Shrinkage of Statically Compacted Cement-Phosphogypsum Mixtures

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Title: Shrinkage of Statically Compacted Cement-Phosphogypsum Mixtures

Author(s): C. X. Ling, K. T. Lin, and W. F. Chang

Publication: Special Publication

Volume: 135

Issue:

Appears on pages(s): 77-94

Keywords: cements; compacting; drying shrinkage; humidity; shrinkage; Materials Research

Date: 12/1/1992

Abstract:
The huge quantity of phosphogypsum which has been stockpiled in Florida has caused increasing concerns with respect to its possible environmental impacts. Many research projects on utilization of phosphogypsum as construction materials have been sponsored by the Florida Institute of Phosphate Research. It was found that phosphogypsum-based materials possess valuable strength sufficient for use in building and road construction after compaction. The aim of the tests in this paper is to investigate the shrinkage properties of phosphogypsum-cement mixtures and the influence of thefactors, such as moisture content (MC), phosphogypsum/cement ratio (P/C), curing conditions, the relation between shrinkage and moisture loss, comparison of shrinkages of the compacted and vibrated specimens, and ambient humidity. A standard 1 x 1 x 11.25-in. (25 x 25 x 285-mm) bar, of which the net length between the two contact points at the two ends is 10 in., was used to measure the linear shrinkage. The specimens covered 14 to 22 percent MC, 10:90-95:5, three 28 days' curing, and 50 to 70 percent ambient humidity. Effect of these factors on the development of drying shrinkage over time is described, and the relationship between drying shrinkage and loss of water is given for each factor involved. The volume change of the specimen in the air is a swelling-shrinkage process with loss of moisture. Shrinkage of compacted specimen is much less than that of vibrated specimen. Curing conditions and ambient humidity are significant to the shrinkage. There is a maximum shrinkage at about 25:75 P/C, and an empirical formula to predict effect of P/C is obtained, using a program which fits least-squares polynomials to bivariate data.