Cements with a low clinker content: versatile use of raw materials

A model for alkaline activation has recently been designed to develop new cementitious systems known as hybrid alkaline cements. These multi-component systems contain a high percentage of mineral additions (fly ashes, slags (BFS), metakaolin (MK), bentonites (BT) …), low proportions (<30%) of Portland clinker and moderately alkaline solid activators. This study explored the mechanical performance of two sodium carbonate-activated hybrid cements, CEM MK (20% CK + 40% BFS + 40% MK) and CEM BT (20% CK + 40% BFS + 40% BT). The reaction kinetics of the two systems were analyzed by isothermal conduction calorimetry. The hydrated matrices were characterized with XRD, SEM/EDX and 29Si and 27Al NMR. Both systems developed high mechanical strength, for both generated a mix of (N,C)-A-S-H and C-A-S-H gels. The proportions of the gels precipitating vary with system composition and initial reactivity, however.