Effect of optimizing curing condition and constitutive materials on improving shrinkage cracking resistance of BFS blended cement concrete exposed to hot environment

Application of blast-furnace slag fine powder blended cement is an important option to achieve low carbon emission from concrete materials in construction. However, concrete using such blended cement (BFS concrete, hereafter) has been believed to be vulnerable to shrinkage cracking and traditionally avoided for use in building construction except for underground structural elements in Japan. To extend the use of BFS concrete in building construction, it is necessary to quantitatively evaluate the shrinkage cracking resistance of BFS concrete. Based on the above background, the ultimate goal of this research is to establish shrinkage cracking controlling design for BFS concrete building construction. Toward this goal, the scope of this study is to experimentally improve shrinkage cracking resistance of BFS concrete with particular attention to effects of high ambient temperature simulating construction work under hot weather. In experiments, restraint shrinkage cracking experiments were conducted with modified BFS concrete mainly subjected to 30°C in comparison with normal concrete, where we adopted cracking age in the restraint tests as a performance index representing cracking resistance. In the experiments, effects of initial curing condition before drying on cracking resistance were also investigated. Modified BFS concretes were mixed by optimizing SO₃ contents in blended cement and course aggregate type. As a result of the experiment, BFS concretes' low shrinkage cracking resistance under hot environment can be substantially improved by using modified BSF concrete with high SO₃ content BFS and limestone coarse aggregate. Furthermore, water curing before drying at 7 day age shows visible cracking age enhancing effects compared with sealed curing. As a result of this study, we found practical cracking resistance strengthening measure for BFS concrete under hot environment, which appears to extend the concrete's application.