Formulation of an alkali-free accelerator and its effects on hydration and mechanical properties of Portland cement

An alkali-free accelerator (AMD) mainly composed of aluminum sulfate, magnesium sulfate and diethanolamine (DEA) was formulated and its effects on hydration and mechanical properties of Portland cement were investigated. Results indicate that AMD accelerator can efficiently shorten the setting time and enhance the early strength of Portland cement. The rapid setting and hardening properties were achieved by promoting the formation of ettringite (AFt), Mg(OH)2 and MgAl-hydrotalcite (MgAl-LDHs). Although AMD accelerator retarded early hydration of alite due to the accelerated hydration of C3A and caused higher porosity, it had no negative effect on or even slightly increased long-term strength development. Except for environmentally-friendly advantage, this type of alkali-free accelerator is more beneficial to strength development compared to accelerators with fluoride salts.