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<p>Beyond clay type, the calcium sulfate source plays a critical role in Portland cement hydration. However, its influence remains insufficiently understood in cements based on calcined clay and limestone (LC<sup>3</sup>). In this study, LC<sup>3</sup> cement pastes incorporating an ultrafine calcined kaolinitic clay, with high specific surface area, were prepared using two calcium sulfate sources, gypsum and hemihydrate, and evaluated in the presence of a superplasticizer. Electrical conductivity, zeta potential, isothermal calorimetry, rheological properties, and mechanical strength were measured over time. The results showed that as PCE was incorporated into LC<sup>3</sup> cements, the zeta potential became less negative and required an optimized sulfate content (3.5% SO<sub>3</sub>) to ensure adequate hydration and rheology. The hemihydrate accelerates all hydration kinetics and increases the yield stress and viscosity of the pastes, compared to LC<sup>3</sup> cements produced with gypsum. Consequently, the compressive strength of the paste was significantly affected by this mineralogical change in calcium sulfate.</p>

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Impact of calcium sulfate source on hydration, rheology and mechanical strength of LC3 cements in the presence of superplasticizer

  • 期刊论文

  • 发表日期：

    2026年2月4日

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  • Francisco Roger Carneiro Ribeiro,
  • Paulo Ricardo de Matos,
  • Ana Paula Kirchheim

摘要

Beyond clay type, the calcium sulfate source plays a critical role in Portland cement hydration. However, its influence remains insufficiently understood in cements based on calcined clay and limestone (LC3). In this study, LC3 cement pastes incorporating an ultrafine calcined kaolinitic clay, with high specific surface area, were prepared using two calcium sulfate sources, gypsum and hemihydrate, and evaluated in the presence of a superplasticizer. Electrical conductivity, zeta potential, isothermal calorimetry, rheological properties, and mechanical strength were measured over time. The results showed that as PCE was incorporated into LC3 cements, the zeta potential became less negative and required an optimized sulfate content (3.5% SO3) to ensure adequate hydration and rheology. The hemihydrate accelerates all hydration kinetics and increases the yield stress and viscosity of the pastes, compared to LC3 cements produced with gypsum. Consequently, the compressive strength of the paste was significantly affected by this mineralogical change in calcium sulfate.