Introduction
The size, shape, grading of aggregate and their surface moisture affect directly the workability and strength of concrete whereas soundness, alkali-aggregate reaction and presence of deleterious substances adversely affect the soundness and durability of concrete.
The following tests are conducted to ensure satisfactory performance of aggregate.
1. Particles size distribution test (IS 2386 Part 1)
Sample of fine aggregate, coarse aggregate or all-in-aggregate, as required to be tested, are taken in sufficient quantities. The minimum weight of sample for the test should be as follows.
The air dried sample is placed on a set of specific sieves with largest size on the top. The set of sieve is shaked for 2 minutes. Arrangement of sieve for different types of aggregate is as follow
2. Flakiness index and Elongation index test (is 2386 part 2)
Because of large number of flaky particles in the coarse aggregate more voids are formed in the concrete consequently more mortar is required to fill the voids, resulting in uneconomy. Also, durability of concrete will be affected.
For flakiness index (F.I) and elongation index (E.I) sufficient quantity of aggregate is taken so as to provide at least 200 pieces of any fraction to be tested.
F. I = [Weight of aggregates passing through the slot of the thickness guage. /Total weight of the sample]*100
For determining E.I, the aggregate are sieved through the corresponding sieves. Aggregate retained on each sieve are separated. Then each aggregate piece is passed through the corresponding slot of length gauge.
E.I = [Weight of aggregates retained on length guage. / Total weight of aggregates ]*100
3. Deleterious materials and orgabic impurities test (IS 2386 PART 3)
1. Determination of clay lumps.
The sample of aggregate is dried to constant weight at a temperature not exceeding 110°C.
The sampleis spreadin a thinlayeron thebottomof containerandexaminedfor clay lumps.The percentage of clay lumps
L =(W-R/L)*100
Where W = Weight of sample.
R = Weight of sample after removal of clay lumps.
2. Determination of clay, fine silt, and fine dust.
Sedimentation method is used to determine clay, fine silt and dust, including particles up to 20 micron.
For testing fine aggregate for clay, fine silt and dust weight approximately 300g of the air dried sample, passing the 4.75 mm IS sieve, and place it in the screw-topped glass jar, together with 300 ml of diluted sodium oxalate solution.
The jar is then rotated about its long axis (with this axis horizontal) at a speed of 80 rpm for 15 minutes. The suspension is then poured into 1000 ml measuring cylinder and the residue washed by gentle swirling and decantation of successive 150 ml portions of sodium oxalate solution, the washings being added to the cylinder until the volume is made up to 1000 ml. For coarse aggregate the sample is placed in a suitable container, covered with a measured volume of sodium oxalate solution (0.8 g/l), agitated vigorously and the liquid suspension transferred to the 1000 ml measuring cylinder.
The process is repeated until all clayey material is transferred to the cylinder. The volume is made upto 1000 ml with sodium oxalate solution. The percentage of fine clay, silt and dust,
A, is determined by the folliwng Formula
A = 100/W1(1000W2/V-0. 8)
Where W1= weight of original sample (g)
W2= weight of dried sample (g)
V = volume of pepette. (ml)
0. 8 = weight of sodium oxalate (g) in one liter of the diluted solution.
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