Highway Research Record

VI. RESEARCH WORK DONE IN ACADEMIC INSTITUTIONS RELATED TO THESIS WORK
B. PAVEMENT ENGINEERING AND PAVING MATERIALS
Effect of Aggregate Shape and Gradation on the Performance of Bituminous Mixes

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

Scope and Objective
(i) To critically evaluate the MORTH specification for combined shape index for aggregates
(ii) To evaluate the effect of particle shape (flaky and elongation Indices) on the performance of bituminous mixes in terms of      fatigue and permanent deformation behaviour.

Methodology
Aggregates were collected from various sources and their combined shape index was determined as per MORTH guidelines. The shape index of these aggregates was also determined using a superpave shape guage with 1:5 ratio. The superpave specification of 10% was compared with the results obtained as per the MORTH requirement.
Bituminous concrete mixes were prepared with aggregates having different shape indices. These specimens were tested for their fatigue performance using a repeated indirect tensile strength test. Static indentation tests were also conducted on the specimens prepared using aggregates having different shape factors

Findings and Conclusions

(i) The MORTH specification for combined shape index appears to be extremely severe compared to the Superpave      requirement. It is found that a combined index value of about 70% is at par with the 10% requirement of Superpave for      1:5 gauge. The 70% critical shape index value has also been obtained from rutting (static indentation) test results.
(ii) The permanent deformation (rutting) of the mixes increases with the increase in percentage of flaky and elongated      particles.
(iii) Particle shape doesn’t have significant effect on the performance of bituminous mixes in terms of fatigue life (repetitions).