共查询到19条相似文献,搜索用时 109 毫秒
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选用粉煤灰、矿粉作为掺合料以单掺和复掺的形式掺入到硅酸盐水泥混凝土中,检测其坍落度和3d、28d抗压强度以及早期抗开裂性能。研究结果表明:矿粉、粉煤灰均会降低混凝土3d强度,矿粉可以提高混凝土28d强度,粉煤灰掺量过大会降低混凝土28d强度。随着矿粉掺量的增加,混凝土坍落度随之降低,粉煤灰刚加入时会使混凝土坍落度降低,但是随着掺量的升高,坍落度会逐渐增大;开裂方面:单掺时,粉煤灰与矿粉都在掺量为37%时,抗开裂效果最佳,其中粉煤灰效果最好,复掺时,随着矿粉相对掺量的变大,裂缝的面积和数目都在增大。 相似文献
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温度控制是大体积混凝土配制和施工的关键部分。C3A含量过高导致混凝土的坍落度经时损失增加,水化放热反应量升高,温峰提前。研究发现:适当提高砂率和粉煤灰掺量,并选用缓凝型高效减水剂有利于提高混凝土的和易性,减小经时坍落度损失。西固黄河大桥C50塔柱大体积混凝土的砂率控制在40%,粉煤灰掺量25%,并选用缓凝型高效减水剂,配制出混凝土的坍落度为220 mm,扩展度为600~590 mm,1 h内坍落度损失为零,凝结时间达到20 h。 相似文献
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为研究双掺超细粉煤灰和矿渣高性能混凝土最优配比,借助室内正交试验的手段测试了不同掺量超细粉煤灰与矿渣对高性能混凝土坍落度、力学及耐久性能的影响.结果表明:复掺超细粉煤灰与矿渣能有效改善混凝土试件的坍落度,随着超细粉煤灰掺量的下降,坍落度有所降低,但降低的幅度很小对高性能混凝土工作性能没有影响;在超细粉煤灰和矿渣总量保持... 相似文献
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本文对Ⅰ级、Ⅱ级粉煤灰按不同掺量替代水泥进行了胶砂强度试验,及混凝土工作性能试验。结果表明,在掺灰量为15~25%范围内,相同掺量下掺I粉煤灰水泥各龄期胶砂强度均高于掺Ⅱ级灰水泥;相对纯水泥混凝土,掺量为20%的两种粉煤灰混凝土初始坍落度均会增大,坍落度保持能力也有所提高,且掺活化湿排灰的混凝土工作性保持能力更优;在混凝土力学性能方面,掺Ⅰ级粉煤灰的混凝土各龄期强度均大于掺Ⅱ级灰的混凝土各龄期强度,其中3天和7天分别超出33.6%和25.5%。 相似文献
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为了实现大流动性自燃煤矸石全轻预拌混凝土在工程中的普及应用,拌合物坍落度经时损失的研究尤为重要.本文首先对萘系和聚羧酸系两个品种减水剂进行了坍落度经时损失的对比试验,结果表明聚羧酸系较萘系对自燃煤矸石集料配制的混凝土有更好的适应性,且减水剂掺量少、减水率高,经时损失少.接下来通过单掺羧甲基纤维素、粉煤灰及引气剂,研究其对坍落度经时损失的影响.试验结果表明,复合使用聚羧酸系减水剂与引气剂,能更有效地控制混凝土拌合物坍落度的经时损失且使其具有良好的工作性.研究结果为自燃煤矸石全轻预拌混凝土在工程中的应用提供了参考. 相似文献
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The effect of four water-reducing and retarding admixtures, and three superplasticizers on the consistency (slump) of fresh concrete, was studied at 21°C and 32°C in concrete mixes, made of OPC containing 10% fly ash, and subjected to prolonged mixing for up to 180 min. The effect of such mixing on compressive strength of concrete, at the ages of 3, 7, 28 and 90 days, was also studied. It was found that the admixtures in question accelerated the rate of slump loss at all ages, concrete compressive strength linearly increased with mixing time. The rate of slump loss, and the water demand of the concrete mixes increased within the temperature range studied. 相似文献
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Influence of moisture states of natural and recycled aggregates on the slump and compressive strength of concrete 总被引:6,自引:0,他引:6
The influence of moisture states of natural and recycled aggregates on the properties of fresh and hardened concretes was investigated. Concrete mixes were prepared with natural and recycled aggregates at different proportions. The moisture states of the aggregates were controlled at air-dried (AD), oven-dried (OD) and saturated surface-dried (SSD) states prior to use. The ratio of cement to free water was kept constant for all of the mixes. At the fresh state, the slump loss for various concrete mixtures was determined, while the compressive strength was determined after curing for 3, 7 and 28 days. The test results showed that the initial slump values of the concrete mixtures were dependent on the initial free water contents, and the slump loss values of the mixtures were related to the moisture states of the aggregates. Slump loss was significant when 100% AD or OD recycled aggregate was used. The effect of the moisture states of the aggregates on the strength of the concretes prepared with OD and SSD state aggregates at early age (i.e., 3 and 7 days) was noticeable. The concrete prepared with the AD aggregates achieved the highest average strength values at 3, 7 and 28 days. However, at 28 days, the concrete strengths prepared with different types of aggregates were similar. The results suggested that an AD aggregate that contains not more than 50% recycled aggregate is optimum for producing normal strength recycled aggregate concrete. 相似文献
