Journal Published Online: 01 June 1998
Volume 20, Issue 1

Expansion of Cement Containing Crystalline Magnesia With and Without Fly Ash and Slag



Crystalline magnesia (periclase) is traditionally considered an undesirable compound in cements since it hydrates slowly at normal temperatures and, hence, causes a delayed expansion. This delayed expansion may be more harmful to the concrete structure than the “early” expansion due to free lime hydration in terms of the soundness of cements. Autoclave expansion tests, such as ASTM C 151, were designed to determine the soundness of cements containing MgO or CaO, or both. On the other hand, the controlled expansion of cements containing magnesia is beneficial, especially to mass concrete. The rate and amount of expansion of cements containing magnesia depend on many factors including the quantity, fineness and calcination temperature of magnesia, cement constituents and strength, presence of mineral admixtures such as fly ash and slag, and storage or service conditions (temperature and moisture). The expansion behavior of portland cements containing magnesia under normal (service) conditions is different from that under the autoclave conditions (high temperature and high pressure). The expansion behavior also differs in the presence of fly ash and slag. The autoclave expansion of portland cement containing magnesia is larger than the expansion at normal temperatures. In the presence of slag, however, cement containing magnesia expands less under the autoclave conditions than under the normal conditions. This implies that one should be cautious when applying the autoclave expansion test to the cement containing slag or other mineral admixtures. The addition of fly ash and slag reduces the expansion of cements containing magnesia with their increasing concentrations. Fly ash is more effective in reducing expansion of cements containing magnesia than slag at the same concentration. These results are summarized in this investigation.

Author Information

Liu, Z
Materials Laboratory, Institute for Research in Construction, National Research Council, Ottawa, Canada
Tang, M
Nanjing University of Chemical Technology, Nanjing, P.R., China
Cui, X
Nanjing University of Chemical Technology, Nanjing, P.R., China
Pages: 6
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Stock #: CCA10452J
ISSN: 0149-6123
DOI: 10.1520/CCA10452J