發(fā)布時間：2018-04-06 01:08

  本文選題：收縮　切入點：粗骨料　出處：《清華大學》2014年博士論文

【摘要】：混凝土是當前用量最大的建筑材料，但其早期收縮易引發(fā)開裂而帶來眾多危害。本文以現(xiàn)代混凝土為研究對象，從普通粗骨料、預吸水輕骨料（pre-saturatedlightweight aggregate，簡寫為PSLWA）內養(yǎng)護、永久性模板外防護三方面針對高、中、低強混凝土早期收縮及內部濕度的調控展開了試驗和理論研究。 在普通粗骨料調控現(xiàn)代混凝土早期收縮研究中，試驗測量了密封和干燥條件下不同粗骨料體積分數(shù)的高、中、低強混凝土早期收縮和內部濕度隨齡期的發(fā)展。粗骨料體積分數(shù)增大，高、中、低強混凝土早期干燥收縮、自收縮均明顯逐漸降低，且粗骨料對混凝土干燥收縮的調控作用更突出。粗骨料體積分數(shù)增大，混凝土彈性模量單調增大，且力學性能總體呈改善趨勢。粗骨料體積含量對混凝土早期內部濕度發(fā)展和等效水分擴散系數(shù)的影響較小，對水泥水化度發(fā)展的影響也可忽略。改進的混凝土收縮兩階段預測模型可較好地模擬不同粗骨料含量的高、中、低強混凝土早期干燥收縮和自收縮的發(fā)展。 在PSLWA調控現(xiàn)代混凝土早期收縮研究中，測量了內養(yǎng)護及普通高、中、低強混凝土密封和干燥條件下早期收縮和內部濕度的發(fā)展，以及單面干燥的混凝土板早期內部濕度的分布及其隨時間的發(fā)展。PSLWA能顯著延緩高強混凝土早期收縮增長及內部濕度下降；內養(yǎng)護水平提高，對高強混凝土早期收縮的調控效果越好。干燥條件下，PSLWA對高、中、低強混凝土早期干燥收縮的調控效率均較低。混凝土水膠比增大，PSLWA調控早期干燥收縮和內部濕度的效率逐漸變差。改進的混凝土兩階段收縮模型可基本較好模擬內養(yǎng)護及普通高、中、低強混凝土早期收縮的發(fā)展。混凝土板的濕度場研究中，干燥條件下，PSLWA能明顯提高高強和中強混凝土板早期整體的內部濕度，延緩內部濕度下降，降低板中的濕度梯度。但PSLWA內養(yǎng)護不能根除高、中、低強混凝土板早期的表面干燥現(xiàn)象。建立的一維濕度場模型可較好模擬單面干燥下內養(yǎng)護及普通高、中、低強混凝土板早期內部濕度場，并進而分析了PSLWA對高、中、低強混凝土板中早期收縮分布和發(fā)展的影響。鋼環(huán)約束試驗結果表明，PSLWA內養(yǎng)護可改善單面干燥及密封條件下高強和中低強混凝土的早期抗裂性。 永久性模板外防護調控混凝土干燥收縮的研究表明，永久性模板外防護與PSLWA內養(yǎng)護復合作用時可有效調控高、中、低強混凝土的早期干燥收縮；二者可產生疊加和互促效應�；炷了z比越低，，復合減縮技術對早期干燥收縮的調控效率越高。但復合減縮技術仍不能根除高、中、低強混凝土的早期干燥收縮。
[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.
【學位授予單位】：清華大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TU528

【參考文獻】

相關期刊論文 前10條

1 邵正明,張超,仲曉林,孫躍生,宮武倫,鄭旗,彭杰;國外減縮劑技術的發(fā)展與應用[J];混凝土;2000年10期

2 安明U

本文編號：1717280