Evaluation of Influential Factors for Analysis of Bonding Strength Between RCC and Sand Asphalt Membrane Interlayer

Although laying an asphalt concrete overlay on the old existing surface is a common method used for pavement improvement, weak bonding strength between the existing old layer and the new overlay is a concern that can decrease the pavement service life significantly. A common method for increasing bonding between pavement layers is using tack coat between pavement layers Therefore, this paper aims at evaluating the bonding strength between sand asphalt layer and RCC and considers different parameters including type of tack coat, tack coat dosage and the existing layer surface temperature. Four tack coat types including grade 60-70, modified grade 60-70 with crumb rubber, CSS and CRS emulsions were considered and in order to determine the most proper dosage of tack coat, 200, 400 and 600 gr/m2 tack coats were applied to the existing layer surface. The RCC layer surface temperatures were 0, 25 and 60 centigrade degrees. Bonding strength test was determined using LPDS test device on cylindrical specimens. Results showed that grade 60-70 modified with crumb rubber significantly increases bonding strength but shows weak bonding in low surface temperature. Bottom layer surface temperature (RCC layer), showed to have significant effect on bonding strength between layers. When the surface temperature is around zero degrees centigrade, bonding strength decreases significantly especially when high tack coat dosage is applied. Evaluating different amount of tack coat showed that the optimum dosage for CRS and CSS emulsion is 400 and 200 gr/m2 respectively. Increasing tack coat dosage for grade 60/70 and modified 60/70 to 600 gr/m2 showed great increase in bonding strength.