共查询到19条相似文献,搜索用时 187 毫秒
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粉煤灰及水胶比对水泥净浆抗硫酸盐侵蚀性能影响的试验研究 总被引:1,自引:0,他引:1
通过5%的硫酸钠溶液对净浆进行长期浸泡试验,以粉煤灰等量取代水泥(0%、20%、30%、40%)以及固定粉煤灰等量取代20%水泥,水胶比在0.35~0.7之间变化来分析粉煤灰以及水胶比对水泥净浆抗硫酸盐侵蚀性能的影响.结果表明:在本试验条件下, W/B=0.5时,清水养护条件下,粉煤灰掺量为20%时在后期拥有最高的抗折强度,粉煤灰掺量为30%时具有最高的强度增长率;5%硫酸钠溶液浸泡条件下,其抗折强度先升高后降低,粉煤灰对改善水泥净浆的抗硫酸盐腐蚀是有利的,且随着粉煤灰掺量的增加,抑制腐蚀破坏效果越明显.但是考虑到试件本身的强度值,其掺量也不宜过高,可取20%~30%;20%粉煤灰的掺入并不能改变水泥净浆随水胶比增大其抗硫酸盐腐蚀性能下降的规律. 相似文献
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通过建立正交试验并使用刀口法研究温度、水胶比和粉煤灰掺量对高温热害隧洞衬砌混凝土早期抗裂性的影响,结果表明:温度、水胶比和粉煤灰掺量三个因素中,温度是影响混凝土早期抗裂性的主要因素,粉煤灰掺量次之,水胶比对试验指标无明显影响。混凝土早期抗裂性能随温度的增加而降低;当温度高于60℃时,粉煤灰对提高混凝土的早期抗裂性有明显贡献,试验确定的最优粉煤灰掺量为25%;由最优尺度回归模型建立的方程为单位面积总开裂面积=0.879×温度-0.178×粉煤灰掺量。 相似文献
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本文使用再生粗骨料全部替代天然粗骨料,用粉煤灰分别替代20%、30%、40%、50%和70%(质量分数)水泥,制备了不同水胶比(0.36、0.40和0.45)的全再生自密实混凝土,通过抗折强度试验和抗压强度试验,分析了粉煤灰掺量和水胶比对全再生自密实混凝土性能的影响规律,得到了粉煤灰的合理掺量,提出了适用于全再生自密实混凝土抗折强度的计算公式。结果表明:当粉煤灰掺量由20%增至40%时,所有全再生自密实混凝土拌合物的坍落扩展度呈先增加后降低趋势,且均表现出良好的间隙通过能力,但混凝土拌合物扩展时间T500受粉煤灰的影响不显著;随着粉煤灰掺量增加,全再生自密实混凝土的抗压强度和抗折强度均呈先增加后降低趋势,抗折强度受粉煤灰掺量的影响程度要高于抗压强度;全再生自密实混凝土抗压强度和抗折强度受水胶比的影响程度相同;综合粉煤灰掺量对全再生自密实混凝土工作性能和力学性能的影响,建议粉煤灰对水泥的取代率为30%。 相似文献
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试验采用高强页岩陶粒及Ⅰ级粉煤灰制备工作性能良好的自密实轻骨料混凝土(SCLC),通过环形约束收缩试验,进行密封与外侧面干燥两种条件下的约束收缩试验,研究自密实轻骨料混凝土约束收缩应变随着龄期发展规律及抗裂性能.研究结果表明:自密实轻骨料混凝土在3 d前的自生收缩与干燥收缩大于普通混凝土,14 d后的自生收缩与干燥收缩低于普通混凝土;掺加Ⅰ级粉煤灰可以明显提高新拌SCLC浆体的工作性能,也能有效抑制SCLC的自生收缩,但其掺量应该控制在25%以内较合适;以开裂风险系数η作为混凝土的抗裂性能评价指标,自密实轻骨料混凝土的抗裂能力要高于普通混凝土,但SCLC在达到临界开裂状态后很快产生贯穿性裂缝,其开裂的时间反而比普通混凝土早. 相似文献
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为探究水胶比、粉煤灰掺量以及沙漠砂替代率对沙漠砂混凝土劈裂抗拉性能的影响,采用正交试验设计来进行劈裂抗拉强度试验研究。结果表明:在掺加粉煤灰与沙漠砂的情况下,水胶比为0.48、粉煤灰掺量为30%、沙漠砂取代率为30%时混凝土劈裂抗拉强度达到最大值,并根据同批次的抗压度值与抗拉强度值回归出二者之间的函数关系式。 相似文献
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The replacement of cement by mineral admixtures in concrete has been of increasing interest in the construction industry. Nevertheless, several of the potential replacements, such as fly ash class F, lower the compressive strength of concrete at early age. This project investigates the use of nanosilica to compensate for such loss of compressive strength. A statistical experimental design involving mixtures of Portland cement, fly ash and nanosilica, in addition to water/binder ratio as an external factor, is proposed to study their combined effect on the compressive strength of concrete. This design allows estimating a cubic regression model that properly accounts for the effects of the mixture components within a constrained experimental region. The range of each factor was selected according to levels normally used in the industry. Finally, an optimisation strategy permits to recommend the use of nanosilica when high percentages of cement replacement by fly ash are present. 相似文献
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我国煤矿生产事故频发,顶板垮落、瓦斯爆炸、机电事故、突水、矿井火灾、放炮等隐患时刻影响着煤矿安全生产,当前矿井开采以井下开采为主,井下开采存在技术要求高、开采难度大的问题,导致煤矿事故发生数和死亡人数相对其他行业居于首位。因此,为改善煤矿事故发生情况,提高煤矿安全生产,将粉煤灰应用到煤矿生产中,替代部分水泥,降低成本,降低混凝土水化热及渗透性,提高灌注混凝土工作性与耐久性。通过试验验证表明:采用Ⅰ级粉煤灰的混凝土较采用Ⅱ级粉煤灰的混凝土抗压强度、轴拉强度和极限拉伸值均略高,且干缩率较低,掺加Ⅱ级粉煤灰的混凝土的抗冻性能优于掺加I级粉煤灰的混凝土,I级粉煤灰对混凝土抗冻性能负面影响严重。同强度等级、同水胶比条件下,Ⅰ级粉煤灰混凝土抗冲磨强度比Ⅱ级粉煤灰混凝土抗冲磨强度及抗水冲蚀能力稍高,对预防及应对煤矿安全问题具有重要意义。 相似文献
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研究了海水环境下掺入硅灰、粉煤灰、矿渣对硫铝酸盐水泥抗压强度、化学收缩和水化产物的影响规律.结果表明:当硅灰的掺量为2.5%时,水泥浆体的抗压强度比空白组高.矿渣掺量为10%的水泥浆体28 d抗压强度明显超过掺入硅灰和粉煤灰时的强度,60 d强度高于空白组.掺入2.5%硅灰后,水泥浆体的化学收缩增大;在水化早期,粉煤灰和矿渣的火山灰活性很低,导致水泥浆体的化学收缩降低.掺入10%硅灰加快了硫铝酸盐水泥3 d水化反应,钙矾石生成量增多,水泥浆体早期强度比掺其它掺合料有所提高,但体积过快膨胀会破坏其内部结构,对水泥浆体的强度发展不利. 相似文献
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《应用陶瓷进展》2013,112(4):197-201
