantity of water collected (V) (c.c) 350

Time of collection t (sec) 270

2.

340

3.

360

S.NO.

Head over the v q  cc/sec sample (H) t

k

qL cm/sec AH

1.30

100

2.10 x 10-3

270

1.26

100

2.04 x 10-3

270

1.33

100

2.16 x 10-3

Avergage coefficient of permeability =

2.10 x 10-3

Result: Average coefficient of permeability of the given soil sample = 2.10 x 10-3 cm/sec

QUESTIONS 1.

What is permeability and coefficient of permeability?

2.

What are laminar and turbulent flows? What type of flow is expected in soils?

3.

If there are two soils with following properties, coefficient of permeability is more in which type of soil: Soil A

Soil B

Void ratio

0.4

0.8

Grain size

2 mm

1 mm

4.

What is the effect of temperature on permeability of soil?

5.

How is the value of average coefficient of permeability evaluated in a stratified deposit if the flow is (i) parallel and (ii) perpendicular to bedding planes? Which of the two values is greater?

6.

What is the unit of coefficient of permeability? What is the range of its value for gravel, sand, silt and clay?

7.

What are the field applications of coefficient of permeability of soils?

29

PERMEABILITY TEST – VARIABLE HEAD METHOD IS : 2720 (Part 17) - 1986 Aim: To determine the co-efficient of permeability of the given soil sample at desired density by variable head method. Equipment & Accessories: Permeameter with all accessories, filter papers, compaction device, measuring jars etc. Theory: The property of the soils which permit water (fluids) to percolate through the continuously connected voids is known as permeability. In all the cases, flow is taken as laminar and it is assumed that Darcy’s law is valid. Discharge of water = Q = KiA where K = Coefficient of permeability A = c/s area of the soil i = hydraulic gradient The co-efficient of permeability expresses the degree of permeability and has the velocity dimensions. The value of K depends on viscosity and unit weight of fluids, shape and arrangement of soil grains, void ratio and the climatic conditions. It may be determined in the laboratory by conducting the following tests: i. Constant head method – suitable for coarse grained soils. ii. Variable head method-suitable for fine grained soils.

30

Fig. 1 Principle of variable head method Procedure: 

Remove the cover of the mould and apply a little grease on the sides of the mould.



Measure the internal diameter and effective height of the mould and then attach the collar, base plate to the mould. Place brass dummy plate in the base plate for compaction.



Disturbed sample is prepared by compacting 3 kg of air dried soil added with sufficient water to achieve required density (Instead Undisturbed sample may also be used).



Remove the collar and base plate, trim off the excess soil and level with top of the mould.



Put the porous plate in the mould and a filter paper above which the soil sample is kept. On this sample another filter paper is placed.



Over this assembly washer and cover are positioned.



Connect the reservoir with water to the inlet at the top of the mould and allow the water to flow in till the sample gets saturated.



Connect the stand pipe to the inlet at the top plate and fill the stand pipe with water.



Open the stop cock at the top and allow the water to flow out so that all the air in the cylinder is removed.



Allow water to flow through the soil till a steady flow is established.



Record the time intervals for the head to fall from h1 to h2 for five times and tabulate the results as follows.

Observations and Calculations a = C/s area of stand pipe = 1 cm2 Diameter of the mould/ sample = 10 cm C/S area of the sample A = 78.53 cm2 Length of soil sample, L = 12.73 cm S.No.

h1, m

h2, m

Time interval ‘t’ in min

1 2 3

1 1 1

0.4 0.6 0.5

20 15 17

h aL log 10 1 At h2 -4 1.24 x 10 cm/s 9.19 x 10-5 cm/s 1.1 x 10-4 cm/s

K = 2 .3

Result: Coefficient of permeability of the given soil sample = 1.07 x 10-4 cm/s 31

QUESTIONS 1.

What is the effect of permeability on consolidation of a soil?

2.

What are the two types of permeability tests available?

3.

Variable head method is applicable for which type of soil?

4.

What is the effect of entrapped air on coefficient of permeability of soils?

5.

How the entrapped air is removed during the experiment?

6.

What are field applications of coefficient of permeability of soil?

32

STANDARD PROCTOR COMPACTION TEST IS : 2720 (Part 7) - 1980 Aim: To determine the relationship between water content and dry density of the given soil and then to determine optimum moisture content and maximum dry density. Equipment & Accessories: Cylindrical metal mould of capacity 1000cc., metal rammer weighing 2.6 kg, and having a drop of 31cm, steel straight edge, balance, oven, water content container, mixing equipment, sample extruder, IS Sieve (20mm & 4.75mm).

Fig. 1 Standard proctor compaction apparatus Theory: Compaction is a process by which the soil particles are artificially rearranged and packed together into a closer state by mechanical means to decrease the porosity. In 1933, proctor showed that there existed a definite relationship between the soil water content and degree of dry density to which the soil might be compacted. Optimum water content may be defined as the water content at which a particular soil attains a maximum dry density for a specific amount of compaction energy. In the field, soils are compacted with addition of optimum moisture content to achieve the maximum dry density obtained in the laboratory. Procedure: 

Take about 20kg of air dried and mixed soil for 1000cc mould (10cm dia) or 45 kg for 2250cc mould (15cm dia).



Sieve this soil through 20mm and 4.75mm sieve.

33



Calculate the percentage retained on 20mm and 4.75mm sieves and passing from 4.75mm sieve.



Do not use the soil retained on 20mm sieve.



Use a 10cm dia mould if percentage retained on 4.75mm sieve is less than 20 or use a mould of 15cm diameter if percentage retained on 4.75mm sieve is more than 20.



Mix the soil retained on and passing through 4.75mm sieve thoroughly.



Take about 2.5 kg of the soil for 1000cc (6kg. for 2250cc mould)



Add water to it to bring its moisture content to about 4% in coarse grained soil and 8% in fine grained soils.



Clean the mould and apply grease inside and also to the base plate. Weigh the mould with base plate and fit the extension collar.



Compact the wet soil in three equal layers by rammer of mass 2.6kg having free fall of 31cm with 25 evenly distributed blows on each layer for 10cm diameter mould and 56 blows for 15cm diameter mould.



Remove the collar and trim off the soil flush with top of the mould.



Clean the outside of the mould and base plate, weigh the mould with soil and base plate.



Take a representative sample for water content determination.



Repeat the above procedure till the weight of the soil decreases with increase in water content and tabulate as follows:

Observations & Calculations Wt. of mould = 1933g Volume of mould, V = 944 g Table. 1 Calculation of dry density Sample no Mass of compacted soil and mould, g Mass of empty mould, g Mass of wet soil, Mg Wet density = w M/V g/cc Container No Mass of empty container, M1

1

2

3

4

5

3457.2

3721.2

3909.0

3782.5

3715.2

1933

1933

1933

1933

1933

1524.2

1788.2

1976

1849.5

1782.2

1.61

1.89

2.09

1.96

1.89

4

16

22

34

46

33.24

36.47

32.18

38.44

39.24 34

Mass of container soil, M2 Mass of container soil, M3 Moisture = (

−

−

empty + Wet

46.85

47.18

45.32

48.66

45.15

empty + Dry

45.82

46.15

43.83

47.28

44.27

8.2

10.6

12.8

15.65

17.4

1.49

1.71

1.86

1.69

1.61

content ) × 100

Dry Density, d =

Graph: Plot the water content on x-axis and dry density in y-axis, draw the smooth curve, called compaction curve.

Standard Proctor Compaction Test

Dry Density, g/cc

2.00 1.90 1.80 1.70 1.60 1.50 1.40 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Moisture Content (%)

Fig.2 Dry density vs moisture content relationship Result: Maximum dry density: 1.88 g/cc Optimum moisture content: 13% QUESTIONS 1.

What is compaction? Why is it done? 35

2.

Differentiate between compaction and consolidation of soils?

3.

What is maximum dry density of soils at its OMC? Does it mean that density can not be more than this for a given soil?

4.

What is optimum moisture content?

5.

What is meant by dry side and wet side of optimum? Which side is preferred in field compaction? Explain

6.

What is the meaning of field compaction control?

7.

How does laboratory compaction result help in the control of field compaction?

36

MODIFIED PROCTOR COMPACTION TEST IS : 2720 (Part 8) - 1983 Aim: To determine the relationship between water content and dry density of the given soil and to determine optimum moisture content and maximum dry density. Equipment & Accessories: Cylindrical metal mould of capacity 1000 cc., metal rammer weighing 4.89 kg and having a drop of 45 cm, steel straight edge, balance, oven, water content containers, mixing equipment, sample extruder. IS sieves (20mm & 4.75mm). Theory: Compaction is a process by which the soil particles are artificially rearranged and packed together into a close state by mechanical means to decrease the porosity. In 1933, proctor showed that there existed a definite relationship between the soil water content and degree of dry density to which the soil might be compacted. Optimum water content may be defined as the water content at which a particular soil attains a maximum dry density for a specific amount of compaction energy. Procedure: 

Take air dried and mixed soil of about 20kg for 1000cc mould (10cm dia) or 45 kg for 2250cc mould (15cm dia).



Sieve this soil through 20mm and 4.75mm sieve.



Calculate the percentage retained on 20mm and 4.75mm sieves and passing from 4.75mm sieve.



Do not use the soil retained on 20mm sieve.



Use 10cm diameter mould if percentage retained on 4.75mm sieve is less than 20 or use a mould of 15cm diameter if percentage retained on 4.75mm sieve is more than 20.



Mix the soil retained on and passing through 4.75mm sieve thoroughly.



Take about 2.5 kg of the soil for 1000cc (6kg. for 2250cc mould)



Add water to it to bring its moisture content to about 4% in coarse grained soil and 8% in fine grained soils.



Clean the mould and apply grease inside and also to the base plate. Weigh the mould with base plate and fit the extension collar.



Compact the wet soil in five equal layers by rammer of mass 4.89kg and free fall 45cm with 25 evenly distributed in each layer for 10cm diameter mould and 56 blows for 15cm diameter mould.



Remove the collar and trim off the soil flush with top of the mould. 37



Clean the outside of the mould and base plate, weigh the mould with soil and base plate.



Take a representative sample for water content determination.



Repeat the above procedure till the weight of the soil decreases with increase in water content and tabulate as follows:

Observations & Calculations Weight of mould = 5310 g Volume of mould = 1000 cc Table. 1 Calculation of dry density Sample no Mass of compacted soil and mould, g Mass of empty mould, g Mass of wet soil, Mg Wet density = w M/V g/cc Container No Mass of empty container, M1 Mass of empty container + Wet soil, M2 Mass of empty container + Dry soil, M3 Moisture content = (

−

−

) × 100

Dry Density, d g/cc =

1

2

3

4

5

7180

7450

7586

7500

7400

5310

5310

5310

5310

5310

1870

2140

2276

2190

2090

1.87

2.14

2.28

2.19

2.09

4

16

22

34

46

33.24

36.47

32.18

38.44

39.24

46.85

47.18

45.32

48.66

45.15

45.82

46.15

43.83

47.28

44.27

8.2

10.6

12.8

15.65

17.4

1.73

1.93

2.02

1.89

1.78

Graph: Plot the water content on x-axis and dry density on y-axis, draw the smooth curve, called compaction curve.

38

Modified Proctor Compaction Test

Dry Density, g/cc

2.10 2.00 1.90 1.80 1.70 1.60 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Moisture Content (%)

Fig.1 Dry density vs moisture content relationship Result Maximum dry density: 2.01g/cc Optimum moisture content: 13%

QUESTIONS 1. What is compaction? Why is it done? 2. Differentiate between compaction and consolidation of soils? 3. What is maximum dry density of soils at its OMC? Does it mean that density can not be more than this for a given soil? 4. What is optimum moisture content? 5. What is meant by dry side and wet side of optimum? Which side is preferred in field compaction? Explain 6. What is the meaning of field compaction control? 7. How does laboratory compaction result help in the control of field compaction?

39

CALIFORNIA BEARING RATIO TEST (HEAVY COMPACTION) IS : 2720 (Part 16) - 1979 Aim: To determine the california bearing ratio (C.B.R) of a compacted soil sample. Equipment & Accessories: Loading machine, cylindrical mould (2250cc), compaction rammer, annular weights, placer discs, water content cans, oven, balances (1gm to 0.01 sensitivity).

Fig. 1 CBR test set up Theory: The C.B.R test developed by california division of highways as a method of classifying and evaluating soil subgrade and base course materials for flexible pavements. The C.B.R. is a measure of shearing resistance of the material under controlled density and moisture conditions. The C.B.R. is defined as the ratio of the test load to the standard load, expressed as percentage, for a given penetration of plunger. C.B.R. =

Test load x 100 s tan dard load

40

Where standard load is the penetration resistance of the plunger into a standard sample of crushed stone for the corresponding penetration. Standard loads adopted for different penetrations for the standard material with a CBR value of 100% are given below: Penetration of plunger (mm) Standard load (kg)

2.5 5.0 1370 2055

7.5 2630

10.0 12.5 3180 3600

The Indian Road congress recommends that the test must always be performed on remoulded samples of soil using static compaction whenever possible instead of dynamic compaction. The CBR values are usually calculated for penetrations of 2.5mm and 5mm and the greater value is used for the design. Generally, the CBR value for 2.5mm penetration will be greater than that at 5mm penetration. However if the CBR value corresponding to a penetration of 5mm exceeds that for 2.5mm, the test is repeated. If identical results follow, the CBR value corresponding to 5mm penetration is taken for design. Procedure: A. Preparation of Specimen 

Take about 7.5kg of dry soil passing through 20mm I.S. sieve.



Mix the soil with water up to the optimum moisture content.



Place the placer disc over the base plate and compact the soil in the mould with collar in five layers giving 55 blows per each layer using a rammer weighing 4.89 kg. falling from a height of 45 cm.



Remove the collar and trim off excess soil and determine the weight of soil.



Turn the mould upside down and remove the placer disc.

B. Penetration test 

Keep the annular weights to produce surcharge equal to the weight of base material and pavement expected in actual construction.



Place the mould assembly on the loading machine.



Seat the penetration piston at the center of the specimen.



Set the load and displacement dial gauges to zero. Apply the load on the penetration plunger at the rate of 1.25mm/min. Record the load readings at penetration of 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, …., 12.5 mm.



At the end of the penetration test, detach the mould from loading machine. Take a representative soil sample and determine its moisture content. 41

Observations & Calculations: Table. 1 Calculation of dry density 10917 6270 4647 2250 2.07 41 35.59 137 123.48 15.38 1.79

Wt. of mould + soil, g = Wt. of mould, g = Wt. of soil, g = Volume of mould, cc = Bulk density, g/cc = Can No. = Wt. of can, g = Wt. of can + wet soil, g = Wt. of can + dry soil, g = Moisture content, %= Dry density, g/cc = Proving ring constant = 2.33 kg/Division

Table.2 Load vs Penetration Observation Penetration (mm)

Proving ring reading

0.00 0.50 1.00 1.50 2.00 2.50 3.00 4.00 5.00 7.50 10.00 12.50

0 17 35 52 61 67 73 83 92 115 135 154

Load in kg. 0.0 39.6 81.6 121.2 142.1 156.1 170.1 193.4 214.4 268.0 314.6 358.8

Graph: Plot the load penetration curve. If the curve is convex upwards, no correction is required. On the other hand if the initial portion of the curve is concave upwards a correction should be applied by drawing a tangent to the curve at the point of greatest slope and the point where this tangent meets the abscissa is the new origin.

