单面干燥条件下受约束高强混凝土的早期开裂研究

Investigation into Early-Age Cracking of Restrained High-Strength Concrete with Casting Surface Exposed to Dry Environment

在单面干燥条件下应用自行研制的混凝土早期收缩应力测试仪及非接触式混凝土收缩变形测试仪测试了水灰比为0.26、0.40的高强混凝土的早期弹性模量和自由收缩变形,通过改进的环向约束试验观测了受约束试件内部的收缩应力及应力梯度,并在上述试验基础上研究了单面干燥条件下受约束高强混凝土的早期开裂趋势.结果表明,高强混凝土水灰比越小,单面干燥条件下的早期自由收缩变形、弹性模量、受约束状态下的内部收缩应力增长越快,干燥表面越容易发生塑性收缩开裂,早期开裂趋势越明显.

In this paper, two devices were respectively developed for the measurements of early-age shrinkage stress and non-contact shrinkage. Then, by exposing the casting surface to the dry environment, the early-age elastic modulus and free shrinkage of the high-strength concrete with the water-to-cement ratios of 0. 26 and 0. 40 were determined respectively using the two devices. Moreover, the inner shrinkage stress and stress gradient of the restrained specimens were investigated through a modified restrained ring test, and the early-age cracking tendency of the restrained high-strength concrete was finally investigated based on the above-mentioned experiments. The results indicate that, for the high-strength concrete, when the water-to-cement ratio decreases, the early-age free shrinkage, the elastic modulus and the inner shrinkage stress under restrained condition all increase, and that the potential of plastic shrinkage cracking on the drying surface improves. It is thus concluded that the high-strength concrete with a low water-to-cement ratio exhibits high tendency of early-age cracking.