Alkali activated binding composition with phosphogypsum

Abstract

Ordinary Portland Cement (OPC) concrete is most popular building material. However, OPC production requires a lot of energy and consumes a lot of natural raw materials. CO2 emitted during the manufacturing of OPC which pollutes the environment. New types of binders, such as alkali activated binders, could be an environmentally friendly alternative to OPC systems. Aluminosilicate precursor and alkali activator should be used to produce alkali activated binders. Calcium-based additives have a significant influence on the main properties of alkali activated binders. The hardening of alkali activated systems are close related with the addition of calcium cations as stated Davidovits. In the alkali activated systems different types of compounds with calcium cations could introduced. Aboulayt et al. investigated the influence of calcite on the alkali activated metakaolin system. It was concluded that calcite acted as micro filer and do not react with another components, do not form new compounds. Another type of chemical compound with calcium cations is CaO and Ca(OH)2, which have been incorporated into fly ash geopolymers. The mechanical properties of the samples with calcium compounds were increased by curing them at room temperature. However, when curing the samples at a higher temperature, i.e. i.e. at 70 °C, the mechanical properties were lower. Gijbels et al. used the additive of phosphogypsum (PG) in alkali-activated ground granulated blast furnace slag system. This additive shortened initial setting time but prolonged final setting time. Higher polymerization level and positive mechanical properties development was reached for the samples with optimal amount of PG. The aim of this study is to investigate the PG additive on the main properties of alkali activated slag and biomass ash systems.