Early reaction on waterglass-activated slag cements. Influence on the rheological behavior

Resumen del trabajo presentado al 15th International Congress on the Chemistry of Cement (ICCC), celebrado en Praga (República Checa) del 16 al 20 de septiembre de 2019.Partial or total replacement of clinker by supplementary cementitious materials (SCMs), most of them being industrial by-products, has become one the most effective routes to obtain more eco-efficient and sustainable cements. Alkali-activated cements (AAM), also named alkaline cements or geopolymers, have received increasing attention during the last decades due to their lower environmental impact than Portland cement, great engineering properties and durability. However, rheological properties of alkali-activated slag (AAS) cements still remain unclear, mainly when waterglass (WG) is used as an activating solution. Previous studies have confirmed the dependence of the rheological behavior of AAS pastes and mortars on the concentration and siliceous modulus of waterglass. Furthermore, the formation of a primary C-S-H has been claimed to be the responsible of the poor rheological properties of AAS pastes and mortars, although its formation has not been. The aim of the present study is to identify and characterize the early hydration products of WG-AAS pastes and define its relationship with the rheology of mortars and concrete. WG-AAS pastes have been characterized at early hydration times (up to 5 h) by different techniques such as in-situ synchrotron XRD, FTIR and NMR. Results indicate that the initial loss of fluidity could be related to the formation of an alumino-silicate gel