Shrinkage characteristics of calcium sulphoaluminate cement concrete

Abstract

Shrinkage is an important scientific and engineering issue in the study of cement concrete, involving the risk of cracking, safety and durability of the structure. For Ordinary Portland cement (OPC) concrete, capillary tension, represented by internal relative humidity, is normally considered as the main driving force of shrinkage. However, for calcium sulphoaluminate cement (CSA) concrete, it may be completely different. In the present paper, shrinkage performance of normal and high strength CSA concrete is experimentally investigated. Characteristics of shrinkage of CSA concrete comparing to OPC concrete are analyzed and the possible mechanisms are explored. The results show that development of shrinkage of CSA concrete since set obeys two-stage mode, fast growth stage before 2 h and a slowly developing stage after 2 h. In the initial 2 h after set of concrete, more than 85% of the total shrinkage at 28 days is finished. Development of internal relative humidity of CSA concrete also undergoes a moisture saturated stage and a decline stage since casting. In humidity decline stage, less than 15% of the shrinkage of 28 days is developed in the later age although the internal relative humidity is obviously decreased as well in this period. Water content and chemical shrinkage test further confirm that faster water consumption and larger chemical shrinkage are expected for CSA paste and also for CSA concrete, comparing to that of OPC paste or concrete. Hydration particle size test results reveal that the deformability of hydration products of CSA under drying is less than that of hydration products of OPC. This may partially explain why low drying shrinkage of CSA concrete is observed.