Title:
Statistical Extrapolation of Shrinkage Data--Part I: Regression
Author(s):
Z. P. Bazant
Publication:
Materials Journal
Volume:
84
Issue:
1
Appears on pages(s):
20-34
Keywords:
concretes; deformation; diffusion; drying; errors; extrapolation; regression analysis; shrinkage; statistical analysis; volume change; Materials Research
DOI:
10.14359/1947
Date:
1/1/1987
Abstract:
A large series of data on carefully controlled shrinkage tests of concrete involving groups of large numbers of identical specimens is reported. The data are used to compare existing shrinkage formulas in ACI, CEB-FIB, and BP models. By far, the best agreement is obtained for the BP model. Assuming that only the measured data for a certain initial period are known, predictions are made for long times and are compared with the subsequently observed shrinkage strains. In this manner, various possible statistical regression models are examined and compared. Best predictions are obtained when the shrinkage formula is fitted to test data using nonlinear optimization, then linear regression in transformed variables is used to obtain the confidence limits for long-time predictions. It is concluded that good long-time predictions of shrinkage can be obtained on the basis of shrinkage test results on 80 mm diameter cylinders for a 3-week duration. These predictions involve only the intrinsic uncertainty of the material, on which the uncertainty due to random environment, curing history, and differences in concrete composition must be superimposed for practical application.