42

400 350

Load in kg

300 250 200 150 100 50 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Penetration, mm

Fig.2 Load Vs Penetration CBR at 2.5 mm (%) =

.

CBR at 5.0 mm (%) =

. ×

× 100 = 11.4%

= 10.4%

Result: California bearing ratio of sample = 11.4% QUESTIONS 1. Why is it called bearing ratio test? 2. What are standard loads? Explain 3. What are field applications of CBR value? 4. What is the rate of penetration applied in CBR test?

43

CALIFORNIA BEARING RATIO TEST – LIGHT COMPACTION IS : 2720 (Part 16) - 1979 Aim: To determine the california bearing ratio (C.B.R) of a compacted soil sample. Equipment & Accessories: Loading machine, cylindrical mould (2250cc), compaction rammer, annular weights, placer disc, water content cans, oven, balances (1gm to 0.01 sensitivity).

Fig. 1 CBR test set up Theory: The C.B.R test developed by california division of highways as a method of classifying and evaluating soil subgrade and base course materials for flexible pavements. The C.B.R. is a measure of shearing resistance of the material under controlled density and moisture conditions. The C.B.R. is defined as the ratio of the test load to the standard load, expressed as percentage, for a given penetration of plunger.

C.B.R. =

Test load x 100 s tan dard load 44

Where standard load is the penetration resistance of the plunger into a standard sample of crushed stone for the corresponding penetration. Standard loads adopted for different penetrations for the standard material with a CBR value of 100% are given below: Penetration of plunger (mm) Standard load (kg)

2.5 5.0 1370 2055

7.5 2630

10.0 12.5 3180 3600

The Indian Road congress recommends that the test must always be performed on remolded samples of soil using static compaction whenever possible instead of dynamic compaction. The CBR values are usually calculated for penetrations of 2.5mm and 5mm and the greater of the two values is used for the design. Generally, the CBR value for 2.5mm penetration will be greater than that at 5mm penetration. However if the CBR value corresponding to a penetration of 5mm exceeds that for 2.5mm, the test is repeated. If identical results follow, the CBR value corresponding to 5mm penetration is taken for design. Procedure: A. Preparation of specimen 

Take about 7.5kg of dry soil passing through 20mm I.S. sieve.



Mix the soil with water up to the optimum moisture content.



Place the placer disc over the base plate and compact the soil in the mould with collar in three layers giving 55 blows per each layer using a rammer weighing 2.6 kg. falling from a height of 31 cm.



Remove the collar and trim off excess soil and determine the weight of compacted soil.



Turn the mould upside down and remove the placer disc.

B. Penetration test 

Keep the annular weights to produce surcharge equal to the weight of base material and pavement expected in actual construction.



Place the mould assembly on the loading machine.



Seat the penetration piston at the center of the specimen.



Set the load and displacement dial gauges to zero. Apply the load on the penetration plunger at the rate of 1.25mm/min. Record the load readings at penetration of 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, …., 12.5 mm.



At the end of the penetration test, detach the mould from loading machine. Take a representative soil sample and determine its moisture content.

Observation and Calculations 45

Table. 1 Calculation of dry density 10760 6440 4320 2250 1.92

Wt. of mould + soil, g = Wt. of mould, g = Wt. of soil, g = Volume of mould, cc = Bulk density, g/cc = Can No. = Wt. of can, g = Wt. of can + wet soil, g = Wt. of can + dry soil, g = Moisture content, %= Dry density, g/cc =

353 31.79 145.62 130.21 15.66 1.66

Proving ring constant = 2.33 kg/Division Table.2 Load vs Penetration Observation Penetration (mm)

Proving ring reading

0.00 0.50 1.00 1.50 2.00 2.50 3.00 4.00 5.00 7.50 10.00 12.50

0 7 13 17 19 21 22 24 25 28 29 30

Load in kg. 0.0 16.3 30.3 39.6 44.3 48.9 51.3 55.9 58.3 65.2 67.6 69.9

Graph: Plot the load penetration curve. If the curve is convex upwards, no correction is required. On the other hand if the initial portion of the curve is concave upwards a correction should be applied by drawing a tangent to the curve at the point of greatest slope and the point where this tangent meets the abscissa is the new origin.

46

80 70

Load in kg

60 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Penetration, mm

Fig.2 Load Vs Penetration CBR at 2.5 mm (%) =

.

CBR at 5.0 mm (%) =

.

Result:

× 100 = 3.57% × 100 = 2.8%

California bearing ratio of sample = 3.57% QUESTIONS 1. Why is it called bearing ratio test? 2. What are standard loads? Explain 3. What are field applications of CBR value? 4. What is the rate of penetration applied in CBR test?

47

CONSOLIDATION TEST IS : 2720 (Part 15) - 1986 Aim: To determine the consolidation properties of disturbed or undisturbed soil by conducting one dimensional consolidation test. Apparatus: Consolidometer with its accessories, balance, filter papers, loading device, dial gauge, stop watch, water reservoir.

Fig. 1 Consolidation test set up Theory: Compression of saturated soil resulting from long term static load and the consequent escape of pore water is known as “consolidation”. On the other hand, the process of increase in water content due to increase in volume of voids is called “Swelling”. When there is pressure increment, it will be first taken by pore water which is known as excess hydrostatic pressure. As water starts escaping out, this excess hydrostatic pressure gets dissipated gradually and the pressure will be transmitted to the soil grains. Then the whole of the pressure increment is carried as effective pressure on the soil solids, no more water escapes from voids and a condition of equilibrium is attained. Under different applied pressures, soil attains equilibrium or final void ratios. The delay caused in consolidation by slow drainage of water out of a saturated soil mass is called hydrodynamic lag. The reduction in volume of soil which is due principally to squeezing out of water from voids is known as primary consolidation. Even after reduction of all excess hydrostatic pressure, source compression of soil takes place at a very slow rate and is known as secondary consolidation. By conducting one dimensional consolidation test the following consolidation properties can be calculated. 48

i) Coefficient of consolidation

Cv 

0.197d 2 t 50

0.848d 2 Cv  t 90

[log fitting method]

[square root fitting method]

ii) Compression index (Cc) To determine the compression index, a plot of void ratio ‘e’ versus log ‘σ’ is drawn. The initial compression curve would be a straight line and the slope of this line would give the compression index. iii) Coefficient of compressibility av 

0.435C c '

σ’ = average pressure for the increment iv) Coefficient of permeability (k) k

Cv av w 1 e

Procedure: A) Preparation of soil sample from representative samples 

Compact the soil at the desired water content and density in a large mould.



Clean the specimen ring and weigh it empty.



Gradually insert the specimen ring into the mould, by pressure with hands.



Trim the sample smooth and flush with the top and bottom of the ring.



Clean the ring from outside and weigh it.

B) Preparation of mould assembly 

Saturate the porous stones and assemble the consolidometer with the soil specimen and porous stones at top and bottom of the specimen, providing a filter paper in between.



Position the pressure pad centrally on the top porous stone.



Mount the assembly on loading frame and center it such that load is applied is axially.



Position the dial gauge to measure vertical compression of the specimen.



Connect the mould assembly to water reservoir and saturate the sample.

49



Apply an initial load (should not be less than 0.05kg/cm2) and should be allowed to stand until there is no change in dial gauge reading for two consecutive hours or maximum of 24 hours.

Test Procedure 

Note the final dial reading under initial setting load.



Apply first load of intensity 0.1kg/cm2 and start the stop watch simultaneously with loading.



Record the dial gauge readings at various time intervals. Primary consolidation is generally reached within 24 hours.



At the end of the period specified above, take the dial gauge reading and time reading. Double the load intensity and take the dial readings at various intervals.



Repeat this procedure for successive load increments. The usual load increments are as follows: 0.1, 0.2, 0.5, 1.2, 4 and 8 kg/cm2.



After the last loading is completed. Reduce the load to 1/4th of the value of the last load and allow it to stand fro 24 hours.



Reduce the load further in steps of 1/4th the previous intensity till an intensity of 0.1 kg/cm2 is reached. Take the final reading of the dial gauge.



Reduce the load to the initial setting load, keep it for 24 hours and note the final dial reading.



Quickly dismantle the specimen assembly and remove the excess surface water by blotting. Weigh the ring with consolidation specimen. Dry the soil specimen in oven and determine dry weight.

Observation and Calculation Thickness of sample = 2 cm Present increment = 0.1 kg/cm2 Least count of dial gauge = 0.01 mm Square root of time method Table. 1 Dial gauge readings for different time intervals Elapsed time (minutes) 0

√t 0

Dial gauge readings 200 50

0.25 1 2.25 4 6.25 9 12.25 16 20.25 25 36 49 64

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 6 7 8

182 172 166 160 155 147 143 137 132 126 119 113 110

From Fig.1 t90 = 7.0 t90 = 49 min cv =

.

=

.

×

= 0.017 cm2/min

210 200 190

Dial gauge readings

180 170 160 150 140 130 √t90 = 7.0

120 110

a 1.15 a

100 0

2

4

6

8

10

12

sqrt(t)

Fig.1 Square root time method Result: Coefficient of consolidation = 0.017 cm2/min 51

QUESTIONS 1. What are the units of coefficient of consolidation? 2. What is the meaning of single drainage and double drainage? 3. What is length of drainage path? Explain? 4. What is the use of coefficient of consolidation in field problems? 5. What is the role of permeability on coefficient of consolidation of soil? 6. What is elastic settlement, primary consolidation, and secondary consolidation? 7. Why consolidation test is mainly done on clay? Why not on sand and gravel? 8. Why the sample is kept saturated during consolidation test? If the sample is unsaturated what happens?

52

UNCONFINED COMPRESSION TEST IS : 2720 (Part 10) - 1973 Aim: To determine the unconfined compressive strength of clayey soil. Eqipment and Accessories: Compression device, sample ejector, oven, balances, sampling tubes, split mould.

Fig. 1 Unconfined compression test set up Theory: Cylindrical specimen of saturated clay (3.75cm dia and 7.5cm height) is subjected to major principal stress till it fails due to shearing along a critical plane failure. This test is essentially an undrained test as the rate of loading does not allow the pore water pressure to dissipate. Since there is no confining stress, Mohr’s circle passes through origin which is also the pole. Substituting the value of φu = 0, σ3 = 0 and α = 45 +

 2

in the equation, σ1 = σ3 tan2α + 2 cu tanα we get σ1 = 2cu When Mohr’s circle is drawn, its radius is equal to σ1/2 = cu The failure envelope is horizontal σ = σ1/2 = qu/2 = τf = cu qu = Unconfined compressive stress at failure. Τf = Shear strength at failure cu = cohesion 53

Sensitivity is defined as the ratio of unconfined compressive strength of undisturbed soil sample to the unconfined compressive strength of remoulded sample at constant water content. Generally soils having sensitivity less than four are considered good for the construction purposes. This is the simplest and quickest test for determining the cohesion and shear strength of the cohesive soils. These values are used for checking the short term stability of foundations and slopes, soil consistency. Soil consistency can be known from the value of unconfined compressive strength. Procedure: A) Preparation of test specimen 

Undisturbed cylindrical specimen may be obtained from bigger sample by pushing the sampling tube in to the soil.



Coat the inside of the split mould with thin layer of grease or oil.



Extrude the specimen from the sampling tube to the split mould with the help of the sample extractor and knife.



Remoulded sample may be prepared by compacting the soil at desired water content and dry density.



In both the cases the density and water content of the specimen is determined.

B) Compression test 

Measure the initial length and diameter of the specimen. Also determine the weight of the specimen.



Place the specimen between the moving base and the top plate connected to the proving ring.



Take the dial gauge reading and proving reading at regular intervals.



Apply compressive load till the sample fails or 20% strain occurs.

Observations & Calculations Diamter of the specimen = 3.8 cm Cross sectional area of sample (A) = 11.34 cm2 Length of sample = 7.6 cm Table. 1 Calculation axial stress and strain

54

Dial gauge readings

Deformation ΔL (mm)

Strain, ε= ∆L/L

Corrected area, Ac in cm2 = A/(1-ε)

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6

0.000 0.026 0.053 0.079 0.105 0.132 0.158 0.184 0.211 0.237 0.263 0.289 0.316 0.342 0.368 0.395 0.421 0.447 0.474

11.34 11.65 11.97 12.31 12.68 13.06 13.47 13.90 14.37 14.86 15.39 15.96 16.58 17.24 17.96 18.74 19.59 20.52 21.55

Proving Load, P ring in kg reading 0 15 22 27 32 34 38 40 41 43 45 46 46 46 46 44 41 36 34

Stress, σ in kg/cm2 = P/A

0.00 3.96 5.81 7.13 8.45 8.98 10.03 10.56 10.82 11.35 11.88 12.14 12.14 12.14 12.14 11.62 10.82 9.50 8.98

0.000 0.340 0.485 0.579 0.666 0.687 0.745 0.760 0.753 0.764 0.772 0.761 0.733 0.704 0.676 0.620 0.553 0.463 0.417

Graph: Plot graph between axial stress and axial strain. Obtain the peak stress from the graph. This stress is known as unconfined compressive strength of soil (qu).

55

0.85 0.80 0.75 0.70

2

Axial stress, kg/cm

0.65 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Axial strain

Fig.2 Axial stress vs strain Result: Unconfined Compressive strength (qu) = 0.77 kg/cm2 Cohesion (cu) =

qu = 2

.

= 0.385 kg/cm2 QUESTIONS

1. What is unconfined compressive strength of soil? 2. Whether unconfined compressive strength can be determined for all types of soils? Explain? 3. What is corrected area? How is it obtained? 4. What are the drainage conditions in unconfined compressive strength test? 5. What is the difference between unconfined compression test and unconsolidated triaxial test? 6. How the shear parameters are determined from unconfined compression tests? 56

7. If there are two samples from the same cohesive soil, one wet and other is fully saturated, what difference is expected in shear parameters and angle of failure plane? 8. What is sensitivity? How is it estimated? 9. What is undisturbed and remoulded soil sample? 10. What is the meaning of stress controlled and strain controlled tests?

57

TRIAXIAL COMPRESSION TEST IS : 2720 (Part 11) – 1971 IS : 2720 (Part 12) - 1981 Aim: To determine the shear strength parameters of the soil by triaxial testing machine. Equipment and Accessories: Triaxial cell, load frame, constant pressure system and pore pressure arrangement, sample tubes and other accessories.

Fig. 1 Triaxial cell

Fig. 2 Constant pressure system

58

Theory: The shear strength of the soil is the resistance to deformation by continuous shear displacement of soil particles upon the action of shear. The relationship between major and minor principal stresses is

 1   3 tan 2   2c tan  σ1, σ3 = major and minor principal stresses c = cohesion α = Angle of failure plane = 45 + /2 Shear resistance can be determined in the laboratory under three types of drainage conditions. a) Undrained test or quick test (Q-test) b) Consolidated undrained test (R-test) c) Drained test or slow test (S-test)

Fig. 3 Pore water pressure measurement device

Fig. 4 Volume change measurement Triaxial test used for all types of soils under different drainage conditions. Cylindrical specimen is stressed under the conditions of axial symmetry. In the first stage the specimen is

59

consolidated under all round confining pressure. Second stage additional axial stress, known as deviator stress is applied. Sample Preparation: 

The undisturbed specimen of size 37.5 mm diameter, and 75mm height may be cut from the bigger sample, obtained from the field.



Remoulded soil sample can be obtained by compacting the soil at required density and water content in a mould and then trimming to the required size.

