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.
