预制混凝土早期强度试验研究
发布时间：2018-11-24 16:51
【摘要】：随着我国不断推广建筑工业化和号召资源节约型、环境友好型社会的建设。预制混凝土行业逐步成为主导今后混凝土发展的潮流。在很多工程领域应用越来越广泛(如：市政工程和建筑工程)。但目前人们关注的主要问题是：生产效益和生产周期,预制混凝土的早期强度成为当前必须解决的关键问题。根据对国内很多预制混凝土生产厂进行的调查来看,为了提高早期强度、缩短周期、加速模板周转,很多厂家在混凝土预制构件生产中普遍采用蒸汽养护工艺,消耗了大量的煤炭资源,同时产生了大量的温室气体。因此免蒸养技术提高预制混凝土早期强度势在必行。本课题针对上述问题从两方面入手：一是从外加剂入手,试验研究合成了一种早强型聚羧酸减水剂：二是从石膏入手,研究了四家石膏厂生产的三种无水石膏和四种半水石膏,得到了其对砂浆早后期强度的影响规律。进而确定了一种有利于提高预制混凝土早期强度的石膏。然后通过逐一试验和正交试验验证两种方法确定了该石膏在砂浆中的最佳掺量及部分复配掺合料的掺量。将此石膏及对应的最佳掺量用于混凝土正交试验中,优化配制了C40预制混凝土,发现早期1-3d强度可提高50%以上,完全试现了早拆模的标准。最后在原理上分析了石膏对预制混凝土早期强度提高的原因和机理。混凝土中加入适量的石膏可以大大降低熟料中铝酸三钙和含铁相矿物水化速度,从而使水泥水化时间变长,保证其在足够时间内具有可塑性,有利于早期强度的发展。适量的石膏可以跟水泥中化学成分反应形成适量的钙矾石,对水泥内部孔隙进行填充,增加密试程度,形成较强的结构骨架,从而使早期强度得到增强；但在水泥中如果加入过多的石膏,会形成很多具有膨胀性的物质,使强度降低,因此石膏的掺量有一个最佳比例。对于使用普通硅酸盐水泥的混凝土,通过本文的研究确定了半水石膏的最佳掺量。在多次试验的基础上我们可以断定当水泥换了生产厂家或水泥种类,导致各个组分的含量发生了变化时,该掺量也就不适用了,所以半水石膏的掺量与水泥的化学成分及比例有关。本文的研究还发现,无水石膏的掺量和水泥的组分含量达到最佳比例时,其早期、后期强度可能会超过半水石膏,这个最佳比例的确定还有待后续研究。
[Abstract]:Along with our country unceasingly popularizes the construction industrialization and calls for the construction of resource-saving and environment-friendly society. Precast concrete industry has gradually become the leading trend of concrete development in the future. It is more and more widely used in many engineering fields (e.g. municipal engineering and building engineering). But at present, the main problem that people pay attention to is: production benefit and production cycle, the early strength of precast concrete becomes the key problem that must be solved at present. According to the investigation conducted by many prefabricated concrete production plants in China, in order to increase early strength, shorten the period and speed up the turnover of formwork, many manufacturers generally adopt steam curing technology in the production of concrete prefabricated components. It consumes a lot of coal resources and produces a lot of greenhouse gases. Therefore, it is imperative to improve the early strength of precast concrete by steaming-free technique. This subject aims at the above problems from two aspects: first, starting with admixture, a kind of early-strength polycarboxylic acid water-reducing agent is studied; second, starting with gypsum, three kinds of anhydrous gypsum and four kinds of hemihydrate gypsum produced by four gypsum plants are studied. The effect of mortar strength on the early and late stage of mortar strength was obtained. Furthermore, a kind of gypsum which is propitious to improve the early strength of precast concrete is determined. Then the optimum content of gypsum in mortar and the content of partial admixture were determined by one experiment and by orthogonal test. By applying the gypsum and the corresponding optimum amount to the orthogonal test of concrete, the C40 precast concrete was optimized and it was found that the strength of the early stage 1 to 3 d could be increased by more than 50%, and the standard of early demoulding was completely tested. Finally, the reason and mechanism of early strength improvement of prefabricated concrete by gypsum are analyzed in principle. The hydration rate of tricalcium aluminate and iron-bearing minerals in clinker can be greatly reduced by adding proper amount of gypsum in concrete, thus the hydration time of cement becomes longer, and the cement has plasticity in sufficient time, which is beneficial to the development of early strength. Proper amount of gypsum can react with the chemical composition of cement to form appropriate amount of ettringite, which can fill the internal pores of cement, increase the degree of density test, and form a strong structural skeleton, so that the early strength is enhanced. However, if too much gypsum is added to cement, a lot of expansive substances will be formed, and the strength will be reduced, so there is an optimum proportion of gypsum content. For concrete with ordinary Portland cement, the optimum content of gypsum is determined by the research in this paper. On the basis of many experiments, we can conclude that when the cement is changed by the manufacturer or the type of cement, the content of each component changes, and the content of the cement is not suitable. So the content of gypsum hemihydrate is related to the chemical composition and proportion of cement. It is also found that the strength of anhydrous gypsum may exceed that of hemihydrate gypsum in the early stage when the content of anhydrous gypsum and cement content reaches the optimum ratio.
