Application of surface-modified silica nanoparticles with dual silane coupling agents in bitumen for performance enhancement

Bitumen is a black and highly viscous liquid that holds stone aggregate together in road pavement. Oxidation aging of bitumen can accelerate overall pavement deterioration and shorten pavement service life. Use of silica nanoparticles (SNPs) have been promoted as a sustainable construction practice to delay bitumen oxidation. Nonetheless, adequate dispersion of SNPs in bitumen has been a challenge since their first employment. Surface functionalization of SNPs with (3-aminopropyl) triethoxysilane (APTES) has demonstrated its efficiency to improve dispersion of SNPs in bitumen at relatively high loading of SNPs with low mechanical energy input. As the amount of APTES increases in the process of surface modification of SNPs, however, average size of the resultant SNPs and their agglomeration in bitumen also increase due to APTES self-condensation reaction on SNP surface. This research investigated surface modification of SNPs with other silane coupling agents including 3-(trihydroxysilyl) propyl methylphosphonate (THPMP) and (3-glycidyloxypropyl) trimethoxysilane (GPTMS) as well as dual silane combinations: APTES with THPMP and APTES with GPTMS. The intention was to minimize agglomeration of SNPs in bitumen and to further improve overall performance of SNP-containing bitumen. The comparative experimental results indicated that the surface-modified SNPs with dual silanes (APTES-GPTMS) outperformed the sole APTES-modified SNPs regarding dispersion in bitumen, resulting in bitumen with more enhanced anti-aging and low temperature properties. The results of this study inform and promote the application of SNPs in road pavement with enhanced performance and sustainability.