The effects of specimen size and geometry on drying shrinkage of paste, mortar and concrete were investigated. Drying shrinkage-weight loss curves showed that ultimate shrinkage is independent of member size and shape Development of drying shrinkage over time can be accurately described using a modified Ross equation. It includes a shrinkage-half time coefficient which is linearly proportional to the volume-to-surface (V/S) ratio on a semilogarithmic scale. The equation was tested on long-term shrinkage measurements and found to be accurate for concretes of V/S ratios up to 4.2 in. and drying times later than about 30 days. The equation can be used with a single shrinkage measurement at 30 days or later to predict ultimate shrinkage. The predicted error using this approach was within (+OR-)20 percent of the measured shrinkage. This is a substantial improvement over current ACI procedures which have prediction errors of about (+OR-)63 percent. A constitutive model for predicting ultimate drying shrinkage was tested. It showed excellent agreement with experimental results of different sizes and shapes of paste, mortar and concrete. The effects of water-to-cement (W/C) ratio, curing time, and aggregate content on drying shrinkage versus relative humidity (RH) in the range of 0 to 100 percent were investigated. A relative humidity correction factor was developed in the range of 11 to 100 percent RH which is independent of W/C ratio, curing time, and aggregate content. The present findings suggest that ACI procedures may overestimate shrinkage in the RH range of 40 to 100 percent. Ultimate drying shrinkage of paste was modeled in terms of the Gibbs-Bangham and the capillary stress shrinkage mechanisms. These two mechanisms were described by two different relationships which incorporate nitrogen surface areas. The proposed equations were tested on shrinkage results obtained from the literature on well-hydrated pastes and found to be accurate.Ph.D.Civil engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/161198/1/8702673.pd
