Comparison of Bond Strength Evaluation Methods Between Pavement Layers

Tack coats are generally used to facilitate a bonding between pavement layers in construction of hot-mix asphalt pavements and overlays. The goal of applying a tack coat material is to ensure the new or consecutive pavement layers respond monolithically under loading and avoid premature failure caused by debonding, mat slippage, or fatigue cracking. Multiple different in-situ and laboratory tests have been developed to evaluate bond strength of tack coat materials under tension, shear, and mixed-mode loading mechanisms. However, there is no universally accepted bond strength test method or performance criteria for tack coats within the United States. While some specifying agencies have gained familiarity and comfort with a particular bond strength test, a gap exists for many states that have not adopted a testing procedure. The objective of this paper is to compare current and newly developed tack coat bond strength tests to help determine which is most indicative in predicting field performance. Field cores from four different pavement sections with varying traffic loading conditions and early bond strength performance were sampled and tested in the laboratory using four different bond strength evaluation methods. Statistical analysis of bond strength testing results shows a strong linear correlation between pull-off and shear strength testing. Meanwhile, a novel approach to tack coat bond testing under cyclic tensile loading was explored and showed appreciable discrimination between sample locations and agreement with early field performance.