Petrographic Examination of Carbonate Aggregate Prism Specimens Treated with Chemical Solutions Normally Occurring in Portland Cement Concrete

Report No: 79-R58

Published in 1979

About the report:

The original rock prism specimens were prepared and the early length change data were taken as part of a Federal Highway Administration project on the behavior of carbonate aggregates in concrete. It had been shown that the length changes of the aggregates bore a direct relationship to the pH of the solution in which they were tested. The present study shows that the chemical reactions causing the length changes can be detected in the prisms by quantitative measurements of the mineral composition by means of X-ray diffraction and by examination of thin sections under a petrographic microscope. It is concluded that chemical solutions of pH over 12 can cause expansion and dedolomitization in carbonate rocks susceptible to alkali reactions and that chemical solutions of low pH may cause dissolution of carbonate rocks and shrinkage. It is noted that detailed, statistically defensible conclusions regarding the exact nature of the reactions occurring between the chemicals of concrete paste and the carbonate aggregates therein will probably require that data be obtained from replicate reactions and that weight changes as well as length changes be measured.

Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.

Authors

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Hollis N. Walker

Last updated: January 26, 2024

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