EVALUATION OF PARAMETERS INFLUENCING INTERLAYER BOND STRENGTH OF BITUMINOUS MIXES

Abstract

Slippage failures and delamination failures caused by frequent acceleration and turning movements by vehicles on flexible pavements are because of the inadequate bonding between the asphalt layers. Applying tack coat between these layers is a widely accepted solution for this problem. However, clarifications regarding many factors which affect the tack coat performance yet need to be found out. This paper intended to find out the effect of factors such as laying temperature, tack coat application rate, surface roughness on interlayer bonding strength between BC-2 (Bituminous Concrete) and DBM-2 (Dense Bituminous Macadam) layers of asphalt pavement. Leutner shear test was used to evaluate the interlayer shear strength of laboratory prepared 150 mm diameter cylindrical samples. 140°C, 150°C and 160°C were chosen for laying BC layer. Application rate of 0.2 kg/m2 , 0.25 kg/m2 and 0.3 kg/m2 as per MoRTH specification was chosen for applying RS-1 (Rapid Setting emulsion) as tack coat above the DBM-2 layer. For analyzing the effect of interlayer surface roughness, rough and smooth interfaced samples were considered. For rough interfaced samples, the top surface of DBM-2 layer was grooved and the tack coat was applied on this grooved surface. For smooth interfaced samples, the surface where the tack coat applied was leveled. Leutner test was conducted on rough interfaced and smooth interfaced samples for the above mentioned laying temperatures and application rates of tack coat and the results were compared. It was found that the laying temperature, application rate and interface surface roughness have impact on interlayer bond strength. Also, rough interfaced samples presented more shear strength than the smooth interfaced samples irrespective of laying temperature and application rate. For smooth interfaced samples, the interlayer bond strength decreased with increase in temperature while that for rough interfaced samples the trend was found to be opposite ie., as the interlayer bond strength increased with increase in temperature. An application rate of 0.25 kg/m2 was found to be optimum for both smooth and rough interfaced samples.