The Analysis Of The Effects On Filler-to-bitumen Ratios To Low-temperature Features Of Bitumen Mortar

Low temperature cracking of asphalt mixture pavement seriously impacts on the performance of the pavement. Moreover, this problem reduces the service life of the pavement. The cracking types caused by the low material strength mainly happen at the interface between bitumen mortar and aggregates under the tensile stress and shear stress. The contact surface between bitumen and mineral aggregates exhibits two mechanical failure modes: cohesive failure, in which bitumen strength is reduced, and adhesive failure at the bitumen and mineral interface.The main factors affecting bitumen mortar cohesion strength are bitumen strength itself and the compatibility between bitumen and mineral powder. Besides, the adhesion strength has impacts on the binding effects between the bitumen mortar and the surface of aggregates.In this paper, experimental materials mainly choose the common limestone mineral powder, mineral stone, and SBS modified bitumen mortar. Based on the cracking characteristics of asphalt pavements, our research team developed a quantitative testing technology for the low-temperature mesoscopic strength of asphalt mixtures, by which the cohesion strength test data of different ratio mineral power to bitumen could be obtained in low-temperature conditions. Besides, in order to analyze the low-temperature effect mechanism of the interface between SBS modified bitumen and the limestone aggregate, the least-squares principle and image processing were applied to achieve the quantitative test of cohesion and adhesion strength. The main conclusion and results are following:(1) The proposed quantitative testing technology can be used to evaluate the strength of the SBS-modified bitumen under different low-temperature conditions. The adhesive and cohesive strength of bitumen at specific low temperatures are fitted accurately according to the least-squares principle. The adhesive and cohesive strengths of the contact surface between bitumen and mineral aggregate can be tested quantitatively based on the image processing technology.(2) At-5°C~-15°C, the strength increases as the temperature decreases. However, it decreases sharply at the extremely low temperature.The parameter of cohesive strength presents the mechanical strength of the bitumen material itself, and the adhesive strength reflects the cementation between bitumen and mineral materials.The overall tensile strength signifies the ultimate strength of the bitumen and mineral interface. The mixing of SBS could increase the low-temperature strength of bitumen mortar. Simultaneously, it is beneficial to reducing the low-temperature sensitivity of bitumen mortar. However, there is little effect on the change of the point of bitumen embrittlement.(3) The mixing content of mineral powder fillers significantly influences the effects of the low-temperature cohesive strength of asphalt. If the low-temperature cohesive strength of asphalt mortar is considered the control index, then the optimal filler-to-bitumen ratio cannot be easily determined until the temperature effects are fully considered as well.The asphalt matrix possesses high low-temperature cohesive strength at the low-temperature environments of-5 °C and-15 °C. Therefore, the mixture of mineral fillers into asphalt can improve this strength considerably. However, the incorporation of excessive amounts of mineral power into asphalt induces filler agglomeration in the interior of the asphalt mortar, which significantly reduces the low-temperature cohesive strength of asphalt mortar. Thus, the optimal filler-to-bitumen ratio is 1.2:1 at-5 °C and-15 °C. The asphalt binder is completely embrittled at the low-temperature conditions of-25 °C and-35 °C. Moreover, the cohesive strength of asphalt matrix decreases, and additional damage points can be established easily on the interface between the asphalt matrix and the filler. Conversely, these points can easily connect to one another and form a macroscopic crack interface. Thus, the optimal mixing content of mineral powder fillers is 0.8:1. The process of determining the optimal filler-to-bitumen ratio should be combined with the low-temperature characteristics of the region at which engineering is conducted. In addition, the effects of the influencing factors must be comprehensively considered, including asphalt matrix strength, mineral power filler agglomeration, asphalt matrix embrittlement and the adhesive strength of the interface between the asphalt and the mineral power fillers.