DETERMINATION OF AGGREGATE IMPACT VALUE.
- 1. Experiment no: 01 Aggregate Impact Value Engr.Sayed Shajedul Hasan.
- 2. Engr.Sayed Shajedul Hasan. Impact test The aggregate impact test is carried out to evaluate the resistance to impact of aggregates. Scope & significance: Aggregate Impact Value The aggregate impact value gives a relative measure of the toughness or the resistance of aggregate sudden shock or impact is not proportional to the resistance to a slowly applied compressive load. Aggregate Impact Value The property of a material to resist impact is known as toughness. Due to movement of vehicles on the road the aggregates are subjected to impact resulting in their breaking down into smaller pieces.
- 3. Engr.Sayed Shajedul Hasan. Apparatus for Aggregate Impact Test Aggregate Impact Value Apparatus Balance (i) A testing machine weighing 45 to 60 kg and having a metal base with a painted lower surface of not less than 30 cm in diameter. It is supported on level and plane concrete floor of minimum 45 cm thickness. The machine should also have provisions for fixing its base. (ii) A cylindrical steel cup of internal diameter 102 mm, depth 50 mm and minimum thickness 6.3 mm. . (iii) A metal hammer or cup weighing 13.5 to 14.0 kg the lower end being cylindrical in shape, 50 mm long, 100.0 mm in diameter, with a 2 mm chamfer at the lower edge and case hardened. The hammer should slide freely between vertical guides and be concentric with the cup. Free fall of hammer should be within 380±5 mm. (iv) A cylindrical metal measure having internal diameter 75 mm and depth 50 mm for measuring aggregates. (v) Tamping rod 10 mm in diameter and 230 mm long, rounded at one end.
- 4. Engr.Sayed Shajedul Hasan. Figure 1: Impact test setup
- 5. Engr.Sayed Shajedul Hasan. The test sample consists of aggregates sized 10.0 mm 14.0 mm. Procedure of Aggregate Impact Test (i) Sieve the material through 14.0 mm and 10.0mm sieves. The aggregates passing through 14.0 mm sieve and retained on 10.0mm sieve comprises the test material. (ii) Pour the aggregates to fill about just 1/3rd. depth of measuring cylinder. (iii) Compact the material by giving 25 gentle blows with the rounded end of the tamping rod. (iv) Add two more layers in similar manner, so that cylinder is full. (v) Strike off the surplus aggregates. (vi) Determine the net weight of the aggregates to the nearest gram(W). (vii) Bring the impact machine to rest without wedging or packing up on the level plate, block or floor, so that it is rigid and the hammer guide columns are vertical. (viii) Fix the cup firmly in position on the base of machine and place whole of the test sample in it and compact by giving 25 gentle strokes with tamping rod. (x) Remove the crushed aggregate from the cup and sieve it through 2.36 mm IS sieves until no further significant amount passes in one minute. Weigh the fraction passing the sieve to an accuracy of 1 gm. Also, weigh the fraction retained in the sieve.
- 6. Engr.Sayed Shajedul Hasan. Observations of Impact Test Observations Sample 1 Sample 2 Total weight of dry sample (W1 gm) 350gm 354gm Weight of portion passing 2.36 mm sieve (W2 gm) 54gm 78gm Aggregate Impact Value (percent) = W2 / W1 X 100 15% 22% Result of Impact Test Aggregate Impact Value = 15% & 22% COMMENTS The aggregate impact value indicates a relative measure of the resistance of the aggregate to a sudden shock or impact which in some aggregates differs from its resistance to a slow compressive load. From the calculations done we came to know that the sample 1 is a Strong aggregate and sample 2 is also close to the maximum allowable limit for good aggregates.
- 7. Engr.Sayed Shajedul Hasan. Recommended Aggregate Impact Test Values Classification of aggregates using Aggregate Impact Value is as given below: