Laboratory Evaluation of Bond Between Bituminous Paving Layers For Civil Engineering

[Ghanshyam]

A bituminous pavement is a multi-layered structure generally made up of surfacing, base and sub base courses on a sub grade. An interface is said to be a boundary between any two consecutive layers. So an adequate bond between the layers at the interfaces must be ensured so that multiple layers perform as a single composite structure. In case of non-bituminous layers or bituminous-non bituminous layers, adequate bond is established as such due to the mechanical interlocking between the aggregate surfaces. However, the state of bond at the interface between any two bituminous layers has a significant influence on the stress distribution across pavement layers under traffic loads and hence on the overall performance of the pavement.
To increase the adhesion or bonding between two bituminous layers, bituminous tack coats are applied prior to overlay.This study is an attempt to evaluate the interface bond strength between two types of
bituminous layer combinations in the laboratory. The cylindrical specimens have been tested for bond strength at four normal service temperatures, namely 250, 300, 350 and 400C by applying different types of tack coat at varying application rates. The specimens have been prepared using normal Marshall Procedure first for the underlying layer, followed by application of tack coat and finally overlaying with the top layer in the same mould in an appropriate manner.
Two types of layer combinations have been tried, namely

1. Bituminous Concrete (BC) layer on Dense Bituminous Macadam (DBM) samples
   
2. Semi Dense Bituminous Concrete (SDBC) layer on Bituminous Macadam (BM) samples
   

Similarly, different types of tack coat materials namely bitumen, Cationic Rapid Setting with low viscosity (CRS-1) and Cationic Medium Setting with high viscosity (CMS-2) emulsions have been used for the interface bond between the said bituminous layers. The samples thus prepared have then been tested on a specially fabricated attachment (named bond strength device) fixed to the loading frame of the Modified Marshall Testing Apparatus. It is observed that the interlayer bond strength depends on the test temperature and this decreases with increase in test temperature. It is also observed that the bond strength depends on the type of tack coat used and conditions of the type of combinations. The optimum amount of tack coat has been found to vary for tack coat type and layer combination type.

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