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Existing experimental and physicochemical evidence regarding carbonation of the constituents of portland cement is reviewed and indicates that substantially all of the constituents of cement are subject to ultimate carbonation under ideal conditions.
Humidity during exposure to carbon dioxide appears to be a major factor influencing the shrinkage directly produced by carbonation. Concentration of carbon dioxide and size of specimen also have important effects, possibly produced by indirect changes in humidity within the specimen. Increased subsequent volume stability to moisture change was obtained by prior carbonation.
The influence of high-pressure steam curing procedures (temperatures and duration) on some physical properties of cement pastes containing siliceous additions is presented. The amount of water vapor adsorbed at 36 per cent relative humidity is a measure of the amount and nature of the hydration product and is influenced by siliceous additions and decreased during curing at elevated temperatures. This fundamental characteristic of the hydration product is closely related to the elastic modulus, water-loss shrinkage, carbonation shrinkage, degree of carbonation, and water permeability of the paste.
The strict physicochemical significance of the phenolphthalein color test for estimating depth of penetration by carbon dioxide gas is questioned.
Manager, Portland Cement Assn., Chicago, Ill.