Study of warm mix technologies for asphalt concrete

Abstract

As Singapore continues its expansion of road infrastructure to meet the nation’s growing road demands, it is inevitably constrained by its small land area. The Urban Redevelopment Authority (URA) proposes an ingenious solution to this problem by expanding Singapore’s development underground. This allows valuable surface land to be allocated for more habitable use, such as for housing and community spaces purposes. However, the move to expand road infrastructure underground sees its own shortcomings.

Road construction in tunnels has been notoriously worrisome. Traditionally, Hot-Mix Asphalt (HMA) is used to surface most public roads in Singapore. This could see paving temperatures up to 180ºC. Compared to paving roads on the surface, underground paving means that there is no place for heat or fumes to readily dissipate. This not only endangers road workers, but also poses an energy consumption concern when large exhaust and suction fans are brought in to cool asphalt mixes and to redirect polluted fumes. The problem of energy consumption is further exacerbated by HMA’s already-high energy consumption production method.

One possible technology worth exploring is Warm-Mix Asphalt (WMA). WMA is a relatively new technology that aims to reduce the temperature required for mixing and paving by adding additives. These additives help retain the mixture performance of HMA whilst lowering heating temperatures by 20-40ºC. Its use has been well documented and studied in Europe. However, WMA is still not fully applied in Singapore’s context.

This study evaluated the feasibility of using WMA in replacement of HMA in underground road construction. Both WMA and HMA samples were made following W3B wearing course mix. Samples of WMA were made using Pen 60/70 binder and Sasobit and samples of HMA were made using PG-76 binder. These samples are subjected to performance indicator tests to examine the respective mechanical performance. The tests include Marshall Stability Test, Moisture Susceptibility Test, Dynamic Creep Test, and, Indirect Tensile Strength Test.

The optimum binder content (OBC) of WMA was determined to be 5% via compliance testing. Results of WMA specimens obtain comparable, if not better, results for both Dynamic Creep test and Indirect Tensile Test. This signals that the switch from WMA to HMA may improve cracking and rutting resistance. However, WMA specimens perform poorly when subjected to moisture damage, as shown through the Moisture Susceptibility Test. This suggests that, with the addition of anti-stripping agents, the switch from HMA to WMA in road tunnel construction may prove to be feasible and environmentally beneficial.