SPECIFIC GRAVITY AND WATER ABSORPTION TESTS ON COARSE AGGREGATES

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Complete Report and observation sheet: https://drive.google.com/file/d/1n7lI... • Experiment performed at: Civil Engineering Department, R.V. College of Engineering, Bangalore • INTRODUCTION • The coarse aggregate specific gravity test is used to calculate the specific gravity of a coarse aggregate sample by determining the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water. • The coarse aggregate specific gravity test measures coarse aggregate weight under three different sample conditions: •  Oven-dry (no water in sample). •  Saturated surface-dry (SSD, water fills the aggregate pores). •  Submerged in water (underwater). • Using these three weights and their relationships, a sample’s apparent specific gravity, bulk specific gravity and bulk SSD specific gravity as well as Water absorption can be calculated. • Aggregate specific gravity is needed to determine weight-to-volume relationships and to calculate various volume-related quantities such as voids in mineral aggregate (VMA), and voids filled by asphalt (VFA). Absorption can be used as an indicator of aggregate durability as well as the volume of asphalt binder it is likely to absorb. • APPARATUS USED • The apparatus shall consist of the following: • 1. Balance -A balance or scale of capacity not less than 3 kg, readable and accurate to 0.5 g and of such a type and shape as to permit the basket containing the sample to be suspended from the beam and weighed in water. • 2. Oven - A well ventilated oven, thermostatically controlled, to maintain a • temperature of 100 to 110%. • 3. A wire basket of not more than 6-3 mm mesh or a perforated container of convenient size, preferably chromium plated and polished, with wire • hangers not thicker than one millimeter for suspending it from the balance. • 4. A stout watertight container in which the basket may be freely suspended. • 5. Two dry soft absorbent cloths each not less than 75 x 45 cm. • 6. A shallow tray of area not less than 650 ems. • 7. An airtight container of capacity similar to that of the basket. • TEST SAMPLE • A sample of not less than 2000 g of the aggregate shall be tested. Aggregates which have been artificially heated shall not normally be used. If such, material is used the fact shall be stated in the report. Two tests shall be made, and it is recommended that the two samples should not be tested concurrently. • TEST PROCEDURE • 1) The sample shall be thoroughly washed to remove finer particles and dust, drained and then placed in the wire basket and immersed in distilled water at a temperature between 22°C and 32°C with a cover of at least 5 cm of water above the top of the basket. • 2) Immediately after immersion the entrapped air shall be removed from the sample by lifting the basket containing it 25 mm above the base of the tank and allowing it to drop 25 times at the rate of about one drop per second. • 3) The basket and aggregate shall remain completely immersed during the • operation and for a period of 24 + l/2 hours afterwards. • 4) The basket and the sample shall then be jolted and weighed in water at a • temperature of 22 to 32°C. If it is necessary for them to be transferred to a • different tank for weighing, they shall be jolted 25 times as described above • in the new tank before weighing (weight A1). • 5) The basket and the aggregate shall then be removed from the water and • allowed to drain for a few minutes, after which the, aggregate shall be • gently emptied from the basket on to one of the dry clothes, and the empty • basket shall be returned to the water, jolted 25 times and weighed in water • (weight A2). • 6) The aggregate placed on the dry cloth shall be gently surface dried with the cloth, transferring it to the second dry cloth when the first will remove no further moisture. It shall then be spread out not more than one stone deep on the second cloth, and lest exposed to the atmosphere away from direct sunlight or any other source of heat for not less than 10 minutes, or until it appears to be completely surface dry (which with some aggregates may take an hour or more). The aggregate shall be turned over at least once during this period and a gentle current of unheated air may be used after the first ten minutes to accelerate the drying of difficult aggregates. The aggregate shall then be weighed (weight B). • 7) The aggregate shall then be placed in the oven in the shallow tray, at a • temperature of 100 to 110°C and maintained at this temperature for 24+ l/2 • hours. It shall then be removed from the oven, cooled in the airtight • container and weighed (weight C).

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