Early Hydration Heat of Calcium Sulfoaluminate Cement with Influences of Supplementary Cementitious Materials and Water to Binder Ratio

Jun Zhang,Yuzhang Liu,Guoju Ke

doi:10.3390/ma14030642

Jun Zhang, Yuzhang Liu + Show 1 more

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https://doi.org/10.3390/ma14030642

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Abstract

Compared to ordinary Portland cement (OPC), calcium sulfoaluminate cement (CSA) displays very early-age strength and faster heat-releasing rate during hydration. In the present paper, the early hydration heat of CSA paste with influences of supplementary cementitious materials (SCMs) and water to cement (or binder) ratio (w/c) is systematically studied by measuring the heat-releasing rate using a calorimeter. Three traditional SCMs—silica fume (SF), fly ash (FA) and ground granulated blast furnace slag (SL)—were used in the study. A water to cement or binder ratio (w/c) between 0.19 and 0.73 was used in the mixtures. The results show that three exothermic peaks were presented during hydration—dissolution exothermic peak and two reaction exothermic peaks. With the w/c of 0.3, the first and second reaction peaks of the CSA paste are as high as 17.8 times and 4.1 times that of OPC paste, and the occurring time is much earlier than that of the OPC paste. The second reaction peak appears earlier, and the third reaction peak appears later in the pastes with addition of SF than in those without SF. Decreasing w/c can greatly reduce the two reaction peaks of the paste, and it looks that there is a critical value of w/c between 0.24 and 0.30. Above the critical value, the effect of w/c is minor, and below that the influence is obvious. An optimal use of SCMs in CSA pastes under different w/c can greatly decrease the heat releasing while maintaining the required strength.

Highlights

Calcium sulfoaluminate cement (CSA) has lower CO2 emission and firing temperature during production compared with ordinary Portland cement (OPC) [1]
In order to identify the crystalline phases in the hydration products of the CSA paste and, further, to analyze the effect of supplementary cementitious materials (SCMs) on the hydration of CSA and compare with OPC, the cement paste of mixtures Nos. 1 to 6 in Table 2 were tested at 3 days after mixing by X-ray diffraction (XRD) and TG-DTG
For CSA paste, the crystalline phase in the hydration products is ettringite after 3-days hydration

Summary

Introduction

Calcium sulfoaluminate cement (CSA) has lower CO2 emission and firing temperature during production compared with ordinary Portland cement (OPC) [1]. Recent studies have revealed that concrete made with CSA displays relatively low shrinkage, especially drying shrinkage, compared to OPC concrete [2,3,4]. CSA may be chosen as one of the most promising low CO2 alternatives to OPC in view of the sustainable development and long-term durability of modern concrete [5,6,7,8,9,10]. A number of existing studies have shown that a higher releasing heat of cement hydration will adversely affect the long-term performance of the structures [11,12,13,14]. A higher temperature rise in large-volume concrete structures may lead to the potential of delayed expansion of ettringite (AFt) [15,16,17,18]

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