AbstractAbstractThis paper reports results on the porosity and pore size distribution (PSD) of cement paste containing simulated desulphurised waste (SDW). The SDW was chosen due to the variability in chemical composition of real desulphurised waste. The SDW is a combination of fly ash and gypsum. The content of fly ash in the SDW changed from 0 to 100% by weight. The water to binder ratio was 0·5. The binder consists of cement and SDW. Cement in the pastes was partially replaced with 25 wt-% SDW. The porosity and PSD of cement pastes at 28 days of curing is reported. Increasing amount of gypsum does not seem to greatly change the pore volume; however, there is tendency of obtaining coarser pore structure in the presence of gypsum. The compressive strength increases with increasing amounts of gypsum. Correlation between strength and PSD is conducted. 相似文献
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Self-desiccation shrinkage (SDS) is closely related to the interior water consumption and the relative humidity (IRH) drop in the cement paste. Substantial self-desiccation shrinkage has been observed at very early-age for high performance concrete. However, it is difficult to investigate the IRH by conventional method of hygrometer at this time because the materials are still in the superhygroscopic range. In this paper, an automatically measuring system of meniscus depression is developed on the base of the mechanism of tensiometer and Laplace formula. The interior water consumption and the IRH changing within the paste could be automatically monitored at the very early-age (here specially refers to the stage from the beginning of casting till several hours after final setting). By using this system, the effects of water to binder ratio and replacement of cement by fly ash and ground granulated blast furnace slag on the self-desiccation were investigated for the very early-age cement paste. Experimental results could potentially explain the mechanism of the SDS at very early-age as well as determine the “time-zero” of SDS corresponding to its definition. 相似文献
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Influence of fly ash fineness on strength, drying shrinkage and sulfate resistance of blended cement mortar 总被引:4,自引:0,他引:4
In this paper, the influence of fineness of fly ash on water demand and some of the properties of hardened mortar are examined. In addition to the original fly ash (OFA), five different fineness values of fly ash were obtained by sieving and by using an air separator. Two sieves, Nos. 200 and 325, were used to obtain two lots of graded fine fly ash. For the classification using air separator, the OFA was separated into fine, medium and coarse portions. The fly ash dosage of 40% by weight of binder was used throughout the experiment. From the tests, it was found that the compressive strength of mortar depended on the fineness of fly ash. The strength of mortar containing fine fly ash was better than that of OFA mortar at all ages with the very fine fly ash giving the highest strength. The use of all fly ashes resulted in significant improvement in drying shrinkage with the coarse fly ash showing the least improvement owing primarily to the high water to binder ratio (W/B) of the mix. Significant improvement of resistance to sulfate expansion was obtained for all fineness values except for the coarse fly ash where greater expansion was observed. The resistance to sulfuric acid attack was also improved with the incorporation of all fly ashes. In this case the coarse fly ash gave the best performance with the lowest rate of the weight loss owing probably to the better bonding of the coarse fly ash particles to the cement matrix and less hydration products. It is suggested that the fine fly ash is more reactive and its use resulted in a denser cement matrix and better mechanical properties of mortar. 相似文献