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掺高效减水剂水泥砂浆的早期开裂研究 总被引:9,自引:0,他引:9
采用多通道椭圆环收缩开裂试验、自由收缩试验和强度试验综合评价了萘系(UNF)、聚羧酸类(PC)高效减水剂对水泥砂浆体积稳定性及早期开裂的影响.结果表明,高效减水剂的掺入延长了水泥砂浆的初始开裂时间,从而降低了水泥砂浆的开裂敏感性.高效减水剂降低水泥砂浆开裂敏感性的效果为:聚羧酸类〉高浓型萘系〉普通型萘系.掺高效减水弃1均增大了水泥砂浆的自由收缩值,且水泥砂浆自由收缩值随着高效减水剂掺量的增加而增大.高效减水剂控制水泥砂浆体积稳定性的效果为:聚羧酸类〉普通型萘系〉高浓型萘系.聚羧酸类高效减水剂的掺入减小了水泥砂浆的最大裂纹宽度,而萘系高效减水剂的掺入则加快了水泥砂浆最大裂纹宽度的发展速度.在干燥养护条件下,掺聚羧酸类高效减水剂比掺萘系高效减水剂更能有效地提高水泥砂浆28d的强度. 相似文献
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聚羧酸系减水剂用于水泥基自流平砂浆相关问题的研究 总被引:1,自引:0,他引:1
聚羧酸系减水剂(PC)作为一种新型高性能减水剂,用其配制水泥基自流平材料,可以充分发挥其低掺量、高减水率、良好的流动度保持性、良好的增强效果和低收缩等优点.试验对比掺加PC、萘系高效减水剂(PNS)和密胺系高效减水刺(PMS)自流平砂浆的流动度、流动度保持性、抗折和抗压强度及收缩值,结果表明,掺加PC的自流平砂浆其各项性能更优. 相似文献
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通过试验研究了高效减水剂种类以及在相同水灰比和相同流动度两种情况下聚羧酸系高效减水剂掺量对砂浆自收缩和干燥收缩的影响。结果表明:同水灰比、同流动度时,萘系和脂肪族减水剂增大砂浆收缩,聚羧酸系减水剂能降低砂浆收缩。同水灰比下,聚羧酸系减水剂掺量在0.6%~1.5%范围,砂浆自收缩随掺量增加变化不大,砂浆干燥收缩随掺量增加而增大。同流动度下,聚羧酸减水剂掺量在0.6%~1.5%范围,砂浆自收缩随掺量增加而增加,而砂浆干燥收缩随掺量增加而减小。 相似文献
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一、UNF—2型高效减水剂它是一种高效非引气性萘系减水剂。掺加少量这种减水荊,就能增大混凝土坍落度,减少用水量,提高早期及后期抗压、抗折、抗拉强度,提高弹性模量、抗渗性、耐水性。掺入量一般为水泥重量的0.5~0.7%,可节约水泥10~20%。该减水剂对矿渣水泥、普通水泥、火山灰水泥都有效。对自然养 相似文献
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采用体积法就4种高效减水剂(聚羧酸系、萘系、三聚氰胺系和脂肪族)对水泥砂浆早期自收缩的影响进行了试验研究,并测定了各高效减水剂溶液不同浓度时的表面张力.结果表明:各高效减水剂均增大水泥砂浆的自收缩;掺萘系、三聚氰胺系及脂肪族高效减水剂水泥砂浆的自收缩随其掺量的增加而增大,掺聚羧酸系高效减水剂水泥砂浆的自收缩则随其掺量的增加呈先增后减的趋势;在水泥砂浆流动度相同时,4种高效减水剂增大水泥砂浆早期自收缩程度由大到小的顺序为:萘系、脂肪族、三聚氰胺系及聚羧酸系.分析表明,高效减水剂改变浆体孔径分布是其影响水泥砂浆早期自收缩性能的主要原因. 相似文献
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通过与木质素磺酸钙减水剂和萘系高效减水剂对比,系统研究改性木质素磺酸钙高效减水剂对砂浆抗渗性、抗碳化性和收缩等耐久性指标的影响.结果表明:掺加0.4%改性木质素磺酸钙高效减水剂的砂浆90d抗渗比为220%,28d碳化深度为25.5mm,180d收缩值比为86%.进一步通过模糊数学评价表明:最优掺量下,掺改性木质素磺酸钙高效减水剂的砂浆耐久性优于掺木质素磺酸钙减水剂及萘系高效减水剂.综合考虑价格和环保因素,在砂浆工程中使用改性木质素磺酸钙高效减水剂具有较大的经济效应和环境效应 相似文献
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《Construction and Building Materials》2007,21(11):2017-2022
The addition of superplasticizers is an important approach to prepare high performance cement-based materials. The effect of polynaphthalene series superplasticizer (PNS) and polycarboxylate type superplasticizer (PC) on early-age cracking and volume stability of cement-based materials was investigated by means of multi-channel ellipse ring shrinkage cracking test, free shrinkage and strength test. The general effect of PNS and PC is to increase initial cracking time of mortars, and decrease cracking sensitivity of mortars. As for decreasing cracking sensitivity of mortars, PC > H-UNF (high-thickness-type PNS) > C-UNF (common-thickness-type PNS). To incorporate superplasticizers is apparently to increases free shrinkage of mortars when keeping the constant W/B ratio and the content of cement pastes. As for the effect of controlling volume stability of mortars, PC > C-UNF > H-UNF. Maximum crack width of mortars with PC is lower, but the development rate of maximum crack width of mortars with H-UNF is faster in comparison with control mortars. Flexural and compressive strength of mortars and concretes at 28 days increased with increasing superplasticizer dosages under drying conditions. C-UNF was approximate to H-UNF, but PC was superior to PNS in the aspect of increasing strength of cement-based materials. 相似文献
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研究了掺与不掺膨胀剂HME的水泥净浆、砂浆和混凝土在直接干空养护条件下的收缩变形,分析了膨胀剂HME对水泥净浆、砂浆以及混凝土的干燥收缩影响规律,并探讨了膨胀剂HME在干空养护条件下的减缩作用机理。结果表明,膨胀剂HME在干空养护条件下仍然具有水化反应能力,产生有效膨胀,可以完全消除水泥净浆、砂浆以及混凝土的早期干燥收缩,并对其中后期干燥收缩也有较好的补偿作用。 相似文献
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《Construction and Building Materials》2007,21(1):176-181
