RESEARCH ON VISUALIZATION OF FRACTURE PROCESS OF SUPER-HIGH-STRENGTH CONCRETE

粗骨料的抗压强度、弹性模数、韧性等力学性能对配制超高强混凝土具有重要意义。为了研究粗集料对超高强混凝土抗压强度的影响，对几种人工粗集料以不同方式布置的平板试件进行了抗压试验。试验时，拍摄了受压裂纹萌生和扩展的图像，并用纸质应变片测量了应变集中和分布。试验结果总结如下：1.在粗骨料的弹性模量大于砂浆的弹性模量，且粗骨料与砂浆之间的粘结强度很小的情况下，粘结裂缝出现在加载初期。当粘结强度存在一定程度时，粘结裂缝出现在最大应力的一半水平。2.在粗集料抗压强度高于砂浆抗压强度的情况下，如果粗集料的含量较小，则不能指望粗集料止裂。3.为了制备抗压强度超过120 Mpa的超高强混凝土，应注意以下几点：(1)粗集料和砂浆的抗压强度都在120 Mpa以上；(2)粗集料与砂浆的弹性模量相差不大；(3)粗集料韧性较差；(4)粗集料含量较大。

Mechanical properties of coarse aggregate such as compressive strength, modulus of elasticity and toughness are important for making super-high-strength concrete. In order to investigate the effect of coarse aggregate on compressive strength of super-high-strength concrete, plate specimens, in which a few types of artificial coarse aggregates were arranged in some ways, were tested in compression. When tested, the pictures of initiation and propagation of cracks under compression were taken, and the concentration and distribution of strain were measured by paper strain gauges. The test results are summarized as follows :1.In the case that modulus of elasticity of coarse aggregates are higher than that of mortar and bond strength between coarse aggregates and mortar is very small, bond cracks occur at the early stage of loading. If the bond strength exsists in some extent, bond cracks occur at the half level of maximum stress.2.In the case that compressive strength of coarse aggregates are higher than that of mortar, crack arresting by coarse aggregates cannot be expected if the content of coarse aggregates is small.3.In order to make super-high-strength concrete with compressive strength of more than 120 MPa, the attention should be payd to the followings.(1) Both coarse aggregate and mortar have compressive strength more than 120 MPa.(2) Difference of modulus of elasticity between coarse aggregate and mortar is small.(3) Coarse aggregate is tough.(4) Relatively large amount of coarse aggregate exsist.