In both the cases the dry density and water content of the specimen is determined. Procedure: 

A rubber membrane is stretched over a membrane stretcher applying suction between stretcher and membrane by inhalation.



Place non porous stones on either end of the specimen.



Specimen with non porous stones is placed on the pedestal of the triaxial cell and sealed by rolling a rubber O ring onto the membrane.

Fig. 5 Cell pressure and deviator stress 

On the upper stone cap is placed and a rubber O ring is rolled to seal the membrane with cap. 60



The specimen is checked for its verticality and co-axiality with the cylinder chamber.



The chamber along with plunger is placed over the top of cap without disturbing the soil specimen. The cylinder is attached to the base tightly by tightening the nuts.



When the sample is setup, water is filled into cell allowing the air to escape by opening the air valve. Once the cell is completely filled with water air valve is closed.



By connecting constant pressure system, pressure of filled water is increased and maintained constantly. This pressure applies all round confining pressure on the sample.



The vertical load is applied at constant strain rate of 2% per min.



Take the readings of proving ring dial gauge at 0.5, 1.0, 1.5, 2.0% of strain and for every 1.0% strain thereafter up to failure or 20% strain whichever is earlier.



Repeat the test with three samples of different confining pressures.

Observations and calculations: Diameter, (D): 3.8 cm Length, (L): 7.6 cm Cross sectional area, (A): 11.34 cm2 Initial Volume (V) : 86.19 cm3 Proving ring constant : 0.264 kg/Div Table. 1 Calculation axial stress and strain sample 1 Confining pressure = 0.5 kg/cm2 Dial gauge readings

Deformation ΔL (mm)

Strain, ε= ∆L/L

Corrected area, Ac in cm2 = A/(1-ε)

0 20 40 60 80 100 120 140 160 180 200 220

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

0.000 0.026 0.053 0.079 0.105 0.132 0.158 0.184 0.211 0.237 0.263 0.289

11.34 11.65 11.97 12.31 12.68 13.06 13.47 13.90 14.37 14.86 15.39 15.96

Proving Load, P ring in kg reading 0 10 16 20 23 25 27 29 30 31 33 33

0.00 2.64 4.22 5.28 6.07 6.60 7.13 7.66 7.92 8.18 8.71 8.71

Stress, σ in kg/cm2 = P/A 0.000 0.227 0.353 0.429 0.479 0.505 0.529 0.551 0.551 0.551 0.566 0.546 61

240 260 280 300 320

2.4 2.6 2.8 3 3.2

0.316 0.342 0.368 0.395 0.421

16.58 17.24 17.96 18.74 19.59

34 32 29 26 23

8.98 8.45 7.66 6.86 6.07

0.542 0.490 0.426 0.366 0.310

Table. 2 Calculation axial stress and strain sample 2 Confining pressure = 1.0 kg/cm2

Dial gauge readings

Deformation ΔL (mm)

Strain, ε= ∆L/L

Corrected area, Ac in cm2 = A/(1-ε)

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2

0.000 0.026 0.053 0.079 0.105 0.132 0.158 0.184 0.211 0.237 0.263 0.289 0.316 0.342 0.368 0.395 0.421

11.34 11.65 11.97 12.31 12.68 13.06 13.47 13.90 14.37 14.86 15.39 15.96 16.58 17.24 17.96 18.74 19.59

Proving Load, P ring in kg reading 0 12 21 26 29 31 32 34 36 38 39 40 40 38 36 35 32

0.00 3.17 5.54 6.86 7.66 8.18 8.45 8.98 9.50 10.03 10.30 10.56 10.56 10.03 9.50 9.24 8.45

Stress, σ in kg/cm2 = P/A 0.000 0.272 0.463 0.557 0.604 0.627 0.627 0.646 0.662 0.675 0.669 0.662 0.637 0.582 0.529 0.493 0.431

Table. 3 Calculation axial stress and strain sample 3 Confining pressure = 1.5 kg/cm2 Dial gauge readings

Deformation ΔL (mm)

Strain, ε= ∆L/L

Corrected area, Ac in cm2 = A/(1-ε)

0 20 40

0 0.2 0.4

0.000 0.026 0.053

11.34 11.65 11.97

Proving Load, P ring in kg reading 0 15 22

0.00 3.96 5.81

Stress, σ in kg/cm2 = P/A 0.000 0.340 0.485 62

60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360

0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6

0.079 0.105 0.132 0.158 0.184 0.211 0.237 0.263 0.289 0.316 0.342 0.368 0.395 0.421 0.447 0.474

12.31 12.68 13.06 13.47 13.90 14.37 14.86 15.39 15.96 16.58 17.24 17.96 18.74 19.59 20.52 21.55

27 32 34 38 40 41 43 45 46 46 46 46 44 41 36 34

7.13 8.45 8.98 10.03 10.56 10.82 11.35 11.88 12.14 12.14 12.14 12.14 11.62 10.82 9.50 8.98

0.579 0.666 0.687 0.745 0.760 0.753 0.764 0.772 0.761 0.733 0.704 0.676 0.620 0.553 0.463 0.417

63

0.85 0.80 0.75 0.70 0.65 0.60 2

Axial stress, kg/cm

0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Axial strain

Fig.6 Axial stress vs strain for three samples

Table. 4 Cell pressures and deviator stress Cell pressure (kg/cm2) 0.5 1.0 1.5

Strain gauge reading

Proving ring reading

200 180 200

33 38 45

Load on sample kg 8.71 10.03 11.88

Correct area A/(1-Є) 15.39 14.86 15.39

Deviator stress Kg/cm2 0.566 0.675 0.772

Table. 5 Major and minor principal stress Sample No.

Cell pressure, Kg/cm2

1 2

0.5 1.0

Deviator stress, Kg/cm2 0.566 0.675

Minor principal stress, Kg/cm2

Major principal stress, Kg/cm2

0.5 1.0

1.07 1.67 64

3

1.5

0.772

1.5

2.27

Mohr's Envelop

Shear Stress(kg/Sq.cm)

1.00 0.75 0.50 0.25 0.00 0.0

0.5

1.0

1.5

2.0

2.5

3.0

Normal Stress (kg/sq.cm)

Fig.7 Determination of cohesion and angle of internal friction

Result: Cohesion = 22.6 kg/cm2 Angle of internal friction = 9

QUESTIONS 1. How do you classify the test based on drainage conditions? Explain 2. How do you ensure the sample is completely consolidated? 3. How do you ensure the complete drainage during shear? 4. Two samples from a pure clay soil are subjected to triaxial test at confining pressures of 50 kpa and 100 kpa. If the first sample fails at a deviator stress of 20 kpa, what would be the failure deviator stress for second sample? 5. What are the effective strength parameters and total stress parameters? Which will be higher? Explain.

65

DIRECT SHEAR TEST IS : 2720 (Part 13) - 1986 Aim: To determine the shear parameters of the soil with the shear box. Equipment and Accessories: Shear box equipment, load frame, set of weights, proving ring with dial gauge, and other accessories.

Fig. 1Direct shear test set up Theory: The shear strength of the soil is the resistance to deformation by continuous shear displacement of soil particles upon the action of shear stress. The shear strength of soil is expressed as a function of principle stresses (Coulomb) as   f ( 1 ,  2 ,  3 )

or τ = c + σ tanφ where c, φ are called shear parameters τ = Shear strength (KN/m2 or Kg/cm2) σ = Normal stress (KN/m2 or Kg/cm2) c = Cohesion (KN/m2 or Kg/cm2) φ = Angle of internal friction (degrees) The shear strength of a soil is constituted basically of three components. Namely i) Structural resistance ii) Frictional resistance iii) Cohesion. Shear resistance can be determined in the laboratory under three types of drainage conditions a) Undrained test or Quick test – (Q-test) 66

b) Consolidated – Undrained test – (R-test) c) Drained test or slow test – (S-test) Direct shear test is a simple and most commonly used test. This test can be conducted under all the three drainage conditions. The failure plane is predetermined and is horizontal. This test is strain controlled test as the shear strain is made to increase at constant rate. Preparation of soil sample: 

The undisturbed specimen is prepared by pushing a cutting ring of size 10cm diameter and 2cm high in the undisturbed soil sample obtained from field. Then the square specimen of size 6 cm x 6cm is cut from this circular specimen.



Non-cohesive soils will be tamped in the shear box with base plate and grid plate at the bottom of the box.



Cohesive remoulded soil samples can be obtained by compacting the soil at required density and water content in a bigger mould and then trimming to the required size.

Procedure: 

Position the base plate inside the bottom half of shear box, the bottom half is fixed to the upper half by locking screws.

Fig. 2 Direct shear test 

Place the porous stone in the base plate (For undrained test the porous stone may be replaced with other suitable plate).



For undrained test, place the grid plate on the porous stone keeping the serrations at right angle to the direction of shear. For consolidated undrained and drained tests, use perforated grid in place of plain grid.



For drained test place a filter paper on the grid plate over which prepared soil specimen placed. 67



Place the upper grid, porous stone and loading pad in the order on soil specimen.



The shear box with specimen is to be placed on the loading frame.



Set the lower part of the shear box to bear against the load jack and upper part to bear against the proving ring. Set the proving ring dial to zero.



Keep the loading yoke on the top of the loading pad and apply the normal stress. The arm of the load hanger should be adjusted to be horizontal.



Remove the locking screws and apply the horizontal shear load to failure at a constant rate of 1 to 2.5mm/minue.



Take the proving ring readings corresponding to horizontal displacements at regular intervals, till the sample fails. Also note the vertical dial gauge readings.



Remove the sample from the shear box and repeat the above procedure on the sample under different normal stresses.

Observations and calculations Cross sectional area, A = 6cm x 6cm = 36cm2 Proving ring constant (load applied per division): 0.229 kg/Div Normal stress = 0.7 kg/cm2 Table.1 Calculation of shears stress for sample 1

Sl.No

Horizontal Displacement d (mm)

Corrected Area (Adx6) Cm2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6

36.00 35.88 35.76 35.64 35.52 35.40 35.28 35.16 35.04 34.92 34.80 34.68 34.56 34.44 34.32 34.20 34.08 33.96 33.84

Proving ring divisions

Shear load in kg

Shear Stress kg/cm2

0 9 15 21 28 34 39 44 48 51 54 56 58 59 60 60 60 60 61

0.00 2.16 3.35 4.83 6.40 7.74 9.00 10.04 10.86 11.60 12.27 12.87 13.24 13.54 13.61 13.69 13.69 13.76 13.83

0.00 0.06 0.09 0.14 0.18 0.22 0.26 0.29 0.31 0.33 0.35 0.37 0.38 0.39 0.40 0.40 0.40 0.41 0.41 68

20 21 22 23 24

3.8 4.0 4.2 4.4 4.6

33.72 33.60 33.48 33.36 33.24

61 60 60 59 59

13.83 13.76 13.69 13.54 13.39

0.41 0.41 0.41 0.41 0.40

Table.2 Calculation of shears stress for sample 2

Sl.No

Horizontal Displacement d (mm)

Corrected Area (Adx6) Cm2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8

36.00 35.88 35.76 35.64 35.52 35.40 35.28 35.16 35.04 34.92 34.80 34.68 34.56 34.44 34.32 34.20 34.08 33.96 33.84 33.72

Proving ring divisions

Shear load in kg

Shear Stress kg/cm2

0 16 22 24 34 52 75 88 95 98 99 100 100 99 97 96 94 93 90 88

0.00 3.61 4.92 5.58 7.79 11.89 17.22 20.00 21.64 22.46 22.63 22.79 22.79 22.55 22.22 21.97 21.56 21.15 20.58 20.17

0.00 0.10 0.14 0.16 0.22 0.34 0.49 0.57 0.62 0.64 0.65 0.66 0.66 0.65 0.65 0.64 0.63 0.62 0.61 0.60

Table.3 Calculation of shears stress for sample 3

Sl.No

Horizontal Displacement d (mm)

Corrected Area (Adx6) Cm2

1 2 3 4 5 6 7 8 9 10

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

36.00 35.88 35.76 35.64 35.52 35.40 35.28 35.16 35.04 34.92

Proving ring divisions

Shear load in kg

Shear Stress kg/cm2

0 27 57 90 112 123 130 136 140 141

0.00 6.25 12.99 20.68 25.49 28.09 29.82 31.16 31.93 32.22

0.00 0.17 0.36 0.58 0.72 0.79 0.85 0.89 0.91 0.92 69

11 12 13 14 15 16 17 18

2.0 34.80 141 32.32 2.2 34.68 141 32.13 2.4 34.56 139 31.74 2.6 34.44 136 31.16 2.8 34.32 135 30.78 3.0 34.20 132 30.11 3.2 34.08 129 29.53 3.4 33.96 127 28.95 Table.4 Nornal stress and Failure shear stress Normal stress, kg/cm2 0.7 1.2 1.7

1 2 3

0.93 0.93 0.92 0.90 0.90 0.88 0.87 0.85

Shear stress, kg/cm2 0.41 0.66 0.93

Graph: Plot the graph between normal stress and shear stress at failure, starting with origin as (0,0) and adopting same scale for both the axes. The Y-intercept when σ = 0 is cohesion and angle made with horizontal is φ.

Shear stress. kg/cm

2

2

1.5

1

0.5 φ

0 0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Normal stress. kg/cm

Fig. 3 Determination of Cohesion and angle of shear resistance Results Cohesion = 0 kg/cm2 (almost zero) Angle of shearing resistance =  = 27 QUESTIONS 1. What is shear strength of soil? 70

2. What are shear strength parameters? Are these constant or variable for one type of soil? 3. What are undrained, consolidated undrained and drained tests? When are they performed? 4. What is the role of pore water pressure on shear strength of soils? 5. What are the methods to increase the shear strength of soils? 6. What are applications of shear strength parameters in the field problems? 7. What is the rate of strain in the conducted test?

71

VANE SHEAR TEST IS : 2720 (Part 30) - 1980 Aim: To determine the shear strength of clay soil using laboratory vane shear apparatus. Equipment and Accessories: Apparatus consists of a torque head mounted on a bracket. Four shear vanes are fixed on a shaft and the shaft is fixed in the lower end of a circular disk graduated in degrees. A torsion spring is fixed between torque head and circular disk. A maximum pointer is provided to facilitate reading the angle of torque. As the strain indicating pointer rotates when the torque is applied, it moves the maximum pointer, leaving it in position when the torque gets released at failure and the vane returns to its initial position. Turing the torque applicator handle effects rotation of the vane.

Fig. 1 Vane shear test setup

72

Theory: In soil, shear strength is contributed by the two properties. (1) Cohesion and (2) Angle of internal friction. In pure clays the shear resistance is due to internal friction is negligible. Hence, complete shear strength in clays is due to cohesion.

Procedure: 

Clean the apparatus thoroughly. Apply grease to the lead screw.

Fig. 2 Principle of vane shear test 73



Fill-up the sampling mould with remoulded soil at required density and moisture content or the undisturbed soil sample.



Level the surface of the sample with the mould.



Mount the sampling tube with sample under the base of the unit and clamp it in position.



Bring the maximum pointer into contact with the strain indicating pointer. Note down the initial reading of these pointers on the circular gradated scale.



Lower the bracket until shear vanes go into soil sample to their full length.



Operate the torque applicator handle until the specimen fails, which is indicated by the return of the strain-indicating pointer or rotation of drum.



Note down the readings of the maximum pointer.



The differences between the two readings (initial and final) give the angle of torque.



Repeat the steps 3 to 8, on a number of samples to obtain the average shear strength of the sample.

