Title:
Soil Physics Principles Validated for Use in Predicting Unsaturated Moisture Movement in Portland Cement Concrete
Author(s):
Bonnie Mae Savage and Donald J. Janssen
Publication:
Materials Journal
Volume:
94
Issue:
1
Appears on pages(s):
63-70
Keywords:
Soil physics; moisture; concretes;
DOI:
10.14359/286
Date:
1/1/1997
Abstract:
Moisture movement in concrete is of primary concern for many aspects of long-term concrete performance, but most researchers have concentrated on saturated hydraulic conductivity (permeability) when studying concrete. While the field of soil physics has made considerable advancement in the modeling of unsaturated moisture movement in soil and other porous solids, differences in the pore systems between concrete and soils have prevented general acceptance of the application of soil physics principles to concrete. The purpose of the work described below was to determine if soil physics principles can be applied to unsaturated moisture movement in concrete. A desorption environment, assuming 1-D moisture movement, was imposed on concrete specimens from four different mix proportions. Five different desorption environments were used in the experimental work: 97, 92, 75, 53, and 31 percent relative humidity, respectively. Each represented a different constant boundary condition. Intermediate and equilibrium moisture contents were determined using mass loss measurements, and a closed-form solution was developed using van Genuchten moisture characteristics parameters along with other fundamental physical relationships. Validation was completed by comparing experimentally determined moisture contents against those predicted by the closed-form analytical solution. Prediction of experimentally determined moisture contents was very good, with the percentage difference between measured and predicted values being less than 10 percent for all combinations of boundary conditions and mix proportions. Variations in most cases were 5 percent or less. Hence, the success of the general prediction equation indicated a valid application of soil physics principles to unsaturated moisture movement in PCC.