Influence of mix proportion of asphalt mixture on Marshall Index

The Marshall Index of asphalt mixtures were remarkably affected by the gradation. Via controlling the pass percentage of key sieve size, the asphalt mixtures with high performance can be realized. In this work, the relationships between the usage between the adjacent sieve sizes and the Marshall Index (Marshall Stabilities and Flow Values) were studied for two kinds of gradations of screen size, AC25 and AC13. For each kind of gradation, according to the orthogonal test method, the usage of aggregate between the adjacent sieve size is changed to form 50 pieces of gradation for the Marshall tested with asphalt. The SPSS software was adopted for the regression analysis of the data. The results show that the key sieve sizes, which remarkably influence the Marshall Index of asphalt mixtures, are 0.075mm, 0.3mm, 0.6mm, 2.36mm, 13.2mm, 16mm, 26.5mm for AC25. In the case of AC13, the key sieve sizes are 0.3mm, 0.6mm, 2.36mm, other than only a sieve size of 2.36mm in the Chinese specification. Meanwhile, once the modified asphalt is used, the dependency of the gradation on the Marshall Index of asphalt mixtures becomes poor apparently. Therefore, great attentions should be paid to the design of gradation and the control of key sieve size for the conventional asphalts mixture design.