Alkali-activated slag cements produced with a blended sodium carbonate/sodium silicate activator

An alkali-activated slag cement produced with a blend of sodium carbonate/sodium silicate activator was characterised. This binder hardened within 12 h and achieved a compressive strength of 20 MPa after 24 h of curing under ambient conditions, which is associated with the formation of an aluminium substituted calcium silicate hydrate as the main reaction product. Carbonates including pirssonite, vaterite, aragonite and calcite were identified along with the zeolites hydroxysodalite and analcime at early times of reaction. The partial substitution of sodium carbonate by sodium silicate reduces the concentration of carbonate ions in the pore solution, increasing the alkalinity of the system compared with a solely carbonate-activated paste, accelerating the kinetics of reaction and supplying additional silicate species to react with the calcium dissolving from the slag as the reaction proceeds. These results demonstrate that this blend of activators can be used effectively for the production of high-strength alkali-activated slag cements, with a microstructure comparable to what has been identified in aged sodium-carbonate-activated slag cements but without the extended setting time reaction usually identified when using this salt as an alkali activator

Will Geopolymers Stand the Test of Time?

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Milestones in the analysis of alkali-activated binders

The use of alkali activation to achieve environmental savings in the production of construction materials is currently an extremely active area of research and development. There is now a diverse range of chemistries and applications that have been developed within the broader theme of ‘alkali-activated materials’, including the subclass of lower-calcium binders which are also known as ‘geopolymers’. Academic research and commercial development have combined to bring these materials to a level of technological maturity where larger scale deployment is now taking place. This paper reviews some of the key aspects of alkali-activation technology which have brought the field to this point, with a particular view towards re-assessing key points and comments which have been raised in several historical reviews and discussions of this class of materials. Conclusions are therefore drawn regarding which among these key questions have been answered, and which remain outstanding in an engineering or scientific sense