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<p>This study aims to evaluate the performance of Libyan bentonite as a sustainable alternative to supplementary cementitious materials and the effect of heat treatment on its properties. Bentonite, sourced from the Umm al-Razam area in Libya, was mechanically activated through grinding and thermal treatment at 200&#xa0;°C, 400&#xa0;°C, 600&#xa0;°C, and 800&#xa0;°C and used to replace cement at 5%, 10%, and 20% levels. Comprehensive microstructural and mineralogical characterisation of raw and calcined bentonite was performed using scanning electron microscopy and X-ray diffraction (XRD). The performance of the modified mortars was then evaluated using standard tests, including strength activity index, soundness, workability, compressive strength, and ultrasonic pulse velocity (UPV) measurements conducted in compliance with ASTM standards. The results showed that the heat treatment leads to noticeable changes in the structure of the bentonite, especially at 800&#xa0;°C, where the particles become more agglomerated and the surfaces become denser. XRD results also revealed gradual mineralogical transformations with increasing temperatures, most notably the disappearance of kaolinite and montmorillonite minerals at higher temperatures, which enhances pozzolanic activity. The study indicated that the heat-treated Libyan bentonite meets the requirements of ASTM C618 (2019)&#xa0;for natural pozzolan as shown by chemical analysis and Strength Activity Index (SAI), exceeds the minimum requirement of 75%, with the SAI of the 800&#xa0;°C sample reaching 136.2% in 28&#xa0;days. In addition, high proportions of bentonite reduced workability, but intermediate curing temperatures (400–600&#xa0;°C) mitigated this effect. Curing at 800&#xa0;°C improved workability, bringing the consistency closer to the reference mix. Blends containing 5–10% bentonite cured (400–800&#xa0;°C) showed a significant improvement, with a 20% blend at 800&#xa0;°C recording a 35% increase in 28&#xa0;days. UPV values decreased as the bentonite increased, indicating a decrease in homogeneity, but heat treatment improved the values over time. The observation demonstrates the high potential of thermally activated bentonite as a sustainable supplementary cementitious material, contributing to reduced cement consumption while maintaining acceptable performance characteristics in mortar applications.</p>

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Thermally Activated Libyan Bentonite for Sustainable Mortar: Microstructural and Mechanical Performance

  • 期刊论文

  • 发表日期：

    2025年6月24日

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  • Maha F. Hamid,
  • Mahmoud A. T. Khatab,
  • Musab Alhawat,
  • Mohamad Gabar,
  • Aeid A. Abdulrazeg

摘要

This study aims to evaluate the performance of Libyan bentonite as a sustainable alternative to supplementary cementitious materials and the effect of heat treatment on its properties. Bentonite, sourced from the Umm al-Razam area in Libya, was mechanically activated through grinding and thermal treatment at 200 °C, 400 °C, 600 °C, and 800 °C and used to replace cement at 5%, 10%, and 20% levels. Comprehensive microstructural and mineralogical characterisation of raw and calcined bentonite was performed using scanning electron microscopy and X-ray diffraction (XRD). The performance of the modified mortars was then evaluated using standard tests, including strength activity index, soundness, workability, compressive strength, and ultrasonic pulse velocity (UPV) measurements conducted in compliance with ASTM standards. The results showed that the heat treatment leads to noticeable changes in the structure of the bentonite, especially at 800 °C, where the particles become more agglomerated and the surfaces become denser. XRD results also revealed gradual mineralogical transformations with increasing temperatures, most notably the disappearance of kaolinite and montmorillonite minerals at higher temperatures, which enhances pozzolanic activity. The study indicated that the heat-treated Libyan bentonite meets the requirements of ASTM C618 (2019) for natural pozzolan as shown by chemical analysis and Strength Activity Index (SAI), exceeds the minimum requirement of 75%, with the SAI of the 800 °C sample reaching 136.2% in 28 days. In addition, high proportions of bentonite reduced workability, but intermediate curing temperatures (400–600 °C) mitigated this effect. Curing at 800 °C improved workability, bringing the consistency closer to the reference mix. Blends containing 5–10% bentonite cured (400–800 °C) showed a significant improvement, with a 20% blend at 800 °C recording a 35% increase in 28 days. UPV values decreased as the bentonite increased, indicating a decrease in homogeneity, but heat treatment improved the values over time. The observation demonstrates the high potential of thermally activated bentonite as a sustainable supplementary cementitious material, contributing to reduced cement consumption while maintaining acceptable performance characteristics in mortar applications.