缓凝剂和早强剂与聚羧酸减水剂复合使用对蒸养混凝土强度的影响

发布时间：2018-12-10 19:13

【摘要】：使用减水剂或减水类复合外加剂提高蒸养混凝土的强度,特别是早期强度,不但有利于节能降耗,而且能够加快模具周转率,提高预制构件生产效率。目前,聚羧酸减水剂在蒸养预制混凝土中应用越来越广泛,提高该类减水剂对蒸养混凝土强度的增效作用是预制构件领域研究的热点,关于将适量无机盐和小分子有机物与聚羧酸减水剂复合使用方面的研究,虽有报道,但研究较少。有鉴于此,本文较为系统地研究了微量(掺量小于胶凝材料用量的0.05%)的缓凝剂和适量早强剂与聚羧酸减水剂复合使用对蒸养混凝土强度的影响,并对影响机理进行了探讨。六偏磷酸钠、三聚磷酸钠、正磷酸钠、葡萄糖酸钠和蔗糖是混凝土常用的缓凝剂,一般不用于蒸养混凝土中,但本文研究表明:磷酸盐与聚羧酸减水剂复合使用,掺量较大时起缓凝作用,当掺量较低时(胶凝材料的0.01%左右),对蒸养混凝土早期强度和后期强度均有增效作用,其顺序为六偏磷酸钠三聚磷酸钠正磷酸钠,掺入0.01%六偏磷酸钠可使蒸养混凝土12h脱模强度提高14.7%,蒸养后28d强度提高15.3%;葡萄糖酸钠掺量小于0.05%时,对蒸养混凝土强度无增效作用,但掺量增大,蒸养混凝土强度明显降低;蔗糖掺量小于0.03%时,对蒸养混凝土早期强度几乎无增效作用,对后期强度有一定的增效作用,但掺量较大时则起缓凝作用。氯化钙、硫酸钠、硫代硫酸钠、硅酸钠和三乙醇胺是混凝土常用的早强剂,本文研究表明,与六偏磷酸钠相比,早强剂提高蒸养早期强度的掺量往往较高,且对后期强度增长作用不大。氯化钙与聚羧酸减水剂复合使用,早强效果最优,蒸养早期强度增效作用强于微量六偏磷酸钠,后期增效作用却不如六偏磷酸钠;硫酸钠、硅酸钠、硫代硫酸钠早强效果依次降低,硫酸钠和硫代硫酸钠对后期强度无提升作用,硅酸钠能略微提高后期强度,但效果不如磷酸盐;微量三乙醇胺对蒸养混凝土早、后期强度基本无影响。X射线衍射分析(XRD)、扫描电子显微镜分析(SEM)以及饱和Ca(OH)2溶液浓度检测等研究结果表明,微量磷酸盐,特别是六偏磷酸钠对蒸养混凝土强度增效作用的原因,主要是因为微量磷酸盐能降低混凝土孔溶液中Ca(OH)2浓度,促进水泥水化,同时使得水泥水化产物晶体形貌生长致密和分布均匀,对蒸养强度发展有利。但掺量过大,磷酸盐与钙离子反应生成的络合物会覆盖在水泥颗粒表面,延缓水泥水化,对蒸养强度反而无增效作用。
[Abstract]:The use of water-reducing agent or water-reducing compound admixture to improve the strength of steaming concrete, especially the early strength, is not only conducive to energy saving and consumption reduction, but also can accelerate the mold turnover rate and improve the production efficiency of prefabricated components. At present, polycarboxylic acid superplasticizer is more and more widely used in steaming precast concrete. Increasing the synergistic effect of this kind of water reducing agent on the strength of steaming concrete is a hot spot in the field of prefabricated components. The research on the compound use of proper amount of inorganic salts and small molecular organic compounds with polycarboxylic acid superplasticizer has been reported, but little has been done. In view of this, this paper systematically studied the influence of the small amount of retarder (less than 0.05% of the amount of cementitious material) and proper amount of early strength agent and polycarboxylic acid superplasticizer on the strength of steaming concrete. The influence mechanism is also discussed. Sodium hexametaphosphate, sodium tripolyphosphate, sodium orthophosphate, sodium gluconate and sucrose are common retarders for concrete. When the amount of cement is low (about 0.01% of the cementitious material), it has synergistic effect on the early strength and later strength of steaming concrete, and its order is sodium hexametaphosphate, sodium tripolyphosphate, sodium orthophosphate, sodium hexametaphosphate, sodium orthophosphate, and sodium hexametaphosphate. Adding 0.01% sodium hexametaphosphate can increase the demoulding strength of steaming concrete for 12 hours, and increase the strength of steaming concrete for 28 days by 15.3; When the content of sodium gluconate is less than 0.05, the strength of steaming concrete has no synergistic effect, but the strength of steaming concrete decreases obviously when the content of sodium gluconate is increased. When the content of sucrose is less than 0.03, there is almost no synergism to the early strength of steaming concrete, but it has a certain synergistic effect on the later strength, but when the content of sucrose is larger, it plays a retarding effect on the strength of steaming concrete. Calcium chloride, sodium sulfate, sodium thiosulfate, sodium silicate and triethanolamine are commonly used as early strength agents in concrete. And it has little effect on the later strength increase. The combination of calcium chloride and polycarboxylic acid superplasticizer had the best effect at early strength. The synergistic effect of early steaming was stronger than that of sodium hexametaphosphate in the early stage, but the synergism was not as good as sodium hexametaphosphate in the later stage. The early strength of sodium sulfate, sodium silicate and sodium thiosulfate decreased in turn. Sodium sulfate and sodium thiosulfate had no effect on the later strength. Sodium silicate could increase the later strength slightly, but the effect was not as good as phosphate. Trace triethanolamine has no effect on the strength of steaming concrete at early and late stage. The results of X-ray diffraction (XRD) (XRD), scanning electron microscopy (SEM) and saturated Ca (OH) _ 2 solution concentration measurement show that the trace phosphate, In particular, the reason why sodium hexametaphosphate can enhance the strength of steamed concrete is mainly because trace phosphate can reduce the concentration of Ca (OH) _ 2 in concrete pore solution and promote the hydration of cement. At the same time, the crystal morphology of cement hydration product is compact and uniform, which is beneficial to the development of steaming strength. However, the complex formed by the reaction of phosphate with calcium ion will cover the surface of cement particles and delay the hydration of cement, but has no synergistic effect on the evapotranspiration strength.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528.042

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