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间歇浇筑板式混凝土的早期约束收缩效应分析 总被引:2,自引:0,他引:2
以桥梁高性能混凝土为研究对象,测试老混凝土约束下新混凝土板的收缩变形。通过试验分析界面粗糙度对其影响,并考察混凝土内部早期温、湿度变化与收缩应变的关系,分析养护时间对混凝土材料收缩应力的影响。结果表明:老混凝土约束下的新混凝土厚度随新老混凝土黏结界面粗糙度的提高而增大,新混凝土内部拉应力随界面粗糙度的提高而降低,但新、老混凝土界面粗糙度对黏结面处的收缩影响不显著;距黏结面越近的截面收缩应变越小,在黏结面处达到最小,表现出显著的不均匀性,并随龄期逐渐增大。延长养护时间可减小混凝土收缩变形和内部由于不均匀收缩导致的拉应力,降低混凝土板早期开裂的风险。 相似文献
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约束程度与混凝土早期开裂敏感性评价 总被引:1,自引:0,他引:1
收缩变形是混凝土早期开裂的驱动力,然而是否会发生开裂还与约束条件密切相关。此外,初龄期混凝土力学性质的发展也受约束程度影响。采用了单轴约束试验方法,分析了不同约束程度下混凝土约束应力、松弛性质和弹性模量的发展,并讨论了约束程度对早期开裂敏感性评价的影响。 相似文献
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混凝土早期开裂敏感性评价 总被引:1,自引:0,他引:1
温度变形和自生收缩变形等受约束形成的拉应力,是引起混凝土早期开裂的主要驱动力;单轴约束试验是试验室评价混凝土早期开裂敏感性的有效方法。文章通过温度-应力试验分析混凝土早期开裂的机理,并探讨了温度历程和自生收缩变形对混凝土开裂敏感性的影响。 相似文献
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自行设计了混凝土约束收缩试验装置,对水灰比分别为0.25、0.30、0.35和0.40的高性能混凝土在完全约束条件下的内部拉应力的发展规律进行了研究,并对拉应力水平的发展进行了分析,建立了通过拉应力水平预测混凝土工程中早期开裂的预测模型。对于拟用于工程中的混凝土,可在试验室条件下对待测混凝土进行约束收缩试验,依据开裂预测模型对混凝土用于工程中后的开裂情况做出初步判断。 相似文献
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通过对再生骨料替代率为0、30%、50%、70%、100%混凝土及配筋混凝土进行收缩测试,研究分析混凝土的干燥收缩、收缩应力,及对不同替代率、不同龄期的立方体混凝土抗压强度.试验结果分析表明:再生混凝土的干燥收缩高于普通混凝土;在相同龄期下,其普通混凝土的立方体抗压强度高于再生混凝土;配置钢筋的混凝土构件,受到钢筋的约束作用而产生收缩应力,其再生混凝土的收缩应力高于普通混凝土,在180d龄期,100%替代率的收缩应力约为普通混凝土的3倍,对再生混凝土收缩应力的研究,对实际工程中再生混凝土构件尺寸设计有一定的理论指导. 相似文献
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介绍了一种评价混凝土收缩开裂的试验和评价方法,该法能够准确测量约束状态下混凝土干燥收缩时其内部产生的拉应力,特别是能够客观评价补偿收缩混凝土在弹性限制条件下抵御收缩应力的能力;提出了干燥收缩开裂概率C的概念,并将混凝土发生干燥收缩开裂的概率划分为C≥60%(高开裂风险),40%≤C<60%(中等风险)和C<40%(低风险)三种状态;试验表明,补偿收缩混凝土能够在混凝土中建立一定的自应力,可以有效降低混凝土的干燥收缩开裂概率。 相似文献
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为了揭示受约束混凝土内部的应力发展情况,以便更好地预测混凝土的开裂时间,本文在前人理论分析混凝土环收缩开裂的基础上,综合考虑了自由收缩、徐变、约束度和弹性模量等因素对混凝土环开裂的影响,推导出混凝土环应力公式。将混凝土环应力公式与最大抗拉应力破坏准则相结合,预测混凝土环开裂时间。预测得到的开裂时间与混凝土环约束试验的实测结果吻合良好。 相似文献
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Shrinkage strains of concrete slabs in a multi‐storey building are restrained internally by reinforcement bars as well as externally by supporting members such as columns or walls. These strains may induce tensile stresses in concrete members and lead to cracks due to excessive shrinkage stress. In this study, a practical shrinkage stress analysis method for application to concrete slabs in a multi‐storey building is proposed. The proposed approach considers both internal restraint of reinforcement bars and external restraint variations resulting from construction sequence. The shrinkage stress due to external restraint is obtained by multiplying the relaxation coefficient by the elastic shrinkage stress. The additional shrinkage stress due to internal restraint is obtained by the residual strain calculated via a linear elastic analysis for external restraints. A verification example was comparatively analysed using the proposed method and a commercially available analysis program that is capable of time‐dependent analysis of concrete. The results of a 10‐storey sample building suggest that the internal restraint due to reinforcement considerably increases the shrinkage stress at slabs under loose external restraint. Copyright © 2008 John Wiley & Son, Ltd. 相似文献
