Studies on effects of steam curing and alkali hydroxide additions on pore solution chemistry, microstructure, and alkali silica reactions. (Volumes I and II).

摘要

Various aspects of alkali silica reaction (ASR) in concrete were investigated. The major experimental methods involved includes analysis of changes in pore solution chemistry, measurements of mortar bar expansion, SEM microstructure investigation, and determination of ettringite and calcium hydroxide by DSC.; It was found that a steam curing cycle (up to 95{dollar}spcirc{dollar}C) of mortar containing alkali reactive aggregate (Beltane opal or cristobalite) induces significant immediate expansion during the steam curing process, and results in accelerated expansion on subsequent exposure to 100% RH. The immediate expansion was due to ASR; the subsequent expansions were due to a combination of accelerated ASR and secondary ettringite deposition (SED) induced by the steam curing. SED took place preferentially in ASR-induced cracks, and likely widened the cracks and induced others. The SED effects were more prominent on 22{dollar}spcirc{dollar}C exposure than on exposure at 38{dollar}spcirc{dollar}C.; Unexpected effects were found, when alkali hydroxide was added in mixing water to boost the original alkali content of the cement for ASR studies. The added alkali hydroxide reacts immediately with the calcium sulfate of the cement, significantly reducing the expected increase in OH{dollar}sp-{dollar} ion concentrate and leaving high concentration of SO{dollar}sb4sp{lcub}2-{rcub}{dollar} ions in the pore solution.; Examinations of effects of added LiOH on ASR indicated that substantial portion of the LiOH added is absorbed by the cement paste itself. Low dosages of LiOH were found to be ineffective in preventing ASR, but a sufficiently high dose reduced effects of the reaction and the measured expansion.