Examining Effect of Carbon-enriched Fly Ash on Microstructural Development of Portland-Limestone-based Cement Mortars

Abstract

The goal of this study was to better understand the effects of carbon-enriched supplementary cementitious materials (SCMs) on concrete’s microstructure and reactivity. For the last century, the concrete industry has implemented sustainable technologies, such as supplementary cementitious materials (SCMs), to decrease concrete’s carbon emissions while improving strength and durability. Carbon-enrichment is an emerging technology that seeks to aid concrete sustainability efforts. During carbon-enrichment, fly ash is ground in a CO₂ pressurized environment which encourages calcium carbonate precipitation onto the fly ash particle. Because fly ash reacts with free lime in cementitious systems to form calcium silicate hydrates, precipitating CaCO₃ onto the particle may have adverse effects on its reactive properties and ability to aid in the densification of concrete microstructure. Furthermore, adding carbon-enriched fly ash with inert CaCO₃ precipitates to a portland limestone cement (PLC) mixture containing higher limestone content may change the rate at which the concrete microstructure develops due to a combined dilution effect. To better understand the potential issues posed, this study characterized the chemical composition and reactive properties of carbon-enriched fly ash using various characterization methods such as X-ray diffraction, thermogravimetric analysis, and the R³ Method, ASTM C1897. To study the potential combined dilution effect, scanning electron microscopy was used to monitor early microstructural development of PLC mortar cubes with carbon-enriched fly ash. To measure the early-stage performance of this carbon-enriched ash in mortar, compressive strength tests were also conducted.