11. Laboratory Evaluation of Gilsonite Modified Bituminous Concrete
Date of Start

December 2005
Central Road Research Institute, New Delhi (R, I) Indian Institute of Technology, New Delhi (S)


Scope and Objectives

(i) Evaluate the Gilsonite mix modifier for its ability to show superior mix performance as compared to conventional mix, by forming a custom-tailored interlayer between the inorganic aggregate/filler surface and asphalt binder without dispersing into the binder and degrading the low and intermediate temperature properties.

(ii) Consequently, carry out the cost analysis of Gilsonite modified mix and conventional mix to establish the economy of Gilsonite modified mix.

In the present study, design of bituminous concrete (BC) is considered. The optimum content of bitumen in conventional mix of 60/70 grade bitumen is obtained by Marshall mix design and on this optimum content of binder the optimum content of Gilsonite is fixed from Marshall mix design. The further performance testing on the mixes were done only by preparing samples at these optimum binder and Gilsonite content. The economics of mixes were based on only the fatigue life of mixes obtained from beam fatigue test.

The methodology adopted is of lab experimentation. As actual field performance study of pavement is a long term process, to simulate the behaviour of field in lab various accelerated specified test were conducted in laboratory. Various relevant tests are to be carried out with this Gilsonite modifier and results are to be compared with the conventional bituminous mix for judging the superiority of Gilsonite modifier.
Findings and Conclusions
From the study, it was observed that-

(i) The addition of equivalent amount of Gilsonite as otherwise used in preparation of mix to the bitumen has significantly affected low and intermediate temperature properties of the base binder.

(ii) The elastic recovery has improved for Gilsonite modified bitumen as compared to conventional 60/70 bitumen.

(iii) Modification of bitumen with Gilsonite directly could hamper the properties of mix at low and intermediate temperature and make them liable to cracking and other problems. So, the method of addition of Gilsonite adopted in this project of adding it to pre-heated aggregates before addition of binder in the mix fair out well as shown by results of the project.

(iv) The stability values of Gilsonite modified mix were better and the retained stability has improved to conventional mix, suggesting better resistance to deformation and less susceptibility to moisture induced stripping.

(v) The indirect tensile strength has improved for Gilsonite modified mix and indicates its better ability to take stresses.

(vi) Resilient modulus value has increased in Gilsonite modified mix. The results have shown better stiffness of Gilsonite modified mix at all temperature and especially at high temperatures, where conventional mix has behaved very miserably.

(vii) The fatigue studies at different stress suggest that fatigue life of Gilsonite modified mix has improved more than twice as compared to conventional mix.

(viii) The experimental work of project suggests great savings in cost with Gilsonite modified mix.

(ix) The results of project clearly suggested that use of Gilsonite as modifier in bituminous mixes has given really a high performance economical mix, which has better resistance to rutting, cracking, stripping and enhanced durability.