Determination of the Flakiness and the Elongation Determination of Angularity Number

September 12, 2017 | Author: Faisal Sardar | Category: Porosity, Concrete, Construction Aggregate, Density, Water
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[FAISAL SARDAR] 2009-CIV-122

EXPERIMENT #1 DETERMINATION OF THE FLAKINESS AND THE ELONGATION INDEX OF THE GIVEN AGGREGATE SAMPLE.

RELATED THEORY SHAPES OF PARTICLES The usual shapes of the particles are;  Rounded (river gravel)  Flaky (laminated rock)  Elongated  Angular( crushed rock) ROUNDED AGGREGATES are preferred in concrete roads (rigid pavements) as the workability of concrete increases due to the less friction between the surfaces. ANGULAR SHAPE of the particles is desirable in granular base coarse (flexible pavement) due to better interlocking and increased stability. FLAKY and ELONGATED PARTICLES are considered as a source of weakness.

FLAKY PARTICLE :  A flaky particle is the one whose least dimension (thickness) is than 0.6 times the mean size.  These are the materials of which the thickness is small as compared to the other two dimensions.  Limit of flaky particles in the mixes is 30%. If the flaky particles are greater than 30% then the aggregate is considered undesirable for the intended use.

FLAKINESS INDEX: It is the percentage by weight of flaky particles in a sample. The Flakiness index is calculated by expressing the weight of flaky particles as a percentage of the total weight of sample

ELONGATED PARTICLES : These are the particles having length considerably larger than the other two dimensions and it is the particle whose greater dimension is 1.8 times its mean size. Limit of elongated particles in the mixes is 45%. Thus, if the elongated particles are greater than 45%, then the aggregate is considered undesirable for the intended use.

ELONGATION INDEX : It is the percentage by weight of elongated particles in a sample. The Elongated index is calculated by expressing the weight of Elongated particles as percentage of total weight of the sample.

SCOPE & SIGNIFICANCE:

[FAISAL SARDAR] 2009-CIV-122

This test is used to determine the particle shape of the aggregate and each particle shape being preferred under specific conditions. The significance of flakiness & elongation index is as follows;      

The degree of packing of the particles of one size depends upon their shape. Due to high surface area to volume ratio, the flaky and elongated particles lower the workability of concrete mixes. Flaky and elongated particles are considered undesirable for base coarse construction as they may cause weakness with possibilities of braking down under heavy loads. BS-1241 specifies a Flakiness index not exceeding 30% irrespective of the aggregate size. Maximum permitted Elongated index is 35, 40 or 45% for aggregate sizes 2 ½’’ – 2’’, 1 ½’’ – ¾’’ & ½’’ – 3/8’’. Both Flakiness and Elongation tests are not applicable to sizes smaller then 6.3mm i.e. ¼’’ sieve.

APPARATUS:  Thickness/Flakiness Index Gauge  Length/Elongation Index Gauge  Aggregate sample to be tested

Test Procedure for Determining Flakiness Index: The apparatus consist of standard thickness gauge.

Sieve analysis is done on the sample.  Then The aggregates are first sorted into a number of closely limited particle size groups – 2 ½’’ – 2’’, 1 ½’’ – ¾’’ & ½’’ – 3/8’’  Each group (fraction) is weighed and tested for thickness on appropriate opening of the thickness gauge by passing each particle through slot of specified thickness along least dimension.  The weight of particles passing the thickness gauge is recorded for each fraction. This is the weight of flaky particles.  The flakiness index is calculated by expressing the weight of flaky particles as a percentage of total weight of the sample.

