Published: Jan 1950
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This paper may be considered as a supplement to an earlier paper dealing with the properties of mortars and concretes containing portland-pozzolan cements and other blends. Herein, for mortars there are given the strengths and volume changes up to the age of 10 yr. and the resistance to the action of sodium-sulfate solutions up to the age of one year.
Mortar specimens containing portland cements within the ordinary range of composition, under laboratory conditions of continuous wet storage, exhibited retrogression in both tensile and compressive strengths. Corresponding specimens containing cement replacements of finely divided pozzolanic materials in general showed no such retrogression. Those containing the less active volcanic glasses, such as pumicite, continued to increase in tensile strength up to the age of 10 yr.; those containing the more active opaline shales generally acquired their maximum strength at an earlier age, but some continued to increase in compressive strength up to the age of 10 yr.
Under continuous drying conditions, after a preliminary period of moist curing, mortars containing portland cements within the ordinary range of composition continued to increase in strength up to the age of 10 yr. This was also true for blended cements where the replacement was 30 per cent or less, including not only such pozzolanic materials as volcanic glasses, opaline shales, and calcined clays, but also including limestone dust.
In general, the long-time drying shrinkage of mortars containing blended cements was greater than that of mortar containing the corresponding straight portland cement; blended cements containing limestone replacements were exceptions. The long-time drying shrinkage of mortars containing cements high in tricalcium silicate was less than that for corresponding mortars containing cements low in tricalcium silicate. The long-time expansion of mortars under continuously wet conditions was somewhat greater for portland-pozzolan cements than for the corresponding straight portland cement.
The use of such pozzolans as Monterey shale and pumicite in blended cements materially improved resistance to sulfate action. In general, blends containing calcined or uncalcined clays, and crystalline silicas such as quartz and granite were little, if any, more resistant to sulfate action than the corresponding straight portland cement. The use of limestone dust led to some improvement in sulfate resistance.
Professor of Civil Engineering and Director of the Engineering Materials Laboratory, University of California, Berkeley, Calif.
Chief Chemist and Chemical Engineer, California Portland Cement Co., Colton, Calif.
Research Engineer, University of California, Berkeley, Calif.