Autogenous Shrinkage Research Of Cement-based Materials Based On Full-field Deformation Analyse

As important features of high-performance cement-based materials,low water-binder ratio and high-volume mineral admixture result in large autogenous shrinkage(AS)compared with ordinary cement-based materials,which has become a hotspot in the field.Moreover,the heterogeneity of cement-based materials will result in heterogeneous deformation,which will lead to the local stress concentration and accelerate the process of destruction of the material.In order to study the the heterogeneity of AS,this paper used digital volume correlation(DVC)to analyze the full-field deformation.Firstly,the full-field AS deformation of cement paste was obtained by DVC.Under certain experimental and computational conditions,the displacement field is about 0.4 microns in accuracy,and the precision of the strain field is about 70 microstrain,which is sufficient for the measurement of AS.Compared the shrinkage value calculated by DVC with the macroscopic shrinkage value measured by corrugated tube method,it was found that the measurement result of corrugated tube method is relative small,which may be due to the existence of frictional resistance in the measurement process of corrugated tube method,and the corrugated tube itself has elastic modulus that restrict the deformation,and the size of sample measured by DVC has huge differences with the size of the sample measured by corrugated tube and so on.In this context,the self-contraction of the deformation field was in-depth analysed.In the spatial domain,it was found that the displacement fields exhibits heterogeneity and is approximately linearly distributed.For the strain field,the laws shown in the different strain windows are quite different.When the strain window is about 720 microns,the shear strain is numerically negligible with respect to the normal strain,and the strain field is approximately evenly distributed.The deformation information reflected is closer to the macroscopic deformation information,but in the frequency domain,The strain field exhibits heterogeneity.When the strain window is 320 microns,the strain field exhibits strong heterogeneity.When the strain window is 160 microns,the degree of heterogeneity is further enhanced.Secondly,in order to find the source of AS heterogeneity,the strain window size is controlled below the representative volume unit,the volumetric content of unhydrated cement particles in the sub-volume/strain-window and displacement/strain were analyzed statistically respectively.As a result,it was found that the degree of heterogeneity of the deformation field is diminished as the hydration reaction progresses.This indicated that unhydrated cement particles are one of the sources of heterogeneity of the deformation,limiting the AS deformation of cement-based materials.Finally,in order to solve the problem that the traditional DVC encounters the boundary error,an automatic method of boundary problem based on image segmentation was proposed.It was proved that this method has a strong ability to deal with complex boundary by using the writing deformation calculation of foam aluminum.