Lab Tests on Aggregate to Determine Quality for Use in Road Work

Aggregate plays a vital role when it comes to pavement construction. To a great extent, the affect of aggregate decides the load transfer capability of the pavements. Apart from that, the aggregate should be strong and posses great durability. Moreover, they should come equipped with proper shape and size to enable the pavement act uniformly. To ensure perfect quality of aggregates, they are tested on the grounds of toughness, hardness, absorption, strength as well as water absorption. For the purpose of analyzing the suitability of the aggregate for their utilization in the construction of the pavement, following tests are undertaken.

Aggregate Crushing Test – The aggregate crushing value gives the relative measure of resistance against crushing under crushing load applied gradually.The aggregate test is standardized by IS: 2386 part-IV and used to determine the crushing strength of aggregates. Se-Test India aggregate crushing value provides a relative measure of resistance to crushing under gradually applied crushing load. Se-Test India The test consists of subjecting the specimen of aggregate in standard mould to a compression test under standard load conditions aggregates passing through 12.5 mm sieves and retained 10 mm sieves are filled in a cylindrical measure of 11.5 mm diameter and 18 cm height in 3 layers. Each and every layer is tamped 25 times with at standard tamping rod. The aggregate crushing test sample is weighed and placed in the test cylinder in three layers each layer being tamped again. The specimen is subjected to a compressive load of 40 tonnes gradually applied at the rate of 4 tonnes per minute. Then crushed aggregates are then sieved through 2.36 mm sieve and weight of passing material (W2) is expressed as percentage of the weight of the total sample (W1) which is the aggregate crushing value.

Aggregate crushing value = (W1/W2)*100
A value < 10 signifies an exceptionally strong aggregate while above 35 would normally be regarded as weak aggregates.
Also Read: Crushing Test Procedure of Aggregate

Abrasion Test – This test is conducted for evaluating the hardness property of aggregates and for decidingwhether they are perfect for the pavement construction works or not. Se-Test Abrasion test is carried out to test the hardness property of aggregates and to decide whether they are suitable for different pavement construction works. Se-Test India Los Angeles abrasion test is a preferred one for carrying out the hardness property and has been standardized in India (IS: 2386 part-IV). Se-Test Los Angeles machine consists of circular drum of internal diameter 700 mm and length 520 mm mounted on horizontal axis enabling it to be rotated (see Fig-2). Se-Test India aggregate crushing valueabrasive charge consisting of cast iron spherical balls of 48 mm diameters and weight 340-445 g is placed in the cylinder along with the aggregates. The number of the abrasive spheres varies according to the grading of the sample. The quantity of aggregates to be used depends upon the gradation and usually ranges from 5-10 kg. The aggregate crushing cylinderAbrasion test is then locked and rotated at the speed of 30-33 rpm for a total of 500 -1000 revolutions depending upon the gradation of aggregates.

The aggregate crushing value maximum value of 40 percent is allowed for WBM base course in Indian conditions. Se-Testbituminous concrete, a maximum value of 35 percent is specified.

Impact Test – The impact test for aggregates is done for the purpose of evaluating the resistance of aggregates against impact. Se-Test aggregate impact test is carried out to evaluate the resistance to impact of aggregates. Se-Test India Aggregates passing 12.5 mm sieve and retained on 10 mm sieve is filled in a cylindrical steel cup of internal dia 10.2 mm and depth 5 cm to a metal base of impact testing machine. Theaggregate crushing material is filled in 3 layers where each layer is tamped for 25 numbers of blows (see Fig-3). Se-Test Metal hammer of weight 13.5 to 14 Kg is arranged to drop with a free fall of 38.0 cm by vertical guides and the test specimen is subjected to 15 numbers of blows. The aggregate crushed Impact test is allowed to pass through 2.36 mm IS sieve. The impact test for aggregates value is measured as percentage of aggregates passing sieve (W2) to the total weight of the sample (W1).

Aggregate Impact Value = (W1/W2)*100

Se-Test India Aggregates to be used for wearing course, the impact value shouldn’t exceed 30%.AggregateBituminous macadam the maximum permissible value is 35 %. Setest India Water bound macadam base courses the maximum permissible value defined by IRC is 40 %.

Soundness Test of Aggregates– Soundness test is intended to study the resistance of aggregates to weathering action, by conducting accelerated weathering test cycles. Se-Test Soundness test of Aggregates ascertain the durability of such aggregates, they are subjected to an accelerated soundness test as specified in IS: 2386 part-V.Se-Test Indiaspecified size are subjected to cycles of alternate wetting in a saturated solution of either sodium sulphate or magnesium sulphate for 16 – 18 hours and then dried in oven at 105 to 1100C to a constant weight. Afterthatfive cycles, the loss in weight of aggregates is determined by sieving out all undersized particles and weighing.

Shape Tests of Aggregate – The particle shape of the aggregate mass is determined by the percentage of flaky and elongated particles in it. Shape tests of aggregate which are flaky or elongated are detrimental to higher workability and stability of mixes.

Shape tests of aggregateis defined as the percentage by weight of aggregate particles whose least dimension is less than 0.6 times their mean size. Shape tests of aggregateFlakiness gauge is used for this test procedure had been standardized in India. Shape tests of aggregateis is defined as the % by weight of particles whose greatest dimension (length) is 1.8 times their mean dimension. This test is applicable to aggregates larger than 6.3 mm. Elongation index of an aggregate is used for this test.

Specific Gravity and Water Absorption Test – The specific gravity as well as the water absorption capacity of the aggregates are vital properties which are needed for developing. Se-Test India specific gravity of a solid is the ratio of its mass to that of an equal volume of distilled water at a specified temperature. The aggregates specific gravity may contain water-permeable voids, so two measures of specific gravity of aggregates are used:

  • Apparent specific gravity
  • Bulk specific gravity.
Apparent Specific Gravity – Apparent Specific Gravity (Gapp) is computed on the basis of the net volume of aggregates i.e the volume excluding water-permeable voids. Thus

Gapp = [(MD/VN)]/W
Where,
MD = dry mass of the aggregate,
VN = volume of the aggregates excluding the volume of the absorbed matter
W = density of water.
Bulk Specific Gravity, Gbulk, is computed on the basis of the total volume of aggregates including water permeable voids. Thus
Gbulk = [(MD/VB)]/W
Where,
VB = volume of the aggregates including the volume of absorbed water
Absorption of water: The difference between the apparent and bulk specific gravities is nothing but the water permeable voids of the aggregates. Absorption of water can measure the volume of such voids by weighing the aggregates dry and in a saturated surface dry condition, with all permeable voids filled with water. The difference of the above two is MW.

MW = Weight of dry aggregates minus weight of aggregates saturated surface dry condition. Thus

Absorption of water = (MW/MD)*100

. Bitumen Adhesion Test – The Bitumen adhesion test is carried out for determining the bitumen binder’s adhesion capability against the aggregate in the presence of water. Bitumen adheres well to all normal types of road aggregates provided they are dry and free from dust. The Bitumen adhesion test absence of water there is practically no adhesion problem of bituminous construction.Se-Test India laboratory tests are conducted to arbitrarily determine the adhesion of bitumen binder to an aggregate in the presence of water. Se-Test Bitumen adhesion test is one specified by IRC and is quite simple. The principle of the test is by immersing aggregate fully coated with binder in water maintained at 400C temperature for 24 hours.

Written by:- civillabequipment for Aggregate