Study On The Low Temperature Cracking Characteristics Of Asphalt Concrete In Bouton Rock

Bouton rock asphalt concrete pavement has gradually begun to be widely used in our country.Its excellent high temperature stability,water stability,fatigue resistance,and resistance to microbial erosion have formed a consensus in the industry.However,its low temperature and easy cracking characteristics are still the focus and difficulty of the research of experts and scholars.At present,most of the researches on low-temperature cracking of asphalt concrete are based on macro-mechanical tests and related indicators.However,there are few studies on the low-temperature cracking process of asphalt concrete and the influence of its internal pore structure changes on its low-temperature cracking performance.In this study,bouton rock asphalt concrete and its control materials,matrix asphalt concrete and SBS modified asphalt concrete,subject to road conditions such as long-term and short-term aging,ultraviolet aging,freeze-thaw and salt freeze-thaw cycles,were used as the research objects.The trabecular three-point bending test,frost fracture test,and nuclear magnetic resonance test(NMR)under simultaneous observation of DIC,analyze the cracking process of the three asphalt concretes from the macro and micro perspective.The results show that on a macro scale,the bouton rock asphalt concrete cracks at low temperature until the specimen fails.The strain energy density is greater than that of the matrix asphalt concrete and close to the SBS modified asphalt concrete.It can be seen that bouton rock asphalt can improve the matrix.Asphalt concrete has low-temperature cracking performance,but freeze-thaw and salt freeze-thaw cycles have the greatest impact on the low-temperature performance of bouton rock asphalt concrete.From the bending coefficient Su of asphalt concrete,it is known that bouton rock asphalt concrete is similar to SBS modified asphalt concrete at 0℃and-10℃,which belongs to flexible cracking;at-20℃,it is similar to matrix asphalt concrete,which belongs to brittle cracking.The transformation point temperature of bouton rock asphalt concrete is higher than that of the other two asphalt concretes,and the fracture strength and frost-breaking temperature during freezing are close to that of SBS modified asphalt concrete,and are better than matrix asphalt concrete,indicating that the matrix asphalt is mixed with a proper amount bouton rock asphalt can improve its resistance to temperature shrinkage and cracking.On the meso scale,by analyzing the three-point bending DIC cloud diagram,the crack length,and the damage factor D_T of the specimen,it can be known that the crack propagation length of bouton rock asphalt concrete is greater than that of the matrix asphalt concrete and the crack length variation curve obeys the third-order polynomial distribution.The length change curve is analyzed to obtain the key cracking length and the key strain energy density is inversely deduced.It is known that adding an appropriate amount of bouton rock asphalt can delay the appearance of the key points of matrix asphalt concrete cracking.When the temperature is lower than-10℃,bouton rock asphalt concrete The key cracking point and the damage factor change curve of the slab are obviously moving forward,which indicates that the low-temperature anti-cracking performance of bouton rock asphalt concrete is obviously weakened in the low-temperature environment below-10℃.In summary,when applying bouton rock asphalt concrete in negative temperature areas,especially winter cold areas(<-10°C),attention should be paid to its low-temperature crack resistance.From the perspective of pore structure,the analysis of pore structure by nuclear magnetic resonance showed that compared with matrix asphalt concrete and SBS modified asphalt concrete,bouton rock asphalt concrete has a greater range of internal pore diameter changes before and after being damaged by freeze-thaw and salt freeze-thaw cycles.small.The analysis of the correlation between the pore structure and the low-temperature cracking of asphalt concrete shows that the content of harmless and multi-hazardous pores in the asphalt concrete has a strong correlation with the crack resistance of the asphalt concrete.