Laboratory study to investigate the performance of Tack Coat between bituminous layers

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The vehicle ownership rate has been escalating round the world and to accommodate this increasing traffic load the modern trend of designing multi-layered bituminous pavement comes into play. Insufficient pavement interface bonding may lead to major pavement overlay distresses and eventually reduces the pavement service life. A tack coat is usually sprayed in between the bituminous pavement layers for effective stress distribution across pavement layer under heavy traffic loads. This paper presents the experimental results obtained through laboratory and field studies to recommend the effective tack coat materials and optimum application rate. A simple interface direct shear test was performed on 150 mm diameter cylindrical laboratory prepared specimens using two conventionally used tack coat materials in India namely, CMS-2 and CRS-1 sprayed at the interface between Bituminous Concrete (BC) and Dense Bituminous Macadam (DBM) at application rates varying at 0.20 kg/m 2 , 0.25 kg/m 2 and 0.30 kg/m 2 .The test results indicated that CRS-1 as tack coat provides higher interface bond strength value compared to CMS-2. Similarly, irrespective of the types of emulsions used as tack coat, the optimum rate of application is found to be 0.25 kg/m 2 as recommended in MORT&H's specifications. Also the test results obtained from the laboratory prepared specimens were compared with the results obtained from field cored specimens and found higher shear strength value of laboratory prepared specimens compared to field core specimens.