混凝土凝结过程中水分变化规律研究

Water content variations in the process of concrete setting

分层浇筑混凝土层间性能与下层新拌合混凝土凝结过程中的水分状态息息相关,因此本研究主要探究水分变化规律及机理以指导层间混凝土施工。研究采用低场核磁共振技术,并进行相应开发,对不同组成成分、不同水灰比新拌混凝土试样在环境影响下的水分含量及分布进行测试。研究结果表明:凝结过程中水分变化主要由水化耗水、蒸发失水和内部水分迁移三部分组成,在这几种作用的影响下,凝结过程中水分含量及分布随着环境的变化而呈现出相应的规律,表层尤为突出。通过对内部水分迁移的机理及规律进一步研究,研究发现混凝土凝结前期水分迁移主要是密度差异导致的近似层流运动,而凝结后期主要是水分含量梯度导致的扩散运动。研究结果可对分层浇筑混凝土施工提供相应的参考价值。

Interlayer performance of layers-poured mass concrete is closely related to the water state of lower fresh concrete layer. This study focuses on variations in water content of such concrete and the mechanism of water migration and offers a guide for pouring construction in layers. We used the low field nuclear magnetic resonance technology and further developed it to measure the water content and its distribution in fresh concrete with different compositions and different water-cement ratios under various pouring environments. The results indicate that the major factors in water migration during concrete setting are hydration, evaporation and migration and that the trends of variations in water content and its spatial distribution are controlled by changes in the pouring environment, especially those changes in the surface layer. A further examination on the patterns and mechanism of water migrating inside the concrete reveals that the migration is dominated by quasi-laminar flows driven by density differences at early setting stage while by diffusion under humidity gradient at late setting stage.