Properties of Portland Cement Pastes Cured at Elevated Temperatures and Pressures


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Title: Properties of Portland Cement Pastes Cured at Elevated Temperatures and Pressures

Author(s): N. C. Ludwig and S. A. Pence

Publication: Journal Proceedings

Volume: 52

Issue: 2

Appears on pages(s): 673-687

Keywords: no keywords

Date: 2/1/1956

The effects of curing at elevated temperatures and pressures upon several physical properties of hardened neat cement pastes are given. Two cements were studied and data are given for heat of hydration, nonevaporable water content, surface available to water vapor, permeablity to water, and compressive strength of pastes cured at 80 to 400 F, at pressures from atmospheric to 7500 psi, and at ages from 12 hr to 7 days. Results show that changes in compressive strength of hardened cement paste follow the changes in internal surface area. A decrease in strength occurs at high curing temperatures which may be explained by an increase in the particle size of the hydration products. The nonevaporable water content decreased slightly at temperatures in excess of 220 F. This is in agreement with recent composition studies reporting hydration products having lower water content at hgh temperatures. The change in the amount of water required to form a complete unimolecular layer over the surface of cement particles (Vm) was found to be proportional to the change of curing temperature between 220 and 320 F. This suggests that the cement particles increase in size at a rate which is nearly directly proportional to the increase in curing temperature in the range where rapid strength retrogression occurs. Heat of hydration tests show that hydration is nearly complete in pastes cured 7 days at 320 and 400 F, and it is indicated that the total heat of reaction of a neat cement paste cured at high temperatures (steam-curing range) may be less than that of the same cement cured at atmospheric temperatures. The water permeablity of hardened cement pastes was found to be quite low at curing temperatures up to about 160 F. Above this temperature, permeablity increased rapidly as strength and internal surface decreased. Curing pressures up to 1000 psi at temperature of 200 F cause slight increases in heat of hydration, internal surface, and strength at early ages. Pressure in excess of 1000 psi at any age had no great effect. It appears, therefore, that pressures up to 1000 psi increase the early rate of reaction.