Study On Impacts Of Freeze-thaw Cycles On The Performances Of SMA Mixture

Temperature is low and its difference between day and night is large in coldregions and some other areas in our country. And asphalt pavements are often inrepeated freezing and thawing which results in freeze-thaw cycles damage of varyingdegrees to them. There are few researches particularly on bituminous mixtures’damage of freeze-thaw cycles at present. SMA is a kind of excellent asphalt mixtureof high performance. And it is widely used in recent years. Therefore, it is necessaryto study on impacts of freeze-thaw cycles on the performances of SMA mixture.Raw materials were selected and their performances were tested, the ratio ofSMA mixture, conditions of freeze-thaw cycles and testing methods were designed.Marshall specimens of SMA mixture were grouped into different groups according tothe initial volume of air voids. Mass loss rate, volume of air voids, Marshall Stability,Marshall Flow, Marshall Modulus, Splitting Tensile Strength and Splitting TensileStrength Ratio(TSR) were tested after SMA mixture was subjected to freeze-thawcycles. And two new indexes were proposed, they were Residual Marshall Stabilityand Residual Marshall Modulus after freeze-thaw cycles. The number of times thatResidual Marshall Stability and TSR reached80%was used to evaluate SMAmixture’s moisture susceptibility after freeze-thaw cycles. The test results showedthat initial volume of air voids has great influences on SMA mixture’s volumeperformances and moisture susceptibility after freeze-thaw cycles. Besides, lime andcement can significantly enhance SMA mixture’s volume performances and moisturesusceptibility after freeze-thaw cycles. What is more, lime is better than cement toincrease SMA mixture’s volume performances and moisture susceptibility.The number of times of rolling SMA rut boards was determined. And the rutboards were formed. In addition, conditions of freeze-thaw cycles and testing methodswere designed. And Dynamic Stability, percentage of rut depth and total rut depth ofSMA rut boards were tested after freeze-thaw cycles. What was more, ResidualDynamic Stability was proposed as a new evaluation index. The number of times thatthe new evaluation index above reached80%was used to evaluate high-temperaturestability of SMA mixture after freeze-thaw cycles. Water permeability coefficients ofSMA rut boards were tested to further explo re the influence of freeze-thaw cycles toSMA mixture’s volume of air voids. The test results showed that SMA mixture’s high-temperature stability decreases, while water permeability coefficient of rutboards increases after freeze-thaw cycles. Besides, lime and cement have great effectson increasing SMA mixture’s high-temperature stability, and lime is better thancement after freeze-thaw cycles. The more initial volume of air voids of SMA rutboards, the greater water permeability coefficient is. Rut boards mixed with lime havethe maximum initial volume of air voids, but their ability of resistance to waterpermeability is still good after freeze-thaw cycles.Ultrasonic velocity of SMA mixture’s Marshall specimens was tested, theinfluences of water in Marshall specimens to ultrasonic velocity were analyzed, andthe modified experiential formula about the propagation time of ultrasonic wasproposed. Besides, the relationships between the revised ultrasonic velocity andMarshall Stability, Splitting Tensile Strength were built after freeze-thaw cycles. Inaddition, the fitting empirical formula was proposed. The test results showed that therevised ultrasonic velocity has good correlations with Marshall Stability and SplittingTensile Strength of SMA mixture after freeze-thaw cycles.