Unrestrained Short-Term Shrinkage of Calcium-Hydroxide-Based Alkali-Activated Slag Concrete

A total of 34 concrete mixtures were tested to examine the unrestrained shrinkage behavior of calcium-hydroxide (Ca(OH)(2))-based alkali-activated (AA) ground-granulated blast-furnace slag (GGBS) concrete. The main parameters investigated were water-binder ratio (w/b), unit water content (W-c), and fine-aggregate-to-total-aggregate ratio (S/A). From the regression analysis of test results, the comprehensive basic design equations were formulated to predict the 28-day shrinkage strain and time function, which can be expanded to long-term shrinkage strain or ultimate results of Ca(OH)(2)-based AA-GGBS concrete. The test results showed that the increasing rate of shrinkage strain against age and the amount of 28-day shrinkage strain of Ca(OH)(2)-based AA-GGBS concrete were significantly affected by the w/b, Wc, and the type of auxiliary activators, while they were minimally influenced by the S/A. When the w/b was higher than 0.35, a higher 28-day shrinkage strain was observed in Ca(OH)(2)- and Na2CO3-activated GGBS concrete than in Ca(OH)(2)- and Na2SiO3-activated GGBS concrete. The proposed equations showed a significantly better accuracy in the test results than the existing empirical models of which agreement was dependent on the mixing proportions of the concrete tested.