TEST T-607 SAND STABILITY TEST

The sand stability test is conducted by means of a machine which was developed and patterned after the one described in "Public Roads," Vol. 6, No. 4, April 1925, Page 38, except the lever arm system was changed to a single straight lever arm. The equipment consists of a four-legged stand on which is mounted a lever arm and a sand-bearing cup. On one end of the lever arm is a counterbalance, and on the other end is a bucket suspended by a spring balance graduated in pounds. The load is applied to the lever arm by water which is allowed to run from the funnel, mounted on a leg of the stand, into the bucket. In the middle of the stand is mounted, on an adjustable screw, the base for the sand cup. This cup is three (3) inches in diameter and three (3) inches deep. Directly over the center of this base a small ball bearing is welded to the underside of the lever arm. The purpose of this ball bearing is to transfer the load from the lever arm through a small circular bearing plug to the sample in the sand cup. The ball bearing is usually placed at one-fourth the distance from the lever arm fulcrum to the knife edge on the end of the arm from which the spring balance is suspended. This method gives a lever arm ratio of four (4) for the machine. The bearing plug is circular, has a bearing face of one (1) square inch, and has a socket in the center of its top surface into which can fit the ball bearing. Before the loading test is started, the lever arm can be leveled by the screw adjustment on the sand cup base, and can be balanced by the counterweights on the end of the arm. A bearing plate is provided which is approximately three (3) inches in diameter and which will fit into the cup to compress the sample before the test is made.

The procedure in conducting the test is to oven-dry the sample to constant weight. To 600 grams of the oven-dried material, with all lumps broken up, is added 10.5 cc. of water; then mix uniformly. The cup is filled with the sample material. A bearing plate covering the sample is placed and an initial pressure, by hand, is given the material. The plate is removed and material is heaped up in the cup. The bearing plate cover is again placed on the material and hand pressure applied. The excess above the top of the cup is removed and a total pressure of 1,200 pounds is applied. The large bearing plate is then removed and the small bearing plug of one (1) square inch area is placed in the center of the cup resting lightly on the surface of the material. The lever arm of the machine is then leveled and balanced. The test is made by applying a constant increasing load by allowing the water to run from the funnel into the bucket until the pressure on

the bearing plug is great enough to upset the stability of the sample. At failure the load, as indicated by the spring balance, is recorded. The load or the stability is in pounds and is calculated by multiplying the balance reading by four (4) or by the figure which is the lever arm ratio of the machine.

The above stability test was originated and developed by the Florida State Road Testing Department. As mentioned above, the soil-bearing machine of the Public Roads Administration was used as a model. This test has been adopted by many State highway departments which include sand asphalt pavements in their highway specifications and is recommended for a method of predetermining the suitability of sand aggregate for bituminous mixtures.

In addition to the application of the stability test to sands that do not comply with specified gradations, this test may be utilized to check the stability of the matrix of any accepted mixtures. In such cases the test should be conducted on that portion of the mineral aggregate which passes the No. 10 mesh sieve. In all instances, the stability test should be conducted at one and three-fourths (14) percent moisture content which is obtained from measurements given above.