Including asphalt cooling and rolling regimes in laboratory compaction procedures

Abstract

Given the various changes occurring in the asphalt construction industry, improved process and quality control is becoming essential. The significance of appropriate rolling and compaction for the quality of asphalt is widely acknowledged and vital for improved process control. But what constitutes appropriate rolling and what are appropriate instructions for operators? Existing laboratory procedures generate a single compaction temperature based on binder viscosity. However, in practice, roller operators choose various windows in terms of both time and temperature for compaction activities. This makes it difficult to design the compaction process and give proper instructions to operators. This research project has aimed to (1) develop laboratory compaction procedures that take account of asphalt cooling during compaction and (2) determine the effects of different compaction strategies on the asphalt quality. Field compaction processes for two mixtures, an AC 16 base/bind and SMA 11 surf, were simulated in the laboratory using different temperature windows and applying different rolling regimes using a slab compactor and a 2.5 ton roller to produce 500 mm square slabs. The resultant densities and Indirect Tensile Strengths (dry and retained) were assessed based on 16 cores drilled from each slab. The experimental results show that it can be important to design rolling strategies within clearly defined temperature windows. If an SMA 11 surf is compacted outside the optimal temperature window, or using a sub-optimal rolling strategy, the density may drop by 30 kg/m3 and the Indirect Tensile Strength fall by up to 10%. Such experimental results are vital if one is to design appropriate rolling regimes and give appropriate instructions to roller operators. Also, the results can help to close the gap between field processes and laboratory compaction techniques. Overall, the results reflect a valuable step in the quest toward improved process and quality control.