Coarse aggregates make up the largest volume of material used in concrete. The aggregates must be clean, properly graded, strong, durable and free from chemicals or other foreign materials that may restrain the bond between the cement and aggregate. The test must be performed to make sure that the aggregate meets all these criteria. There is various test are conducted to check the quality of the coarse aggregate.
Flakiness index test is used to determine the particle shape of the coarse aggregate. The particle shape of the aggregates is obtained by the percentages of flaky and elongated particles accommodate in it. For base coarse and construction of cement concrete types, the presence of flaky and elongated particles are considered undesirable. It causes inherent weakness with possibilities of breaking down under heavy loads. Therefore, the evaluation of the shape of the particles, particularly with respect to flakiness and elongation is necessary.
The flakiness index of coarse aggregate is defined in percentage by weight of aggregate particles and least dimension (thickness) of those particles should not be less than 0.6 times their mean area. Flakiness index test is not applicable for aggregates sizes smaller than 6.3mm. Flaky or elongated coarse aggregates are disadvantageous to higher workability and stability of mixes.
Flakiness index test is conducted by using a metal thickness gauge. An adequate quantity of coarse aggregate is taken such that the minimum number of 200 pieces of any fraction can be tested. Each fraction is gauged in turn for thickness on the metal gauge. The total amount passing in the gauge is weighed to an accuracy of 0.1 % of the weight of the samples.
The elongation index of aggregates is expressed as a percentage by weight of particles. Those particles’ maximum dimension (length) is greater than 1.8 times their mean dimensions. The elongation index test is not applicable to size smaller than 6.3mm.