【作者】 李丽；

【导师】 孙伟；

【作者基本信息】 东南大学 ， 材料学， 2004， 硕士

【摘要】 本课题主要研究如何防治、评估和预测高性能混凝土因水化、温湿度变化引发的收缩和开裂。主要进行了早期(加水拌和开始至24h内)平板式混凝土塑性收缩和开裂试验和研究,早期(加水拌和开始至72h)砂浆自生收缩试验和研究以及长龄期(大于28d)混凝土有约束(圆环法)和无约束(棱柱体)干燥收缩试验和研究。混凝土塑性收缩和开裂试验采用的是我国《混凝土结构耐久性设计与施工指南》(送审稿)中推荐了一个混凝土(砂浆)早期抗裂性试验设计和评价方法,该法可在试验室条件下实现快速、准确评价不同配合比混凝土(砂浆)早期抗裂性能等级。自生收缩试验改进了前人设计的一套测量设备,自生收缩的测量采用体积法,结合不同配比的单个试件具体的水泥用量,依据每单位水泥用量对应的自生收缩体积变形量评价不同配比砂浆自生收缩的大小。有约束干缩试验采用了大圆环法成型细集料混凝土圆环试件,沿环高度方向取不同高度的三个点测量干缩裂缝的裂宽,以此评价相同约束条件下聚丙烯纤维、矿物掺合料对混凝土干燥收缩影响的效果。自由干缩试验采用的是棱柱体试件,其六个面同时处于干燥环境下,通过测量轴向收缩应变比较不同掺合料单掺、双掺对混凝土0-90d干燥收缩的影响效果。 为了从理论上解释混凝土收缩和因收缩引发开裂的问题,本文先从线弹性断裂力学中裂缝引发理论开始,讨论了非线性准脆性材料(混凝土)平滑表面上裂缝引发的三个必要条件,提出了用黏性裂缝模型解释在混凝土平滑表面裂缝引发、扩展、停止和闭合的过程。之后又从混凝土内水分消耗、迁移和散失方面对混凝土收缩机理进行了分析,讨论并结合本文试验结果验证了收缩预测模型。 对高性能混凝土收缩和开裂研究表明,如果各配合比的单位体积用水量为定值,则水胶比也等于说单位体积胶凝材料用量是影响混凝土收缩和抗裂性的最显著因素,单位体积胶凝材料量较大的混凝土不但自生收缩相对减小,早期抗裂性也有提高。其次是矿物掺合料的影响,矿物掺合料对混凝土收缩和抗裂性的具体影响效果因品种和细度不同也各异。掺入减缩剂和聚丙烯纤维是当前公认的提高高性能混凝土早期抗裂性效果最为显著的两种途径。更多还原

【Abstract】 The project studies on how to prevent and cure the cracking initiated by high performance concrete shrinkage and by the changes of circumstantial temperature and relative humidity. It also studies on how to evaluate the cracking grades and to predict the total shrinkage microstrains. It investigates with early-age plastic shrinkage and cracking slab test on high performance concrete, early-age autogenous shrinkage test on mortar and restrained and unrestrained drying shrinkage test high performance concrete. Early-age plastic shrinkage and cracking slab test is based on the suggesting test design of new Manual for Concrete Structure Endurance Design and Construction of China. This test design is proved to be a fast and correct way to evaluate the concrete cracking grade. Autogenous shrinkage test appliance improves on other researchers’ invention. Autogenous shrinkage measures the volume changes of mortar. Restrained drying shrinkage is also called ring test. Restrained drying shrinkage initiates cracking which grows at the height direction of the ring specimen. So the crack width is measured at three different heights of the ring. Prism specimen is used in unrestrained drying shrinkage. Six sides of the prism are exposed to the drying circumstance. Axial shrinkage strain is measured and recorded. In order to theoretically explain the cracking initiated by shrinkage, it discussed the three necessary crack initiation conditions on smooth surface of non-linear brittle materials based on the crack initiation of linear elastic fracture mechanics. It also adopted the adhesive crack model to explain the process of crack initiation, development, stop and closure. It studied on the moisture loss, consumption and migration to explain concrete shrinkage mechanism. Shrinkage predict models were discussed and one of the predict model was used to predict the drying shrinkage strains compared the measured shrinkage strains in this project. Conclusively, the study on the shrinkage and cracking of high performance concrete shows the best prominent influencing factor is water binder ratio. With a high water binder ration, autogenous shrinkage is reduced and early-age cracking resistance capability is improved. Active mineral admixture and polypropylene fibers are better prominent influencing factor. Active mineral admixture efficiency varies with its species and fineness. Polypropylene fiber is much helpful to prevent early-age cracking of concrete. Shrinkage-reducing admixture and polypropylene fiber are widely considered as the best solution to prevent and cure early-age shrinkage and cracking of high performance concrete.更多还原