Microcosmic Analysis Of Effect Of Voidage On Strength Performance Of Asphalt Mixture

When the asphalt mixture is used in the design of mix ratio,the voidage is often used as an indicator to control the quality standard.At present,only the macroscopic method is used to determine the voidage of the mixture,and the effect of the space distribution of the void ratio on the performance of the mixture is not affected.The mesostructure image of the mixed material was obtained by CT technology.The effect of voidage on the mechanical properties of the asphalt mixture was obtained through laboratory tests and virtual mechanical tests.First,the SMA-13 bituminous mastic asphalt was subjected to a uniaxial compression test and a vacuum saturated splitting test.The CT scan was used to obtain a detailed image of the asphalt mixture before and after the failure.The asphalt mixture image was processed using MATLAB software.Calculate the ratio of the pixel occupied by the gap to the overall pixel to obtain the voidage.The results show that the mechanical strength of asphalt mixture gradually decreases with the increase of voidage;the void distribution of Marshall specimens shows a symmetrical state along the height direction of the specimen,which is "large and small on both sides".After the splitting test and the uniaxial compression test were performed on the mixed materials,the overall voids had a certain degree of increase.However,due to the cracks,the distribution of the voids was changed to“small middle size on both sides".Then,using CT technology to continuously scan the cross section of the mixture,the image was reconstructed by Mimics software.The bimodal method was applied to threshold segmentation of all images,and the threshold ranges of asphalt mortar,aggregates and voids were obtained.The difference in the volume content between the three materials and the actual specimens was analyzed to control the quality of the model reconstruction.In the condition of the overall spatial distribution of voidage,there are often many externally connected voids at the edge of the specimen.The influence of the void distribution on the overall mechanical properties of the asphalt mixture is analyzed by the subsequent two-dimensional finite element calculation.Finally,the obtained microscopic images were subjected to a virtual splitting test of the asphalt mixture model of two-dimensional asphalt mixture,and the finite element model of the asphalt mixture and the aggregate was established through the vectorization process,and obtained through a uniaxial static load test.Burgers model parameters.The virtual splitting test is performed on the model.The test results show that the internal stress of the mixture is mainly transmitted along the load loading direction,and the position where the maximum stress occurs is often in the middle;at the interface between the asphalt mixture and the aggregate in the mixture.It is often the weakest position of the mix,and the voids in the load path will cause stress concentration and reduce the strength of the overall model.Comparing the indoor experiment with the virtual experiment,the virtual mechanical experiment can well complete the prediction of the test results.