Abstract
Hydration characteristics and mechanical properties of calcium sulphoaluminate (CSA) cement with different contents of CaCO3 and gypsum under NaCl solutions were studied, using the testing methods of isothermal calorimetry, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), linear shrinkage, and compressive strength. Results show that CaCO3 can promote hydration and reduce the hydration heat of CSA cement. The reaction between gypsum and C4A3 releases a large quantity of heat in the initial hydration period; however, over 3 days of accumulation, the level of hydration heat is reduced. Under NaCl solutions, the aluminate phase has difficulty reacting with CaCO3 to form carbonate phase but combines with chloride ions to form Friedel’s salt. On the contrary, gypsum reduces aluminate phase, and the content of Friedel’s salt is also reduced. Furthermore, CaCO3 and gypsum both increase the total porosity of the CSA cement paste under NaCl solutions during the early curing phase, and over the long-term, pore structure is also optimized. CaCO3 and gypsum reduce the linear shrinkage of CSA cement paste under NaCl solutions. Overall, the compressive strength of CSA cement is reduced with the addition of CaCO3, and the trend will be sharper with the increase in CaCO3. However, when it comes to gypsum, the compressive strength is almost the same during early curing, but in the long-term, compressive strength improves. Essentially, the compressive strength of CSA cement mortar with CaCO3 and gypsum will improve under NaCl solutions.
Highlights
With the exploration of marine resources and the development of the marine industry, requirement for the construction of offshore infrastructure is increasing
The heat flow and total cumulated heat curves of Calcium sulphoaluminate (CSA) cement and the mixed samples with CaCO3 or gypsum at a w/c of 0.5 over 72 h are shown in Figures 4 and 5
It is clear that the hydration of CSA cement mixed with CaCO3 or gypsum can be divided into five stages [37]: (1) pre-induction period; (2) induction period; (3) acceleration period; (4) retarding period; and (5) stable period
Summary
With the exploration of marine resources and the development of the marine industry, requirement for the construction of offshore infrastructure is increasing. During the last two centuries, ordinary Portland cement (OPC) was widely used in marine engineering construction. The total amount of energy consumption and carbon dioxide emission during the production of OPC was huge. Demand for new low-carbon cementitious materials with high corrosion resistance is increasing. Calcium sulphoaluminate (CSA) cement is a kind of cementitious material with low carbon emissions and low energy consumption, as well as good performance in resisting seawater erosion. It has been drawing great interest among industry experts and scientists since the 1970s [3,4,5,6,7]. CSA cement was independently researched and invented by China’s
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