Observations and calculations: Diameter of vane (d) = 1.2 cm Height of vane (h) = 2.4 cm Spring constant, K = 13.8 Deg/kg-cm T Shear strength,  = 2 d h d3 (  ) 2 6

Sl.No

1 2 3

Initial reading, θ1º

Final reading, θ2º

0 0 0

24 23 25

Angle of Torque, T = Shear Torque, θ = K strength,   θ1 – θ2 (kg/cm2) 180 24 1.84 0.41 23 1.76 0.39 25 1.92 0.42



Result: Avearge Shear strength of soil,  = 0.42 kg/cm2

QUESTIONS 1. For which type of soil, the vane shear test is used? 2. In vane shear test the obtained shear strength of soil denoted as cohesion, why? 74

3. Why do we rotate vanes in the clock wise direction only? 4. When soil fails, the spring pointer tries to come back to initial reading but it will not reach it until we remove the soil below the vanes. Why? 5. How does moisture content affect the shear strength of soil?

75

SHRINKAGE LIMIT IS : 2720 (Part 6) - 1972 Aim: To determine shrinkage limit, shrinkage ratio and volumetric shrinkage of the given soil fraction passing through 425micron I.S. Sieve. Equipment and Accessories: Evaporating dishes (2 Nos.), shrinkage dish of non corroding metal (45mm dia & 15mm high, 3Nos.), glass cup, glass plates, one should be plain and other with three metal prongs, spatula, straight edge, 425 micron sieve, balance (0.01 & 1gm sensitivity) oven, mercury, distilled water, water content cans. Theory: Shrinkage limit is defined as the maximum water content at which a reduction in water content will not cause a decrease in the volume of a soil mass. It is the lowest water content at which a soil can still be completely saturated. Shrinkage ratio is defined as the ratio of a given volume change expressed as percentage of dry volume to the corresponding change in water content above the shrinkage limit expressed as a percentage of the weight of the oven-dried soil. Shrinkage ratio of a soil is equal to the mass specific gravity of the soil in the dry state. Volumetric shrinkage or Volumetric change is defined as the decrease in the volume of a soil mass, expressed as a percentage of the dry volume of the soil mass when the water content is reduced from a given percentage to the shrinkage limit. The following equation gives the relation between shrinkage limit (ws), shrinkage ratio (SR) and volumetric shrinkage (VS) when the water content is reduced from w1 to ws. VS = (w1 – ws) SR

Fig.1 Principle of shrinkage limit Stage I Soil in shrinkage dish is saturated Stage II Soil colour changed to light by air dry Stage III Soil is oven dried Procedure: 76



Take about 100gm of soil sample passing through 425 micron IS sieve.



Place about 30gm of the soil in evaporating dish and mix it thoroughly with distilled water such that water added will completely fill the voids in the soil and make the soil pasty enough to be readily worked out into the shrinkage dish without entrapping airbubbles.



Weigh a clean and dry shrinkage dish.



Place the shrinkage dish in evaporating dish, fill it with mercury, remove the excess mercury, clean the dish and find the weight of mercury in the shrinkage dish.



Volume of shrinkage dish will be obtained by dividing the weight of mercury by its unit weight. Volume of the wet soil pat will be equal to the volume of shrinkage dish.



Apply a thin coat of grease on the inside of the shrinkage dish.



Place the soil paste at the center of the dish and tap it on firm surface and allow the paste to flow towards edges. Continue the tapping till the soil is compacted and entrapped air is removed. Repeat the process till the dish is completely filled with soil.



Weigh the shrinkage dish with wet soil.



Keep the dish in air till the colour turns from dark to light and then keep it in oven for 24 hours at constant temperature of 105ºC.



Cool the dish and weigh it immediately.



Determine the volume of dry soil pat by immersing it in mercury and measuring the volume of mercury displaced.



Repeat the procedure for two more samples.

Fig. 2 Determination of volume of dry pat Observations and Calculations: Wt. of evaporating dish = W = 24.56 g Wt. of mercury + evaporating dish = 132.6 g 77

Wt. of mercury = 108.06 g Volume of mercury or evaporating dish = Wt. of mercury/ unit weight of mercury = 7.94 ml Volume of wet soil = V = Volume of mercury = 7.94 ml Volume of mercury displaced by the dry soil pat = 5.40 ml Vd = Volume of dry soil pat = 5.40 ml Wt. of dry soil pat = Wd = 10.9 g Weight of dish + wet soil = W1 = 41.06 g Weight of dish + dry soil = W2 = 35.46 g Moisture content, W1 =

= 51.37%

v  vd  Shrinkage limit = ws  W 1  = wd  

7.94  5.4   0.514  10.9  = 0.28 = 28%  

Result: Shrinkage limit: 28% QUESTIONS 1. What is shrinkage limit? 2. What is the significance of shrinkage limit test? 3. Plot the variation between the water content and volume of clay soil 4. Explain volumetric shrinkage and shrinkage ratio with range of values for different types of clays

78

SPECIFIC GRAVITY OF SOIL IS 2720 (Part 2) - 1980 Aim: To determine the specific gravity of the soil sample. Apparatus & Accessories: Density bottle of 50ml or 100ml capacity with stopper, balance sensitive to 0.01gm, vacuum source, distilled water, 4.75mm I.S. sieve.

Fig.1 Density bottle Theory: Specific gravity is defined as the ratio of the weight of a given volume of soil solids at a given temperature to the weight of equal volume of distilled water at that temperature both the weights being taken in air. It is denoted by the letter ‘G’. It can also be defined as the ratio of unit weight of soil solids to that of water. By definition G =

Ws Ww

Where Ws = Wt. of given soil solids of volume V Ww = Wt. of equal volume of distilled water. But Ws = V x γs and Ww = V x γw Where γs and γw are the unit weights of soil solids and water respectively

G

V  s  s  V  w  w

As per I.S. specifications, the specific gravity should be reported at 27º C. If the test is conducted at any other temperature, say t1º C, then

79

G( at , 27C )  G( at ,t1  c ) 

sp.gravity of water at t1  C sp.gravity of water at 27 C

Procedure: 

Take a clean and dry density bottle and weigh it with stopper. Let the weight be W 1.



Take about 10 to 20 gm of oven – dried soil sample into it and find the weight of the bottle and the soil with stopper, let it be W2.



Add distilled water so that the bottle is about half full; remove the entrapped air by connecting it to vacuum source.



Fill the bottle completely with distilled water, put the stopper and wipe it clean. Determine the weight of the bottle and its contents (W3).



Empty the bottle and clean it thoroughly. Fill it with distilled water, put the stopper and wipe the bottle dry on outside. Find its weight (W4).



Repeat the steps (2) and (5) on two more samples of the given soil and tabulate the results as shown below

Observations and calculations The specific gravity of the soil is determined by the relation G

(W2  W1 ) (W2  W1 )  (W3  W4 )

Trial (1)

Trial (2)

1. Wt. of empty density bottle with stopper (W1)

87.62

96.26

84.83

2. Wt. of bottle with stopper + dry soil (W2)

106.47

112.87

101.44

3. Wt. of bottle with stopper + soil + water (W3)

142.4

148.5

137.0255

4. Wt. of bottle with stopper + water (W4)

130.66

138.0877

126.6577

2.65

2.68

2.66

Specific gravity (G)

Trial (3)

Average specific gravity at room temperature = 2.66 Result: The specific gravity of the given soil sample at room temperature = 2.66 QUESTIONS 1. What is the difference between the specific gravity of soils and soils? 2. What are the normal ranges of specific gravity for gravel, clay and organic soils? 3. What are the units for density and specific gravity of soil grains in MKS system of units? 80

4. What are the field applications of specific gravity of soil grains? 5. Instead of water, if any other liquid is used in the specific gravity test, how the expression will be changed? 6. During the test, if air is not completely removed, what will be its effect on the value of specific gravity? 7. If soil used in the test is not completely dry, what is the effect on the value of specific gravity? 8. If coarse grained soil is crushed to powder, what happens to its specific gravity value? Why?

81

AGGREGATE CRUSHING VALUE (IS 2386 – Part 4) Aim/Objective: Determination of aggregate crushing value of coarse aggregate Apparatus: 15 cm diameter open ended steel cylinder, plunger, base plate, tamping rod 16mm diameter of 45 to 60 cm long rounded at one end, balance of 3 kg of accuracy 1 gram, IS Sieves of sizes 12.5, 10 and 2.36 mm, compression testing machine capable of applying a load of 40 tonnes and which can be operated to give a uniform rate of loading so that the maximum load is reached in 10 minutes, cylindrical metal measure of 11.5 cm diameter and 18.0 cm height to measure the aggregate sample. Theory: Aggregate crushing value gives a measure of the resistance of an aggregate to crushing under a gradually applied compressive load. With aggregate of aggregate crushing value 30 or higher, the result may be anomalous, and in such cases the ‘ten percent fines value’ should be determined instead. The crushing value of aggregate is restricted to 30% for concrete used for roads and pavements and 45% for other structures Procedure: 

The size of aggregate shall be varying between 10mm and 12.5mm, to achieve this size the sample of aggregates are sieved through 12.5mm and retained in 10mm sieves.



Aggregate shall be tested in a surface-dry condition. If dried by heating, the period of drying shall not exceed four hours, the temperature shall be 100° to 110°C and the aggregate shall be allowed to arrive at room temperature before testing.



The aggregate shall be filled in the cylindrical measure in three different layers and each layer is tamped 25 times with the rounded end of the tamping rod and finally levelled using the tamping rod as a straight-edge.



The depth of aggregate in the cylindrical measure shall be maintained as 10cm after tamping and levelling in three layers.



The aggregate is weighed in the balance (Weight A).



The steel cylinder of the test apparatus shall be put in position on the base-plate and the test sample is added in one third depth as layer and applied 25 strokes by the tamping rod. The remaining aggregate in two different layers shall be filled in the steel cylinder.

82



The surface of the aggregate shall be carefully levelled and the plunger inserted so that it rests horizontally on this surface, care being taken to ensure that the plunger does not jam in the cylinder.



The apparatus, with the test sample and plunger in position, shall then be placed between the platens of the testing machine and loaded at as uniform a rate as possible so that the total load of 40 tonnes is reached in 10 minutes.



Load shall be released and the material is removed from the steel cylinder, placed in a 2.36-mm IS Sieve and sieved.



The crushed aggregate passed through the sieve shall be weighed (Weight B) .

Observations: Weight of crushed aggregate passed through the 2.36mm sieve, B = Weight of aggregate (after filling 3 layers in cylindrical measue), A = . Calculation: Aggregate crushing value = × 100 = Precaution and safety 

× 100 = 26.43%

Care shall be taken to avoid loss of fines while conducting the test. 83



Loading frame shall be carefully calibrated to attain a load of 40 tonnes in 10 minutes

Conclusion: Aggregate crushing value is 26.43% which is less than 30%. Therefore this aggregate can be used in concrete for roads and pavements. Question/Viva, Answer: 1. In aggregate crushing value test _______ load is applied in _______ minutes. Ans. 40 Tons, 10 2. Type of aggregate used in aggregate crushing value test Ans. Surface dry condition 3. In aggregate crushing value test, aggregate sample is tamped in _____ layers by giving _____ no. of strokes. Ans. 3, 25 References IS: 2386 (Part 4) – 1963 Methods of Test for Aggregates for Concrete – Part IV Mechanical properties. S.K. Khanna and C.E.G. Justo (1971), Highway Material Testing: Laboratory Manual.

84

AGGREGATE IMPACT VALUE (IS 2386 – Part 4) Aim/Objective: Determination of aggregate impact value of coarse aggregate Apparatus: Impact testing machine shown in Figure. 1 of total weight more than 60 kg nor less than 45 kg., metal base, cylindrical steel cup of 102 mm diameter and depth 50 mm, hammer weighing 13.5 to 14.0 kg sliding freely between the guides, accessories to raise the hammer, IS Sieves of sizes 12.5, 10 and 2.36 mm, cylindrical metal measure, straight metal tamping rod of circular cross-section 10 mm in diameter and 230 mm long, rounded at one end, balance of capacity not less than 500 g, readable and accurate to 0.1 g, thermostatically controlled oven to maintain a temperature of 100 to 110°C.

Figure 1. Aggregate impact testing machine Theory: Aggregate impact value gives a relative measure of the resistance of an aggregate to sudden shock or impact, which in some aggregates differs from its resistance to a slow compressive load. Aggregate impact value shall be less than 45% for aggregate used in concrete for concrete other than wearing surface and 30% for concrete used in wearing surface. 85

Procedure: 

Test sample shall consist of aggregate passing 12.5-mm IS Sieve and retained on 10mm Sieve.



The aggregate comprising the test sample shall be dried in an oven for a period of four hours at a temperature of 100 to 110°C and cooled.



Measure shall be filled about one-third full with the aggregate and tamped with 25 strokes of the rounded end of the tamping rod.



Similar quantity of aggregate is added and further tamping of 25 strokes given.



Measure shall finally be filled to overflowing, tamped 25 times and the surplus aggregate struck off, using the tamping rod as a straight-edge.



The net weight of aggregate in the measure shall be determined to the nearest gram (Weight A) and this weight of aggregate shall be used for the duplicate test on the same material.



The cup shall be fixed firmly in position on the base of the machine and the whole of the test sample placed in it and compacted by a single tamping of 25 strokes of the tamping rod.



The hammer shall be raised until its lower face is 380 mm above the upper surface of the aggregate in the cup, and allowed to fall freely on to the aggregate.



The test sample shall be subjected to a total of 15 such blows each being delivered at an interval of not less than one second.



The crushed aggregate shall then be removed from the cup and the whole of it sieved on the 2.36-mm IS Sieve until no further significant amount passes in one minute.



The fraction passing the sieve shall be weighed to an accuracy of 0.1 g (Weight, B).



The fraction retained on the sieve shall also be weighed (Weight C).



Two tests shall be made.

Observations: B = weight of fraction passing the 2.36mm sieve, and A = weight of oven-dried sample. Calculation: The ratio of the weight of fines formed to the total sample weight in each test shall he expressed as a percentage, the result being recorded to the first decimal place: Aggregate impact value = × 100=

× 100=8.79%

86

Precaution and safety 

The impact machine shall rest without wedging or packing upon the level plate, block or floor, so that it is rigid and the hammer guide columns are vertical..



If the total weight (B+C) is less than the initial weight (Weight A) by more than one gram, the result shall be discarded and a fresh test made.

Conclusion: Aggregate impact value is 8.79%. Question/Viva, Answer: 1. In aggregate impact test the sample shall be subjected to _______ number of hammer blows. Ans. 15 2. Type of aggregate used in aggregate impact test Ans. Oven dry 3. In aggregate impact test, aggregate sample is tamped in _____ layers by giving _____ no. of strokes in measure. Ans. 3, 25 References IS: 2386 (Part 4) – 1963 Methods of Test for Aggregates for Concrete – Part IV Mechanical properties. S.K. Khanna and C.E.G. Justo (1971), Highway Material Testing: Laboratory Manual.

87

SPECIFIC GRAVITY AND WATER ABSORPTION (IS 2386 – Part 3) Aim/Objective: Determination of specific gravity, and water absorption of aggregates of size larger than 10mm. Apparatus: Balance, Thermostatically controlled oven of 100 to 110C, wire basket of 6.3 mm mesh, stout water tight container, two dry soft absorbent cloths, shallow tray, airtight container of capacity similar to that of the basket.

