高吸水性树脂对高强混凝土早期减缩效果及机理研究

发布时间：2018-04-22 11:36

本文选题：高强混凝土 + 高吸水性树脂　；参考：《清华大学》2013年硕士论文

【摘要】：混凝土的收缩开裂严重危害了结构物的安全性和耐久性。对高强混凝土（HSC）来说，早期的湿度收缩（包括自收缩和干燥收缩）是造成其开裂的主要原因。利用高吸水性树脂（SAP）内养护的方法可以有效减小HSC的湿度变形，对HSC的早期防裂有很好的效果。但是，SAP的减缩机理至今尚未完全揭示。本文全面研究了掺入SAP对水泥水化、水泥石微观结构及混凝土力学性能等的影响规律，重点研究了掺入SAP后HSC早期自收缩和干燥收缩的减缩效果。结果表明：有效水灰比相同时，加入预吸水SAP可以明显减小HSC的早期自收缩和干燥条件下的总收缩，适宜掺量下14d的自收缩减缩率可达90%以上，，干燥条件下总收缩可减少75%；SAP一定程度上延缓了HSC的早期水化放热，但提高其28天水化度；改变水泥石的孔隙分布，使其大孔和小毛细孔含量提高，中间孔含量降低；延后相对湿度从100%下降的时间，使同龄期混凝土内部湿度大幅升高；SAP对混凝土的强度有不利作用，但对后期强度的影响要小于早期。与简单增加拌合水量相比，加入预吸水SAP对HSC水化进程、孔隙结构、力学性能、收缩变形等各项性能的影响都有很大的差异，这些差异与自由拌合水与内养护水在混凝土中不同的空间分布状态有关。根据所获的实验结论并结合已有的自身-干燥收缩一体化计算模型对SAP的减缩机理进行了讨论。模型计算结果表明，该模型很好地适用于HSC早期湿度变形的拟合和预测；相同龄期时远高于空白混凝土的内部湿度是掺有SAP高强混凝土大幅减缩的主要原因之一；SAP会大幅减小相对湿度维持在100%阶段内化学减缩转化为宏观变形的比率，这对减缩也有重要的贡献。根据模型拟合的结果对混凝土早期总变形进行了分离，获得了混凝土早期的自膨胀曲线。结果表明，采用冀东水泥制得的混凝土，在开始变形测试后不久都出现了明显的膨胀现象；增大水灰比及掺入预吸水SAP都可以显著提高混凝土的早期膨胀量；混凝土化学外加剂（减水剂、缓凝剂等）通过影响混凝土工作性、水泥水化进程、凝结时间及力学性能发展等因素，对混凝土早期变形性能造成重要影响；水泥种类及组成对混凝土的早期膨胀变形有决定性的影响；大体积的Ca(OH)2和钙矾石晶体在水化早期大量生成是引起混凝土早期膨胀变形的主要原因，高碱含量下生成的C-K-S-H凝胶也是早期膨胀的来源之一。
[Abstract]:Shrinkage and cracking of concrete seriously harm the safety and durability of structures. For high strength concrete (HSC), early moisture shrinkage (including autogenous shrinkage and drying shrinkage) is the main cause of its cracking. The method of using high water absorbent resin (SAP) can effectively reduce the moisture deformation of HSC and prevent early cracking of HSC. Good results. However, the mechanism of SAP reduction has not yet been fully revealed.
The effects of SAP on cement hydration, microstructure of cement stone and mechanical properties of concrete are studied in this paper, and the shrinkage effect of autogenous shrinkage and drying shrinkage in early HSC after adding SAP is studied. The results show that the effective water cement ratio is at the same time, and the early self shrinkage and drying conditions of HSC can be obviously reduced by adding the pre absorbent SAP. Under the total shrinkage, the autogenous shrinkage and reduction rate of 14d can be over 90%, and the total shrinkage can be reduced by 75% under dry conditions; SAP to a certain extent postpones the early hydration heat of HSC, but improves the hydration degree of 28 days; it changes the pore distribution of the cement stone, increases the content of the pores and small capillary holes, and reduces the content of the middle hole; and the delayed relative content is reduced. The humidity of the concrete in the same age is greatly increased from 100% to 100%, and the strength of concrete has a negative effect on the strength of concrete, but the effect on the later strength is less than that in the early stage. Compared with the simple adding amount of water, the effects of adding pre absorbent SAP on the properties of HSC hydration process, pore structure, mechanical properties, shrinkage deformation and other properties are all affected. These differences are related to the different spatial distribution of free mixed water and internal curing water in concrete.
Based on the experimental conclusions obtained and combined with the existing self drying shrinkage calculation model, the shrinkage mechanism of SAP is discussed. The model calculation results show that the model is well suited to the fitting and prediction of the early humidity deformation of HSC, and the internal humidity of the same age is far higher than that of the blank coagulant soil with SAP high strength concrete. One of the main reasons for a large reduction is that SAP will significantly reduce the ratio of chemical shrinkage to macro deformation in the 100% stage of relative humidity, which also contributes greatly to the reduction.
According to the results of the model fitting, the early total concrete deformation was separated and the early self expansion curve of concrete was obtained. The results show that the concrete produced by Jidong Cement has obvious expansion phenomenon after the initial deformation test, and the concrete can be significantly increased by increasing the water cement ratio and adding the pre absorbent SAP. Early expansion of concrete, concrete chemical admixtures (water reducer, retarder and so on) have an important influence on the early deformation performance of concrete by influencing the workability of concrete, the process of cement hydration, the setting time and the development of mechanical properties, and the cement type and composition have a decisive influence on the early expansion and deformation of concrete; large volume of concrete. The formation of Ca (OH) 2 and Ettringite crystals at the early stage of hydration is the main cause of the early expansion and deformation of concrete. The C-K-S-H gel formed under high alkali content is also one of the sources of early expansion.

【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU528.31

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