Analysis of Contaminants on Ground Glass Pozzolan and the Effects on Pozzolan Performance in Mortar

Abstract

Using ground glass pozzolan as a replacement for portland cement can reduce the CO2 emissions associated with concrete production and utilize waste glass that would otherwise end up in landfills. In the United States, municipal solid waste (MSW) stream recycling operations collect plastic, glass, paper, and other recyclables together in single stream recycling. Glass collected in this manner can contain an unknown concentration of various contaminants on its surface, which can cause concern for concrete producers concerned about the effect on performance. Using analytical chemistry techniques combined with mortar physical testing, it is possible to better understand what kinds of contaminants are present on recycled glass and how they affect cement mortar compressive strength. Primary targets of contaminant analysis were surfactants and carbohydrates such as sugars and cellulose. Gas chromatography-mass spectrometry (GC-MS) was used to assess the presence of the surfactant sodium dodecyl sulfate and glucose. Colorimetric phenol-sulfuric acid assays (PSA) were used to detect and quantify the amount of carbohydrates on the surfaces of the glass pozzolans. Results indicate carbohydrates to be the primary contaminant on the recycled glass surface, with glucose being a confirmed contaminant using GC-MS. Using the contaminant concentrations determined through analytical techniques, contaminant-dosed mortars were produced, and the effects on compressive strength and flow were measured. It was found that samples dosed with 0.5 wt.% glucose had decreased compressive strength at day one but gained strength over time and reached or surpassed compressive strengths similar to control mixes by 28 days.