Theory: Specific gravity of a aggregate is the ratio of its mass to that of an equal volume of distilled water at a specified temperature. Specific gravity of aggegate is used in design calculation of concrete mixes to convert the weight into volume and vice-versa. Specific gravity generally ranges from 2.62 to 2.88 depending on type of the parent rock. Procedure: 

A sample of 2 kg of aggregate shall be thoroughly washed to remove finer particles and dust.



Drained aggregate shall be placed in the wire basket and immersed in distilled water at a temperature between 22°C and 32°C with a cover of at least 5 cm of water above the top of the basket.



Immediately after immersion the entrapped air shall be removed from the sample by lifting the basket containing it 25 mm above the base of the tank.



The basket containing aggregate sample shall be allowed to drop 25 times at a rate of one drop per second.

88



Basket and aggregate shall remain completely immersed during the operation and for a period of 24 ± l/2 hour afterwards.



The basket and the sample shall then be jolted and weighed in water at a temperature of 22 to 32C. Let the weight of aggregate be A1.



Basket and the aggregate shall then be removed from the water and allowed to drain for a few minutes.



The aggregate shall be gently emptied from the basket on to one of the dry clothes and the empty basket shall be returned to the water, jolted 25 times and weighed in water (weight, A2).



Aggregate placed on the dry cloth shall be gently surface dried with the cloth, transferring it to the second dry cloth when the first will remove no further moisture.



Aggregate shall then be spread out not more than one stone deep on the second cloth and exposed to atmosphere for more than 10 minutes until it appears to be completely surface dry (with some aggregates this may take an hour or more).



The aggregate shall be turned over at least once during this period and a gentle current of unheated air may be used after the first ten minutes to accelerate the drying of difficult aggregates. Aggregate shall then be weighed (weight B).



Aggregate shall then be placed in the oven in the shallow tray, at a temperature of 100C to 110°C and maintained at this temperature for 24 ± l/2 hours.



It shall then be removed from the oven, cooled in the airtight container and weighed (weight C).

Observations: A1 = weight of basket and sample in water = 1760.8g A2 = weight of empty basket in water = 909.6g B = weight of saturated surface dry aggregate = 1345g C = weight of oven dried aggregate = 1330.9g Calculation: Specific gravity of aggregate, G =

Water absorption (% of dry weight) = Precaution and safety

= (

)

=

(

.

(

.

.

. )

=2.69

. )

= 1.09%

89



Aggregate shall not be subjected to direct heat or sun light for drying.



Care shall be taken to bring the aggregate to saturated surface dry condition.

Conclusion: Specific gravity of aggregate is 2.69. Water absorption of aggregate is 1.09%. Question/Viva, Answer: 1. The apparatus used to find the specific gravity of aggregate of size larger than 10mm. Ans. Wire Basket 2. Define specific gravity Ans. 3. What is water absorption? Ans. References IS: 2386 (Part 4) – 1963 Methods of Test for Aggregates for Concrete – Part III Specific gravity, density, voids, Absorption, Bulking. S.K. Khanna and C.E.G. Justo (1971), Highway Material Testing: Laboratory Manual.

90

AGGREGATE ABRASION TEST (DEVAL MACHINE) (IS 2386 – Part 4) Aim/Objective: Determination of aggregate abrasion value of coarse aggregate by the Deval Machine Apparatus: i) Deval abrasion testing machine will consist of two hollow cast iron cylinders closed at one end and furnished with a tightly fitting iron cover at the other end. The inside diameter of the cylinders is 20 cm and depth 34 cm. The cylinders shall be mounted on a shaft at an angle of 30 degrees with the axis of rotation of the shaft. (Fig .1) ii) IS sieve 1.7 mm, iii) abrasive charge shall consist of six cast iron spheres or steel spheres approximately 48 mm in. diameter and each weighing between 390 and 445 g.

Fig. 1Deval Abrasion test Theory: Testing of aggregate against wear is an important test for aggegate to be used for road constructions, ware house floors and pavement construction. The abrasion value should not be more than 30% for concrete for wearing surface and not more than 50% for concrete other than wearing surface. Procedure: 

Coarse aggregate shall be separated by sieving in to various sizes.



Test sample shall consist of clean dry coarse aggregate made up of percentages of the various sizes conforming to one of the gradings shown in Table below. Grading

Passing IS sieve

Retained on IS sieve

A

20 mm 25 mm 40 mm 50 mm

12.5 mm 20 mm 25 mm 40 mm

Percentage of sample 25 25 25 25 91

20 mm 25 mm 40 mm 20 mm 25 mm 12.5 mm 20 mm 10 mm 12.5 mm

B C D E

12.5 mm 20 mm 25 mm 12.5 mm 20 mm 4.75 mm 12.5 mm 4.75 mm 10 mm

25 25 50 50 50 50 50 50 50



Material separated into various size shall be washed and dried.



Grading used shall nearly represent the coarse aggregate furnished for the work.



Weight of the test sample depends on its average specific gravity as given below:

Range of specific gravity



Weight of sample, g

> 2.8

5500

2.4 to 2.8

5000

2.2 to 2.39

4500

< 2.2

4000

Test sample and the abrasive charge shall be placed in the Deval abrasion testing machine and the machine rotated for 10,000 revolutions at a speed of 30 to 33 rev/min.



After the completion of the test, the material shall be removed from the machine and sieved on a 1.70-mm IS Sieve.



The material retained on the sieve shall be washed, dried, and accurately weighed to the nearest gram.

Observations: B = weight of fraction retained on 1.7mm sieve = 4736g A = weight of oven-dried sample = 5000g Calculation: Percentage of wear: The difference between the original weight and the final weight of the test sample shall be expressed as a percentage of the original weight of the test sample. 92

Percentage of wear = Precaution and safety 

× 100 =

× 100 = 5.28%

Aggregates subjected to abrasion and the finer/dust particles are not allowed escape out.

Conclusion: Aggregate abrasion value is 5.28%. Question/Viva, Answer: 1. In aggregate abrasion test, the machine is rotated at a speed of _______revolutions/min. Ans. 30 to 33 2. Type of aggregate used in aggregate abrasion test Ans. Oven dry 3. Weight of aggregate required for conducting abrasion test for different gradings depend on _____ of aggregate Ans. Specific gravity of aggregate References IS: 2386 (Part 4) – 1963 Methods of Test for Aggregates for Concrete – Part IV Mechanical properties. S.K. Khanna and C.E.G. Justo (1971), Highway Material Testing: Laboratory Manual.

93

AGGREGATE ABRASION TEST (Los Angeles Machine) (IS 2386 – Part 4) Aim/Objective: Determination of aggregate abrasion value of coarse aggregate by the Los Angeles Machine Apparatus: i) Los Angeles abrasion testing machine consists of a hollow cylinder closed at both ends having an inside diameter of 700 mm and an inside length of 500 mm, cylinder is mounted on stub shafts attached to the ends of the cylinder and may be rotated about its axis in a horizontal position. An opening in the cylinder shall be provided for the introduction of the test sample. The opening shall be closed dust-tight with a removable cover bolted in place. A removable steel shelf, projecting radially 88 mm into the cylinder and extending its full length, shall be mounted along one element of the interior surface of the cylinder (Fig .1) ii) IS sieve 1.7 mm, iii) abrasive charge shall consist of cast iron spheres or steel spheres approximately 48 mm in. diameter and each weighing between 390 and 445 g.

Fig. 1Los Angeles Abrasion test Theory: Testing of aggregate against wear is an important test for aggegate to be used for road constructions, ware house floors and pavement construction. The abrasion value should not be more than 30% for concrete for wearing surface and not more than 50% for concrete other than wearing surface. Procedure: 

The test sample shall consist of clean aggregate which has been dried in an oven at 105 to 110°C to substantially constant weight, A.



The aggregate sample shall conform to one of the gradings mentioned in Table. 1

Sieve Size (Square Hole)

Weight in g of test sample for grade 94

Passing Retained mm on, mm

A

B

C

D

E

F

G

80

63

-

-

-

-

2500

-

-

63

50

-

-

-

-

2500

-

-

50

40

-

-

-

-

5000

5000

-

40

25

1250

-

-

-

-

5000

5000

25

20

1250

-

-

-

-

-

5000

20

12.5

1250

2500

-

-

-

-

-

12.5

10

1250

2500

-

-

-

-

-

10

6.3

-

-

2500

-

-

-

-

6.3

4.75

-

-

2500

-

-

-

-

4.75

2.36

-

-

-

5000

-

-

-

Table. 1 Grading of test samples 

The grading or gradings used shall be those most nearly representing the aggregate furnished for the work.



The abrasive charge, depends on the grading of the sample as described below

Grading

Number of spheres

Weight of charge, g

A

12

5000±25

B

11

4584±25

C

8

3330±20

D

6

2500±15

E

12

5000±25

F

12

5000±25

G

12

5000±25

95



The test sample and the abrasive charge shall be placed in the Los Angeles abrasion testing machine and the machine rotated at a speed of 20 to 33 rev/min.



For gradings A, B, C and D, the machine shall be rotated for 500 revolutions; for gradings E, F and G, it shall be rotated for 1000 revolutions.



The machine shall be so driven and so counter-balanced as to maintain a substantially uniform peripheral speed.



At the completion of the test, the material shall be discharged from the machine and a preliminary separation of the sample made on a sieve coarser than the l.70 mm IS Sieve.



Material coarser than 1.7 mm IS sieve shall be washed dried in an oven at 105 to 110C to a substantially constant weight and accurately weighed as B.

Observations: B = weight of fraction retained on 1.7mm sieve = 4736g A = weight of oven-dried sample = 5000g Calculation: Percentage of wear: The difference between the original weight and the final weight of the test sample shall be expressed as a percentage of the original weight of the test sample. Percentage of wear = Precaution and safety 

× 100 =

× 100 = 5.28%

Aggregates subjected to abrasion and the finer/dust particles are not allowed escape out.

Conclusion: Aggregate abrasion value is 5.28%. Question/Viva, Answer: 1. In aggregate abrasion test, the machine is rotated at a speed of _______revolutions/min. Ans. 20 to 33 2. Type of aggregate used in aggregate abrasion test Ans. Oven dry 3. Weight of aggregate required for conducting abrasion test for gradings A, B, C and D is _____ Ans. 5 kg 96

References IS: 2386 (Part 4) – 1963 Methods of Test for Aggregates for Concrete – Part IV Mechanical properties. S.K. Khanna and C.E.G. Justo (1971), Highway Material Testing: Laboratory Manual.

97

FLAKINESS INDEX (IS 2386 – Part 1) Aim/Objective: Determination of flakiness index of coarse aggregate Apparatus: Balance of accuracy of 0.1 percent of weight of the test sample. Thickness gauge shown in Fig.1, IS Sieves of sizes shown in Table.1 below. Aggregate sample sufficient to provide a minimum of 200 pieces of any fraction to be tested, sample divider.

Fig. 1Thickness Gauge Table.1 Dimensions of thickness and length gauges Size of aggregate Thickness gauge*, Length gauge#, mm Passing through IS Retained on IS mm Sieve Sieve 63 mm 50 mm 33.9 50 mm 40 mm 27.00 81.0 40 mm 25 mm 19.50 58.5 31.5 mm 25 mm 16.95 25 mm 20 mm 13.50 40.5 20 mm 16 mm 10.80 32.4 16 mm 12.5 mm 8.55 25.6 12.5 mm 10 mm 6.75 20.2 10 mm 6.3 mm 4.89 14.7 * This dimension is equal to 0.6 times the mean sieve size # This dimension is equal to 1.8 times the mean sieve size

98

Theory: Flakiness index of an aggregate is the percentage by weight of particles in it whose least dimension or thickness is less than three-fifth of their mean dimension. This test is not applicable to aggregate of size smaller than 6.3 mm. One of the major contributing factors to the quality of concrete is the quality of aggregates used therein. The shape of aggregate is an important characteristic since it affects the workability of concrete. The characteristic of parent rock and type of crusher will influence the shape of aggregate. The combined flakiness and elongation index of bituminous layers shall be less than 30%. Procedure: 

Aggregate sample shall be selected from material which has been thoroughly mixed and which contains sufficient moisture to prevent segregation.



The weight of sample available shall be not less than the weight given in Table. 2. Table. 2 Minimum weight for Sampling Minimum size present in substantial proportions, mm 63 50 40 25 20 16 12.5 10.0 0.3

Minimum weight of sample for testing, kg 100 100 50 50 25 25 12 6 3



The sample shall be brought to an air-dry condition before weighing and sieving.



This may be achieved either by drying at room temperature or by heating at a temperature of 100°C to 110°C.



The air-dry sample shall be weighed and sieved successively on the appropriate sieves starting with the largest. Care shall be taken to ensure that the sieves are clean before use.



Each sieve shall be shaken separately over a clean tray until not more than a trace passes, but in any case for a period of not less than two minutes.



The shaking shall be done with a varied motion, backwards and forwards, left to right, circular clockwise and anti-clockwise, and with frequent jarring, so that the material is kept moving over the sieve surface in frequently changing directions. 99



Material shall not be forced through the sieve by hand pressure. Lumps of fine material, if present, may be broken by gentle pressure with fingers against the side of the sieve.



Light brushing with a soft brush on the under side of the sieve may be used to clear the sieve openings.



On completion of sieving, the material retained on each sieve, together with any material cleaned from the mesh, shall be weighed.



Separation of Flaky material- Each fraction shall be gauged in turn for thickness on a metal gauge of the pattern shown in Fig. 1 or in bulk on sieves having elongated slots.



The width of the slot used in the gauge or sieve shall be of the dimensions specified in co1. 3 of Table 1 for the appropriate size of material.



Weighing of Flaky Material - The total amount passing the gauge shall be weighed to an accuracy of at least 0.1 percent of the weight of the test sample.

Observations: Total weight of sample = 7830g Size of aggregate Passing through Retained on IS Sieve IS Sieve 1 63 mm 50 mm 2 50 mm 40 mm 3 40 mm 25 mm 4 31.5 mm 25 mm 5 25 mm 20 mm 6 20 mm 16 mm 7 16 mm 12.5 mm 8 12.5 mm 10 mm 9 10 mm 6.3 mm Total weight of aggregate passing the thickness gauge

Sl. No

Weight of aggregate passing respective sieve size (g) 0 45 120 120 164 86 72 43 33 683

Calculation: Flakiness Index = =

× 100 = 8.72%

× 100

Precaution and safety 

Bottom of sieve shall be cleaned with wire brush after sieving.



All flaky aggregate passing thickness gauge shall be separated correctly.

100

Conclusion: Flakiness index of aggregate sample is 8.72%. Question/Viva, Answer: 1. The flakiness index of aggregate measures which property? Ans. Size of aggregate 2. Mention the name of IS code for determination of Flakiness Index? Ans. IS 2386 – Part 1 3. Flakiness and elongation index should be less than _______% for Bituminous layers Ans. 30% 4. An aggregate is known as flaky aggregate if its least dimension is less than _____ times the mean size of aggregate. Ans. 0.6. References IS: 2386 (Part 1) – 1963 Methods of Test for Aggregates for Concrete – Part 1 Particle size and Shape. S.K. Khanna and C.E.G. Justo (1971), Highway Material Testing: Laboratory Manual.

101

ELONGATION INDEX (IS 2386 – Part 1) Aim/Objective: Determination of elongation index of coarse aggregate Apparatus: Balance of accuracy of 0.1 percent of weight of the test sample. Length gauge shown in Fig.1, IS Sieves of sizes shown in Table.1 below. Aggregate sample sufficient to provide a minimum of 200 pieces of any fraction to be tested, sample divider.

