Aggregate Testing

Grading analysis greatly influences the performance of the pavement layers. As such, the aggregate from the quarry stockpile was sieved to obtain the combined gradation. Aggregate grading is carried out to determine the proportion of aggregate required from each stockpile to fit into the given specification as stated in JKR/SPJ/1988.

This test is used to derive the percentage by mass of clay, silt and dust in aggregates, which are to be used for making concrete, road construction and pavement design. The method involves weighing the specimen, then removing such material by wash sieving, followed by re-weighing the sample. Limiting values of clay, silt and dust content are normally included in concrete, road construction and pavement design specifications to avoid their deleterious properties on concrete, road construction and pavement design.

Aggregate Crushing Value (ACV) gives a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load. This test is normally carried out on material passing the 14.00mm and retained on the 10.00mm B.S sieve ½ inch deep bed of aggregate in a 6 inch diameter mould is submitted to a gradually applied load of 40 tons (400kN) over a period of 10 minutes. The load is then released and the amount of material passing a 2.36mm B.S sieve is determined. This weight, expressed as a percentage of the total weight of the sample is termed the Aggregate Crushing Value.

Aggregate impact Value (AIV) gives a relative measure of the resistance of an aggregate to sudden shock or impact. The test is carried out by subjecting the aggregate which has been sieved through the 14.00mm and retained on the 10.00mm B.S sieve, to 15 blows of a 30 – 31 Ib. hammer falling through a height of 15” (B.S. 812 : 1990). After impact, the material passing the 2.36mm B.S sieve is expressed as a percentage of the total weight of the original sample and termed the Aggregate Impact Value.

10% fines value (TFV) gives a measure of the resistance of an aggregate to crushing which is applicable to both weak and strong aggregate. This test is perform on 3/8″ - 1/2″ aggregate, 4 inches deep in a 6-inch diameter mould. A load is applied and increased until 10% by weight of fines is formed. The load required to produce 10% of fines is the “10% fines value”.

These tests are used to determine the percentage of unsuitably shaped particles for aggregate to be used in concrete, Road work and pavement design. The Flakiness Index of an aggregate is the percentage by weight of particles whose least dimension (thickness) is less than three-fifth of their mean dimension; the mean dimension as used in each instance is the average of the two adjacent sieve aperture size between which the particles being measured is retained by sieving. Aggregate particles are classified as flaky when they have a thickness of less than 0.6 of their mean sieve size.
Elongation Index is the percentage by weight of particles in it, whose largest dimension (i.e. length) is greater than one and four-fifths times its mean dimension. The aggregate particles are classified as elongated when they have a length of more than 1.8 of their mean sieve size. The elongation index is calculated as the percentage by mass of aggregate particles that are regarded as elongated.

For Specific Gravity Test the aggregate is soaked in distill water for 24 hours, and weighed in water at the end of this period. It is then surface-dried and weighed in air, and then oven dried for 24 hours and then weighed in air (B.S. 812:1995). Specific Gravity of an aggregate is an important factor in the design of some engineering structures, e.g. wharves. The SG is a useful index of rock quality, and can indicate the degree of weathering or chemical alteration of the rock.
The Water Absorption of an aggregate is usually determined in conjunction with the SG determination. The water Absorption of an aggregate is determined by measuring the increase of an oven-dried sample when immersed in water for 24 hours (the surface water being removed) (B.S 812:1990). Water absorption values are                                       obtained by weighing aggregate samples before and after soaking in water.

California Bearing Ratios Tests is a penetration test developed by California state highway department (USA) for evaluating the bearing capacity of sub-base/road-base for design of flexible pavement. The test is carried out on natural or compacted DCR in water soaked or un-soaked conditions and the results obtained are compared with the curves of standard test to have an idea of the DCR strength of the sub-base/road-base.

Los Angeles Abrasion Value (LAAV) is designed to measure durability against abrasion. A specified quantity of aggregate is placed in a 28 inch diameter by 20 inch long cylindrical drum mounted longitudinally on a horizontal shaft; fitted to the inside of the drum is a 3½ inch wide shelf running from one end of the drum to the other. After adding a standard charge of steel balls of about 17/8 inch diameter, the drum is rotated at 30 – 33 r.p.m for 500 revolutions. The aggregate is than sieve through ASTM No. 12 sieve (B.S. 9.50mm).

Soundness Test is intended to study the resistance of aggregate to weathering action by conducting accelerated weathering test cycles. The porous aggregate subjected to freezing and thawing are likely to disintegrated prematurely. To ascertain the durability of each aggregate, they are subjected to an accelerated soundness test as specified in B.S 812 : Part 121: 1989. Aggregate of specified size are subjected to cycles of alternate wetting in a saturated solution of either sodium sulphate or magnesium sulphate at temperature of 70 + 2°F between 16 – 18 hours and then dried in oven at 105 - 110°C to a constant weight. After 5 cycles, the loss in weight of aggregate is determined by
sieving out all undersized particles and weighing.

The total sulphate content of aggregate is usually measured to assess whether the aggregate's contribution to the total sulphate content of a concrete mix will be low enough to prevent any deleterious effects.

The total chloride content of aggregate is usually measured to assess whether the aggregate's                                             
contribution to the total chloride content of a concrete mix will be low enough to prevent the early                                                            
onset of corrosion of any embedded steel reinforcement.
The test can be conducted in a variety of chemical means, from approximate dip-stick measures                                                             
through to potentiometric methods. The usual method is by titration.

This test method covers procedures for an approximate determination of the presence of injurious organic impurities in fine aggregate that are to be used in hydraulic cement mortar or paste. The principle value of this test is to serve as a warning that an aggregate may contain organic impurities and should be investigated further. It involves comparing the colour of the supernatant of the sample when mixed with sodium hydroxide to that of a standard solution.

This test is an indirect method to determine compressive strength of a sample. The point load strength index, Is (50) by using correlation UCS = 20 X Is (50) to determine compressive strength. The sample can be categorised based on the point load strength index.

The PSV of an aggregate is a measure of the resistance of an aggregate to polishing. The value is established by subjecting the aggregate to a standard polishing process, and then testing the aggregate with the Portable Skid Resistance Tester to determine its PSV.