共查询到18条相似文献,搜索用时 171 毫秒
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商品混凝土的塑性裂缝及防治 总被引:7,自引:0,他引:7
塑性裂缝是指混凝土浇筑后尚处于可塑状态时产生的裂缝。商品混凝土由于坍落度大 ,用水量多 ,水泥用量多 ,砂率大 ,凝结时间长等原因 ,塑性裂缝出现频繁 ,时而困扰商品混凝土站及施工单位。1 塑性裂缝成因及防治原理塑性裂缝根据成因的原理分为沉降收缩裂缝和塑性收缩裂缝。沉降收缩裂缝是混凝土硬化前因骨料等比重大的颗粒下沉 ,竖向体积缩小而产生的塑性变形裂缝 ;塑性收缩裂缝是指浇筑后还处于塑性状态的混凝土因风吹日晒 ,表面失水过快 ,产生急剧的体积收缩而出现的裂缝。这两种裂缝经常共生 ,很难区别 ,故统称为塑性裂缝。1 1 沉降收… 相似文献
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关于高强混凝土裂缝控制的研究 总被引:1,自引:0,他引:1
针对高强混凝土水泥用量多,砂率高,产生裂缝的潜在危险大.在工程实践中出现裂缝的情况比较多。总结了高强混凝土裂缝产生的规律,将裂缝分成混凝土塑性收缩裂缝、干燥收缩裂缝、骨料塑性沉落裂缝、温度应力裂缝几类,系统地分析了裂缝的形成原因,提出从优化混凝土设计、加强混凝土生产质量和混凝土施工管理3个方面对裂缝进行有效控制。 相似文献
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高强混凝土非结构性裂缝形成原因及控制方法 总被引:2,自引:0,他引:2
高强混凝土水泥用量多,砂率高,产生裂缝的潜在危险大,在工程实践中出现裂缝的情况比较多。文章总结了高强混凝土非结构性裂缝产生的规律,将裂缝分成混凝土塑性收缩裂缝、干燥收缩裂缝、骨料塑性沉落裂缝、温度应力裂缝几类,系统地分析了裂缝的形成原因,提出从优化混凝土设计、加强混凝土生产质量和混凝土施工管理3个方面对裂缝进行有效控制。 相似文献
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流态混凝土 ,特别是在高强度、大流动性条件下 ,具有水泥用量多 ,用水量大 ,砂率高 3个主要特点 ,所以产生裂缝的潜在危险大 ,在工程实践中梁板构件出现裂缝的情况比较多 ,对此必须引起足够的重视 总结了流态混凝土梁板构件非结构性裂缝产生的规律 ,将裂缝分成混凝土塑性收缩裂缝、干燥收缩裂缝、骨料塑性沉落裂缝、温度应力裂缝几类 ,系统地分析了以上几类裂缝的形成原因以及相关因素 提出从优化混凝土设计、提高混凝土生产质量、加强混凝土施工管理 3个方面对裂缝进行有效控制 相似文献
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参考国际建筑官员协会ICBO标准,采用平板约束试验、自制的混凝土塑性应力测试装置以及压汞法,分析了再生细骨料粒径、取代率以及混凝土水灰比、砂率等对再生细骨料混凝土塑性应力、孔结构及塑性收缩开裂性能的影响.结果表明:随着再生细骨料粒径范围的减小,再生细骨料混凝土塑性收缩开裂风险逐渐降低;再生细骨料取代率的增加,使得再生混凝土塑性收缩开裂风险增大;再生细骨料混凝土水灰比对其抗塑性收缩开裂性能至关重要,过大或过小均会提高其塑性收缩开裂风险;选择适当的砂率可以控制再生细骨料混凝土的塑性收缩开裂程度. 相似文献
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暴露在高蒸发速率环境下的新拌混凝土很容易产生塑性收缩裂缝,特别是表面积与体积的比率很大的时候,目前的研究都证明了,减少拌合水的表面张力是减少塑性裂缝的一种很有效的办法。我们将传统混凝土和高强混凝土掺加超塑化剂和减缩剂,在塑性阶段暴露干燥,测量毛细孔压、沉降、内部温度和蒸发速率,结果显示减缩剂对减少混凝土甚至是高强混凝土的塑性裂缝都是很有效的,这主要由于蒸发速率减少,原因是孔中弯液面的发展导致毛细管压的峰值出现延迟和较低的沉降率。 相似文献
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This paper investigates the influence of the use of coal bottom ash as a replacement for natural fine aggregates on the properties of concrete in the fresh state. Tests for water loss through bleeding, and the determination of the setting times and plastic shrinkage, were carried out in order to evaluate the material in the presence of bottom ash. The influence of the porosity of bottom ash on the potential water absorption and water loss of the material, as well as on the water consumption of concretes produced with bottom ash, is also discussed. The results showed that in the fresh state the concretes produced with the bottom ash are susceptible to water loss by bleeding and the higher the percentage of bottom ash used as a natural sand replacement the lower the deformation through plastic shrinkage. The results also showed that the setting time is affected by the presence of bottom ash in the concrete. In conclusion, different forms of bottom ash mix result in concretes with different properties in the fresh state, but the behavioral tendencies are maintained when bottom ash is employed as a replacement for natural aggregates. 相似文献
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A. Darquennes M.I.A. Khokhar E. Rozière A. Loukili F. Grondin S. Staquet 《Construction and Building Materials》2011,25(4):1836-1847