Fig. 1Length Gauge Table.1 Dimensions of thickness and length gauges Size of aggregate Thickness gauge*, Length gauge#, mm Passing through IS Retained on IS mm Sieve Sieve 63 mm 50 mm 33.9 50 mm 40 mm 27.00 81.0 40 mm 25 mm 19.50 58.5 31.5 mm 25 mm 16.95 25 mm 20 mm 13.50 40.5 20 mm 16 mm 10.80 32.4 16 mm 12.5 mm 8.55 25.6 12.5 mm 10 mm 6.75 20.2 10 mm 6.3 mm 4.89 14.7 * This dimension is equal to 0.6 times the mean sieve size # This dimension is equal to 1.8 times the mean sieve size Theory: The elongation index of an aggregate is the percentage by weight of particles whose greatest dimension (length) is greater than one and four-fifths times their mean dimension. This test is not applicable to aggregate of size smaller than 6.3 mm. One of 102

the major contributing factors to the quality of concrete is the quality of aggregates used therein. The shape of aggregate is an important characteristic since it affects the workability of concrete. The characteristic of parent rock and type of crusher will influence the shape of aggregate. The combined flakiness and elongation index of bituminous layers shall be less than 30%. Procedure: 

Aggregate sample shall be selected from material which has been thoroughly mixed and which contains sufficient moisture to prevent segregation.



The weight of sample available shall be not less than the weight given in Table. 2. Table. 2 Minimum weight for Sampling Minimum size present in substantial proportions, mm 63

Minimum weight of sample for testing, kg 100

50

100

40

50

25

50

20

25

16

25

12.5

12

10.0

6

0.3

3



The sample shall be brought to an air-dry condition before weighing and sieving.



This may be achieved either by drying at room temperature or by heating at a temperature of 100°C to 110°C.



The air-dry sample shall be weighed and sieved successively on the appropriate sieves starting with the largest. Care shall be taken to ensure that the sieves are clean before use.



Each sieve shall be shaken separately over a clean tray until not more than a trace passes, but in any case for a period of not less than two minutes.



The shaking shall be done with a varied motion, backwards and forwards, left to right, circular clockwise and anti-clockwise, and with frequent jarring, so that the material is kept moving over the sieve surface in frequently changing directions. 103



Material shall not be forced through the sieve by hand pressure. Lumps of fine material, if present, may be broken by gentle pressure with fingers against the side of the sieve.



Light brushing with a soft brush on the under side of the sieve may be used to clear the sieve openings.



On completion of sieving, the material retained on each sieve, together with any material cleaned from the mesh, shall be weighed.



Separation of Elongated material- Each fraction shall be gauged individually for length on a metal length gauge of the pattern shown in Fig. 1.



The gauge length used shall be that specified in co1 4 of Table 1 for the appropriate size of material.



The total amount retained by the length gauge shall be weighed to an accuracy of at least 0.1 percent of the weight of the test sample.

Observations: Total weight of sample = 9830g Sl. No 1

Size of aggregate Passing through Retained on IS IS Sieve Sieve 63 mm 50 mm

Weight of aggregate retained on respective sieve size (g) 0

2

50 mm

40 mm

55

3

40 mm

25 mm

110

4

31.5 mm

25 mm

130

5

25 mm

20 mm

184

6

20 mm

16 mm

96

7

16 mm

12.5 mm

62

8

12.5 mm

10 mm

63

9

10 mm 6.3 mm Total weight of aggregate retained on the length gauge

53 753

Calculation: Elongation Index = = Precaution and safety

× 100 = 7.66%

× 100

104



Bottom of sieve shall be cleaned with wire brush after sieving.



All elongated aggregate retained on the length gauge shall be separated correctly.

Conclusion: Elongation index of aggregate sample is ______. Question/Viva, Answer: 1. Use of elongated aggregate in concrete or bituminous mix _________ its strength. Ans. Decreases 2. The Elongation index of aggregate measures which property? Ans. Size of aggregate 3. Mention the name of IS code for determination of Elongation Index? Ans. IS 2386 – Part 1 3. Flakiness and elongation index should be less than _______% for Bituminous layers Ans. 30% 4. An aggregate is known as elongated aggregate if its longest dimension is larger than _____ times the mean size of aggregate. Ans. 1.8. References IS: 2386 (Part 1) – 1963 Methods of Test for Aggregates for Concrete – Part 1 Particle size and Shape. S.K. Khanna and C.E.G. Justo (1971), Highway Material Testing: Laboratory Manual.

105

BITUMEN PENETRATION TEST IS: 1203 - 1978 Aim/Objective: Determination of penetration value of bitumen. Apparatus: Metal or glass cylindrical flat bottom container, needle, water bath, transfer dish, penetration apparatus, thermometer, time device such as stop watch Theory: Penetration of a bituminous material is the distance in tenths of a millimetre that a standard needle will penetrate vertically into a sample of the material under standard conditions of temperature, load and time.

Fig.1 Principle of penetration test Procedure: 

Soften the material to a pouring consistency at a temperature not more than 90°C for bitumens above the respective approximate softening point and stir it thoroughly until it is homogeneous and is free from air bubbles and water.



Pour the melt into the container to a depth at least 10 mm in excess of the expected penetration.



Protect the sample from dust and allow it to cool in an atmosphere at a temperature between 15 to 30°C for 1 to 2 h for 45 mm deep container and 1 to 1 h when the container of 35 mm depth is used.



Place it along with the transfer dish in the water bath at 25.0 ± 0.1 C and allow it to remain for 1 to 2 h and 1 to 1 h for 45 mm and 35 mm deep container respectively.



Testing shall be carried out at 25.0 ± 0.1C.



Fill the transfer dish with water from the water bath to a depth sufficient to cover the container completely.



Place the sample in it and put it upon the stand of the penetration apparatus.



Adjust the needle (previously washed clean with benzene, carefully dried, and loaded with the specified weight ) to make contact with the surface of the sample.

106



This may be accomplished by placing the needle point in contact with its image reflected by the surface of the material from a suitably placed source of light.



Unless otherwise specified, load the needle holder with the weight required to make a total moving weight (that is, the sum of the weights of the needle, carrier and superimposed weights) of 100 ± 0.25 g.



Note the reading of the dial or bring the pointer to zero.



Release the needle and adjust the points, if necessary to measure the distance penetrated.



Make at least three determinations at points on the surface of the sample not less than 10 mm apart and not less than 10 mm from the side of the dish.



After each test, return the sample and transfer dish to the water bath, and wash the needle clean with benzene and dry.



In the case of material of penetration greater than 225, three determinations on each of two identical test specimens using a separate needle for each determination shall be made, leaving the needle in the sample on completion of each determination to avoid disturbance of the specimen.

Observation and Calculation: Express the depth of penetration of the needle in tenths of millimetre. The value of penetration reported shall be the mean of not less than three determinations Precaution and safety 

If the sample contains extraneous matter, it should be sieved through IS Sieve 30.



To avoid overheating at the bottom of the container, use of an air oven or sand hath is recommended.



While the needle is penetrating into the sample, if there is any movement of the container, that determination shall be discarded.

Conclusion: Penetration of bituminous material 200 in 1/10 of mm. Question/Viva, Answer: 1. What is the total moving weight of needle. Ans. 100g 2. Penetration observations shall not be closer than _____ mm Ans. 10 107

References IS: 1203 1978 Indian Standard methods for testing tar and bituminous materials: Determination of penetration. Highway Engineering, S.K. Khanna & C.E.G. Justo, Nemchand & Bros. 7th edition (2000).

108

DUCTILITY TEST IS: 1203 - 1978 Aim/Objective: Determination of ductility of bitumen. Apparatus: Brass mould with shape, dimensions and tolerances as shown in Fig. 1, water bath, testing machine, thermometer

Fig. 1 Mould for ductility test Theory: The ductility of a bituminous material is measured by the distance in centimeters to which it will elongate before breaking when a briquette specimen is pulled apart at a specified speed and at a specified temperature. Procedure: 

Completely melt the bituminous material to be tested to a temperature of 75 to 100C above the approximately softening point until it becomes thoroughly fluid.



Assemble the mould on a brass plate and in order to prevent the material under test from sticking, thoroughly coat the surface of the plate and interior surfaces of the sides of the mould with a mixture of equal parts of glycerine and dextrine.



In filling, pour the material in a thin stream back and forth from end to end of the mould until, it is more than level full.



Leave it to cool at the room temperature for 30 to 40 min, and then place in a water bath maintained at the specified temperature for 30 min after which cut off the excess bitumen by means of a hot, straight-edged putty knife or spatula so that the mould shall be just level full.

109



The test shall be conducted at a temperature of 27.0 ± 0.5C and at a rate of pull of 50 ± 2.5 mm/min.



Place the brass plate and mould with briquette specimen, in the water bath and keep at the specified temperature for about 85 to 95 minutes.



Remove the briquette from the plate, detach the sidepieces, and test the briquette immediately.



Attach the rings at each end of the clips to the pins or hooks in the resting machine and pull the two clips apart horizontally at a uniform speed as specified until the briquette ruptures.



Measure the distance in centimeters through which the clips have been pulled to produce rupture.



While the test is being made, make sure that the water in the tank of the testing machine covers the specimen both above and below it by at least 25 mm and is maintained continuously within ±0.5C of the specified temperature.

Observation and Calculation: A normal test is one in which the material between the two clips pulls out to a point or to a thread and rupture occurs where the cross-sectional area is a minimum. Report the average of three normal tests as the ductility of the sample, provided the three determinations be within ±5 percent of their mean value. If the value of three determinations do not lie within ± 5 percent of their mean but the two higher values are within ± 5 percent of their mean then record the mean of the two higher values as test result. If a normal test is not obtainable on three successive tests, report the ductility as being unobtainable under the conditions of test. Precaution and safety If the bituminous material comes in contact with the surface of the water or the bottom of the bath, the test shall not be considered normal. Adjust the specific gravity of the water in the bath by the addition of either methyl alcohol or sodium chloride so that the bituminous material does not either come to the surface of the water, or touch the bottom of the bath at any time during the test. Conclusion: Elongation of bitumen is 5 cm. Question/Viva, Answer: 1. What is the rate of pull of the testing machine? 110

Ans. 50 ± 2.5 mm/min 2. Ductility of bitumen is a measure of _________ of bitumen. Ans. elongation References IS: 1208 1978 Indian Standard methods for testing tar and bituminous materials: Determination of ductility. Highway Engineering, S.K. Khanna & C.E.G. Justo, Nemchand & Bros. 7th edition (2000).

111

SOFTENING POINT TEST IS: 1205 - 1978 Aim/Objective: Determination of softening point of bitumen. Apparatus: Ring and Ball Apparatus, steel balls, ball guide, support, thermometer, bath, stirrer.

Fig. 1 Assembly of apparatus for determination of softening point (Ring and ball – two rings)

Fig.2 Principle of sofening point test Theory: The temperature at which the substance attains a particular degree of softening under specified condition of test. Procedure: Preparation of test sample: 

Heat the material to a temperature between 75°C and 100°C above its softening point, stir until it is completely fluid and free from air bubbles and water, and filter, if necessary, through Is Sieve 30

112



Place the rings, previously heated to a temperature approximating to that of the molten material, on a metal plate which has been coated with a mixture of equal parts of glycerine and dextrine, and fill with sufficient melt to give an excess above the level of the ring when cooled.



After cooling for 30 minutes in air, level the material in the ring by removing the excess with a warmed, sharp knife.

Materials of Softening Point-Below 80°C 

Assemble the apparatus with the rings, thermometer and ball guides-in position, and fill the bath to a height of 50 mm above the upper surface of the rings with freshly boiled distilled water at a temperature of 5°C.



Maintain the bath at a temperature of 5°C for 15 minutes after which place a ball, previously cooled to a temperature of 5°C, by means of forceps in each ball guide.



Apply heat to the bath and stir the liquid so that the temperature rises at a uniform rate of 5.0 ± 0.5% per minute until the material softens and allows the ball to pass through the ring.



Make two observations

Materials of Softening Point-Above 80°C 

The procedure for materials of softening point above 80°C is similar to that described above with the difference that glycerine is used in place of water in the bath and the starting temperature of the test is 35°C.



Make two observations.

Observation and Calculation: 

Record for each ring and ball, the temperature shown by the thermometer at the instant the sample surrounding the ball touches the bottom plate of the support, if any, or the bottom of the bath.



Report to the nearest 0.5°C the mean of the temperature recorded in duplicate determinations as the softening point.

Precaution and safety Only freshly boiled distilled water shall, be used in the test, as otherwise air bubbles may form on the specimen and affect the accuracy of the results. The prescribed rate of heating shall be rigidly adhered to for ensuring accuracy of results. A sheet of filter paper or thin amalgamated sheet, placed on the bottom of the glass vessel and conveniently weighed 113

would prevent the material from sticking to the glass vessel, and considerable time and trouble in cleaning would thereby be saved. Conclusion: Softening point of bitumen is 48C. Question/Viva, Answer: 1. What is softening point of bitumen? Ans. The temperature at which the substance attains a particular degree of softening under specified condition of test. References IS: 1205 - 1978 Indian Standard methods for testing tar and bituminous materials: Determination of softening point. Highway Engineering, S.K. Khanna & C.E.G. Justo, Nemchand & Bros. 7th edition (2000).

114

FLASH AND FIRE POINT TEST IS: 1209 - 1978 Aim/Objective: Determination of flash point and fire point of asphaltic bitumen. Apparatus: Cleaveland apparatus, Thermometer - Low Range: -7 to 110C, Graduation 0.5 C High Range: 90 to 370C Theory: Bituminous materials leave out volatiles at high temparatures depending upon their grade. These volatile catch fire causing a flash. This condition is very hazardous and it is therefore essential to quantify thid temperature for each bitumen grade. The flash point of a material is the lowest temperature at which the application of .test flame causes the vapours from the material momentarily catch fire in the form of a flash under specified conditions of test. The fire point is the lowest temperature at which the application of test flame causes the material to ignite and burn at least for 5 s under specified conditions of test. Procedure: 

Heat the bitumen between 75 and 100C and remove the air bubbles and water by stirring the sample.



Fill the cup with the bitumen to be tested up to the mark & place it on the bath.



Fix the open clip; insert the thermometer of high or low range as per requirement and also the stirrer, to stir the sample.



Light the test flame and supply heat at such a rate that the temperature increase recorded using a thermometer is neither less than 5C/min nor more than 6C/min. Stirring is done at a rate of 60 revolutions per minute.



Note the temperature at which first flash appears when test flame is bought close to the surface of the material. This temperature is noted as Flash point temperature. The true flash of the bitumen vapour shall be identified and it shall not be confused with the bluish halo that sometimes surrounds the test flame.



The flash point is taken as the temparature read on the thermometer at the time of the flame application that causes a bright flash in the interior of the cup in closed system.



For open cup it is the instance when flash qppears first at any point on the surface of the material.

115



After flash point is obtained, heating is continued at such a rate that the increase in temperature recorded by the thermometer is neither less than 5C/min nor more than 6C/min.



A test flame is lighted and adjusted such that it has a bead of size 4mm in diameter. First flame application is made at least 17C below the actual flash point and then at every 1C and 3C.



Stirring is discontinued during application of the test flame.



Finally note that thermometer at which the application of test flame causes the material to ignite and burn for at least 5 seconds. This temperature is noted as Fire point temperature.

