Highway Research Record

An Investigation on the Effect of Some Aggregate Characteristics on the Performance of Bituminous Mixes

Date of Start:May 2004
Indian Institute of Technology, Kharagpur (S, I) ]

Scope and Objective
(i) To develop a simple device to measure workability of bituminous mixes and to evaluate the workability of different mixes.
(ii) To evaluate the permeability characteristics of different types of bituminous mixes
(iii) To examine the effect of dust on the performance bituminous mixes.

A simple device was developed to measure workability of bituminous mixes. The electrical current drawn is taken as a measure of the torque offered by the mix to a rotating spindle. The current measurement is thus a measure of workability of mix. A number of mixes were prepared with different gradations and different binder contents. The variation in workability value with varying temperatures was measured for all the mixes.

A simple device was developed for measuring the permeability of different types of bituminous mixes. Experiments were conducted with specimens of different mixes to evaluate their permeability characteristics.

To evaluate the effect of dust on the performance of bituminous mixes, different quantities of dust was added to the aggregates before the bituminous binder was added and mix prepared. Moisture susceptibility tests and strength tests were conducted to evaluate the effect of dust on different engineering properties of bituminous mixes.

Findings and Conclusions

(i) The workability of bituminous mixes was found to be affected by maximum nominal aggregate size in the mix, aggregate      gradation, binder type and content.
(ii) Mixes with modified (rubber and polymer) binders were found to be less workable compared to normal mixes.
(iii) Compaction temperatures have been suggested for different types of mixes on the basis of the workability test results      instead of fixing the compaction temperatures on the basis of binder viscosity.
(iv) Air void content has significant influence on the permeability of bituminous mixes. 8% air voids appear to be critical as the      rate of permeability increased significantly for higher air void contents.
(v) The presence of dust was found to have significant influence on the moisture susceptibility characteristics of the mixes.      However, the indirect tensile strength of mixes was not affected.