现代混凝土收缩调控研究

发布时间：2018-04-06 01:08

本文选题：收缩　切入点：粗骨料　出处：《清华大学》2014年博士论文

【摘要】：混凝土是当前用量最大的建筑材料，但其早期收缩易引发开裂而带来众多危害。本文以现代混凝土为研究对象，从普通粗骨料、预吸水轻骨料（pre-saturatedlightweight aggregate，简写为PSLWA）内养护、永久性模板外防护三方面针对高、中、低强混凝土早期收缩及内部湿度的调控展开了试验和理论研究。在普通粗骨料调控现代混凝土早期收缩研究中，试验测量了密封和干燥条件下不同粗骨料体积分数的高、中、低强混凝土早期收缩和内部湿度随龄期的发展。粗骨料体积分数增大，高、中、低强混凝土早期干燥收缩、自收缩均明显逐渐降低，且粗骨料对混凝土干燥收缩的调控作用更突出。粗骨料体积分数增大，混凝土弹性模量单调增大，且力学性能总体呈改善趋势。粗骨料体积含量对混凝土早期内部湿度发展和等效水分扩散系数的影响较小，对水泥水化度发展的影响也可忽略。改进的混凝土收缩两阶段预测模型可较好地模拟不同粗骨料含量的高、中、低强混凝土早期干燥收缩和自收缩的发展。在PSLWA调控现代混凝土早期收缩研究中，测量了内养护及普通高、中、低强混凝土密封和干燥条件下早期收缩和内部湿度的发展，以及单面干燥的混凝土板早期内部湿度的分布及其随时间的发展。PSLWA能显著延缓高强混凝土早期收缩增长及内部湿度下降；内养护水平提高，对高强混凝土早期收缩的调控效果越好。干燥条件下，PSLWA对高、中、低强混凝土早期干燥收缩的调控效率均较低。混凝土水胶比增大，PSLWA调控早期干燥收缩和内部湿度的效率逐渐变差。改进的混凝土两阶段收缩模型可基本较好模拟内养护及普通高、中、低强混凝土早期收缩的发展。混凝土板的湿度场研究中，干燥条件下，PSLWA能明显提高高强和中强混凝土板早期整体的内部湿度，延缓内部湿度下降，降低板中的湿度梯度。但PSLWA内养护不能根除高、中、低强混凝土板早期的表面干燥现象。建立的一维湿度场模型可较好模拟单面干燥下内养护及普通高、中、低强混凝土板早期内部湿度场，并进而分析了PSLWA对高、中、低强混凝土板中早期收缩分布和发展的影响。钢环约束试验结果表明，PSLWA内养护可改善单面干燥及密封条件下高强和中低强混凝土的早期抗裂性。永久性模板外防护调控混凝土干燥收缩的研究表明，永久性模板外防护与PSLWA内养护复合作用时可有效调控高、中、低强混凝土的早期干燥收缩；二者可产生叠加和互促效应。混凝土水胶比越低，，复合减缩技术对早期干燥收缩的调控效率越高。但复合减缩技术仍不能根除高、中、低强混凝土的早期干燥收缩。
[Abstract]:Concrete is the most widely used building material at present, but its early shrinkage can lead to cracking and bring a lot of harm.In this paper, modern concrete is taken as the research object. It aims at high and middle protection from three aspects: common coarse aggregate, pre-absorbent lightweight aggregate (PSLWA-PSLWA), permanent template external protection, etc.The early shrinkage and internal humidity control of low strength concrete have been studied experimentally and theoretically.In the study of controlling the early shrinkage of modern concrete by ordinary coarse aggregate, the development of early shrinkage and internal humidity with age of different coarse aggregate volume fraction under sealed and dry conditions were measured.The volume fraction of coarse aggregate increased, high, medium and low strength concrete early drying shrinkage, autogenous shrinkage gradually decreased, and coarse aggregate on the dry shrinkage of concrete is more prominent.When the volume fraction of coarse aggregate increases, the elastic modulus of concrete increases monotonously, and the mechanical properties of concrete increase.The volume content of coarse aggregate has little effect on the internal humidity development and equivalent moisture diffusion coefficient of concrete, and the influence on the hydration degree of cement can be neglected.The improved two-stage prediction model of concrete shrinkage can well simulate the development of early drying shrinkage and autogenous shrinkage of concrete with different coarse aggregate content.In the study of early shrinkage of modern concrete regulated by PSLWA, the development of early shrinkage and internal humidity of high, medium and low strength concrete under sealing and drying conditions were measured.PSLWA can significantly delay the early shrinkage growth and the decrease of internal humidity of high strength concrete, and improve the internal curing level.The better the control effect of early shrinkage of high strength concrete.The control efficiency of PSLWA on early drying shrinkage of high, medium and low strength concrete is low under dry condition.When the water / binder ratio of concrete increases, the efficiency of early drying shrinkage and internal humidity of PSLWA becomes worse.The improved two-stage shrinkage model of concrete can simulate the development of early shrinkage of high, medium and low strength concrete.In the study of moisture field of concrete slabs, PSLWA can obviously increase the internal humidity of high strength and moderate strength concrete slabs in the early stage, delay the decline of internal humidity and decrease the humidity gradient in concrete slabs.However, the early surface drying of high, medium and low strength concrete slabs can not be eradicated by internal curing of PSLWA.The one-dimensional humidity field model can well simulate the internal humidity field of high, medium and low strength concrete slabs under single surface drying. Furthermore, the influence of PSLWA on the early shrinkage distribution and development of high, medium and low strength concrete slabs is analyzed.The results of steel ring confinement test show that the internal curing of PSLWA can improve the early crack resistance of high strength and low strength concrete under the condition of single surface drying and sealing.The study on controlling the drying shrinkage of concrete with the outer protection of permanent formwork shows that the early drying shrinkage of high, medium and low strength concrete can be effectively controlled by the combination of the outer protection of permanent template and the curing of PSLWA, and the two can produce superposition and mutual promoting effect.The lower the water-binder ratio of concrete is, the higher the control efficiency of composite shrinkage technology is to the early drying shrinkage.But compound shrinkage reduction technology still can not eradicate the early drying shrinkage of high, medium and low strength concrete.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU528

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