| Hydration is the chemical reaction of cement and water in concrete which produces hydrated compounds such as C-S-H and Ca (OH) 2. These products have a smaller specific volume than the constituents which results in chemical shrinkage. At low water cement ratios external water will not be able to replace the lost volume which results in autogenous shrinkage. Even when drying is prevented, internal shrinkage can occur. In some cases, this can lead to internal micro-cracking. To measure chemical shrinkage the cement paste has to be water saturated to replace the volume decrease due to hydration. Chemical shrinkage can be measured using dilatometry which is based on the direct measurement of the length or volume change of water and is considered a quick test for rates of hydration. The National Institute of Standards and Technology (NIST) has made some efforts to develop a standard test method to evaluate the rate and extent of chemical shrinkage. ASTM C1608-05 was developed and will be evaluated, improvements implemented and sensitivity as well as ruggedness tests performed. Tests were also run at low water cement ratios to look at the effects of chemical shrinkage. |
