Waste Glass as a Primary Precursor and Secondary Aluminosilicate Source in Geopolymer Mortars

Abstract

Widespread use of concrete as a construction material has led to concerns with the level of CO2 emissions from the production of portland cement. This has led to the development of alternative cements; geopolymers are one of these binders and the focus of this research. Geopolymers are formed through the combination of an aluminosilicate source and an alkaline activator. One of the largest contributions to CO2 emissions associated with geopolymers comes from the production of sodium silicate, which is commonly used as an activator. One of the primary goals of this research was to reduce or eliminate the need for sodium silicate in geopolymers by investigating the use of waste glass as a primary precursor or a secondary aluminosilicate source. Two types of geopolymers were produced where waste glass was used both as the main aluminosilicate source (Phase I) and as a supplement to fly ash (Phase II). Three activators with varying ratios of sodium silicate to sodium hydroxide (SS/NaOH) were considered and mixed with various glass sources to determine the effect of glass composition on performance. Fresh properties and compressive strength were measured, and SEM imaging was completed. Curing time, curing temperature, and calcium content were also investigated. Overall, including sodium silicate as an activator reduced the strength of glass-based geopolymers. A SS/NaOH of 1:1 (SiO2/Na2O = 0.95) was found to be optimal to activate the fly ash sources. Waste glass could not fully replace sodium silicate in activating fly ash and had limited success as a partial replacement while reducing the amount of sodium silicate in the activator.