To determine the percent of undesirable particles in the fine aggregate fraction used in the design of Portland cement concrete mixtures. The method is also applicable for determining the relative proportions of detrimental fine dust or claylike material in soils.
Equipment and Materials
The Sand Equivalent test kit consists of the following:
Graduated plastic cylinder
Weighted foot assembly and a siphon assembly
78-liter (1 gallon) bottle
Four measuring tins having a diameter of approximately 57 mm (2. inches) and a capacity of 85 ± 5 ml
Mechanical sand equivalent shaker
Stock calcium chloride solution
75-mm (No. 4) sieve
Prepare fine aggregate passing a 4.75-mm (U.S. standard No. 4) sieve, oven dried and room temperature condition, before testing. Quarter by splitting approximately 1500 grams. Moisten each specimen slightly to prevent loss of fines, and mix each specimen thoroughly. Place each of the four specimens in a closed can.
Siphon 101.6 ± 54 mm (4 ± 0.1 inches) of working calcium chloride solution into the plastic cylinder. Pour one of the prepared specimens into the plastic cylinder using the funnel to avoid spillage. Tap the bottom of the cylinder sharply by hand to release any air bubbles. Allow the material to stand for about 10 minutes.
Place the stopper on the cylinder and vigorously shake it manually to loosen the material. Place the cylinder in the mechanical sand equivalent shaker, set the timer, and allow the machine to run for 45 seconds. Remove the cylinder from the mechanical shaker, remove the stopper, and set it upright on the table.
Insert the irrigator tube into the cylinder and rinse material from the inside surface as it is lowered. Force the irrigator through the material to the bottom of the cylinder by applying a gentle stabbing and twisting action, while the working solution flows from the irrigator tip. This action flushes the fine particles into the suspension above the coarser sand sizes. Continue this irrigation process until the cylinder is filled to the 381-mm (15-inch) mark.
Raise the irrigator slowly without shutting off the flow so that the liquid level is maintained at about 381 mm (15 inches) while the irrigator is being withdrawn. Regulate the flow just before the irrigation is entirely withdrawn and adjust the final level to 381 mm (15 inches).
The flow is supplied through the siphon assembly to a 3.78-liter (1 gallon) bottle of working calcium chloride solution placed on a shelf about 1 meter (3 feet ± 1 inch) above the work surface. Allow the cylinder to now stand undisturbed for 20 minutes. Start the timing immediately after withdrawing the irrigator tube. At the end of the 20-minute sedimentation, read and record the top of the clay suspension. This is referred to as the clay reading. If no clear line of demarcation has formed at the end of the 20-minute period, allow the cylinder to stand undisturbed until a clay reading can be obtained.
Immediately read and record the level of the top of the clay suspension and the total suspension time. If the total sedimentation time exceeds 30 minutes, rerun the test on the other prepared samples of the same material. Read and record the clay column height of the specimen requiring the shortest sedimentation period only.
After the clay reading has been taken, place the weighted foot assembly into the cylinder and lower it gently until it comes to rest on the top of the sand. Be careful not to hit the mouth of the cylinder with the weighted foot assembly. Tip the assembly toward the graduations on the cylinder until the indicator touches the inside wall of the cylinder. Subtract 25.4 cm (10 in.) from the level indicated by the extreme top edge of the indicator and record this as the sand reading. Do not apply pressure to the assembly at any time.
Report the result as a percent, always carrying the sand equivalent (SE) up to the next higher whole number (do not use any decimals). If more than one SE test is made, take the average of each whole number value for each test specimen to the next higher whole number. Use 2.5 mm (0.1 in.) as the smallest unit for the readings and always use the higher graduation if the readings fall between one-tenth inch marks. Calculate the sand equivalent to the nearest 0.1% using the following formula:
SE= (Sand Reading/Clay Reading)*100%
Cleaner aggregates will have a higher SE value. Specifications generally call for a minimum SE on the order of 25 to 35%.