Experimental Studies On Mechanical Properties Of Mortar-natural Aggregate Interface

Aggregate size has significant effects on the propagation of cracks for fully-graded concrect. Most cracks bypass large aggregate and propagate along the interface. In the construction and operation of high arch dam, most macro-cracks occur at the interface of mortar and large aggregate. Therefore, it is important to study the mechanical properties of mortar-aggregage interface. As so far, the researches about the mechanical properties of mortar-aggregate interface are not enough and the specimens with natural aggregate are far less. Based on this point, interfacial specimens of mortar-natural aggregate are prepared and several aspects of work are done in this paper as follows:1. By pasting steel plate on both ends of the specimens and using of ball-hinge to adjust the specimens, direct tension test is used to measure the tensile strength of the interface of mortar-nature aggregate. The results indicated that interface is the weak link of the specimen. The failure occurs at the cohesive layer of interfacial mortar and is characterized by the separation of mortar matrix and aggregate. The fracture surface is smooth. The interfacial tensile strength is discrete, from0.51to1.63MPa. It is far lower than the tensile strength of mortar matrix, only0.2to0.6times of mortar.2. Four-point shear beam test is used to measure the interfacial shear strength of mortar-nature aggregate. The average interfacial shear strength is1.28MPa higher than the interfacial tensile strength.3. Three-point bending beam specimens with initial crack-depth ratio0.1are used to measure the maximum load, fiexural strength and fracture energy of mortar-natue aggregate interface. With the aid of the finite element software, the initial fracture toughness of interface is calculated. The results are discrete, the interfacial fiexural strength is from0.91to1.71MPa, P\mlPm?x. is from0.40to0.65, the initial fracture toughness of interface is from0.133to0.190MPa-m1/2and the interfacial fracture energy is from36.06to73.84N/m.4. FEM software ABAQUS is used to study the effects of two kinds of material properties, initial crack-depth ratios and the deviation of load point on the bi-material interfacial stress intensity factor under three-point bending condition. Further, mode-II component is analyzed quantitatively, and the feasibility of the three-point bending beam of the interface fracture test is discussed. The results show that it is more reasonable to use specimen with elastic modules ratio less than3and crack-depth ratio less than0.2to study the mode I interface fracture.