A PARAMETRIC STUDY ON SHAPE OF AGGREGATES AFFECTING BITUMINOUS SURFACE OF FLEXIBLE PAVEMENTS

Abstract

It is generally understood in the highway sector that significant shortage of aggregates are imminent in near future. The main reason for this being the aggregates specification, which generally tends to disqualify many marginal aggregates that could otherwise gives service under certain conditions. For conservation of aggregates and economizing the construction costs, it is desirable to utilize the locally available material even if these are marginally unsuitable as per specifications. Use of locally available marginal materials is often very tempting, but the decision to use or reject these materials should be made only after a complete evaluation. Among the various characteristic of aggregates, the shape factors like the flakiness, elongation and angularity number are found to have considerable effect on the resultant mixes. Gravel in India are available in large quantity in many places such as stream bottoms or terraces adjacent to streams, outwash plains and fans adjacent to mountains. In most instances, these aggregates are strong, durable and satisfy the general physical requirements of road aggregates. In the present study, attempts have been made to check whether the combine flakiness and elongation indices can be increased or not, by conducting test with varying combine index values of aggregate. In addition to this attempt has been also made to use gravels by replacing crushed stone aggregates. Various tests such as combine flaky and elongated indices, angularity number, Marshall test, Indirect Tensile Strength, Retained Indirect Tensile Strength, Marshall Retained Strength and Dynamic Creep test have been conducted for judging the suitability of various combine index value of aggregates and percentage of gravels that can replace the crushed stone aggregates. It has been found that 40% combined index in case of both DBM and BC mixes are having all the parameters within the specification of MORTH and are having only minor decrease in various parameters. Also it has been found that 25% gravel can be used successfully in DBM mixes instead of crushed stone aggregates. The economical analysis shows that cost of pavement material is much less for 25% gravel and 75% crushed stone aggregate, in comparison to that of crushed stone aggregates. Further the use of gravel will be much more economical if it is found locally.