Accelerated Curing of Compacted Calcium Silicate Mortars on Exposure to CO2

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Abstract
The parameters affecting strength development in compacted cylinders of 3CaO‐ SiO2 and β‐2CaO‐ SiO2 mortars exposed to CO2 were investigated. Strength increased with time up to 81 min, the duration of the longest detailed study. The β‐2CaO‐ SiO2 develops strength more slowly initially, but both silicates achieved compressive strengths of 7,000 to 10,000 psi. The rate of increase in strength depends on both the amount of water used in molding the compact and the amount of water present in the CO2. Increasing CO2 pressures from 1 to 2 atm increased the rate of reaction, but a further increase to 4 atm had little additional effect. Carbonation occurs mainly in the outer portions of the cylindrical compacts. The initial reaction on exposure to CO2 appears to be accelerated hydration of the silicates to a CaO‐SiO2‐H2O‐like gel and calcite. The gel has a stoichiometry similar to that found in conventional hydration. Further reaction results in progressive carbonation of the gel, which decreases its lime content. The reaction products appear to be intimately dispersed in the microstructure.