| Stone Mastic Asphalt is a common asphalt mixture.Because of its superior durability and anti-rutting performance,SMA is widely used in the construction of highway networks in China.SMA asphalt mixture consists of coarse aggregate,fine aggregate,mineral powder,asphalt and fiber stabilizer.The coarse aggregate accounts for about 70%-80%,and the coarse aggregate acts to form a stone-stone embedded skeleton structure,which provides the asphalt pavement with the main resistance to deformation.It can be seen that a reasonable grading design will have an excellent skeleton structure,which in turn will play a decisive role in the performance of the SMA asphalt mixture.In the existing grading design method,several sets of preliminary grading methods are selected to design the asphalt mixture grading.However,the selection of the initial grading in this method needs certain experience.And the performance of the selected initial test grading may only meet the requirements of the specification,but there is a better space for improvement in all aspects of asphalt mixture.Therefore,this paper studies the grading optimization design of basalt fiber SMA-13 asphalt mixture.The research work carried out is as follows:1.Divide the gradation curve into two power function curves,by adjusting the passing rate of the nominal maximum particle size(in this case,the 13.2mm sieving rate),the 4.75 mm sieving rate,and the 0.075 mm sieving rate to control the change of gradation curve.2.By using the 13.2mm sieving rate,the 4.75 mm sieving rate,the 0.075 mm sieving rate,and the asphalt-aggregate rate as the influencing factors,then taking the volume of air voids,the voids in mineral aggregate,the voids filled with asphalt and the Marshall stability as the response indicators in order to perform a response surface method center composite design.By establishing a functional model between the influencing factors and the response indicators,then set the optimal conditions,finally the optimal gradation design under this condition is obtained.3.The computed tomography(CT)technique was used to obtain the tomographic images of the SMA-13 asphalt mixture.The effects of different filtering methods on the image denoising effect were discussed.The stone,asphalt mastic and void in the asphalt mixture image were extracted by image segmentation to analyze the microstructure of the asphalt mixture.4.The distribution law of the voids in the specimen of the asphalt mixture was studied.The law of longitudinal distribution was studied by analyzing the void ratio in the section of the specimen at different heights.The tomographic image is divided into two equal parts of the inner central circle area and the outer circular area to discuss the lateral distribution law of voids.5.The three-dimensional reconstruction of the tomographic image of the asphalt mixture was carried out,and the influence of the gradation change on the void volume was studied.The void volume is defined as five size ranges of 0-5mm3,5-10mm3,10-50mm3,50-100mm3,and 100mm3.By measuring the void volume and quantity of the asphalt mixture,the influence of the gradation change on its value is analyzed.6.The quantity information of the stone-stone contact points in the asphalt mixture specimen was measured,and the distribution of the contact points was compared to evaluate the advantages and disadvantages of the mixture structure.The advantages of the optimal group grading were discussed.7.The road performance test was carried out on the optimal group grading specimen and the grading median specimen respectively,and the difference between the two sets of specimens was compared with high temperature stability,low temperature crack resistance and water stability.Then the rationality of the response surface method in asphalt mixture gradation design is verified by pavement performance. |
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