Title: Carbon Sequestration of Concrete Masonry Units

Author(s): Don MacMaster and Oscar Tavares

Publication: Materials Journal

Volume: 112

Issue: 6

Appears on pages(s): 775-780

Keywords: calcium carbonate; calcium hydroxide; calcium silicates; carbon sequestration; cement hydration; concrete masonry units; early-age carbonation; relative humidity; water conservation

DOI: 10.14359/51688069

Date: 11/1/2015

Abstract:
Early-age carbonation curing of concrete products results in improved strength, increased surface hardness, and reduced surface permeability to water, as well as the reduction of efflorescence. Carbonation reactions between carbon dioxide and calcium compounds result in permanent fixture of the carbon dioxide in thermodynamic stable calcium carbonate. The moisture content, relative humidity, and temperature profile of the hydrated system have considerable and important influence on the rate and ultimate extent of carbonation. During carbonation, CO2 penetrates the surface of concrete and reacts with cement hydration products—namely, calcium hydroxide and calcium silicate hydrates—to form carbonates. This study quantifies carbon sequestration levels in concrete masonry units using various curing methodologies. The test results of a dynamic pressurized CO2 curing chamber and normal ambient CO2 pressure at various concentrations levels are compared to traditional kiln curing procedures. Early compressive strength profiles for 30% CO2 cured concrete masonry units (CMUs) are equivalent to 100% CO2 cured CMUs and exceed the traditional kiln-cured compressive strengths. Carbon sequestration reduced water requirements by 20% for optimum strength performance and provided water conservation opportunities.