Use of industrial by-products as alkaline cement activators

Abstract

Alkaline (or geopolymer) cements have proven to be a sustainable alternative to the ordinary portland cement material. The laboratory reagents normally used as alkaline activators constitute the most costly and on occasion polluting constituents of such cementitious systems. This study aimed to explore the use of a disposed cleaning solution (CS), coming from the aluminium transformation industry, as an activator for high and low calcium aluminosilicate precursors. For that a Blast Furnace Slag (BFS) and a type F-Fly Ash (FA) were used. Precursors activated with a traditional NaOH solutions were used as a reference. Kinetics of reactions (isothermal calorimetry) were evaluated and mechanical strength of hardened pastes determined. The nature of the reaction products generated in this new systems were also identified by using XRD, FTIR, SEM and 29Si and 27Al MAS NMR. The findings showed that the CS can be effectively used to prepare cementitious materials, particularly when applied to CaO-SiO2-Al2O3 system precursors such as BFS, which require lower alkalinity than FA-based precursors. The nature of the reaction products generated in the CS alkali activated systems was similar than those observed in the reference systems, however Al richer reaction products were observed in the former.