empirical model for determining rutting parameter in rubber modified bitumen

in this study an empirical model which can be used to predict the rutting parameter (g*/sinδ) for neat and powder rubber modified bitumen describes. the model was developed using 36 unique powder rubber modified bitumen combinations, rubber concentrations were varied at 5% intervals between 5 and 20%. the effects of powder rubber particle size on model accuracy were also studied ultimately a model was produced with the capability of predicting rutting parameter values over a range of temperatures and rubber concentrations. by definition, the upper limit of the performance grade is dependent on the rutting parameter value therefore, the relationship was also considered in terms of high end failure temperature. the rubber coefficient for rutting parameter (rcg) was identified as an important parameter in the estimation of rutting parameter (g*/sinδ) with the addition of powder rubber. this term is a quantitative representation of the increase typically witnessed in rutting parameter values with the addition of powder rubber. ambient ground powder rubber exhibited higher rcg values than cryogenically ground particles. additionally, 95% confidence intervals were generated for the predictive model thus providing a range of accuracy for the model. the resulting confidence intervals were approximately +/-1300 pa these confidence intervals were seen to capture 92.6% of the 462 data points used. findings from this research suggest that the differences between cryogenic and ambient powder rubber bitumen are accurately described using the rcg, furthermore bitumen properties may be predicted using an empirical equation.