[FAISAL SARDAR] 2009-CIV-122

TEST PROCEDURE FOR DETERMINING FLAKINESS INDEX: The apparatus consist of length gaug

The aggregates are first sorted into a number of closely limited particle size groups – 2 ½’’ – 2’’, 1 ½’’ – ¾’’ & ½’’ – 3/8’’  Each group (fraction) is weighed and tested for length on appropriate opening of the length. The pieces of aggregates which do not pass through specified gauge length with its long side, are separated and weighted. These are termed as Elongated Particles. .  The Elongation index is calculated by expressing the weight of Elongated particles as a percentage of total weight of the sample

[FAISAL SARDAR] 2009-CIV-122

EXPERIMENT # 2 DETERMINATION OF ANGULARITY NUMBER FOR THE GIVEN AGGREGATE SAMPLE. This test is also carried out for determining shape of the aggregates. Based upon shape the aggregates may be classified as Rounded, Angular or Flaky. Angular particles possess well defined edges formed at the intersection of roughly planer faces and are commonly formed in aggregates prepared by crushing of rocks. Angularity in general is the absence of rounding of particles of an aggregate. This test is performed to determine the angularity number i.e. the absence of roundedness or the degree of angularity of the aggregate specimen

RELATED THEORY SHAPES OF PARTICLES : The usual shapes of the particles are;  Rounded (river gravel)  Flaky (laminated rock)  Elongated  Angular (crushed rock)

ANGULARITY : It is the absence of roundness. An aggregate particle, which is more rounded, is less angular and vice versa.

ANGULARITY NUMBER :  Angularity number of an aggregate is the amount (to the higher whole number) by which the percentage of voids in it after compacting in a prescribed manner exceeds 33.  Where, “33” is the percentage of volume of voids, in a perfectly rounded aggregate. “67” is the percentage of volume of solids in a perfectly rounded aggregate when compacted in specified manner.  The value of angularity number generally lies between 0 & 11.  In road construction angularity number of 7 – 10 is generally preferred.

SIGNIFICANCE   

The degree of packing of particles of single sized aggregate depends upon the angularity of aggregate. The angularity of the aggregate can be estimated from the properties of voids in a sample of aggregate compacted in a specified manner. The angularity number ranges from 0 for a highly rounded grave to about 11 for freshly crushed angular aggregates.

[FAISAL SARDAR] 2009-CIV-122  

Higher the angularity number, more angular and less workable is the concrete mix. In cement concrete roads (rigid pavements) rounded aggregates are preferred because of better workability and higher strength. In bituminous or water bound macadam construction (like flexible pavements), angular aggregates with high angularity number are preferred because of high stability due to better interlocking and friction. Higher the angularity number, more angular and less workable is the concrete mix. In road construction, angularity number of 7 -10 is generally preferred.

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APPARATUS :    

A metal cylinder of about 3-liter capacity. Temping rod of circular cross-section, 16mm Φ, 60cm in length. Rounded at one end. A metal scoop. A weighing balance.

PROCEDURE :  This procedure is for aggregate size ¾ to No.4. If aggregate is coarser than ¾, a cylinder of large capacity shall be required but amount of compactive effort or energy should be proportional to the volume of the cylinder.  10 Kg of the sample is taken for the test. The material should be oven dried. The aggregate is compacted in three layers, each layer being given 100 blows using the standard tamping rod at a rate of 2 blows/second by lifting the rod 5 cm above the surface of the aggregate and then allowing it to fall freely. The blows are uniformly distributed over the surface of the aggregate.  After compacting the third layer, the cylinder is filled to overflowing and excess material is removed off with temping rod as a straight edge.  The aggregate with cylinder is then weighed. Three separate determinations are made and mean weight of the aggregate in the cylinder is calculated.

CALCULATION METHODS : Method – 1 Add measured quantity of water in the compacted aggregate till all the voids are filled and water appears to the surface. Volume of water added is approximately equal to the volume of voids in the compacted aggregate.

Angularity number =

Method – 2 ANGULARITY NUMBER = 67Where W = mean weight of the aggregate filling cylinder. C = Weight/Volume of water that can completely fill the cylinder (= 3 liters = 3000 ml – in our lab) Gs = Specific Gravity of the aggregate

EXPERIMENT NO. 3

[FAISAL SARDAR] 2009-CIV-122

SPECIFIC GRAVITY (RELATIVE DENSITY) AND WATER ABSORPTION TEST FOR AGGREGATES

RELATED THEORY SPECIFIC GRAVITY : It Is Defined As Ratio Of Weight Of Solid To The Weight Of An Equal Volume Of Gas Free Distilled Water (No Dissolved Air/Impurities) At A Stated Temperature.

