共查询到20条相似文献,搜索用时 109 毫秒
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本文把粉煤灰作为混凝土第五组分,建立了粉煤灰混凝土配合比独立的计算方法,而不依赖于基准混凝土。文中推导了粉煤灰混凝土配合比中单位水泥用量理论计算公式。确定了单位水泥用量、净水灰比、灰胶比和砂率为粉煤灰混凝土基本参数。文中还首次提出综合水灰比的概念。阐述了粉煤灰在混凝土中的特殊地位。表明粉煤灰在混凝土中的作用主要是提高混凝土的和易性,而决不是过去所认为的减水作用。该方法与普通混凝土配合比计算方法协调一致、便于掌握、使用方便该方法已由实验资料和算例验证。 相似文献
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通过试验制备坍落度大于200mm,扩展度大于450mm的掺粉煤灰泵送混凝土,测定各组泵送混凝土的工作性能,分析减水剂类别与掺量,水胶比,砂率,粉煤灰掺量等配合比参数对混凝土工作性能的影响。试验结果表明,利用改性萘系减水剂,通过调整减水剂的掺量,掺30%粉煤灰的泵送混凝土不离析,不泌水,坍落度达到220mm,扩展度达到540mm,具有很好的工作性能。 相似文献
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Medium strength self-compacting concrete containing fly ash: Modelling using factorial experimental plans 总被引:1,自引:0,他引:1
Mohammed Sonebi 《Cement and Concrete Research》2004,34(7):1199-1208
Fresh self-compacting concrete (SCC) flows into place and around obstructions under its own weight to fill the formwork completely and self-compact, without any segregation and blocking. The elimination of the need for compaction leads to better quality concrete and substantial improvement of working conditions. SCC mixes generally have a much higher content of fine fillers, including cement, and produce excessively high compressive strength concrete, which narrows its field of application to special concrete only. To obtain maximum benefit from SCC, it has to be adopted in general concrete construction practice. Such practice requires inexpensive and medium strength concrete.This investigation aims to develop medium strength SCC (MS-SCC). The cost of materials will be decreased by reducing the cement content and by using pulverised fuel ash (PFA) with a minimum amount of superplasticizer (SP). A factorial design was carried out to mathematically model the influence of five key parameters on filling and passing abilities, segregation and compressive strength, which are important for the successful development of medium strength self-compacting concrete incorporating PFA. The parameters considered in the study were the contents of cement and PFA, water-to-powder (cement+PFA) ratio (W/P) and dosage of SP. The responses of the derived statistical models are slump flow, fluidity loss, Orimet time, V-funnel time, L-box, JRing combined to the Orimet, JRing combined to cone, rheological parameters, segregation and compressive strength at 7, 28 and 90 days. Twenty-one mixes were prepared to derive the statistical models, and five were used for the verification and the accuracy of the developed models. The models are valid for mixes made with 0.38 to 0.72 W/P, 60 to 216 kg/m3 of cement content, 183 to 317 kg/m3 of PFA and 0% to 1% of SP, by mass of powder. The influences of W/P, cement and PFA contents, and the dosage of SP were characterised and analysed using polynomial regression, which can identify the primary factors and their interactions on the measured properties. The results show tha MS-SCC can be achieved with a 28-day compressive strength of 30 to 35 MPa by using up to 210 kg/m3 of PFA. 相似文献
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针对西部盐湖地区耐腐蚀混凝土的需求和结合当地实际情况,设计了在干燥环境下与浸水环境下,通过对相对动弹性模量、相对质量、综合评价参数及扫描电子显微镜试验的研究来判断镁水泥混凝土的性能.通过研究发现:采用无损检测试验方法进行为期一年的试验后发现,镁水泥混凝土的6种配合比中性能最好的配合比是配合比2,而它所用材料的比例为:水∶MgO∶MgCl2∶石子∶砂子∶磷肥∶减水剂=1∶2.87∶1.09∶8.57∶4.61∶0.07∶0.12. 相似文献
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High-strength concrete with different fine aggregate 总被引:3,自引:0,他引:3