【学位授予单位】：山东建筑大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528
本文编号：2354399
[Abstract]:Along with our country unceasingly popularizes the construction industrialization and calls for the construction of resource-saving and environment-friendly society. Precast concrete industry has gradually become the leading trend of concrete development in the future. It is more and more widely used in many engineering fields (e.g. municipal engineering and building engineering). But at present, the main problem that people pay attention to is: production benefit and production cycle, the early strength of precast concrete becomes the key problem that must be solved at present. According to the investigation conducted by many prefabricated concrete production plants in China, in order to increase early strength, shorten the period and speed up the turnover of formwork, many manufacturers generally adopt steam curing technology in the production of concrete prefabricated components. It consumes a lot of coal resources and produces a lot of greenhouse gases. Therefore, it is imperative to improve the early strength of precast concrete by steaming-free technique. This subject aims at the above problems from two aspects: first, starting with admixture, a kind of early-strength polycarboxylic acid water-reducing agent is studied; second, starting with gypsum, three kinds of anhydrous gypsum and four kinds of hemihydrate gypsum produced by four gypsum plants are studied. The effect of mortar strength on the early and late stage of mortar strength was obtained. Furthermore, a kind of gypsum which is propitious to improve the early strength of precast concrete is determined. Then the optimum content of gypsum in mortar and the content of partial admixture were determined by one experiment and by orthogonal test. By applying the gypsum and the corresponding optimum amount to the orthogonal test of concrete, the C40 precast concrete was optimized and it was found that the strength of the early stage 1 to 3 d could be increased by more than 50%, and the standard of early demoulding was completely tested. Finally, the reason and mechanism of early strength improvement of prefabricated concrete by gypsum are analyzed in principle. The hydration rate of tricalcium aluminate and iron-bearing minerals in clinker can be greatly reduced by adding proper amount of gypsum in concrete, thus the hydration time of cement becomes longer, and the cement has plasticity in sufficient time, which is beneficial to the development of early strength. Proper amount of gypsum can react with the chemical composition of cement to form appropriate amount of ettringite, which can fill the internal pores of cement, increase the degree of density test, and form a strong structural skeleton, so that the early strength is enhanced. However, if too much gypsum is added to cement, a lot of expansive substances will be formed, and the strength will be reduced, so there is an optimum proportion of gypsum content. For concrete with ordinary Portland cement, the optimum content of gypsum is determined by the research in this paper. On the basis of many experiments, we can conclude that when the cement is changed by the manufacturer or the type of cement, the content of each component changes, and the content of the cement is not suitable. So the content of gypsum hemihydrate is related to the chemical composition and proportion of cement. It is also found that the strength of anhydrous gypsum may exceed that of hemihydrate gypsum in the early stage when the content of anhydrous gypsum and cement content reaches the optimum ratio.
【学位授予单位】：山东建筑大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528
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