Sources: Canadian Concrete Masonry Producers Association, Toronto; National Concrete Masonry Association, Herndon, Va.

Researchers at Montreal’s McGill University are gauging the feasibility of curing concrete masonry units with carbon dioxide, which can react with cement to form a hybrid microstructure of calcium carbonate and calcium silicate hydrate, the main binding product of hydrated powder. “Carbonated” CMU can reportedly have strength comparable to steam-cured product, while exhibiting better resistance to shrinkage, absorption, sulfate attack and freeze-thaw cycle deterioration.

The alternative curing represents a prospective means of carbon sequestration on a commercial scale. In economies subject to caps on CO2 emissions, where regulators link the greenhouse gas to perceived climate change, carbon capture technologies become trading credits. Preliminary observations suggest an 8-in. block can capture 3 lb. of CO2, based on what investigators see as “uptake” potential of cement when accompanied in mix designs by fine and coarse aggregate sourced from slag or other calcium-rich industrial byproducts. If the 4.3 billion (8-in. equivalent) CMU produced annually in the U.S. and Canada were cured with the alternative method, investigators project a 6-million-ton CO2 emissions uptake. Cement and concrete masonry interests would stand to realize $120 million in carbon credits trading at $20/ton.

The McGill research is supported by the Canadian Concrete Masonry Producers Association (CCMPA) and Natural Science and Engineering Research Council of Canada. It borrows from findings of 1960s National Concrete Masonry Association and Portland Cement Association research on flue gas carbonation technology to reduce CMUs’ carbonation shrinkage. Industry liaison on the current research is CCMPA President Paul Hargest of Ontario-based Boehmer Block, 519/624-8396; phargest@boehmerblock.com.