sand test

Sand Equivalent Test

NANYANG TECHNOLOGICAL UNIVERSITY School of Civil and Structural Engineering

LABORATORY - PAVEMENT MATERIALS

SAND EQUIVALENT TEST OBJECTIVES To show the relative proportion of clay-like or plastic fines and silt in granular soils and fine aggregates by means of a rapid field test known as the Sand Equivalent (SE).

BACKGROUND Most specifications for unbound granular base have requirements concerning rock strength, weathering resistance and grading. The maximum percentage finer than 0.075 mm usually lies between 7% and 10%. Some specifications go further and stipulate a requirement concerning plasticity of this fines material, for example it should be non-plastic or the Plasticity Index should be less than 6. Others have specified the Sand Equivalent, for example, California: not less than 45, New Zealand: not less than 40. The Sand Equivalent Test was devised by Hveem (1953) as a quick test to determine the "presence of undesirable quantities of adverse clay-like materials ... since an excess of clays is usually detrimental to the performance of any aggregate". Its primary application was for concrete aggregate and sand. O'Harra (1955) applied the test to the fraction of road base aggregates finer than 4.75 mm and made correlation of Sand Equivalent with Plasticity Index and percentage of fines (less than 0.075 mm). He concluded that the quality of a pavement aggregate was always satisfactory if SE > 55 and almost always satisfactory if SE > 35 hence, the figures quoted in the previous paragraph for California and New Zealand.

SUMMARY OF TEST METHOD (ASTM 1998) A measured volume of soil or fine aggregate and a small quantity of flocculation solution are poured into a graduated plastic cylinder and are agitated to loosen the clay-like coatings from the sand particles in the test specimen. The specimen is then ‘irrigated’ using additional flocculation solution forcing the clay-like material into suspension above the sand. After a prescribed sedimentation period,

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Sand Equivalent Test

the height of the clay and sand in the cylinder is determined. The sand equivalent is the ratio of sand height to clay height times 100.

APPARATUS AND WORKING SOLUTION The principal item of equipment is a transparent plastic cylinder with an inside diameter of 32 mm and a height of 432 mm graduated up to 390 mm by 2 mm divisions and a rubber stopper to fit. A weighted foot is also required consisting of a brass rod 445 mm long, having at the lower end a 25 mm diameter foot with a flat smooth under-surface and a conical upper surface. A cylindrical brass weight 51 mm diameter is attached to the upper end of the rod to bring the total weight to 1 kg. An irrigator tube is required that is made of 6 mm copper or brass tubing long enough to reach the bottom of the cylinder and one end closed by flattening the tube to a wedgeshaped point. Two 1-mm holes are drilled laterally through the flat sides of the wedge. The remainder of the equipment comprises plastic tubing, clamps and containers which do not need specifying. The working flocculation solution consists, per litre of solution, • 2.67 g Anhydrous Calcium Chloride • 12.06 g (9.53 ml) BP Glycerine • 0.28 g (0.26 ml) 40% Formaldehyde Solution (as a preservative).

PROCEDURE 1.

The sample must all pass through a 4.75 mm sieve and be in a slightly damp condition. Where the sample has been separated from a coarser material (such as 40 mm base course) care must be taken to collect all fines adhering to the larger stones. By quartering or preferably using a riffle box, samples are split to provide enough material to fill the measuring container to within 10 mm of the brim. Extreme care must be taken to obtain truly representative samples.

2.

Start the siphon so that solution will flow through the irrigator tube.

3.

Fill 102 ± 3 mm of solution into the cylinder.

4.

Pour the test sample into the cylinder and tap the base with heel of the hand to release any air bubbles.

5.

Leave to stand for 10 ± 1 minutes.

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Sand Equivalent Test

6.

Stopper the cylinder and loosen the material by partially inverting the cylinder.

7.

Hold the cylinder horizontally and shake it vigorously from side to side 90 cycles in 30 seconds with an amplitude of 23 ± 3 cm. Alternatively, a mechanical shaker having a throw of 203.2 ± 1.0 mm and operating at 175 ± 2 cycles-per-minute may be used in which the cylinder and its contents are shaken for 45 ± 1 s.

8.

Immediately after shaking, set the cylinder upright on the bench and remove the stopper. Insert the irrigator tube and start the flow, rinsing material from the sides of the cylinder above the liquid level. Push the tube to the bottom of the sample. Stab and twist the tube gently with one hand, and at the same time rotate the cylinder slowly with the other hand. Make sure the fines are dislodged to ‘float’ above the sand column. Remove the irrigator and allow the liquid level to rise to 380 mm.

9.

Allow the cylinder to stand undisturbed and free from vibration for 20 minutes ± 15 seconds. Start the timer immediately after withdrawing the irrigator tube.

10. Read and record the level of the top of the silt/clay suspension. This is called the "Clay Height", which represents the length of the (clay + sand) column.

clear soln

clay height h1

clay

sand height h2

sand

11. Lower the weighted foot assembly very gently into the cylinder until it comes to rest on the sand. Read and record the level of the indicator. The level at the top of the sand column, called the "Sand Height", is determined by subtracting 254 mm from the reading of the indicator.

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Sand Equivalent Test

12. Calculate the Sand Equivalent: SE =

Sand Height (h2) ×100(%) Clay Height (h1)

. . .(1)

The result is quoted to the next higher whole number.

DISCUSSION (a) Report the source of the aggregate, and any pre-treatment it has received, i.e. sieving, washing, heating, drying, etc. (b)

Report the clay and sand heights and the Sand Equivalent.

(c)

Comment on the result.

(d)

Compare your results with other group(s)

REFERENCES 1. ASTM (1998). ASTM D2419-95, Standard test method for sand equivalent value of soils and fine aggregate. 1998 Annual Book of ASTM Standards, Volume 04.03, American Society for Testing and Materials, Philadelphia 19103-1187. 2. Hveem, F.N. (1953). Highway Research Board Proceedings. 3. O’Harra, W.G. (1955). Highway Research Board Proceedings.

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