Shrinkage and Plastic Flow of Pre-Stressed Concrete

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Title: Shrinkage and Plastic Flow of Pre-Stressed Concrete

Author(s): Howard R. Staley and Dean Peabody, Jr.

Publication: Journal Proceedings

Volume: 42

Issue: 1

Appears on pages(s): 229-244

Keywords: none

Date: 1/1/1946

Abstract:
Presents the results of shrinkage and plastic flow measurements on prestressed and unstressed specimens for the duration of a year. Stored at 70 F. and 50 percent relative humidity the shrinkage ot unstressed specimens reached maximum values of 8.7 X IO-4 in. per in. for the concrete and 6.5 X IO-4 for shotcrete. After IO days the shotcrete shrinkage was about 75 percent of the concrete strains. The loaded specimens were stressed to approximately 930 psi (low), I500 psi (intermediate), and 2400 psi (high) for concrete and shotcrete whose ultimate compressive strengths were 4900 psi and 4500 psi, respectively. As shrinkage and plastic flow occurred these stresses decreased until, at I year, the stresses in the concrete were 25 to 33 percent their initial values and the stresses in the shotcrete were about 43 percent of the initial. Plastic flow is defined as the difference between the total strain of the loaded specimen and the shrinkage strain of the unstressed specimen during the same time interval. Plastic flow is assumed equal to the stress multiolied bv a flow coefficient C. At 380 days the flow coefficients varied from 64 X IO-8 to 79 ‘X IO-8 for the concrete and from 50 X IO-8 to 61 X IO-8 for the shotcrete. For the low stress specimens the shotcrete coefficient is 90 percent of the concrete; for the other two stresses the shotcrete coefficient is about 75 percent that of the concrete.