Sulfate resistance of portland cements

• Publisher: Elsevier Science
• Year: 1941
• Tongue: English
• Weight: 59 KB
• Volume: 232
• Category: Article
• ISSN: 0016-0032
• DOI: 10.1016/s0016-0032(41)90088-1

✦ Synopsis

In extensive areas of the West-Central portion of the United States and Canada, many clays and soils occur which contain several per cent. of sulfates, particularly sodium sulfate. The action of these "alkali" soils on portland cement mortar or concrete results in the conversion of the hydrated calcium aluminate of the set cement to calcium sulfoaluminate and gypsum, accompanied by marked expansion. Complete disintegration of the mortar or concrete may eventually occur.

Methods by which the sulfate resistance of portland cement mortar or concrete may be improved, include the following: (I) Steaming the mortar or concrete; (2) prolonged curing of the mortar or concrete at ordinary temperatures;

(3) mixing the cement with a puzzolanic material; (4) increasing the glass content of the cement; (5) altering the chemical composition of the cement.

Experiments by E. P. Flint and Lansing S. Wells which are reported in the Journal of Research for August (RP 141 I), show that the above methods are effective because they bring about the removal from the set cement of tricalcium aluminate hexahydrate, which is unstable in sodium sulfate solutions, and the formation in its place of silica-or iron-containing hydrogarnets, which are stable in such solutions.

Products having an X-ray structure nearly identical with that of grossularite garnet were obtained when mixtures of beta-dicalcium silicate, lime, and dehydrated kaolin were steamed at 300' C. and 420 atmospheres.

Dicalcium silicate and tricalcium silicate are major constituents of portland cement and dehydrated clay, or kaolin, is a common puzzolanic cement admixture.