Multidimensional analysis of foaming process impact on 50/70 bitumen ageing

Multidimensional analysis was carried out to check the impact of bitumen foaming on its properties. Unmodified bitumen 50/70, bitumen 50/70 modified with 2.5% synthetic wax and control bitumen 70/100 were used in the experiment. The main research goal was to establish whether it is possible to predict the Ageing Index (IS) using a data set consisting of three main subsets containing i) foaming parameters (ERm, HL), ii) selected rheological properties of bitumen (for example ZSV, δ) before and after foaming, and (iii) bitumen chemical changes after foaming determined using FTIR spectroscopy. All bitumen types were foamed at various temperatures (110 °C to 180 °C), air pressures (100 kPa to 700 kPa) and water contents (1% to 5%). Due to large multicollinearity between input variables, the input data set was transformed into a new data set that was reduced using Factor Analysis (FA). The use of the FA method together with the data from the FTIR analysis allowed building a highly effective regression model for predicting the Ageing Index. The Ageing Index model had a matching error of 0.1 and the coefficient of determination > 95%. Analysis results were validated against the bitumen 70/100 results. It should be noted that the input data set presented here can be a good starting point for predicting other rheological characteristics of foamed bitumen.