Research On Fracture Properties And Theories Of Mortar

Cement mortar and cement paste are a kind of concrete base material with a large amount of surface,which often plays a weak point in the appearance and propagation of concrete cracks.and it is necessary to study the fracture properties and theory of cement mortar and cement paste materials.Meanwhile,The Theory of Critical Distance is a theory of orifice fracture mechanics combining the microscopic mechanism and macroscopic fracture characteristics.and it was mainly used in the fatigue analysis of metal materials earlier,but it has also been applied to the fracture of quasi-brittle materials such as rock recently.Therefore,this paper attempts to use The Theory of Critical Distance to analyze the fracture characteristics of cement mortar,which is a quasi-brittle material.The fracture toughness and tensile strength of cement mortar are obtained through the combination of experimental research and theoretical analysis.The feasibility and rationality of the theory in mortar materials were analyzed.The specific work is as follows:?1?The three-point bending test of single-sided U-shaped mortar beam specimens with different strengths,notch depths and root radius of the notch were used to study the influence of the above three factors on the fracture performance of cement mortar.Relevant experimental data were recorded by means of strain gauge method and digital image correlation method.The analysis shows that with the increase of mortar strength and root radius,the cracking load value and maximum load value of mortar material will gradually increase.With the increase of notch depth,the cracking load value and maximum load value of mortar material will gradually reduce;the incorporation of fine aggregates will increase the crack resistance of cement mortar in the later stage.?2?The Theory of Critical Distance was applied to analyze the experimental results of the mortar.Firstly,the fracture toughnessK_IC^{in i} of the mortar material was assumed as the fracture toughnessK_IC in The Theory of Critical Distance.The tensile strengths_u of the material was assumed as the intrinsic strengths₀ in The Theory of Critical Distance.and the critical distance value of the mortar material was calculated by the definition formula.Then the finite element software was used to check the critical distance value which has been obtained before.And the result showed that the critical distance L value calculated by the definition formula has good agreement with the L value obtained by the intersection line method;and as the mortar strength increases,the critical distance L value increases gradually.The critical distance L value of the mortar material can be used as a reference value for the length of the fracture process zone.?3?Through the formula derivation,the line form formula in The Theory of Critical Distance and the finite fracture theory formula based on the energy average on the finite distance are expressed in the general form of the U-shaped fracture criterion.And by comparing the predicted value of the line form formula in The Theory of Critical Distance,the finite fracture theory based on the energy average on the finite distance,and the experimental value of the U-shaped slot mortar beam under the dimensionless,it is found that the trend and agreement between the two values is favorable;and the prediction accuracy of the finite fracture theory formula is slightly higher than the prediction accuracy of the line form formula in The Theory of Critical Distance.