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Brittleness and low flexural or tensile strength limit the applications of calcium aluminate cement (CAC)-based composites in high-temperature oil or gas well cementing. The reinforcement of the CAC with whiskers substantially enhances its strength and toughness and is a sophisticated approach to overcome the mechanical limitations of the CAC. In this study, the effect of calcium sulfate whiskers (CSWs) on the mechanical properties of the CAC-based composites was investigated; six cement specimens, with whisker contents of 0–5%, were prepared and tested. The results exhibited an improvement in the compressive and tensile strengths and the toughness of the whisker-reinforced samples over the control samples. The compressive strength of the samples cured at 50°C and then subjected to high temperature (500°C) increased by 25·93% at 14 d and the tensile strength increased by 93·63% with the addition of 4% CSW to the cement. The cement slurry properties were stable when 0–5% of CSWs was added. Finally, X-ray diffraction and scanning electron microscopy were used to determine the phase compositions and micromorphology of the cement composites. The results indicated that the CSWs improved the toughness of the cement binders by forming a stable phase and deflecting cracks in the cement matrix.

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