Simulation for optimal mixture design of low-CO2 high-volume fly ash concrete considering climate change and CO2 uptake

Abstract

High-volume fly ash (HVFA) can reduce CO2 emissions from concrete, but it impairs concrete's carbonation resistance. In particular, carbonation is accelerated due to climate change effects, such as increases in CO2 concentration and temperature. CO2 uptake due to carbonation, however, can alleviate the hazards of CO2 emissions. This study presents a procedure for low-CO2 HVFA concrete mixture designs considering climate change, carbonation, and CO2 uptake. First, net CO2 emissions are calculated by using CO2 emissions from the materials minus CO2 uptake due to carbonation. The strength and carbonation depth are evaluated using a hydration-based integrated model. Second, the genetic algorithm is used to find the optimal mixtures. The object function of the genetic algorithm is net CO2 emissions. The constraints of the genetic algorithm include strength, carbonation, workability, and range of the concrete component. Third, optimal mixtures are determined for different design strengths and climate change scenarios. The analyzed results show that carbonation durability and strength are control factors for low- and high-strength HVFA concrete mixture designs, respectively. After considering climate change, the threshold value between carbonation control and strength control increases. As the strength increases, net CO2 emissions increase, and the CO2 uptake ratio decreases.