Experimental Study On Fatigue Performance Of Large Stone Porous Asphalt Mixture Under The Different Impact Factors

Reflection crack is one of the most common diseases of Asphalt Concrete Overlay (ACO) on the old cement concrete pavement and composite pavement, it is always a major problem in the road engineering field. Large Stone Porous Asphalt Mixture (LSAM) has a large particle size and more voids, this large size porous structure can effectively block the propagation path of crack tip and weaken the transfer ability of tensile stress and tensile strain. Besides, it can effectively remission the joint’s stress concentration of ACO on the old cement concrete slab, but so far there has been little research on the reflection crack propagation behavior in LSAM. This paper researched the fatigue properties of LSAM and expansion behavior of reflection crack on ACO by testing.By Direct Tension Test (DT), Indirect Tensile Test (IT), Three-Point Bending Test (3PB) and Impact Toughness Test to study the influence of particle size, porosity, asphalt species, asphalt content and other parameters to the tensile fatigue and flexural-tensile properties of LSAM under different stress levels. The results showed that four factors all have a more significant effect on the fatigue performance of LSAM. A mechanical assist device which was used for simulating the fatigue test of temperature reflection crack has been developed. MTS and RMT testing machine were applied to conduct fatigue-damage-contrastive experiments on different kinds of ACO structures with the ideal laboratory conditions, the expansion behavior of load-induced and thermal-induced reflection crack was simulated by the machine, and hence the initiating and propagating process of these kinds of overlays were analyzed.The microfracturing process of LSAM and ordinary asphalt concrete is scanned by CT technology, then the joined-up crack’s CT images of asphalt mixture specimen under various loads are obtained. Besides, the change of the asphalt mixture image’s features are analyzed, and hence studying the influence of loading mode and gradation type to the expansion features of reflection crack on ACO. The results showed that the crack of LSAM mainly extend along the asphalt mortar, interfacial layer or voids which all around the large particle aggregate, there is a obvious bifurcation phenomenon, and overall like letter "Z" glyph scaling up gradually. And the crack of ordinary asphalt concrete basically extend upwards along the vertical direction, its extension path is an obviously main line, the crack propagation speed is faster and the slit width is bigger.