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矿渣微粉的研制及应用研究 总被引:4,自引:1,他引:3
矿渣微粉作砼掺合料,有着很好的应用价值。用试验小磨进行了不同比表面积矿粉的性能试验,同时进行了不同矿粉掺量砼的性能试验。结果表明:矿渣微粉的活性指数高,流动性好。生产矿渣微粉的最佳粉磨比表面积为450—500m^2/kg。另外用矿粉代替部分水泥后,砼28d抗压值接近甚至高于对比样;且砼流动性改善明显,1h塌落度损失少;同时还降低了砼的生产成本。所以矿渣微粉是配制高强高性能砼的优质掺合料。 相似文献
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?akir Erdo?du 《Cement and Concrete Research》2005,35(5):907-912
To have concrete possesses the specified engineering properties, its slump loss has to be compensated somehow at construction site so that concrete could be placed and compacted properly. Several attempts have been tried so far to render concrete workable at construction site including starting with a high initial slump at the stationary plant, or retempering with water and/or with chemical admixtures at construction site. In this investigation, ASTM C 494 Type F superplasticizer was used for retempering concrete to restore its initial slump. Concrete mixes having an initial slump of about 19 cm were prepared and subjected to prolonged mixing with different mixing duration such as 30, 60, 90, 120, and 150 min following an initial mixing of 5 min to ensure homogeneity. At the end of each mixing period, cube specimens of 15 cm were cast from concrete retempered to its initial slump level and tested at the age of 28 days for compressive strength. Results revealed that compared to the concrete retempered with water, those retempered with a superplasticizer admixture have yielded significantly higher strength regardless of the mixing duration. 相似文献
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为了更加科学合理地进行高性能混凝土配合比设计,研究各个组分对高性能混凝土的影响,将水泥、矿粉、粉煤灰视为一组总质量不变的混料,细集料和粗集料视为另一组混料,通过组合设计分析了矿物掺合料、水泥、砂率的混料效应,同时得到了以坍落度和抗压强度为目标的回归方程,实现了配合比的优化设计.结果表明,为了得到工作性和抗压强度都较好的高性能混凝土,矿物掺合料的掺量和砂率均不宜过大.矿粉比粉煤灰先发挥强度作用,后期水泥与矿粉对高性能混凝土的抗压强度影响较大.砂率的增大对高性能混凝土的抗压强度影响较小,但会使高性能混凝土的坍落度先增加后降低.粉煤灰和矿粉的增加均会使高性能混凝土的坍落度增加.研究结论能够为高性能混凝土矿物掺合料、砂率的选择和配合比设计提供参考依据. 相似文献
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In this study, effects of prolonged mixing and four different retempering processes on some properties of fresh and hardened concrete, such as temperature, slump loss, and strength, were investigated. Two types of concrete mixtures with different compression strength having 15 cm initial slump were produced in a laboratory mixer. After mixing for 5 min at 20 rpm speed to ensure homogeneity, the mixing was continued at 4 rpm for a period of up to 4 h to simulate the prolonged agitation of ready-mixed concrete in truck mixers. Concrete samples were taken out of the mixer at the end of first, second, third, and fourth hour for estimating the effects of prolonged mixing on properties of fresh concrete. For restoring the initial workability, four different retempering methods were used and their effects on properties of concrete were investigated. Results show that compared to the untempered concrete mixtures, those tempered with solutions prepared by 3% or 4.5% solid superplasticizer by mass of retempering water had significantly less loss of 28-day compressive strength. 相似文献