Research On Influence Of Aggregates On Indirect Tensile Strength Of Asphalt Mixtures

Cracking of an asphalt pavement layer is closely related to the tensile strength of asphalt mixture.Indirect tensile strength is a common property to evaluate the tensile performance of asphalt mixtures.Hence,the influencing factors of tensile strength are worthy of research.There have been many studies focusing on the influence of aggregate gradation,surface texture,test temperature,loading rate on the indirect tensile strength of asphalt mixtures.However,the influence of aggregate strength is rarely studied,and it is often ignored in practice.Therefore,this paper aims to analyze the mechanical behavior of aggregate in mix design and testing of asphalt mixtures,and explore the influence of aggregate strength on the indirect tensile strength of asphalt mixtures,so as to provide further insight into the studies of tensile strength of asphalt mixtures.SMA-13 and AC-13 asphalt mixture specimens were prepared by Marshall compaction and gyratory compaction methods using limestone,diorite and basalt aggregates,respectively.The specimens were subjected to indirect tensile test at room temperature(25℃).The results of multiple linear regression analysis show that the indirect tensile strengths of specimens with different lithology,gradation types and fabrication methods have significant differences.The aggregates of AC-13 and SMA-13 samples prepared by Marshall compaction and gyratory compaction method respectively were extracted for gradation analysis.Taking the original mixture design gradation as reference,the aggregate degradation caused by the compaction process was analyzed,and the cracking behaviors of aggregates were analyzed with respect to their lithology,gradation and compaction method.The results show that degradation of aggregates occurred mostly in the coarse aggregate sizes of 13.2mm ～ 16 mm,9.5mm ～ 13.2mm and 4.75 mm ～ 9.5mm;among which the aggregates with particle size of9.5mm ～ 13.2mm were the most seriously degraded,followed by the aggregates with particle size of 4.75 mm ～ 9.5mm.The proportion of fine aggregates with particle size 2.36 mm and below increased in all test cases.These also provided baseline data for the subsequent analysis of aggregate degradation in the splitting tests.For a split section of a specimen subjected to indirect tensile test,digital image analysis and manual counting of the size and quantity of the aggregate particles on the split faces of test specimens were performed to quantify the effects of aggregate crushing.The results showed that the limestone specimens with the lowest aggregate strength had the largest number of broken aggregate,and their indirect tensile strengths were the lowest.The basalt specimens had a small number of broken aggregate in the split section,and their indirect tensile strengths were the highest.This shows that the strength of coarse aggregates on the split section contributes to the resistance to splitting,and is a factor that affects the indirect tensile strength of the mixture.The samples after splitting were subjected to extraction and screening again to compare the changes in aggregate gradation before and after splitting.The test results show that aggregate gradation became finer after splitting.This suggests that the splitting tests led to aggregate degradation,and the broken aggregates in the split section were indeed produced by the applied force during the splitting process.This further illustrated that aggregate strength is an important factor affecting the indirect tensile strength of asphalt mixtures.