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对混凝土收缩的研究进行了总结,并在此基础上对混凝土产生收缩的机理进行了深入探讨。混凝土产生收缩的原因是由于自干燥导致的弯液面曲率半径的减小和表面张力的提高。混凝土在发生开裂时的拉应力小于当时混凝土的劈裂抗拉强度。环形约束时,当拉应力达到劈裂抗拉强度的55%~62%时,混凝土发生开裂。试验室中可以根据约束混凝土拉应力的发展趋势和开裂的时间来预测工程中混凝土发生开裂的可能性。 相似文献
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介绍了一套用于混凝土及砂浆环形试验的试验装置和用于推测处于约束状态下的混凝土及砂浆出现开裂的可能性的数据计算与分析方法。根据混凝土及砂浆试件在开裂时的应力变化率和相应的开裂龄期对开裂的可能性进行合理推测 相似文献
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Bonded concrete overlays‐stresses resulting from restrained deformations The bonded concrete overlay technique is one of the most widely used methods for repair, retrofitting and rehabilitation of concrete structures. Differential shrinkage is commonly the most crucial factor influencing the performance of the composite system and may result in extensive overlay cracking. Based on strain measurements, fundamental characteristics of overlay strain and stress development under restrained conditions were identified. The restraint of overlay deformations was found to depend less on the relative cross‐sectional dimensions of substrate and overlay than is commonly assumed. A new analytical approach for the design of bonded overlays subjected to differential shrinkage is introduced, based on localised strain conditions at the interface between substrate and overlay. A parameter study of the most important influences on overlay stress development is performed. 相似文献
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Sontaya Tongaroonsri Somnuk Tangtermsirikul 《Construction and Building Materials》2009,23(2):1050-1056
This paper presents the test results on cracking behavior at medium age of uniaxially restrained specimens containing different types of mineral admixture, namely fly ash and limestone powder. In this study, the uniaxially restrained shrinkage, free shrinkage and strength tests were conducted to study the potential of cracking of concrete under restrained shrinkage condition. The influences of water to binder ratio, mineral admixtures and curing period of concrete on cracking behavior were investigated in this study. The investigation showed that cracking age and cracking strain of restrained specimens vary with mix proportion, mineral admixture and curing period. The potential of shrinkage cracking is not influenced only by cracking strain and amount of shrinkage but also on shrinkage rate and tensile creep. Mixture with lower water to binder ratio (w/b = 0.35) shows shorter cracking age than the mixture with higher water to binder ratio (w/b = 0.55). Fly ash and limestone powder significantly increase cracking age of concrete. The cracking age increases with the increase of the replacement ratio of fly ash. The higher shrinkage rate, when exposed to drying, of mixture with longer curing period leads to shorter cracking age. 相似文献