Technical and economic aspects of using GGBFS for crack control mitigation in long span reinforced concrete structures

In 2009, China accounted for half of the global steel production. As a waste material or by-product in the manufacture process, over 160 million tonnes of blast furnace slag is generated annually, of which only 55% is recycled. Blast furnace slag, ground to an appropriate fineness, can be used as a cementitious material in concrete. However, most ground granulated blast furnace slag (GGBFS) in China ends up in low-grade applications, including 'low heat' cementitious material used in low-grade bulk concrete and cementitious material in mortar. A recently started project at XJTLU aims to contribute to the application of GGBFS in long-span concrete structures in China by avoiding/reducing the use of more expensive crack control reinforcement. The use of GGBFS in long-span concrete structures in China is currently held back by the following:Lack of awareness of the potential commercial benefits;Concerns about the steady supply of GGBFS;Difficulties in evaluating the mitigating effects of GGBFS on early-age "thermal loading". This paper reports on the methodology which is adopted to carry out this project. Special considerations are paid to issues associated with concrete early-age thermal contraction. Modelling of a case study of a commercial building in Shanghai is used to compare the cost effectiveness of using conventional crack control steel reinforcement only with the mitigation of thermal crack stresses by adopting GGBFS as a partial replacement for traditional cement. The study includes the use of finite element modelling to investigate the development of heat during the early age cement hydration process and the resulting thermal stresses produced in the concrete.