Investigation of Surface Performance of Chip Seal Layer on Cemented Base Treatment

Chip-seal is one of the preliminary though successful ways to improve road surface of the pavement. Chip-seal is a byproduct of similar sized stones which pour in surface after emulsion bitumen wet the road surface. Chip-seal can deteriorate due to bleeding, aggregate streaking and aggregate removal. The first and second damages are sourced from improper design and implementation whereas the last damage is due to a lot of aspects and this study aims to investigate some of them. The effect of existing road surface, bitumen type, aggregate kind and bitumen percentage are examined in this study. The road surfaces which are evaluated in this research were cement treated base. In this research, two kinds of bitumen including: emulsion and rubber powder modified emulsion was used for chip-seal preparation. According to Iran road code numbered 234, two different mixture aggregate grading were recommended for chip-seal preparation. This study used the third aggregate grading which is generally finer compared to others. Also, in this research two different laboratory tests including; sweep tests and sand patch tests used for examination of the mixtures. The sweep tests were used for investigating the effects of aggregate grading kind, bitumen percentages, bitumen kind and the surface which chip-seal implemented. Also, the sand patch tests were used for investigating the effect of aggregate grading and bitumen kind on texture depth of chip-seal. Results of the laboratory tests indicated that rubber modified emulsion bitumen can decrease chip-seal aggregate removal by approximately 20%~23%. In addition chip-seal aggregate removal has a direct relationship with aggregate grading which results showed 14% decrease in aggregate removal when the finer aggregate grading was used. Moreover, results of sand patch tests indicated that chip-seal implementation of cement treated based can improve road surface friction resistance.