Effects of water-foaming and liquid warm mix additive on the properties and chemical composition of asphalt binders in terms of short term ageing process

This study investigated the effects of water-foaming of asphalt binders containing liquid warm mix additives as an intention to produce warm-mix asphalt with enhanced performance in scope of compaction and moisture resistance. Two paving grade bitumen were used as a base material – a 35/50 and 50/70 paving grade bitumen binders. The investigation involved subjecting the asphalt binders to short-term ageing using rolling thin-film oven test protocol in temperatures ranging from 123 °C to 163 °C to simulate the effects of lowered processing temperatures in warm mix asphalt techniques. The testing methods included standard classification tests, basic evaluation of foaming performance, dynamic viscosity testing, evaluation of high temperature stiffness and non-recoverable compliance using a dynamic shear rheometer as well as evaluation of changes in chemical composition of the binders using Fourier transform infrared spectroscopy. The results have shown that water-foaming of asphalt binders incorporating the liquid warm mix additive led to an additional, significant drop in their dynamic viscosity in the mixing and compaction temperature range, while no significant effects to the performance-related characteristics of the binders were observed. It was found that the small changes in asphalt binder rheology caused by water-foaming were reverted in the course of laboratory short-term ageing. The process of water foaming has induced measurable changes in the chemical structure of the investigated binders associated traditionally with oxidative ageing, however these did not affect the results after the short-term laboratory ageing using the rolling thin-film oven test protocol. Based on the conducted work it was concluded that the simultaneous use of water-foaming and the liquid warm mix additive should not have permanent effects on the performance of the investigated asphalt binders, while enabling enhanced coating and workability of the asphalt mixtures produced in lowered temperatures.