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<p>Coral concrete, primarily composed of natural coral aggregates, has attracted increasing attention as a sustainable building material due to its lightweight nature, high strength potential, and environmental benefits. However, existing studies on the influence of temperature on its carbonation mechanism remain limited. This study investigates the carbonation behavior of coral concrete under different temperatures using low-field nuclear magnetic resonance (NMR) and ultrasonic testing to evaluate porosity and wave velocity. These results collectively reveal the influence of temperature on internal carbonation-induced cracking. In addition, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the internal reaction products and clarify the carbonation mechanism. The results show that elevated temperature (e.g., 30&#xa0;°C) significantly accelerates carbonation, leading to improved mechanical properties and durability. Carbonation products enhance material densification, while also inducing pore structure evolution: the proportion of small pores (&lt; 20&#xa0;nm) decreases, whereas large pores (&gt; 200&#xa0;nm) increase. This suggests that carbonation products initially fill micropores, while later CO₂ diffusion may promote pore enlargement or increased connectivity. SEM and XRD results indicate that at 30&#xa0;°C, carbonation promotes the transformation of hydration products (CH, C–S–H) into aragonite-type calcium carbonate, contributing to initial densification. However, subsequent formation of sulfate minerals (e.g., gypsum) causes slight volume expansion (0.15–0.3%), increasing the risk of microcracking. NMR and ultrasonic results further show that the carbonation process is governed by a competition between pore filling and microcrack propagation. Pore filling dominates the reduction in total porosity, while microcrack development, especially at lower temperatures, primarily reduces wave velocity. The continued decrease in wave velocity is not due to insufficient pore filling but rather to the adverse effect of microcracks on ultrasonic propagation, which outweighs the benefits of densification, ultimately contributing to reduced macroscopic compressive strength and phase transformation behavior.</p>

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Investigation of the carbonation mechanism of coral concrete under different temperature conditions

  • 期刊论文

  • 发表日期：

    2026年7月18日

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  • Peiyang Ying,
  • Qing Wu,
  • Rongrong Ying,
  • Muhammad Akbar,
  • Hongji Cao,
  • Lang Zhang,
  • Jianming Yang

摘要

Coral concrete, primarily composed of natural coral aggregates, has attracted increasing attention as a sustainable building material due to its lightweight nature, high strength potential, and environmental benefits. However, existing studies on the influence of temperature on its carbonation mechanism remain limited. This study investigates the carbonation behavior of coral concrete under different temperatures using low-field nuclear magnetic resonance (NMR) and ultrasonic testing to evaluate porosity and wave velocity. These results collectively reveal the influence of temperature on internal carbonation-induced cracking. In addition, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze the internal reaction products and clarify the carbonation mechanism. The results show that elevated temperature (e.g., 30 °C) significantly accelerates carbonation, leading to improved mechanical properties and durability. Carbonation products enhance material densification, while also inducing pore structure evolution: the proportion of small pores (< 20 nm) decreases, whereas large pores (> 200 nm) increase. This suggests that carbonation products initially fill micropores, while later CO₂ diffusion may promote pore enlargement or increased connectivity. SEM and XRD results indicate that at 30 °C, carbonation promotes the transformation of hydration products (CH, C–S–H) into aragonite-type calcium carbonate, contributing to initial densification. However, subsequent formation of sulfate minerals (e.g., gypsum) causes slight volume expansion (0.15–0.3%), increasing the risk of microcracking. NMR and ultrasonic results further show that the carbonation process is governed by a competition between pore filling and microcrack propagation. Pore filling dominates the reduction in total porosity, while microcrack development, especially at lower temperatures, primarily reduces wave velocity. The continued decrease in wave velocity is not due to insufficient pore filling but rather to the adverse effect of microcracks on ultrasonic propagation, which outweighs the benefits of densification, ultimately contributing to reduced macroscopic compressive strength and phase transformation behavior.