Working mechanisms of superplasticizers on alkali-activated slag cements

Resumen del trabajo presentado al 14th Ceramics Congress (CIMTEC), celebrado en Perugia (Italia) del 4 al 4 de junio de 2018.Concrete is essential in our society for housing and infrastructure. Because of the large amount of concrete and cement yearly consumed, respectivelly 30 Btn/y and 4.5 Bt/y, the cement industry finally accounts for 8-9% of CO2 worldwide emissionsAlkali-activated materials have been deeply studied as an alternative and more ecoefficient cement. These cements are produced by mixing an aluminosilicate (by-products such as blast furnace slag or fly ash) with a highly alkaline solution. Concrete produced with these cements have proven to have suitable enginering properties and high durability against chemical attack. However, their poor rheological properties represents one of the barriers for the implementation of these alternative cements, mainly when sodium silicate is used as an activator. In this paper, give an overview of the impact of superplasticizers with different molecular structures on the rheological properties of alkali-activated slag cements. Results have shown the incompatibility of most superplasticizers with these alternative cements. Furthermore, the mechanism of action of the working admixtures have been resolved by a combination of experimental and modeling techniques. In particular, the obtained results concluded that the dispersion mechanism is dominated by the steric repulsión, an important design criterion for improving the rheological behaviour