约束状态下混凝土盐冻破坏行为和机理的研究

发布时间：2018-02-27 20:55

  本文关键词： 混凝土 冻融循环 表面剥落 内部损伤 约束　出处：《中国建筑材料科学研究总院》2017年硕士论文　论文类型：学位论文

【摘要】：盐冻破坏是寒冷地区混凝土结构面临的重要耐久性问题。形变是混凝土材料受到损伤的表现之一。目前常用的冻融/盐冻试验方法中混凝土试件是自由变形的,与实际服役混凝土受到周围结构的约束无法自由变形不相符合,因而试验结果并不能反映实际结构混凝土损伤情况。本文研究约束状态下混凝土盐冻破坏试验方法、行为和机理,探索更真实的结构混凝土盐冻损伤过程。本文主要工作和取得的成果有:设计不锈钢约束环和约束锚栓限制混凝土冻融循环中的受冻膨胀和收缩,建立了混凝土变形约束装置;设计了专用应变测试锚杆,实时采集冻融循环中混凝土试件的应变;采用表面剥落量、相对动弹性模量损失和残余应变评价混凝土的表面和内部损伤程度。研究建立了一套完整的约束状态下混凝土盐冻破坏试验方法。研究获得了约束状态下混凝土盐冻破坏损伤行为规律。随着冻融循环次数增加,约束状态混凝土的表面和内部损伤程度逐渐加深;提高含气量(1.3%~7.1%)、降低水灰比(0.65~0.45)能够降低约束状态混凝土表面和内部损伤程度;相同条件下,约束状态混凝土的表面损伤程度比自由状态混凝土严重、内部损伤程度比自由状态混凝土轻微。计算了盐冻过程中约束和自由状态混凝土表面最大应力,研究其表面损伤机理。降温至-8℃时,表面最大应力值超过表面抗拉强度,混凝土开始出现表面剥落;继续降温至混凝土内部结冰点-12℃附近时,约束状态混凝土表面最大应力开始明显超过自由状态混凝土,因而其表面损伤更严重。分析和计算了盐冻过程中约束状态混凝土孔隙结构参数和孔隙裂纹应变值,研究其内部损伤机理。约束状态混凝土的孔隙扩展程度、裂纹萌生数量和扩展速率均小于自由试件;降温至-15.8℃~-20℃,饱水混凝土孔隙裂纹发生不可逆应变,产生内部损伤;约束状态混凝土的不可逆应变小于自由状态混凝土的不可逆应变,因此其内部损伤程度更小。
[Abstract]:Salt freezing failure is an important durability problem faced by concrete structures in cold regions. Deformation is one of the manifestations of concrete material damage. In the freeze-thaw / salt freezing test methods, concrete specimens are free deformed at present. This paper studies the test method of concrete salt freezing failure under the condition that concrete in service is restrained by the surrounding structure and can not deform freely, so the test results can not reflect the actual concrete damage. Behavior and mechanism to explore a more realistic process of salt freezing damage of structural concrete. The main work and achievements of this paper are as follows: design of stainless steel confined ring and anchor bolt to limit the expansion and shrinkage of concrete in freeze-thaw cycle. A concrete deformation restraint device is established, a special strain test anchor rod is designed, and the strain of concrete specimen in freeze-thaw cycle is collected in real time. The relative dynamic elastic modulus loss and residual strain are used to evaluate the surface and internal damage of concrete. A set of complete test methods of concrete salt freezing failure in confined state are established. The concrete in confined state is obtained. With the increase of freeze-thaw cycles, The surface and internal damage degree of confined state concrete is gradually deepened, and the surface and internal damage degree of confined state concrete can be reduced by increasing the gas content of concrete by 1.3and reducing the water-cement ratio by 0.65 ~ 0.45), under the same condition, the surface and internal damage degree of confined state concrete can be reduced. The surface damage of confined concrete is more serious than that of free state concrete, and the degree of internal damage is less than that of free state concrete. The maximum surface stress of confined and free state concrete during salt freezing is calculated. The surface damage mechanism is studied. When the temperature reaches -8 鈩，

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