Observation and Calculation: Flash point temparature = 180C Fire point temparature = 200C References IS: 1205 - 1978 Indian Standard methods for testing tar and bituminous materials: Determination of softening point. Highway Engineering, S.K. Khanna & C.E.G. Justo, Nemchand & Bros. 7th edition (2000).

116

NORMAL CONSISTENCY OF CEMENT IS 4031 (Part 4) - 1988 Aim/Objective: Determination of consistency of standard cement paste. Apparatus: Representative sample of cement, Vicat apparatus, balance, gauging trowel. Theory: The procedure for determining the quantity of water required to produce a cement paste of standard consistency is determined. The standard consistency of a cement paste is defined as that consistency which will permit the Vicat plunger to penetrate to a point 5 to 7 mm from the bottom of the Vicat mould.

Fig. 1 Vicat Apparatus Procedure: 

Prepare a paste of weighed quantity of Cement of 300g with a weighed quantity of potable or distilled water. The time of gauging is not less than 3 minutes, nor more than 5 min, and the gauging shall be completed before any sign of setting occurs.



The gauging time shall be counted from the time of adding water to the dry cement until commencing to fill the mould.



Fill the Vicat mould E with this paste, the mould resting upon a non-porous plate.



After completely filling the mould, smoothen the surface of the paste, making it level with the top of the mould. 117



The mould may be slightly shaken to expel the air.



In filling the mould, the operator’s hands and the blade of the gauging trowel shall alone be used.



Place the mould with cement paste on a non porous plate under the rod bearing the plunger.



Lower the plunger gently to touch surface of the cement paste and allow it to sink into the paste.



This operation shall be carried immediately after filling the mould.



Prepare trial pastes with varying percentages of water and test as described above until the amount of water necessary for make up the standard consistency defined above.

Observation and Calculation: Express the amount of water as a percentage by mass of the dry cement to the first place of decimal. Sl No

Weight of cement in g

Volume of water, ml

% of water

Penetration of plunger from bottom, mm

1

300

75

25

28

2

300

90

30

23

3

300

105

35

13

4

300

107

35.66

11

5

300

110

36.66

7

Precaution and safety 

Temperature of moulding room, dry materials and water shall be maintained at 27 ± 2°C. The relative humidity of the laboratory shall be 65 ± 5 percent.



Cement paste shall be mixed thoroughly and uniformly.

Conclusion: Standard consistency of cement is 36.66%. Question/Viva, Answer: 1. Standard consistency of cement paste is the consistency which will allow the plunger to penetrate ________ from bottom of the mould. Ans. 5 to 7 mm 118

2. Name of the apparatus used for finding normal consistency of cement is ________ Ans. Vicat apparatus 3. Name of the device used in vicat apparatus to find normal consistency cement Ans. Plunger References IS: 4031 (Part 4) – 1988 Methods of Physical test for hydraulic cement- Part IV Mechnical Properties. Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

119

FINENESS OF CEMENT IS 4301 (Part 1): 1996 Aim/Objective: Determination of fineness of cement by dry sieving. Apparatus: 90 Micron IS Sieve, Balance, brush for cleaning the sieve. Theory: The fineness of cement is measured by sieving it on standard sieve. The proportion of cement of which the grain sizes are larger than a specified mesh size is determined. Procedure: 

The representative sample of cement shall be mixed thoroughly before testing.



Agitate the sample of cement to be tested by shaking for 2 min in a stoppered jar and wait for 2 minutes.



The resulting cement powder is mixed gently using a clean dry rod to distribute the fines throughout the cement.



A cement sample of 10g is carefully measured to nearest 0.01g and placed on 90 sieve.



Fit a tray under the sieve and lid over the sieve and agitate the sieve by different movements until no more fine material passes through it.



Remove and weigh the residue. Express its mass as a percentage, R 1, of the quantity first placed in the sieve.



Gently brush all the fine material off the base of the sieve into the tray.



Repeat the whole procedure using a fresh 10 g sample to obtain R2. Calculate the residue of the cement R as the mean of R1 and R2 as a percentage.



When the results differ by more than 1 percent absolute, carry out a third sieving and calculate the mean of the three values.

Observations: Initial weight of cement for conducting test = 10g Weight of residue to 90 sieve = w g Calculation: Percentage of residue = Precaution and safety

× 100



The sieving process is carried out manually by a skilled and experienced operator.



Sieve shall be checked periodically for wear and tear. 120

Conclusion: Percentage of residue ______. Question/Viva, Answer: 1. The sieve size used to determine the fineness of cement. Ans. 90 References IS: 4031 (Part 1) – 1996 Method of physical tests for hydraulic cement – Part 1 Determination of fineness by dry sieving. Concrete Technology by M. S. Shetty - S. Chand & Co. :2004

121

INITIAL SETTING AND FINAL SETTING TIME OF CEMENT IS 4031 (Part 4) - 1988 Aim/Objective: Determination of initial setting and final setting time of cement. Apparatus: Representative sample of cement, Vicat apparatus, balance, gauging trowel. Theory: The procedure for determining the quantity of water required to produce a cement paste of standard consistency is determined. The standard consistency of a cement paste is defined as that consistency which will permit the Vicat plunger to penetrate to a point 5 to 7 mm from the bottom of the Vicat mould.

Fig. 1 Vicat Apparatus Procedure: 

Prepare a neat cement paste by gauging the cement with 0.85 times the water required to give a paste of standard consistency.



Potable or distilled water shall be used in preparing the paste.



The time of gauging is not less than 3 minutes, nor more than 5 min, and the gauging shall be completed before any sign of setting occurs.



Start a stop-watch at the instant when water is added to the cement.



Fill the Vicat mould E with a cement paste gauged as above, the mould resting upon a non-porous plate. 122



Fill the mould completely and smooth off the surface of the paste making it level with the top of the mould.



The cement block thus prepared in the mould is the test block.



Immediately after moulding, place the test block in the moist closet or moist room and allow it to remain there except when determinations of time of setting are being made.

Determination of Initial Setting Time 

Place the test block confined in the mould and resting on the non-porous plate, under the rod bearing the needle ( C ).



Lower the needle gently until it comes in contact with the surface of the test block and quickly release, allowing it to penetrate into the test block.



In. the beginning, the needle will completely pierce the test block. Repeat this procedure until the needle, when brought in contact with the test block and released as described above, fails to pierce the block beyond 5.0 ± 0.5 mm measured from the bottom of the mould.



The period elapsing between the time when water is added to the cement and the time at which the needle fails to pierce the test block to a point 5.0 ± 0.5 mm measured from the bottom of the mould shall be the initial setting time.

Determination of Final Setting Time 

Replace the needle ( C ) of the Vicat apparatus by the needle with an annular attachment ( F ).



The cement shall be considered as finally set when, upon applying the needle gently to the surface of the test block, the needle makes an impression thereon, while the attachment fails to do so.



The period elapsing between the time when water is added to the cement and the time at which the needle makes an impression on the surface of test block while the attachment fails to do so shall be the final setting time.



In the event of a scum forming on the surface of the test block, use the underside of the block for the determination.

Observation and Calculation: Results of initial and final setting time are reported below. Initial setting time = 60 min Final setting time = 2h 20 min 123

Precaution and safety 

Clean appliances shall be used for gauging.



All the apparatus shall be free from vibration during the test.



Care shall be taken to keep the needle straight

Conclusion: Initial setting time of cement 60 min. Final setting time of cement 2h 20 min. Question/Viva, Answer: 1. Name of the apparatus used for finding initial setting and final setting time of cement is ________ Ans. Vicat apparatus 2. Name of the device used in vicat apparatus to find initial setting time of cement Ans. Needle References IS: 4031 (Part 5) – 1988 Methods of Physical test for hydraulic cement- Part V Determination of initial and final setting time of cement. Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

124

SOUNDNESS OF CEMENT IS 4031 (Part 3) - 1988 Aim/Objective: Determination of soundness of cement. Apparatus: Representative sample of cement, Le-Chatelier method appratus shown in Fig. 1, balance, water bath. Theory: It is very important that cement after setting shall not undergo a large expansion after setting causing disruption of the set and hardened mass. This causes serious difficulties for the durability of structures when such concrete is used. The testing of cement to ensure that the cement does not show any appreciable subsequent expansion is of prime imporatnce.

Fig.1 Lechatlier Apparatus Procedure: 

Place the lightly oiled mould on a lightly oiled glass sheet and fill it with cement paste formed by gauging cement with 0.78 times the water required to give a paste of standard consistency.



The time of gauging is not less than 3 minutes, nor more than 5 min, and the gauging shall be completed before any sign of setting occurs.



Care shall be taken to keep the edges of the mould together while the mould is filled.

125



Cover the mould with another piece of lightly oiled glass sheet, place a small weight on this covering glass sheet and immediately submerge the whole assembly in water at a temperature of 27 ± 2°C and keep there for 24 hours.



Measure the distance separating the indicator points to the nearest 0.5 mm.



Submerge the mould again in water at the temperature prescribed above. Bring the water to boiling, with the mould kept submerged, in 25 to 30 minutes, and keep it boiling for three hours.



Remove the mould from the water, allow it to cool and measure the distance between the indicator points.



The difference between these two measurements indicates the expansion of the cement.

Observation and Calculation: Calculate the mean of two values to the nearest 0.5 mm to represent the expansion of cement. Precaution and safety 

Clean appliances shall be used for gauging.



Cement and water shall be mixed properly.

Conclusion: Expansion of cement = 1.5 mm (must be less than 10 mm). Question/Viva, Answer: 1. Name of the apparatus used for finding soundness of cement is ________ Ans. Le-Chatelier method 2. Quantity of water added to cement to conduct soundness test Ans. 0.78P (P, Standard consistency of cement) References IS: 4031 (Part 3) – 1988 Methods of Physical test for hydraulic cement- Part III Determination of soundness. Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

126

COMPRESSIVE STRENGTH OF CEMENT IS 4031 (Part 7) - 1988 Aim/Objective: Determination of compressive strength of cement. Apparatus: Representative sample of cement, sand, vibrating machine, poking rod, cube mould of 50 cm2, gauging trowel, balance, graduated glass cylinder. Theory: Compressive strength of hardened cement is one of the important property of cement. Strength tests are not made on neat cement paste because of difficulties of excessive shrinkage and subsequent cracking of neat cement. Strength of cement is indeirectly found on specific proportions of cement and sand. Procedure: 

The material for each cube shall be mixed separately and the quantity of cement, standard sand and water shall be as follows: Cement = 200 g, Standard Sand = 600g, Water =

+ 3.0 percent of combined mass

of cement and sand, where P is P is the percentage of water required to produce a paste of standard consistency. 

Clean appliances shall be used for mixing and the temperature of water and that of the test room at the time when the above operations are being performed shall be 27 ± 2°C.



Potable/distilled water shall be used in preparing the cubes.



Place on a nonporous plate, a mixture of cement and standard sand. Mix it dry with a trowel for one minute and then with water until the mixture is of uniform colour.



The time of mixing shall in any event be not less than 3 min and should the time taken to obtain a uniform colour exceed 4 min, the mixture shall be rejected and the operation repeated with a fresh quantity of cement, sand and water.

Moulding Specimen 

In assembling the moulds ready for use, cover the joints between the halves of the mould with a thin film of petroleum jelly and apply a similar coating of petroleum jelly between the contact surfaces of the bottom of the mould and its base plate in order to ensure that no water escapes during vibration.



Treat the interior faces of the mould with a thin coating of mould oil.



Place the assembled mould on the table of the vibration machine and hold it firmly in position by means of a suitable clamp.



Place the mortar in the cube mould and prod with the rod. 127



The mortar shall be prodded 20 times in about 8 s to ensure elimination of entrained air and honey-combing.



Place the remaining quantity of mortar in the hopper of the cube mould and prod again as specified for the first layer and then compact the mortar by vibration.



The period of vibration shall be two minutes at the specified speed of 12,000 ± 400 vibration per minute.



At the end of vibration, remove the mould together with the base plate from the machine and finish the top surface of the cube in the mould by smoothing the surface with the blade of a trowel.

Curing Specimen 

Keep the filled moulds in moist closet or moist room for 24 ± 1 hours after completion of vibration.



At the end of that period, remove them from the moulds and immediately submerge in clean fresh water and keep there until taken out just prior to breaking.



The water in which the cubes are submerged shall be renewed every 7 days and shall be maintained at a temperature of 27 ± 2°C.



After they have been taken out and until they are broken, the cubes shall not be allowed to become dry.

Testing 

Test three cubes for compressive strength for each period of curing (1, 3 and 7 days).



The cubes shall be tested on their sides without any packing between the cube and the steel plattens of the testing machine.



One of the plattens shall be carried on a base and shall be self-adjusting.



The load shall be steadily and uniformly applied, starting from zero at a rate of 35 N/mm2/min.

Observation and Calculation: The measured compressive strength of the cubes shall be calculated by dividing the maximum load applied to the cubes during the test by the cross-sectional area. Cross sectional area of mould = 50 cm2 Faillure load = 264 kN Compressive strength of cement =

× ×

= 52.8 N/sq.mm 128

Precaution and safety 

Do not consider specimens that are faulty or that give strengths differing by more than 10 percent from the average value of all the test specimens..



Cement and water shall be mixed properly.

Conclusion: Compressive strength of cement 52.8 N/sq.mm. Question/Viva, Answer: 1. The compressive strength of cement is determined at a rate of ________ Ans. 35 N/mm2/min 2. Quantity of water added to the mixture of cement and sand to prepare mortar cube Ans. + 3.0 References

IS: 4031 (Part 6) – 1988 Methods of Physical test for hydraulic cement- Part VI Determination of compressive strength of hydraulic cement other than masonary cement. Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

129

WORKABILITY OF CONCRETE BY COMPACTION FACTOR IS 1199 - 1959 Aim/Objective: Determination of workability of concrete by compaction factor test. Apparatus: It shall consist of the two conical hoppers (A and B) mounted above a cylindrical mould (C).

Fig. 1 compaction factor apparatus Theory: Workable concrete is the one which exihibits very little internal friciton between particle to particle or which overcomes the frictional resistance offered by the formwork surafce or reinforcement contained in the concrete with just the amount of compacting efforts explained in theses tests. Compaction factor lays down the procedure for determining the workability of concrete, where the nominal maximum size of the aggregate does not exceed 38 mm. The test is designed primarily for use in the laboratory, but if circumstances permit, it may also be used in the field. It is more precise and sensitive than the slump test and is particularly useful for concrete mixes of very low workability as are normally used when concrete is to be compacted by vibration; such concrete may consistently fai1 to slump. Procedure: 

A concrete mix either prepared in laboratory at a proportion of 1:2:4 or collected from the mixer shall be placed gently in the upper hopper, using the hand scoop.

130



The hopper shall be filled level with its brim and the trap-door shall be opened so that the concrete falls into the lower hopper.



Certain mixes have a tendency to stick in one or both of the hoppers. If this occurs, the concrete may be helped through by pushing the rod gently into the concrete from the top. During this process, the cylinder shall be covered by the trowels.



Immediately after the concrete has come to rest, the cylinder shall be uncovered, the trap-door of the lower hopper opened, and the concrete allowed to fall into the cylinder.



The excess of concrete remaining above the level of the top of the cylinder shall then be cut off by holding a trowel in each hand, with the plane of the blades horizontal, and moving them simultaneously one from each side across the top of the cylinder, at the same time keeping them pressed on the top edge of the cylinder.



The outside of the cylinder shall then be wiped clean.



