磷酸对石膏胶凝材料性能的影响研究

发布时间：2018-06-11 23:42

本文选题：石膏 + 磷酸　；参考：《长安大学》2017年硕士论文

【摘要】：作为一种古老的建筑材料,石膏具有环保、节能、质轻、保温、耐火、吸声、尺寸稳定等优良性能。但是,石膏材料耐水性较差,这大大限制了它在各个领域的发展。为了解决石膏的耐水性问题,本文分析了导致石膏耐水性差的原因,总结了国内外石膏的改性研究现状。通过内掺和外涂磷酸,从石膏的密度、吸水率、体积稳定性、抗折强度、抗压强度和软化系数的角度,对其进行改性性能评价。实验结果表明,单掺磷酸后石膏产生发泡和缓凝,这导致连通孔和塌模现象。磷酸掺入后,由于发泡导致吸水率升高。掺量超过2%后,随掺量的增加,吸水率降低。XRD和SEM分析发现加入磷酸后生成不溶于水的磷酸一氢钙,这些物质覆盖在石膏晶体表面,导致石膏耐水性的提高。掺加PVA和二水石膏的实验结果表明,加入PVA后稳泡效果较好。加入二水石膏后初凝和终凝时间大大缩短。在磷酸掺量2%时,掺加PVA和二水石膏的效果最佳。与对比样石膏相比,密度降低了14.3%,吸水率降低了12.8%,体积稳定性提高了50%。但是强度较低,绝干抗折强度降低了75.3%,绝干抗压强度降低了85.6%。复掺膨胀珍珠岩的实验结果表明,膨胀珍珠岩可有效改善石膏的力学性能和软化系数。膨胀珍珠岩最佳掺量为1.5%。与未掺膨胀珍珠岩的石膏相比,绝干抗折强度提高了46.9%,绝干抗压强度提高了27.0%,抗折软化系数提高了12.9%,抗压软化系数提高了3.0%。复掺麦秸秆纤维的实验结果表明,最佳纤维掺量2.5%。绝干抗折强度较未掺麦秸秆纤维试样提高了116.8%。绝干抗压强度较未掺麦秸秆纤维试样提高了183.9%。SEM测试发现麦秸秆纤维和石膏结合良好且PVA的加入可阻止麦秸秆纤维被酸腐蚀。外涂磷酸水溶液的实验结果表明,磷酸与水的最佳稀释倍数为1:4。耐水性改善效果较好,吸水率降低了8.5%,抗折软化系数0.57,较空白石膏提高了54.1%,抗压软化系数0.52,较空白石膏提高了44.4%,抗折抗压强度略有降低。最佳涂层厚度为四层。较空白石膏吸水率降低了9.3%,绝干抗折强度提高了4.9%,绝干抗压强度提高了1.8%,抗折软化系数提高了18.9%,抗压软化系数提高了25%。外涂磷酸后,SEM测试发现,石膏表面覆盖了一层物质。与空白石膏相比,晶体与晶体间孔隙有所减少,结晶接触点增多,晶体变得更加密实。
[Abstract]:As an ancient building material, gypsum has environmental protection, energy saving, light weight, heat preservation, fire resistance, sound absorption, size stability and other excellent properties. However, the water resistance of gypsum materials is poor, which greatly limits its development in various fields. In order to solve the problem of water resistance of gypsum, this paper analyzes the causes of poor water resistance of gypsum, and summarizes the research status of gypsum modification at home and abroad. The modification properties of gypsum were evaluated from the aspects of density, water absorption, volume stability, flexural strength, compressive strength and softening coefficient of gypsum. The experimental results show that the gypsum is foamed and retarded after the addition of phosphoric acid, which leads to the phenomenon of connected pores and collapsing modes. After incorporation of phosphoric acid, the water absorption rate increases due to foaming. The results of XRD and SEM analysis show that calcium monohydrogen phosphate, which is insoluble in water, is formed by adding phosphoric acid, which covers the surface of gypsum crystal and improves the water resistance of gypsum. The experimental results of adding PVA and gypsum dihydrate show that the foam stabilization effect is better after adding PVA. After adding gypsum dihydrate, the initial setting time and final setting time are greatly shortened. When the amount of phosphoric acid is 2, the effect of adding PVA and gypsum dihydrate is the best. Compared with the contrast gypsum, the density decreased by 14.3, the water absorption decreased by 12.8and the volume stability increased by 50. But the strength was lower, the dry strength and compressive strength decreased 75.3% and 85.6% respectively. The experimental results of mixed expanded perlite show that expanded perlite can effectively improve the mechanical properties and softening coefficient of gypsum. The optimum content of expanded perlite is 1.5. Compared with the gypsum without expanded perlite, the dry flexural strength, dry compressive strength, flexural softening coefficient and compressive softening coefficient are increased by 46.9, 27.0, 12.9and 3.0, respectively. The experimental results of mixed wheat straw fiber showed that the optimum fiber content was 2.5%. The dry flexural strength was 116.8% higher than that of the unadulterated wheat straw fiber. The compressive strength of wheat straw fiber was 183.9% higher than that of unadulterated wheat straw fiber. SEM test showed that wheat straw fiber combined well with gypsum and the addition of PVA could prevent wheat straw fiber from being corroded by acid. The experimental results show that the optimum dilution ratio of phosphoric acid and water is 1: 4. The water resistance is improved better, the water absorption is reduced by 8.5, the flexural softening coefficient is 0.57, compared with the blank gypsum, the bending softening coefficient is increased by 54.1, the compressive softening coefficient is 0.52, compared with the blank gypsum, the water absorption is increased by 44.4and the flexural strength is slightly reduced. The best coating thickness is four layers. Compared with the blank gypsum, the absorptivity of water was decreased by 9.3%, the dry bending strength was increased by 4.9%, the absolute dry compressive strength was increased by 1.8%, the flexural softening coefficient was increased by 18.9%, and the compressive softening coefficient was increased by 25%. SEM test showed that the gypsum surface was covered with a layer of substance. Compared with the blank gypsum, the porosity between crystal and crystal decreases, the crystal contact point increases, and the crystal becomes more dense.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ177.31

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