Road performance evaluation of the silane coupling agent/diatomite composite modified gneiss asphalt mixture

To improve the adhesion between gneiss aggregate and asphalt, as well as the road performance of gneiss asphalt mixture, the silane coupling agent KH550 and diatomite were used for the composite modification of gneiss asphalt mixture, and the composite modification mechanism of silane coupling agent and diatomite was explained. The Marshall test and freeze-thaw splitting test indicators were used, combining the orthogonal test, to determine the optimal content of KH550 and diatomite and asphalt-aggregate ratio in the KH550/ diatomite composite modified gneiss asphalt mixture. The road performance was evaluated through the dynamic modulus test, semi-circular bending test and freeze-thaw splitting test. The results show that the optimal combination of three factors determined through the orthogonal test is KH550(0.9%), diatomite(7.5%) and asphalt-aggregate ratio (5.8%). At 20℃, 35℃, and 50℃, KH-DM has the largest dynamic modulus at the same frequency. Taking 50℃ and 10 Hz as an example, compared to SCRM, the dynamic moduli of KHM, DM, and KH-DM increase by 26.7%, 50.8%, and 73.3%, respectively. And the change trend of phase angle is basically opposite to that of the dynamic modulus. The fracture energies of DM, KHM, and KH-DM increase by 2.52%, 5.88% and 45.59%, respectively at −20℃, compared to SCRM. The fracture toughness increases with the decrease of temperature. Additionally, the minimum increases in the crack resistance index (CRI) are 0.35%, 6.62% and 41.74%, respectively at −20℃, −10℃ and 0℃. The freeze-thaw splitting strength ratio of SCRM is the smallest, those of KH-DM, DM, and KHM increase by 10.5%, 3.1% and 7.2%, respectively. The composite modification of KH550 and diatomite significantly improves the road performance of gneiss asphalt mixture, and the composite modification is superior to the single modification. The research results provide the technical reference from the composite modification of silane coupling agent and diatomite for road engineering in neutral and acidic source aggregate areas.