Laboratory Evaluation of Inter-layer Bond Strength Between Bituminous Paving Layers

Abstract

Tack coats are normally applied prior to overlaying to provide adequate adhesion or bonding between two bituminous layers. This is a study in the attempt stage to evaluate the inter-layer bond strength between two common types of bituminous paving layer combinations such as (i) bituminous concrete over dense bituminous macadam (DBM-BC) and (ii) semi-dense bituminous concrete over bituminous macadam (BM-SDBC) samples in the laboratory. The specimens representing the said combinations have been prepared in the laboratory using normal Marshall procedure with minor exceptions. The different types of tack coat materials, namely rapid setting (RS) bitumen emulsion and medium setting (MS) bitumen emulsion, VG 10 bitumen and VG 30 bitumen have been used at different application rates for providing the inter-layer bond between the bituminous layers. The samples thus prepared have then been tested at four different test temperatures on a specially fabricated attachment (named inter-layer bond strength tester device) fitted to the loading frame of the Marshall testing apparatus. It is observed that the inter-layer bond strength (ILBS) depends on the test temperature, type of tack coat material, and application rate of a respective tack coat. Out of four tack coat materials considered in this study, MS offers maximum ILBS with minimum quantity requirement in both DBM-BC and BM-SDBC layer combinations.