LAB MANUAL TRANSPORTATION ENGG. LAB. By DR. R. K. KAR
PATT – I TESTS ON AGGREGATES
ABRASION TEST Aim of the Experiment: To determine the abrasion value of given aggregate sample by conducting LosAngeles abrasion Test. Apparatus Required: (i) Los Angeles machine with inside diameter 70cm and inside length of 50cm. (ii) Abrasive charges having diameter 4.8cm and weight 390 to 445 gm (iii)I.S Sieve with 1.7mm opening. (iv)Weighting Balance of 0.1gm accuracy. (v) Metallic Tray Theory and Scope: Abrasion is a measure of resistance to wear or hardness. It is an essentially property for road aggregates especially when used in wearing coarse. Due to the movements of traffic, the road stones used in the surfacing course are subjected to wearing actions at the top. When traffic moves on the road the soil particle (sand) which comes between the wheel and road surface causes abrasion on the road stone. The abrasion test on aggregate is found as per I.S.-2386 part-IV. Abrasion tests on aggregates are generally carried out by any one of the following methods1. Los Angeles abrasion test. 2. Deval abrasion test. 3. Dorry abrasion test. Los Angeles Abrasion Test: The principle of Los Angeles abrasion test is to find the percentage wear due to the relative rubbing action between the aggregates and steel balls used as abrasive charge pounding action of these balls also exist while conducting the test. Maximum Allowable Los Angeles Abrasion Values of Aggregates in Different types of pavement layers as per Indian Road Congress (IRC) are:- For sub-base course a value of 60%. For base course such as WBM, Bituminous Macadam
(B.M.), Built – Up spray grout base course and etc. value of 50%. For surface course such as WBM, BM, Bituminous Penetration Macadam,Built-Up spray grout binder course and etc. a value of 40%. If aggregates are used in surface course as bituminous carpet, bituminous surface dressing, single or two coats, cement concrete surface course and etc. a value of 35%. If aggregates are used for bituminous concrete, Cement concrete pavement as surface coarse than aggregate abrasion value of 30% maximum. Procedure: Clean and dry aggregate sample confirming to one of the grading A to G is used for the test. (Refer table no. 1). Aggregates weighing 5 kg for grading A, B, C or D and 10 kg for gradings E, F or G may be taken as test specimen and placed in the cylinder. The abrasive charge is also chosen in accordance with table no.1 and placed in the cylinder of the machine, and cover is fixed to make dust tight. The machine is rotated at a speed of 30 to 33 revolutions per minute. The machine is rotated for 500 revolutions for gradings A, B, C and D, for gradings E, F and G, it shall be rotated for 1000 revolutions. After the desired number of revolutions, the machine is stopped and the material is discharged from the machine taking care to take out entire stone dust. Using a sieve of size larger than 1.70 mm I.S sieve, the material is first separated into two parts and the finer position is taken out and sieved further on a 1.7 mm I.S sieve. Let the original weight of aggregate be W1 gm, weight of aggregate retained on 1.70 mm I.S sieve after the test be W2 gm. Los Angeles abrasion value %= W1-W2 x100 W1 Two tests are done and the average value to the nearest whole number is reported as abrasion value.