Slump loss


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Title: Slump loss

Author(s): Lewis H. Tuthill

Publication: Concrete International

Volume: 1

Issue: 1

Appears on pages(s): 30-35

Keywords: concretes; cooling; hot weather construction; ice; slump loss; workability.

Date: 1/1/1979

All concrete has slump loss or it would never harden It is when slump is lost at an abnormally fast rate that troublesome results occur. Enough elapsed time can also diminish slump sufficiently to cause difficulty on the job. As slump loss problems go generally, most are due to delays and lost time in getting newly-mixed concrete into place. The second largest contributor to slump loss problems is higher temperatures, both ambient and in the concrete. These speed up the hardening process and the first step is more rapid loss of slump. Other causes may include certain properties of the aggregates, the cement, or the water-reducing admixtures (WRA). More often these are more imagined than real but erve as handy places to lay the blame when actually it lies elsewhere in time or temperature. Most aggregate, except lightweight aggregate, has little capacity for absorption after the mixing period but sprinkling or shading will helpfully lower its effect on the temperature of the concrete. Certain experience indicates incompatability between some cements and some WRA. However, on one large project with five unmodified lignin-base WRA and at least 12 cements used in 7,000,OOO yd3 (5350,000 m3) of concrete during 10 years of all seasons, warm and cold, no slump loss difficulties occurred that were not due to delays rimarily, and to ambient warm temperature. Perhaps, where there has been apparent incompatability, it is due to the modifiers and not to the lignin materials. [Author]