Fundamental characterisation of thermal influence in hot mix asphalt repair

Abstract

The study focuses on the issue of hot mix asphalt pothole repairs, the performance of which is greatly reduced by repair edge disintegration. This is caused by low interface temperatures which result in low density interfaces and poor repair bonding. The study examined heat flow in shallow and deep pothole excavations under controlled pre-heating done in heating-cooling cycles, referred as “dynamic heating”, and the effect of asphalt thermal properties on this. Dynamic heating was applied with an experimental infrared heater operating between 6.6 kW and 7.7 kW heat power and with the heater being stationary or moving above simulated potholes at offsets of 130 mm and 230 mm. The study also examined heat flow in traditional non-heated shallow repairs, referred as “static repairs”, and dynamic shallow repairs and the effect of pothole pre-heating in repair adhesion. Finite Element modelling was also used to enhance understanding of heat flow in the executed repairs. Then, the bonding properties and rutting resistance of the repairs were assessed using shear bond tests (SBT’s) and wheel track tests (WTT’s) respectively. The results showed that irrespective of excavation depth, heating power and heater offset, temperature distribution in the pothole excavation and inside the slabs under dynamic heat was non-uniform. Dynamically heating pothole excavations for approximately 10 minutes yields better heat distribution than 20 minutes heating time while minimising the possibility of asphalt overheating. The temperature profile at the interface of the dynamically heated repair is improved when compared to static repair suggesting better interface adhesion. A significant role in this profile is played by thermal contact conductance which determines the resistance to pavement-repair thermal conduction per unit area at the repair interface. This was reflected in the assessment and simulation of the repairs with the latter generating reasonable transient temperature profiles within the dynamically heated pothole excavation, at the interface of the repairs, and inside the host pavement. Further, the shear strength at the bottom and side interfaces of dynamically heated repairs was 78.2% and 68.4% higher respectively than that of static repairs. On average, static and dynamic repairs showed repair interface rutting depths of 14.82 mm and 10.36 mm respectively. It was concluded that dynamically heating a pothole excavation increases repair interface adhesion and repair durability.