Field evaluation of thin asphalt application in low volume roads in Sri Lanka

Abstract

Thin Asphalt surfacing (TAS) is an innovative idea that has the potential to lower construction and maintenance costs of road construction in Sri Lanka. Laboratory based studies conducted in Sri Lanka have shown that the local materials can be used to produce TAS, and this study focuses on the usability of TAS in the field. Few concerns were found when applying this new technology in the field was taken into consideration before field trial. Such as: (1) The possibility that variations in the gradation of aggregates within the specification limit could negatively affect the characteristics of asphalt mix. Investigations were conducted to look at the impact of coarser and finer gradations on Marshall Properties: these grades represent the upper and lower limits of the proposed specification range, where both mixtures fulfilled the requirements. (2) The impact of the top level of longitudinal profile tolerance on the actual thickness of the asphalt mat. Increase in the proposed layer thickness from 25 mm to 30 mm, and adding additional surface top level correction of the base layer to meet the top level of longitudinal profile tolerance of ±10 mm are the options that have been suggested to meet the specified thickness conditions for TAS, where it was found that both approaches can be advantageous. (3) The rate at which heat is released by an asphalt layer that is thinner than traditional asphalt layer. The results of the laboratory-based testing show that paving around 8 a.m. leaves the least amount of time for compaction. This occurred because the temperature of the ground and the surrounding air was low . Findings on the time for compaction in the morning and evening are quite comparable. This similarity shows that base temperature is more significantly impacted by solar flux than the mix temperature. After the conclusion of surveys and laboratory experiments, it was decided to trial TAS in a road in the Gampaha district with low volume traffic. Construction was done in two sections. Section 1 was constructed with a 30 mm thickness and Section 2 with a 25 mm thickness. Under the test section's field conditions, the results for 30 mm layer thickness were significantly better. The temperature reduction of the asphalt layer surface over time was observed during the trial and the time available for compaction was less than 20 minutes. Through this study it was verified that TAS mixtures within the proposed aggregate gradation limit, satisfy specification requirement, top level surface tolerance of the base layer should be adjusted to ±10 mm, it is advantageous to have 30 mm thick TAS layer rather than 25 mm TAS layer considering the fluctuations of surface level of base layer and sunny noon time is more favourable to lay TAS considering the time available for compaction. It was identified that 30 mm thick TAS sections is more attainable than 25 mm thick TAS section during field applications