Within the last few years, major U.S. admixture suppliers have introduced a new category of chemical admixtures—shrinkage-reducing admixtures (SRAs). These products are aimed at significantly reducing the amount of drying shrinkage that occurs over time in concrete. If shrinkage is reduced, proponents argue that reductions in cracking must follow. Applications targeted by suppliers of the admixture have been flatwork, parking structures, bridge decks and environmental structures such as tanks.
Testing of SRAs by the manufacturers certainly shows them to be effective in reducing drying shrinkage. But as effective as these products seem to be, it's important to interpret the manufacturer’s data carefully since each concrete is different, and the amount of shrinkage reduction will depend upon the materials used. Questions to pose before specifying or using an SRA include:
- What are the effects on fresh and hardened concrete properties?
- What is the effect on durability?
- What is the impact on cost?
- How do the results of shrinkage testing apply to actual structures?