High-strength concrete (HSC) has undergone many developments based on the studies of influence of cement type, type and proportions of mineral admixtures, type of superplasticizer and the mineralogical composition of coarse aggregates. Most studies were carried out using natural sand with rounded and smooth grains. In practice, crushed sands from various sources are frequently used in concrete. In this paper, two aspects of the effect of crushed sands on HSCs are presented. First, the performance of crushed sands in relation to natural sand using a low water/cement (w/c) ratio and fixed coarse aggregate and cement content is analyzed. Results show that concrete with crushed sand requires an increase of superplasticizer to obtain the same slump. It also presents a higher strength than the corresponding natural sand concrete at all test ages, while its elastic modulus is lower at 28 days and is the same after that. Studies on the development of hydration and mortar phase of concrete show that the increase of strength can be attributed to the improvement of paste-fine aggregate transition zone. Second, the influence of the mineralogical source of the crushed sands was studied using three different types of crushed sands (granite, limestone and dolomite) with similar grading. Two mixtures containing 450 and 485 kg/m3 cement and low w/c ratio are analyzed. Results show the adverse effects of shape and texture on workability of concrete, but the compressive strength of concrete is improved. Granite crushed sand appears as the most advantageous sand for this purpose. 相似文献
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为了分析水泥锶渣混凝土用于低交通量道路路面的可行性,采用正交方法分析了水泥用量、用水量(坍落度)、砂率、碎石级配等因素对水泥锶渣混凝土抗压强度和抗折强度的影响规律,优选出合理的材料配合比;试验对不同水泥用量的水泥锶渣混凝土的力学性能、干缩性能、温缩性能和抗冻性能进行了系统评价.结果表明:水泥锶渣混凝土强度低于普通C30混凝土,但“折压比”高,弹性模量小,具有较好的抗裂性能;于缩系数比普通混凝土低20%,温缩系数为普通混凝土的53%,具有优良的抗收缩性能;抗冻性能低于普通混凝土;水泥锶渣混凝土可用于非冰冻地区低交通量道路路面. 相似文献
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The paper reports the influence of the composition of Portland cement (PC)-pulverised fuel ash (PFA)-metakaolin (MK) binders on chloride ingress and strength retardation of PC-PFA-MK concrete exposed to synthetic seawater. PC-PFA-MK concrete covering four different total cement replacement levels (10%, 20%, 30% and 40%) and with various MK:PFA proportions was exposed to synthetic seawater for up to 1.5 years. The chloride concentration-penetration depth profiles and change in compressive strength of the concrete for a range of binder compositions and at various exposure times are compared with those of the control PC concrete. It is established that blending the binders in PC concrete and PC-PFA concrete with MK produces concrete with a reduced strength deterioration factor (SDF) and good resistance to chloride penetration when exposed to seawater. The results presented in this paper form part of an investigation into the performance of concrete incorporating both PFA and MK in the binder to produce high performance concrete. 相似文献
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对于泵送混凝土而言,其坍落度经时损失是非常重要的技术指标。文章详细分析了影响混凝土坍落度经时损失的主要原因——混凝土配合比、组成材料、生产条件和环境因素及其影响关系;在此基础上提出了控制混凝土坍落度经时损失的对应举措。实践证明,选择水灰比为0.45~0.6,砂率为38%~43%,C3A和碱的质量分数分别小于7%和1%的硅酸盐和普通硅酸盐水泥,以及选择细度模数为2.7~2.9的中砂和缓凝型减水剂,就可很好控制混凝土的坍落度经时损失。 相似文献
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This investigation is aimed at developing high-performance concrete and form part of an investigation into the optimization of a blended cementitious system for the development of high-performance concrete. Binary and ternary blended cementitious systems based on ordinary Portland cement (OPC), pulverised fuel ash (PFA) and silica fume (SF) were investigated. PFA up to 40% was used, and to these blends, 0%, 5%, 10% and 15% SF were incorporated as partial cement replacements. Results of compressive strength, tensile strength, oxygen permeability and carbonation of concrete are reported. A water-binder (w/b) ratio of 0.27 was used for the main group of mixes and w/b ratios of 0.40 and 0.50 were used for some selected mixes. Based on the experimentally obtained results, prediction models were developed which enabled the establishment of isoresponse contours showing the interaction between the various parameters investigated. It was found that the incorporation of 8-12% SF as cement replacement yielded the optimum strength and permeability values. 相似文献