水泥基材料早期收缩研究及数值模拟

发布时间：2018-09-08 08:18

【摘要】：本文研究重点为水泥基材料早期收缩,包括混凝土中矿物掺合料、减水剂和增效剂对混凝土早期收缩的影响,寻找水泥净浆早期收缩和相对蒸发量及孔径分布之间的量化关系,并进行初步的混凝土早期收缩数值模拟探索,建立工程实际环境和数值模拟之间的桥梁。采用自行研制的混凝土及水泥净浆早期收缩装置,分别研究了矿物掺合料、增效剂、水化热对水泥基材料的早期收缩影响,更是深入探究了减水剂对水泥基材料相对蒸发量以及内部孔径分布的影响,获得了相对蒸发量和孔径分布与水泥净浆干燥收缩值之间的量化关系：研究表明粉煤灰和矿粉都能够减少混凝土早期收缩,但是规律并不相同,粉煤灰减少早期收缩的作用在掺量超过20%后下降,而矿粉只有在掺量大于20%才能显著减少混凝土早期收缩；增效剂能够提高水泥净浆的和易性,提高粘聚性,防止混凝土离析,并能够降低单方水泥用量、节约成本,但收缩试验表明增效剂加快了混凝土初凝后10小时的收缩速率,从而可能导致最终收缩大于不掺增效剂的基准配合比；研究表明减水剂细化了水泥净浆的孔隙分布,改变了水分蒸发规律,而相对蒸发率的变化和孔径小于50nm的毛细孔数量变化之间的乘积能够较好的反应收缩实测值的变化,并在相对蒸发率这一因素进行了更深入的探究,表明水灰比不同的水泥净浆早期收缩在不同风速下引起的不同相对蒸发率上依然能够满足该量化规律,这是前人研究所未有的；针对水泥基材料中的膨胀阶段,进行了一系列探索性试验以寻找膨胀的机理,排除了骨料化学性质差异、水泥成分变化、减水剂、水化热、骨料物理移动等因素,得出与单方水泥用量以及自由水含量呈正相关关系。此外还初步研究了通过数值模拟来模拟实际工程中混凝土早期收缩的可靠方法。在前述的研究基础上对未来的继续深入研究提出想法：如可以研究混凝土收缩和水分蒸发之间的量化关系,通过表面影响因子将数值模拟和实际工程环境相联系,通过对水泥基材料试件埋入湿度探头来获得混凝土内部的湿度变化,研究湿度与收缩之间的量化关系,并可以将数值模拟得出的混凝土内部湿度结果进行比较,从而可以对数值模拟结果进行修正和完善。
[Abstract]:This paper focuses on the early shrinkage of cement based materials, including the effects of mineral admixture, water reducer and synergist on the early shrinkage of concrete, and to find out the quantitative relationship between the early shrinkage of cement paste and the relative evaporation and pore size distribution. The initial numerical simulation of early shrinkage of concrete is carried out to establish the bridge between the engineering environment and the numerical simulation. The effects of mineral admixture, synergist and hydration heat on the early shrinkage of cement based materials were studied by using the self-developed early shrinkage device of concrete and cement paste. The effect of water reducer on relative evaporation and internal pore size distribution of cement-based materials is also discussed. The quantitative relationship between the relative evaporation and pore size distribution and the drying shrinkage of cement paste is obtained. The results show that both fly ash and mineral powder can reduce the early shrinkage of concrete, but the rules are different. The effect of fly ash on reducing early shrinkage decreases after the addition of more than 20%, but only when the amount of mineral powder is more than 20% can it significantly reduce the early shrinkage of concrete, and the synergist can improve the easiness of cement paste, improve the cohesion and prevent concrete segregation. It can reduce the amount of unilateral cement and save the cost, but the shrinkage test shows that the synergist accelerates the shrinkage rate of 10 hours after the initial setting of concrete, which may lead to the final shrinkage larger than the standard mix ratio without synergist. The results show that the water reducer refines the pore distribution of cement paste and changes the water evaporation law, and the product between the relative evaporation rate and the change of the number of pores with pore diameter smaller than 50nm can better respond to the change of measured values of shrinkage. The relative evaporation rate of cement paste with different water / cement ratio can still satisfy the quantitative law under different wind speed, which has not been found in previous studies, and the relative evaporation rate of cement paste with different water / cement ratio is studied in a more in-depth way. The results show that the relative evaporation rate of cement paste with different water / cement ratio can still satisfy this quantitative rule under different wind speed. In view of the expansion stage of cement based materials, a series of exploratory tests were carried out to find out the mechanism of expansion. The factors such as the difference in the chemical properties of aggregate, the change of cement composition, the water reducing agent, the heat of hydration and the physical movement of aggregate were excluded. It is found that there is a positive correlation between the content of single cement and the free water content. In addition, the reliable method of simulating the early shrinkage of concrete in practical engineering by numerical simulation is studied preliminarily. On the basis of the above research, the following ideas are put forward: for example, the quantitative relationship between concrete shrinkage and water evaporation can be studied, and the numerical simulation can be linked to the actual engineering environment through surface influence factors. The moisture change in concrete is obtained by embedding a humidity probe into the cement based material specimen, and the quantitative relationship between humidity and shrinkage is studied, and the results obtained by numerical simulation can be compared. Thus, the numerical simulation results can be modified and improved.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528

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