Role of organic admixtures on thaumasite precipitation

Thaumasite formation is normally a slow process; however some studies have shown that the presence of sucrose promotes its formation substantially. Many of todayʹs concretes contain organic admixtures and no research has been conducted to date to determine whether the presence of these admixtures may induce or favour thaumasite formation. The present study aimed to ascertain whether, like sucrose, admixtures may further that process, and to propose a working methodology to do so. The methodology used was: mixing sodium carbonate, sulfate and silicate solutions with a CaO solution with eleven commercial admixtures. The precipitates obtained after different curing times (up to 1 year) and temperatures (5 and 25 °C) were characterised with FTIR and XRD. It was possible to distinguish between admixtures that did and those that did not favour thaumasite formation, i.e., products containing lignosulfonates or a mix of sodium carboxylate and polysulfonate as well as aluminium-based accelerating admixtures favoured thaumasite formation.