Laboratory Investigation On Warm Mix Asphalt Incorporating Organo-Silane Additive

Warm mix asphalt (WMA) was developed to reduce asphalt production temperatures and energy consumption. Production of toxic gas emissions can be reduced considerably. However, lowered production temperature results in the presence of trapped moisture in the aggregates that could lead to stripping and subsequently moisture susceptibility problems, and which can be mitigated by using additives. Asphalt mixtures incorporating such additive must exhibit at least similar performance to conventional hot mix asphalts (HMA) which produce at higher temperatures. This paper evaluates the engineering properties and moisture susceptibility of asphalt mixtures incorporating Organo-Silane additive for use as WMA and anti-stripping agent. WMA samples were compacted at 125 degrees C and 115 degrees C and their performance were compared with control HMA specimens. The asphalt mixtures were prepared using similar aggregate gradation and binder types. Mixture workability was quantified in terms of the Compaction Energy Index (CEI) that was measured by integrating the area under the densification curve between gyration 8 and 92% theoretical maximum density. Lower CEI implies a more workable mixture. The CEI of WMA was 76.4, which was much less than the corresponding value for HMA. Samples were also tested for Marshal stability, resilient modulus and wheel tracking (WTT) tests according to ASTM D6927, ASTM D4123 and BS EN12697-22 procedures, respectively. The control samples perform better in the stability test. The resilient modulus of WMA was only about 10% lower compared to HMA. Resistance to permanent deformation was measured from the dynamic stability (DS) or the number of wheel passes per 1 mm rut depth over the last 15 minutes in a 60-minute tracking test. The DS of HMA, WMA compacted at 125 degrees C and 115 degrees C were 3138, 3044 and 2837, respectively. From the rutting resistance standpoint, the results are not significantly different. Hence, incorporation of the additive does not adversely affect mixture rutting resistance despite the lowered production temperature.