Chloride penetration in shrinkage-compensating cement concretes

Shrinkage-compensating cement (a.k.a., Type K expansive agent) is a calcium sulfoaluminate cement with the ability of providing volume expansion during early age, primarily due to the formation of ettringite. Despite the past studies on the strength, shrinkage, and hydration of shrinkage-compensating cement concretes, there was no systematic investigation to understand the performance of this type of concrete under exposure to aggressive agents, particularly chloride ions. To address this gap, a holistic testing program was established in this study to evaluate the strength, dimensional stability, and transport properties of concretes made with various dosages of Type K expansive agent. This included compressive strength, drying shrinkage, rapid chloride penetration, electrical resistivity, rapid chloride migration, and absorption tests. Both helium and mercury intrusion porosimetry analyses were also performed to further explain the experimental test results with the findings related to the distribution of pores. The results of this study confirmed the benefits of using Type K expansive agent (up to a certain dosage) in terms of increased compressive strength and reduced drying shrinkage. However, it was revealed that the permeability of concretes made with this type of cement is adversely affected. This issue was addressed by the identification of optimal dosages of supplementary cementitious materials, including fly ash and silica fume. Upon completing the necessary experiments on the improved mixtures, this study reported how low-shrinkage concretes with low susceptibility to chloride penetration can be developed with the promise of application in a wide variety of civil infrastructures exposed to harsh environmental conditions.