3. Studies on Fatigue Behavior of Polymer –Modified Bituminous Concrete Mixes
Date of Start

August 2004
Indian Institute of Technology Madras (R, C)


Scope and Objectives

(i) To evaluate the physical properties of polymer modified binder and mixes

(ii) To study the mechanical properties of bituminous concrete mixes such as indirect tensile strength, resilient modulus and fatigue tests for failure

(iii) Development of empirical relationship from neat and polymer modified bituminous concrete mixes.

(iv) Characterizing crack growth behavior for polymer modified concrete mixes with fracture mechanics approach.

Neat bitumen binder and binder modified with SBS (STYRENE –BUTADIENE STYRENE) will be tested in the laboratory for different tests at varying temperatures and load conditions. Empirical approach has been considered for crack initiation and fracture mechanics approach was studied for crack propagation of polymer modified bituminous concrete mixtures.
Findings and Conclusions
(i) Use of SBS polymer in neat asphalt binder significantly reduces its penetration value, increased its elastic recovery and softening point value.

(ii) The mix strength parameters such as tensile strength and Marshall stability values of the SBS modified asphalt mixes were higher by 21 % and 25% respectively when compared to neat asphalt mixes.

(iii) The tensile strength ratio was observed to be higher for SBS modified mixes by 5% than neat asphalt mixes. This indicates improved resistance to moistures susceptibility. Also the retained stability value of SBS modified asphalt mixes is higher than neat asphalt mixes by 22%

(iv) The resilient modulus of polymer modified asphalt mixes was about 2 to 2.5 times that of the neat asphalt mixes.

(v) The fatigue life of SBS modified asphalt mixes was 2.1 to 2.4 times higher than that of the neat asphalt mixes.

(vi) Specimens compacted with gyratory compactor had higher fatigue life and resilient modulus than Marshall compacted specimens due to better reorientation of aggregates.

(vii) The reduction in resilient modulus values for neat asphalt mixes due to increase of temperature (30 to 400C) ranges from 34 to 41 percent and 25 to 29 percent for Marshall and SGC compacted specimens, respectively.

(viii) For SBS Modified mixes, the reduction in resilient modulus values due to increase in temperature(30 to 400C) was 23 to 27 percent for Marshall and 21 to 28 percent for SGC specimens, respectively

(ix) The accumulation of horizontal plastic deformation(HPD) and vertical plastic deformation ( VPD)as a function of number of cycles was observed to be higher for neat asphalt mixes than SBS modified asphalt mixes

(x) Crack speed index (CSI) was found to be less for SBS modified asphalt mixes. This means rate of crack propagation is slow in case of SBS modified asphalt mixes when compared to neat asphalt mixes.

(xi) For the constant number of cycles, at the constant temperature, crack length was found to be higher for neat asphalt mixes than SBS modified asphalt mixes.

(xii) The laboratory results obtained from this study show the superiority of SBS modified asphalt mixes in terms of fatigue life, resilient modulus and crack propagation over the neat asphalt mixes. Thus polymer modified mixes can be recommended for National Highways where traffic volume is substantially high.