Understanding the shrinkage compensating ability of type K expansive agent in concrete

Effects of type K expansive agent (KEA) on the hydration process and hydration product of Portland cement, morphology and permeability of hardened cement paste were investigated. Experiment results manifest that calcium hydroxide, ettringite and gypsum were produced in cement paste involving KEA. Short prismatic ettringite crystal was formed on the surface of particle other than the acicular ettringite crystal formed in capillary pore. Permeability of hydrated cement paste with KEA increased due to its enhanced porosity. Effects of KEA on concrete's mechanical property and volume stability such as autogenous shrinkage, drying shrinkage and constrained drying shrinkage were investigated, too. Experiment results show that KEA had basically no effect on the mechanical property of concrete but enhanced volume stability of concrete under the sealed or exposed condition. Excessive dosage of KEA can cause large expansion of concrete even under the water losing condition. The prolonged wet curing can alleviate this effect.