Sensitivity Analysis and A Mathematical Model to Determine The optimum Bitumen Content in Stone Matrix Asphalt

Currently in Iran, the mixing design of stone matrix asphalt mixtures is carried out according to the Marshall method. In Marshall mixing design, the optimum bitumen percentage is determined based on the average amount ​​of the bitumen that leads to the highest Marshall Stability, the highest Specific gravity and the most suitable void percentage in asphalt mixtures with stone matrix asphalt. It doesn’t mean that this bitumen percentage is necessarily the optimum percentage. In this paper, a mathematical model has been developed to determine the optimum bitumen content in stone matrix asphalt by Marshall method, For this purpose, first equations of effective parameters changes in bitumen mix design SMA toward bitumen percent are determined by least squares method and approximating a quadratic polynomial and then relying on these equations and using a multi-purpose mathematical model, optimum bitumen percent is determined in a way that asphalt combination would have all conditions in the code and also would have maximum Marshal stability, the haighest specific gravity and the most appropriate void percentage. After obtaining optimum bitumen content, sensitivity analysis toward very low bitumen percentage on effective parameters (marshall stability, bulk specific gravity of mix asphalt, voids of mix asphalt and voids of aggregate) were done in mix design of stone matrix asphalt. The results of this study indicate that the method of mathematical modeling is more accurate than the traditional method, and sensitivity analysis also showed the effect of error rate on optimum bitumen determination.