Laboratory Determination of Resilient Modulus for Flexible Pavement Design (2004)

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31 ANNEX A-1 SAMPLE PREPARATION (MANDATORY INFORMATION) 1. SCOPE 1.1 The following provides guidelines for reconstituting the material to be tested so as to produce a sufficient amount of material needed to prepare the appropriate sample type (Type 1, 2, or 3) at the designated moisture content and density. 2. PREPARATION FOR COMPACTION 2.1 Sample Conditioning – If the sample is damp when received from the field, dry it until it becomes friable. Drying may be in air or by use of a drying apparatus such that the temperature does not exceed 60°C (140°F). Then thoroughly break up the aggregations in such man- ner as to avoid reducing the natural size of individual particles. Moderate pressure using a rubber-covered implement to push the particles through a 4.75 mm (No. 4) sieve. 2.2 Sample Preparation – Determine the moisture content (w1) of the sample per T265. The mass of the sample for moisture determination shall not weigh less than 200 g for samples with a maximum particle size smaller than the 4.75 mm (No. 4) sieve and not less than 500 g for samples with a maximum particle size greater than 4.75 mm (No. 4) sieve. 2.2.1 Determine the appropriate total volume (V) of the compacted specimen to be prepared. The total vol- ume must be based on a height of the compacted specimen slightly greater than that required for resil- ient testing to allow for trimming of the specimen ends if necessary. Compacting to a height/diameter ratio of 2.1 to 2.2 will provide adequate material for this purpose. 2.2.2 Determine the mass of oven-dry soil solids (Ws) required to obtain the desired dry density (γd) and moisture content (w) as follows: Ws = 453.59 γd V where Ws = Mass of oven-dry solids, g, γd = Desired dry density, lb/ft3 V = Total volume of compacted specimen, ft3. 2.2.3 Determine the mass of the dried sample, (Wad), with the moisture content (w1) required to obtain Ws plus an additional amount Was of at least 500 grams to provide material for the determination of moisture content at the time of compaction. Wad = (Ws +Was)(1+w1/100) where Wad = Mass of sample at water content w1, g, Was = Mass of moisture content specimen (usually 500g), g, w1 = Water content of prepared material, %. 2.2.4 Determine the mass of water (Waw) required to change the water content from the existing water content, w1, to the desired compaction water content, w. Waw = (Ws + Was)[(w-w1)/100] where Waw = Mass of water needed to obtain water content w, g, w = Desired water content of compacted material, %. 2.2.5 Place a sample of mass, Wad, into a mixing pan. 2.2.6 Add the mass of water (Waw), needed to change the water content from w1 to w, to the sample in small amounts and mix thoroughly after each addition. 2.2.7 Place the mixture into a plastic bag. Seal the bag, place it in a second bag and seal it. Cure the sample for 16 to 48 hours, determine the mass of the wet soil and container to the nearest gram, and record this value on Report Form 2. 2.2.8 The material is now ready for compaction. 2.3 Compaction 2.3.1 Refer to Annexes A-2, A-3, and A-4 for vibratory, impact, and kneading compaction methods. 2.3.2 When the compaction process is complete, carefully open the mold and retrieve the specimen. Record the mass and the dimensions of the specimen on Report Form 2 or 3, as appropriate. 2.3.3 Coarse-grained subgrade specimens should be pro- tected from moisture change by immediately apply- ing the triaxial membrane and testing within 1 day of preparation unless saturation, drying, or curing of the specimen is to be carried out. 2.3.4 Store fine-grained subgrade compacted specimens wrapped in impermeable material and placed in a sealed container, for 1 day in a moisture room before testing. 3. PREPARE THE SPECIMEN FOR TESTING 3.1 Place presoaked porous stones no more than 6.25 mm (0.25 in) thick on both the base and the top of the speci- men. If clogging of the porous stones is found to be a problem, presoaked filter paper cut to size can be used between the porous stone and the specimen. 3.2 Place vacuum grease on the sides of the end platens to facilitate a good seal between the membranes and end platens.

32 3.3 Carefully place the specimen on the porous stone/base. Place the membrane on a membrane stretcher, apply a vacuum to the stretcher, then carefully place the mem- brane on the sample and add the top platen. Remove the membrane from the stretcher, cut off the vacuum and remove the membrane stretcher. Seal the membrane to the top and bottom platens with rubber O rings. A second membrane can be added if puncturing of the membrane is a problem due to the presence of sharp aggregate. 3.4 Test for Leaks: Connect the specimen’s bottom drain- age line to the vacuum source through the medium of a bubble chamber. Apply a vacuum of 35 kPa (5 psi). If bubbles are present, check for leakage caused by poor connections, holes in the membrane, or imperfect seals at the cap and base. The existence of an airtight seal ensures that the membrane will remain firmly in contact with the specimen. Leakage through holes in the mem- brane can frequently be eliminated by coating the sur- face of the membrane with liquid rubber latex or by using a second membrane. When leakage has been eliminated, disconnect the vacuum supply line. Carefully clean the O-rings/gaskets used to seal the chamber; also clean all surfaces that the O-rings will contact. 3.5 The specimen is now ready for testing.