Study on the performance and reaction mechanism of alkali-activated clay brick with steel slag and fly ash

This study aims to enhance the utilization of clay bricks by maximizing the application of clay brick (CB) powder. The amount of CB was set at 50% and different percentages of steel slag (SS) powder and fly ash (FA) are added. A CB-SS-FA ternary hybrid geopolymer was prepared through alkali activation, and its performance and reaction mechanisms were investigated. The main parameters used to evaluate the performance under different proportions were volume stability and compressive strength. The microstructure and reaction mechanism were analysed using SEM/EDS, ICP, isothermal conduction calorimetry (ICC), FTIR, XRD, and TG-DTG. The experimental results illustrated that SS provided early compressive strength to the CB-SS-FA system. CB has low activity, but Anorthite within can participate in the reaction. CB provides more Si and Al to the system than FA within 1d at room temperature. FA dissolved at a relatively high rate at 80 celcius, and then supplied Al and Si to the system continuously. FA and CB cooperate to promote the dissolution of Ca2+ in steel slag. CB provide adhesion sites for the generated gel. Moreover, its porous microstructure can provide space to release expansion energy from f-CaO. The optimal content of SS is 30% in this ternary geopolymer. C-(A)-S-H and N-A-S-H gels were formed that wrapped the partially hydrated clay brick and provided strength to the system.