Enhancing slag reaction in cement blends using calcium formate and sodium metasilicate activators
Adrian-Alexandru Pîrvan, Barbara Lothenbach, Miriam Schröder, Michael G. Schwendinger, Joumana Yammine‐Malesys, Frank Winnefeld
Abstract
The reactivity of blast furnace slag in blended cements is rather low at early ages, and thus accelerators are usually used for certain applications. This study describes the effects of accelerators, namely calcium formate and sodium metasilicate on a mixture of Portland cement and blast furnace slag. Both accelerators decrease the induction time of cement hydration and increase ettringite and C-S-H precipitation, leading to higher compressive strengths at 1 day. Calcium formate triggers an earlier reaction of slag compared to the non-activated mix, as determined through selective dissolution experiments, and an increase of the degree of reaction by 10% was observed after 1 year of hydration. Dissolved fomate ions are partially taken up by formate-AFm in a higher extent when calcium formate is used alone as compared to when it is used together with the sodium metasilicate and hydrated lime. Similar evidence was found regarding the dissolved sodium ions; their uptake into C-S-H was higher in the system when metasilicate activator was used alone. This evidence demonstrates the potential of calcium formate to not only accelerate cement hydration, but also to improve the SCM reactivity from early to late ages, while sodium metasilicate has a significant impact only in the first days.