Thermal ageing behaviour of isocyanate-based bitumen additive

Abstract

Asphalt modification has been a good way to improve and prepare pavements to bear increasing traffic loads and temperatures; however, it is important that the additives used have a positive impact throughout the entire life cycle of the pavement. Since the performance enhancing capabilities of isocyanate-bitumen modification have already been documented, in this study, the focus lies on the ageing behaviour of this novel additive from a chemo-mechanical perspective. The chemical oxidative ageing was studied using infrared spectroscopy (ATR-FTIR), while the mechanical/rheological ageing, on the other hand, was studied using different tests performed with the dynamic shear rheometer (DSR), such as BTSV, frequency-temperature sweeps and cryogenic stress tests. Five different samples of unmodified, isocyanate-modified and SBS-modified bitumen were submitted to standard and extended laboratory short and long-term thermal ageing, respectively. Since the isocyanate-based bitumen modification has shown to enable warm-mix asphalt production, one variant was subjected to a short-term ageing at a lower temperature to consider this aspect. From a chemical perspective, the ATR-FTIR measurements show that the isocyanate-modified bitumen produced a higher chemical ageing after short-term thermal ageing compared to the SBS modification. However, on the long-term, this effect disappears. On a rheological level, the different methods used suggest that the mechanical ageing of the isocyanate-modification is comparable to the SBS modification. Moreover, a lower short-term ageing temperature appears to have a benefit on the chemical ageing but not on the mechanical/rheological ageing.