Volume Deformation and Hydration Behavior of Ordinary Portland Cement/Calcium Sulfoaluminate Cement Blends

Abstract

Blends of ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement can be used to adjust the properties of cement for specific applications. In this study, CSA cement was used as a shrinkage-compensating admixture to improve the hydration behavior and performance (compressive strength and drying shrinkage) of OPC; the expansion behavior of the blended cement mortar was evaluate based on the saturation index of ettringite. The experimental results showed that incorporating CSA cement resulted in a delayed effect on the hydration of C3S, shortened the induction periods of the blended cement and decreased the setting time. The CSA cement also improved the early compressive strength and drying shrinkage of the OPC due to its compact microstructure. The drying shrinkage of the OPC mortar decreased by 27.8% when 6% CSA cement was used, but the formation of microcracks due to expansion could negatively impact its late compressive strength development and associated pore structures of the blends when the replacement content of CSA cement exceeded 6 wt.%. The results relevant to the expansion behavior of the CSA cements could induce crystallization stress, enhancing its resistance against shrinkage cracking.

Study on the Properties of Belite Calcium Sulfoaluminate Cement–Ordinary Portland Cement Composite Cementitious System

“…However, the content of C 2 S in CSA clinker is low, which causes a slow growth of the late-age strength [13]. Previous studies have proved [14,15] that in the CSA-OPC composite cementitious system, the CSA can effectively enhance the early-age strength of OPC, while OPC plays an important role in enhancing late-age strength. It should be noted that, when CSA and OPC form a composite cement, the compatibility should be fully considered.…”

“…Piyush et al [16] showed that CSA-OPC composite cement has microexpansion properties, but the dosage of CSA should not be higher than 30%; otherwise, the hardened cement paste will undergo overexpansion and cause cracks, which is due to the excessive crystalline stress caused by the hydration product of AFt. In addition, a too-high dosage of CSA may also result in abnormal setting or even affect the development of strength [14,17], which is frequently solved by the retarder [18].…”

Study on the Effect of Three Types of Calcium Sulfate on the Early Hydration and Workability of Self-Compacting Repair Mortar

“…The C 4 A 3 minerals in SAC and the C 3 S minerals in PC have a mutually encouraging impact on the common hydration process when sulfoaluminate cement and silicate cement are combined, hastening the hydration and setting of the combined cement [ 15 ]. Calcite alumina (AFt), aluminum gel, C-S-H gel, and a minor amount of low-sulfur hydrated calcium sulfoaluminate are the major hydration products of this composite system [ 16 , 17 , 18 ]. The early strength of the system is provided by the creation of AFt, while the development of C-S-H gels ensures the later increase in cement strength [ 13 , 19 ].…”