The weight of the concrete in the cylinder shall then be determined to the nearest 10 g and this weight shall be known as the weight of partially compacted concrete.



The cylinder shall be refilled with concrete .from the same sample in layers approximately 5 cm deep, the layers being heavily rammed or preferably vibrated so as to obtain full compaction.



The top surface of the fully compacted concrete shall be carefully struck off level with the top of the cylinder. The outside of the cylinder shall then be wiped clean. Weight of fully compacted concrete shall be determined.

Observation: Weight of partially compacted concrete, A = 11.4 kg Weight of fully compacted concrete, B = 13.4 kg Calculation The compacting factor is defined as the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete Compaction factor = Precaution and safety 

. .

= 0.84

The opening of trap doors and filling the cylinder with concrete loosely shall be carried out at a place free from vibration or shock.

131



Ensure that the weight of partially compacted and fully compacted concrete is determined by properly leveling the surface of concrete to the top of mould.

Conclusion: Compaction factor of concrete 0.84. Question/Viva, Answer: 1. Define compaction factor Ans. The compacting factor is defined as the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete. 2. Fully compacted concrete is prepared by compacting each layer of concrete in _____ cm thickness. Ans. 5 References IS: 1199 – 1959 Methods of sampling and analysis of concrete. Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

132

WORKABILITY OF CONCRETE BY SLUMP TEST IS 1199 - 1959 Aim/Objective: Determination of workability of concrete by slump test. Apparatus: Mould - The mould for the test specimen shall be in the form of the frustum of a cone having the following internal dimensions: Dimensions

cm

Bottom diameter

20

Top diameter

10

Height

30

Tamping rod

Theory: This method of test specifies the procedure to be adopted, either in the laboratory or during the progress of work in the field, for determining the slump test, the consistency of concrete where the nominal maximum size of the aggregate does not exceed 38 mm. In the case of concrete containing aggregate of maximum size more than 38 mm, the concrete shall be wet-sieved through 1 in screen to exclude aggregate particles bigger than 38 mm. Procedure: 

A concrete mix is prepared in laboratory at a proportion of 1:2:4.



Mould shall be placed on a smooth, horizontal, rigid and non-absorbent surface, such as a carefully levelled metal plate. The mould being firmly held in place while it is being filled.

133



The mould shall be filled in four layers, each approximately one-quarter of the height of the mould.



Each layer shall be tamped with twenty-five strokes of the rounded end of the tamping rod.



The strokes shall be distributed in a uniform manner over the cross-section of the mould and for the second and subsequent layers shall penetrate into the underlying layer.



The bottom layer shall be tamped throughout its depth.



After the top layer has been rodded, the concrete shall be struck off level with a trowel or the tamping rod, so that the mould is exactly filled.



Any mortar which may have leaked out between the mould and the base plate shall be cleaned away.



The mould shall be removed from the concrete immediately by raising it slowly and carefully in a vertical direction.



This allows the concrete to subside and the slump shall be measured immediately by determining the difference between the height of the mould and that of the highest point of the specimen being tested.



Test shall be carried out within a period of two minutes after sampling.



The slump measured shall be recorded in terms of millimeters of subsidence of the specimen during the test.

Observation and Calculation Measure the difference between the height of the mould and that of the highest point of the specimen being tested. Precaution and safety 

Internal surface of the mould shall be thoroughly cleaned and freed from superfluous moisture and any set concrete before commencing the test.



Any slump specimen which collapses or shears off laterally gives incorrect result and if this occurs the test shall be repeated with another sample.

Conclusion: Slump of concrete 30mm. Question/Viva, Answer: 1. Define slump of concrete 134

Ans. Difference between height of the mould and that of the highest point of the specimen being tested. 2. Number of layers of concrete in the slump cone Ans. 4 3. Number of strokes on each layer of concrete to conduct slump test Ans. 25 References IS: 1199 – 1959 Methods of sampling and analysis of concrete. Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

135

WORKABILITY OF CONCRETE BY VEE - BEE CONSISTOMETER METHOD IS 1199 - 1959 Aim/Objective: Determination of workability of concrete by vee-bee consistometer method. Apparatus: Veee-Bee Consistometer consists of: a) A vibrator table resting upon elastic supports, b) A metal pot, c) A sheet metal cone, open at both ends, and d) A standard iron rod.

Vee-bee Consistometer

Theory: The determination of consistency of concrete using a Vee-Bee Consistometer, which determines the time required for transforming, by vibration, a concrete specimen in the shape of a conical frustum into a cylinder. Procedure: 

A concrete mix is prepared in laboratory at a proportion of 1:2:4.



A slump test is conducted in the sheet metal cylindrical pot of the consistometer.

136



A glass disc attached to the swivel arm shall be moved and placed just on the top of the slump cone in the pot and before the cone is lifted up.



The position of the concrete cone shall be noted by adjusting the glass disc attached to the swivel arm.



The cone shall then be lifted up and the slump noted on the graduated rod by lowering the glass disc on top of the concrete cone.



The electrical vibrator shall then be switched on and the concrete shall be allowed to spread out in the pot.



The vibration shall then be continued until the whole concrete surface uniformly adheres to the glass disc and the time taken for this to be attained shall be noted with a stop watch. The time is recorded in sec.

Observation and Calculation Consistency of the concrete shall be expressed in VB-degrees which are equal to the time in seconds recorded. Precaution and safety 

Internal surface of the mould shall be thoroughly cleaned and freed from superfluous moisture and any set concrete before commencing the test.

Conclusion: VB Degrees of concrete 5 sec. Question/Viva, Answer: 1. Define VB degree of concrete Ans. Consistency of the concrete shall be expressed in VB-degrees which are equal to the time in seconds 2. Number of layers of concrete in the slump cone Ans. 4 3. Number of strokes on each layer of concrete to conduct slump test Ans. 25 References IS: 1199 – 1959 Methods of sampling and analysis of concrete. Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

137

COMPRESSIVE STRENGTH OF CONCRETE IS : 516 - 1959 Aim/Objective: Determination of compressive strength of concrete. Apparatus: Testing machine (Fig.1), steel or metal cubes of size 15 x 15 x 15cm, cylinder of 15cm diameter and 30 cm long, vibrating machine, steel tamping rod of 16 mm diameter and 0.6 m long, balance, scale. Theory: Compressive strength of concrete is one of the important property of concrete to assess the quality of work at site. Based on the compressive strength grade of concrete is reported. Compressive strength is obtained by testing of cubes and cylinders. Accelarared strength test is conducted to know the strength of concrete before 28 days.

Fig.1 Compression testing of concrete Procedure: 

Cube specimens are made immediately after mixing and in such a way to produce full compaction of the concrete with neither segragation nor excessive laitence.



Concrete is filled in to the mould in layers approximately 5 cm deep.



The scoop full of concrete is moved around the top edge of the mould to ensure uniform distribution within the mould.



Each layer is compacted by hand or by vibration.



Hand compaction of concrete is carried by tamping rod. For cubical specimens concrete layer is compacted by 35 strokes per layer. For cylindrical specimens the number of blows are 30 per layer.



Strokes are penetrated into the underlying layer and the bottom layer is rodded throughout the depth.



After the top layer is compacted the surface of concrete is brought to the finished level at top of mould. 138



The test specimen are stored in moist air of relative density more than 90% and a temparature of 27 ± 2C for 24 hours from time of addition of water.



After this period the specimen are marked and removed from the mould. Immediately submerged in clean fresh water until just taken out for testing. Specimens are not allowed to dry.



Concrete cubes/cylinders stored in water shall be tested immediately on removal from the water and while they are still in the wet condition.



Surface water and grit shall be wiped off the specimens and any projecting fins removed.



Specimens when received dry shall be kept in water for 24 hours before they are taken for testing. The dimensions of the specimens shall be measured to the nearest 0.2 mm and their weight shall be noted before testing.



The bearing surfaces of the testing machine shall be wiped clean and any loose sand or other material removed from the surfaces of the specimen which are to be in contact with the compression platens.



In the case of cubes, the specimen shall be placed in the machine in such a manner that the load shall be applied to opposite sides of the cubes as cast, that is, not to the top and bottom.



The axis of the specimen shall be carefully aligned with the centre of thrust of the spherically seated platen.



No packing shall be used between the faces of the test specimen and the steel platen of the testing machine.



As the spherically seated block is brought to bear on the specimen, the movable portion shall be rotated gently by hand so that uniform seating may be obtained.



Load shall be applied without shock and increased continuously at a rate of approximately 140 kg/sq cm/min until the resistance of the specimen to the increasing load breaks down and no greater load can be sustained.

Observation: The maximum load applied to the specimen shall then be recorded and the appearance of the concrete and any unusual features in the type of failure shall be noted. Calculation

139

The measured compressive strength of the specimen shall be calculated by dividing the maximum load applied to the specimen during the test by the cross-sectional area, calculated from the mean dimensions of the section and shall be expressed to the nearest kg per sq cm. Average of three values shall be taken as the representative of the batch provided the individual variation is not more than ± 15 percent of the average. Otherwise repeat tests shall be made. Failure load, P = 922.5 kN Compressive strength of concrete =

= Precaution and safety

= ×

.

= 41 N/sq.mm



Specimen shall be loaded axially through the centriodal axis.



Specimen is loaded gradually without any jerks.

Conclusion: Compressive strength of concrete 41 N/sq.mm. Question/Viva, Answer: 1. The rate of load applied on the specimen Ans. 140 kg/sq cm/min References IS : 516 - 1959 Indian standard methods of tests for strength of concrete Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

140

BULKING OF SAND Aim/Objective: Determination of necessary adjustment for bulking of fine aggregate. Apparatus: Sample of sand, 2 Moulds, steel rule. Theory: Sand brought on to a building site or other works may contain an amount of moisture which will cause it, when loosely filled into a container, to occupy a larger volume than it would occupy if dry. If the sand is measured by loose volume, it is necessary in such a case to increase the measured volume of the sand, in order that the amount of sand put into the concrete may be the amount intended for the nominal mix used (based on dry sand). Free moisture forms a film around each particle. This film of moisture exerts surface tension which keeps the neighbouring particles away from it. No point of contact is possible between the particles. This causes bulking of the volume. Depending on the percentage of moisture content and particle size of sand the extent of surface tension and movement of particles differ. The bulking of sand increases with increase of moisture content upto certain limit beyond which further increase of moisture content decreases the volume. Fine sand bulks more than coarse sand. The coarse aggregate also bulks little which can be neglected. Extremely fine sand and manufactured fine aggregate bulks to about 40%. Due to bulking fine aggregate shows completely unrealistic volume. It is necessary that consideration must be given to the effect of bulking in proportoning of the concrete by volume. If bulking is not considered the resulting concrete may be undersanded and harsh. Procedure: 

Put sufficient quantity of the sand loosely into a container. Until it is about two-thirds full.



Level off the top of the sand. Measure the height of sand by pushing a steel rule vertically down through the sand at the middle to the bottom of mould. Suppose this is h cm (Fig.1).



Empty the sand out of the container fill in another container without any lose.



Half fill the first container with water. Put back about half the sand and rod it with a steel rod, about 6 mm in diameter, so that its volume is reduced to a minimum. Then add the remainder of the sand and rod it in the same way.



Smooth and level the top surface of the inundated sand and measure its depth at the middle with the steel rule. Suppose this is h’ cm.

141

Fig.1 Bulking of sand Observation: h= Height of loose sand in the mould in cm = 20 cm h’= Height of top surface of inundated sand in cm = 16 cm Calculation The percentage of bulking of the sand due to moisture shall be calculated from the formula: Percentage of bulking = Precaution and safety

′

− 1 × 100 =

− 1 × 100 =

× 100 = 25%

Conclusion: Percentage bulking of sand 25%. Question/Viva, Answer: References IS:2386 (Part III) – 1963 Indian Standard methods of test for aggregates for concrete, Part III Specific gravity, density, voids, absorption and bulking. Concrete Technology by M. S. Shetty - S. Chand & Co. 2004

142

FLEXURE STRENGTH OF CONCRETE IS : 516 - 1959

Aim: Determination of flexural strength of moulded concrete flexure test specimens. Apparatus & Equipment: The testing machine shall be capable of applying load with a permissible error of less than ± 0.5% of the applied load when a high degree of accuracy is required. In commercial use the applied rate of loading is less than ± 1.5 percent of the applied load. The bed of the testing machine is provided with two steel rollers, 38 mm in diameter, on which the beam specimen is supported. The rollers shall be so mounted that the distance from centre to centre is 60 cm for 15.0 cm specimens or 40 cm for 10.0 cm specimens. Load is applied through two similar rollers mounted at the third points of the supporting span, that is, spaced at 20 or 13.3 cm centre to centre. The load shall be divided equally between the two loading rollers. All rollers shall be mounted in such a manner that the load is applied axially without subjecting the specimen to any torsional stresses. A suitable arrangement satisfying the requirements is shown in Fig. 1 below.

Fig.1 Loading on flexure beam Procedure: 

Concrete is mixed in manner a similar to compression test cube specimens.



The standard size of cubes are casted of size 15 × 15 × 70 cm. Alternatively, if the largest nominal size of the aggregate is less than 19 mm, specimens 10 × 10 × 50 cm may be used. 143



The joints between the sections of the mould shall be thinly coated with mould oil.



The interior faces of the assembled mould shall be thinly coated with mould oil to prevent adhesion of the concrete.



Test specimens stored in water at a temperature of 24° to 30°C for 48 hours before testing, shall be tested immediately on removal from the water while they are still in a wet condition.



Bearing surfaces of the supporting and loading rollers shall be wiped clean, and any loose sand or other material removed from the surfaces of the specimen where they are to make contact with the rollers.



The specimen shall then be placed in the machine in such a manner that the load shall be applied to the uppermost surface as cast in the mould along two lines spaced 20.0 or 13.3 cm apart.



Axis of the specimen shall be carefully aligned with the axis of the loading device.



No packing shall be used between the bearing surfaces of the specimen and the rollers.



Load shall be applied without shock and increasing continuously at a rate such that the extreme fibre stress increases at approximately 7 kg/cm2/min.



The rate of loading of 400 kg/min for the 15.0 cm specimens and at a rate of 180 kg/min for the 10.0 cm specimens.



Load shall be increased until the specimen fails, and the maximum load applied to the specimen during the test shall be recorded.



The appearance of the fractured faces of concrete and any unusual features in the type of failure shall be noted.

Observations and calculations Flexural strength of the specimen shall be expressed as the modulus of rupture fb and obtained as follows. a = Distance between the line of fracture and the nearer support, measured on the centre line of the tensile side of the specimen, in cm 144

If ‘a’ is greater than 20.0 cm for 15.0 cm specimen, or greater than 13.3 cm for a 10.0 cm specimen fb =

×

×

If ‘a’ is less than 20.0 cm but greater than 17.0 cm for 15.0 cm specimen, or less than 13.3 cm but greater than 11.0 cm for a 10.0 cm specimen fb = b = measured width in cm of the specimen,

×

×

d = measured depth in cm of the specimen at the point of failure, l = length in cm of the span on which the specimen was supported, and p = maximum load in N applied to the specimen. If ‘a’ is less than 17.0 cm for a 15.0 cm specimen, or less than 11.0 cm for a 10.0 cm specimen, the results of the test shall be discarded. b = 15 cm d = 15 cm a = 21 cm l = length of specimen = 60 cm p = Failure load = 6.92E+10 N fb =

×

×

=

.

×

×

×

= 12.3 Mpa

Result: Modulus of rupture = 12.3 Mpa

145