Reflective cracking continues to be a concern for pavement materials and design practitioners for overlays on asphalt and primarily concrete pavements. Over the years, various materials and techniques have been used to mitigate reflective cracks to varying degree of success.
Stress Absorbing Membrane Interlayers (SAMI’S) have been used as a practical method to retard reflective cracking on pavements that have adequate structural support since the early 1970’s. Other products have shown mixed results in their ability to retard cracking. Improvements in materials (i.e. mostly the use of polymers) saw the development of engineered asphalt interlayers the 1990’s. This was the introduction of performance-based specifications largely based on the 4-point flexural beam fatigue test to control fatigue cracking. These systems were designed to be relatively impermeable with high asphalt content (typically >8 %) and low air voids (2-3%) and were placed 25 mm thick with a 4.75 mm nominal aggregate size. The overall early performance of this technique also varied to some degree mostly to due climate and availability of appropriate material.
Research continued and by 2006 consistent performance of the high-polymer design improved significantly with a performance-based specification. Koch Materials Company reported an average of 71% improvement in reflection cracking resistance on their high polymer, performance-designed interlayer projects as compared to control sections measured on 18 projects built with control sections that were up to 4 years old. Increased cracking resistance was documented with the addition of a complementary crack-resistant overlay. The advancement of high-strain asphalt interlayers continues, and ongoing research clearly shows that the use of interlayers has become a common method to reduce reflective cracking. This research has also advanced the use of newer and alternative cracking tests (e.g. IDEAL-CT, SCB-IFIT and DCT) for design and acceptance.
More recently, the application of aramid polymer fibres has been successfully used as a viable and local alternative. This paper discusses the design of the high-strain asphalt interlayer using the aramid polymer fibre reinforcement and the associated performance testing based on IDEAL-CT testing. A 2019 case study is presented to illustrate the ease of design, production and laydown of this advanced material that essentially uses locally available materials and generic performance-based specifications.