Cement-based materials suffer from their low tensile strength and poor strain capacity: they are sensitive to cracking, above all to shrinkage cracking. Enhancing the cracking resistance of cementitious materials is the objective of a broad ongoing research programme. In this regard, the aim of this work is the design of a cementitious composite exhibiting high strain capacity before localised cracking. It was assumed that the use of aggregates with low elastic modulus could be a solution. Rubber aggregates obtained from shredded non-reusable tyres were used, conferring an additional environmental interest on the study. As expected, results show that rubberised mortars exhibit a lower modulus of elasticity and have higher tensile capacity for deformation before macrocrack formation. However, there is one drawback: a decrease in the modulus of elasticity of a cement-based material is accompanied by a decrease in its strength. Results also confirm that rubber aggregate incorporation increases length change due to shrinkage. In contrast, ring-test results demonstrate that the strain capacity enhancement provided by rubber aggregate incorporation largely offsets the additional shrinkage length changes: shrinkage cracking is delayed and, when it occurs, the crack network exhibits thin crack openings which are less detrimental. 相似文献
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高碱度水泥基材料早期开裂敏感性研究 总被引:4,自引:0,他引:4
选用粉煤灰、减缩剂和减水剂,采用五路裂缝测定仪和非接触式电阻率测定仪,分别测试了相同水灰比、不同碱类型的水泥砂浆在干燥条件下约束收缩开裂的初始时间与水泥浆体早期水化24h内的电阻率变化,并测定了水泥砂浆在干燥环境下的抗压、抗折强度.结果表明:碱度增加会加速水泥的早期水化硬化以及微结构的形成与发展;Na^ 提高水泥砂浆早期强度、增加约束收缩开裂敏感性的作用要比K^ 的明显,尤其在低水灰比、掺减水剂时其影响更为明显;粉煤灰和减缩荆可延缓水泥(尤其是高碱度的水泥基材料)的早期水化硬化,降低水泥砂浆强度的发展,推迟初始开裂时间. 相似文献
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《Construction and Building Materials》2002,16(6):365-374
The results of an ongoing test program to evaluate the performance of polymer-modified cement-based mortars for repairing surfaces of concrete structures up to a depth of 75 mm (3 inches) damaged due to exposure to cold climates are presented. Twenty-five selected commercially available polymer-modified products, seven containing styrene butadiene rubber (SBR) and 18 containing acrylics were evaluated. They were compared with those of a pure cement-based mortar containing 8% silica fume by weight of the cement, with a water/cementitious materials (cement+silica fume) ratio (W/CM) of 0.31. All of the mortars were subjected to thermal compatibility with base concrete, drying shrinkage, permeability, abrasion-erosion resistance, bond strength, compressive strength and freezing and thawing cycling tests. The thermal compatibility with the base concrete at temperatures from −50 to +50 °C was used as a pre-selection test. This paper also presents the satisfactory performance of the three best selected polymer-modified cement-based mortars (included in the 25 mortars), after 6 years in service on two operating spillways of a dam in a severe cold climate. 相似文献
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普通纤维混凝土因可泵送性差很少用于索塔锚固区。采用多重复合技术,优选纤维混凝土配合比,并研究了各配合比的泵送性能;模拟干热环境,对优选的高性能混凝土(HPC)和钢锚箱锚固区专用高性能钢纤维混凝土(HPSFRC)进行了塑性收缩试验;研究了纤维掺量和减缩剂对塑性收缩和干燥收缩性能的影响,并对其机理进行了探讨。研究表明,经优化的高性能钢纤维混凝土2h内泵送性能优良。随着纤维掺量的增加,塑性收缩的开裂总面积下降,混凝土的抗裂等级提高。当钢纤维的体积掺量为0.8%时,高性能钢纤维混凝土自由干燥90d的收缩值同高性能混凝土相比下降了50%;有约束的干燥收缩66d试验环未见开裂,从而减少混凝土开裂的风湿,提高混凝土结构的耐久性。与同强度等级的高性能混凝土相比,钢纤维的加入也改善了混凝土的力学性能,高性能钢纤维混凝土的抗弯强度和劈拉强度提高了近30%。试验结果还表明,纤维体积率为0.6%的钢纤维与减缩剂复合后,对抑制塑性收缩和干燥收缩效果显著。 相似文献
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通过砂浆收缩率和初始开裂时问等性能的测试,研究了粉煤灰对水泥基材料体系收缩与早期开裂敏感性的影响,并探讨了收缩与开裂的关系。研究表明:粉煤灰可抑制水泥基材料的收缩变形,并在一定程度上降低材料的开裂敏感性。 相似文献