Application of alkali-activated industrial waste

Abstract

In the last decades, several investigations have been developed on alkali-activated materials (AAM) with cementitious properties and for that reason also called binders, with a particular focus on the specific research areas of design and characterization of binders, mechanical behaviour and durability tests. Geopolymers consist of a polymeric framework of Si–O–Al, which is produced by condensation of tetrahedral aluminosilicate units, with alkali metal ions that balance the charge associated with tetrahedral aluminium. The geopolymers are usually synthesized from a two-part mixture, consisting of an alkaline solution (activator) and aluminosilicate solids (precursor), and the reactions occur at room temperature or slightly elevated. These materials can be used as cement and be applied in concrete and mortar. The excellent performance of cement and concrete with AAMs is attributed to the highly refined pore network, forming a denser structure phase of calcium aluminosilicate hydrate (CASH) or sodium aluminosilicate hydrate (NASH). In the last years, there was an intense development of studies focused on AAMs using traditional precursors such as waste-derived precursors such as blast furnace slag or coal fly ash, and synthetic ones as metakaolin. More recently, several research groups are testing different new waste as precursors and as activation reagents. The state of the art is focussed on precursors based on waste from urban, metallurgical, ceramic, construction and demolition and agro-industry activities. Regarding the activating solution, the state of the art also is focussed on waste derived reagents, differentiating between the cases in which the activating solution was prepared totally or partially from waste. Also recycled concrete aggregates (RCA) have been used with positive results in the manufacture of alkali-activated slag concrete (AASc).