掺碱调整pH值对萘系减水剂及混凝土性能的影响

Experimental Study on the Effect of Adjusting pH Value with Alkali on Properties of Naphthalene Highly Effective Water Reducer and Concrete Performance

为解决金沙江干热河谷地区某大型水电工程拌和系统配制萘系减水剂溶液发生变质、导致混凝土凝结时间显著缩短的问题,研究了掺碱调整pH值对萘系减水剂溶液存放品质和混凝土性能的影响,并开展了混凝土生产性试验检验入仓浇筑效果。结果表明,掺碱调整pH值≥9.5可有效抑制萘系减水剂溶液发生变质,延长混凝土拌和物凝结时间,降低坍落度和含气量经时损失,且未对混凝土的力学性能和耐久性产生不利影响;混凝土入仓后和易性良好,仓面初凝时间由调整前的约7 h大幅延长至近13 h,使得现场具备三仓甚至四仓同浇的条件,提高了大坝混凝土的浇筑效率和浇筑质量,产生了较高的综合效益。

The degradation of naphthalene highly effective water reducer(NHWR)in the concrete mixing system of a large-scale hydraulic project situated in dry and hot river valley area of Jinsha River is a critical problem which considerably shortens the concrete setting time.This study investigates the effectiveness of adding alkali to adjust the pH value on NHWR storage quality and the properties of fresh and hardened concrete.A productive experiment on concrete was conducted to examine the consolidation effect at the project site.Results show that a pH level of 9.5 or higher can significantly inhibit the putrefaction of NHWR solution,and remarkably lengthen the setting time of fresh concrete,leading to a decrease in slump and the hourly loss rate of air content.Importantly,there is no detrimental effect on the mechanical property and durability of hardened concrete.Moreover,the concrete mixture produced for the placing area exhibits good workability,and its initial setting time has risen to 13 hours from the previous nearly 7 hours.Consequently,it is now possible to consolidate concrete in three or four placing areas at the same time,which enhances the efficiency and quality of dam concrete placing and produces high comprehensive benefits.