Experimental Studies on Interface Bond Strength of Ultra-Thin Whitetopping Pavements Under Static and Dynamic Loading Conditions

Abstract

The concrete overlays on existing asphalt pavements are classified into three categories namely whitetopping, thin-whitetopping and ultra-thin whitetopping (UTW). The interface bond strength between the existing hot mix asphalt (HMA) pavement and the UTW overlay is the key factor towards the success of UTW overlays. The aim of the present work is to study the interface bond strength of UTW overlays subjected to different interface treatment techniques. Because loss of bond and layer delamination affects the composite behavior of UTW overlay. This will leads to premature failure and reduction in design service life of UTW overlays. Therefore, a good surface preparation method is required to improve the interface bond strength and to meet the design service life of UTW overlays. In order to achieve the objective of the present work experimental studies were conducted under laboratory conditions. An optimized cementitious fiber reinforced concrete (FRC) mix proportion for UTW was arrived using Taguchi method. The HMA mixture specimens of cylindrical and prism were casted using superpave gyrator and compression loading machine, respectively. Later, HMA-UTW composite specimens such as cylindrical and prism were casted with different interface treatment techniques. The different interface treatment techniques adopted for cylindrical specimens are single groove (SG), double groove (DG), piercing and piercing with different percentage of bonding. The HMA-UTW prism composite specimens with different percentage of bonding at the interface were adopted. To enumerate the interface bond strength for different interface treatment techniques two test methods were adopted namely direct shear test and flexural test. Both the tests were conducted under (i) static and (ii) dynamic loading conditions From direct shear test the effect of different interface treatment techniques on interface shear bond strength, k-modulus and number of cycles at failure were obtained. Similarly, in the flexural test, the flexural bond strength and number of cycles at failure were determined for different percentage of bonding. Based on the laboratory test results two interface treatment techniques such as groove interface technique with an inclination of 45 degrees and piercing interface treatment has been proposed. From flexural bond strength test results 75 mm HMA thickness had obtained highest flexural bond strength of 1.71 MPa and 1.4 million number of fatigue cycles. An HMA failure was noticed in 75 mm HMA thick composites subjected to dynamic loading condition.A Finite Element Analysis (FEA) using a contact friction model successfully simulated the interface behavior of HMA-UTW composites. An error of 4 to 14 % were obtained between laboratory test and the simulated model for piercing interface treatment and different HMA thickness subjected to different percentage of bonding.