水泥砂浆断裂韧度与强度的边界效应和尺寸效应

Boundary Effect and Size Effect of Fracture Toughness and Strength of Mortar

通过不同尺寸水泥砂浆试件的三点弯曲试验及强度试验,研究了水泥砂浆断裂韧度与强度等材料参数的边界效应和尺寸效应.结果表明:对于强度参数,随着试块尺寸的增加,强度指标逐渐降低;对于断裂参数,若不考虑虚拟裂缝扩展,试件高度H需达到0.47m才能满足线弹性断裂力学条件;若考虑峰值荷载时的虚拟裂缝扩展,则试件高度H为0.50m时,才接近但仍不能完全满足线弹性断裂力学条件.为了区别于现有尺寸效应模型关注的"绝对尺寸",提出了"相对尺寸"的概念,用来研究确定材料参数的尺寸效应.重点考虑砂浆颗粒尺寸对材料准脆性断裂的影响,给出了满足线弹性断裂力学条件、无尺寸效应的水泥砂浆断裂韧度及弯曲抗拉强度的确定方法.

Boundary effect and size effect of fracture toughness and strength of mortar were studied by three-point-bending test and strength test for mortar specimens with different sizes.Results show that the strength of specimens decreases with increasing block size.If the virtual crack formation at peak load is not considered,the linear elastic fracture mechanics(LEFM)condition can be satisfied until the height of the specimen reaches 0.47 m.On the contrary,if the virtual crack formation at peak load is considered,the specimen height increases over 0.50 m,it is closer to but not large enough to fully ensure the LEFM condition.The concept“relative size”is proposed to study the size effect,which is distinctive compared to those existing size effect model only connected to specimen size.The effect of aggregate size of mortar on quasi-brittle fracture is considered and an associated method for determining simultaneously the fracture toughness and bending strength of mortar is proposed,in which both the fracture toughness and bending strength satisfy the LEFM condition and have no size effect.