Under the project “EcoBéton” (Green concrete) funded by the French National Agency (ANR), concrete mixtures with a high quantity of mineral additions, such as blast-furnace slag and fly ash were studied. A first approach to quantify their cracking risk was to measure their plastic shrinkage evolution. In parallel, the evolution of other parameters such as setting, capillary depression and porosity were also monitored to relate this deformation to the evolution of the microstructure of the studied mixtures. Setting monitoring by means of ultrasonic measurements allows obtaining significant macroscopic information such as hardening process and rigidity evolution. The correlation between these different parameters shows that the plastic shrinkage evolution can be divided into three phases driven by different mechanisms. Moreover, it appears that the use of mineral additions has an effect on the plastic shrinkage behaviour, but this impact is not proportional to the percentage of additions. It depends on the hydration process and the microstructure of the cementitious materials. So, it seems that an optimum content of cement replacement by mineral additions must be sought to limit the development of plastic shrinkage of concretes with mineral additions at early age. However, a high rate of substitution of cement may affect the early age compressive strength of the concrete. So these mixtures were also optimised to obtain a significant compressive strength at an early age, but this optimisation leads to a higher risk of cracking for some of them. 相似文献
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针对水泥砂浆塑性收缩开裂的问题,基于平板法和八字模法,分别对不同水灰比和灰砂比的水泥砂浆,改变其环境参数与聚乙烯醇(PVA)纤维参数,测试其塑性抗拉强度、塑性毛细管收缩应力及失水蒸发速率,通过在室内建立的水泥砂浆塑性收缩开裂本构方程,对水泥砂浆塑性收缩开裂预警机制的建立进行了探索.结果表明:室内建立的基准水泥砂浆抗裂指数基于失水蒸发速率的一元本构方程及掺纤维水泥砂浆的三元本构方程可有效预测室外环境下水泥砂浆的塑性收缩开裂,由此初步建立了水泥砂浆塑性收缩开裂预警机制. 相似文献
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《Construction and Building Materials》2007,21(3):634-645
The paper reports on the changes in properties of concretes with different cement types associated with environmental conditions. Three strength classes with three different cement types (ordinary portland cement PC 42.5 (CEM I 42.5), portland composite cements PKC-A 42.5 (CEM II/A-M 42.5) and PKC-B 32.5R (CEM II/B-M 32.5R)) were used in the study. Also, a mixture was prepared with PC 42.5 and silica fume (SF). The effects of variable ambient conditions on plastic shrinkage of fresh concrete and cement paste, compressive strength, modulus of elasticity, capillary absorption and drying shrinkage of hardened concrete were investigated. In contrast to PC 42.5 cement paste, plastic shrinkage cracks were observed in PKC-B 32.5 and PKC-A 42.5 pastes. Water absorption coefficients of all concretes stored in natural environment were higher at all ages as compared to coefficients of concretes kept in laboratory. Drying shrinkage values of concrete with SF, except the first week, were significantly lower than those of others. Although different behaviors for different cement types were observed, water–cement ratio was one of the dominating factors determining the behavior of concrete. This ratio should be lowered to improve the durability of concrete. 相似文献