WATER ABSORPTION : It is the ratio of weight of water absorbed to the weight of dry sample expressed as a percentage. It will not include the amount of water adhering to the surface of the particles.

COARSE AGGREGATES : Any material which is retained on BS sieve #4 (ASTM sieve 4.75mm) is known as coarse aggregate.

FINE AGGREGATES: Any material which is passing BS sieve #4 (ASTM sieve 4.75mm) is known as fine aggregate.

SATURATED SURFACE DRY (S.S.D.) CONDITION : It is the condition related with the aggregate particles in which the permeable pores of the aggregate particles are filled with water but without free water on the surface of the particles.

OVEN DRIED SPECIFIC GRAVITY: It is the ratio of the oven dried density of the aggregate to the density of the gas free distilled water at a standard temperature (i.e. 4 oC).

SATURATED SURFACE DRY SPECIFIC GRAVITY: It is the ratio of the saturated surface dry density of the aggregate to the density of the gas free distilled water at a standard temperature (i.e. 4 oC).

APPARENT SPECIFIC GRAVITY : It is the ratio of the apparent density of the aggregate to the density of the gas free distilled water at a standard temperature (i.e. 4 oC).

TYPES OF CRUSH AVAILABLE IN PAKISTAN:

[FAISAL SARDAR] 2009-CIV-122 1- SARGODHA CRUSH Sargodha crush possess the following properties;  Greenish/Dark Gray in color  High strength  Usually elongated particles 2- MARGALLA CRUSH Margalla crush possess the following properties;  Light Gray in color  Low in strength 3- SAKHI SARWAR CRUSH Sakhi Sarwar crush possess the following properties;  Whitish in color

SIGNIFICANCE: In this test method we will determine the relative density (i.e. specific gravity) and the water absorption of the coarse aggregates.  The knowledge of the specific gravity is important for the concrete technologist to determine the properties of concrete made from such aggregates.  It is used for the calculation of the volume occupied by the aggregates in various mixes and generally it ranges from 2.5 to 3.  The pores at the surface of the particles affect the bond between the aggregate and the cement paste thus influences the concrete strength. Smaller the number of pores, higher will be the specific gravity hence more will be the bond strength and more concrete strength.  Though higher specific gravity of aggregate is considered as an indication of its high strength; it is not possible to judge the suitability on this basis alone without finding other mechanical properties like aggregate abrasion value etc.  Water absorption is a measure of porosity of aggregates and its resistance to frost action.  Higher water absorption means more pores hence aggregate will be the considered as weak.  Water absorption value ranges from 0.1 – 2.0% for aggregate normally used in roads surfaces.  Aggregates with water absorption up to 4.0% are acceptable in base coarse

APPARATUS:      

Balance 5 Kg capacity readable to 0.5g. Sample container in the form of a wire mesh bucket of capacity 4000 – 7000 cm3 and not more than 6.3mm mesh. Suitable arrangement for suspending the container in water from center of the balance. A container for filling water and suspending the wire mesh bucket. Shallow tray and absorbent cloth. Thermostatically controlled oven.

[FAISAL SARDAR] 2009-CIV-122

SAMPLE: Take representative sample. Reject all material passing #4, weight of sample to be used for the test would depend upon the nominal maximum size as given in table below.

PROCEDURE:     

Thoroughly wash the aggregates to remove any dust. Oven dry and cool the aggregates for 1 to 3 hours and then immerse in water for 24 hours. Remove the specimen from water and roll it in a large absorbent cloth until all visible films of water are removed. Weight the specimen in saturated surface dry conditions. Place the saturated surface dry specimen in wire mesh bucket and weight it in water. Shake the bucket to remove all entrapped air before weighing. Dry the sample to constant weight in oven, cool and weigh

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