Meddah Mohammed Seddik, Abdel-Gawwad Hamdy, Al Owaisi Munira
College of Engineering, Sultan Qaboos University, Al-Khod, 123, Oman.
Raw Building Materials Research Institute, Housing and Building National Research Center, Cairo, Egypt.
Sci Rep. 2024 Oct 11;14(1):23855. doi: 10.1038/s41598-024-74885-5.
This study focuses on the role of low-quality calcined Fanja (FNJ) clay in enhancing the behavior of cured cement mortar (CM) and its resistivity to chloride and sulfuric acid attack. Ordinary Portland cement was replaced with different quantities (10%, 25%, 35%, and 50% by weight) of FNJ, which was calcined at different temperatures (620 °C, 760 °C, and 900 °C). After 28 days of curing, all the hardened mortars were immersed in 5% sulfuric acid for up to 12 weeks. Additionally, a rapid chloride permeability test was conducted on the 91-day cured CM and CM-FNJ samples to evaluate the affinity of calcined FNJs to retard the chloride diffusion into CM. The results showed that all samples containing FNJ900 showed better physical and mechanical properties than the control sample, while CM with NFJ760 recorded nearly similar performance as CM-NFJ900. In contrast, the CM-FNJ620 mixtures showed lower properties than those of other mixtures. In addition to the pozzolanic reactivity of the calcined clay, the presence of hematite in the calcined clay strongly contributed to increasing the mechanical properties of the hardened mortar through forming calcium ferrosilicate hydrate binding phase, as confirmed by X-ray diffraction. Moreover, the existence of hematite increased the resistivity of CM against sulfuric acid attack as it acts as a buffer for an acidic medium. Compared with CM-FNJ900, the CM-FNJ760 is recommended for use as it exhibited a higher strength activity index and comparable resistance to accelerated chloride diffusion and sulfuric acid accompanied by lower energy demand and lower CO emission, achieving the concept of 'sustainability'.
本研究聚焦于低质量煅烧法贾（FNJ）黏土在增强固化水泥砂浆（CM）性能及其对氯离子和硫酸侵蚀的抗性方面的作用。用不同数量（按重量计10%、25%、35%和50%）在不同温度（620℃、760℃和900℃）下煅烧的FNJ替代普通硅酸盐水泥。养护28天后，将所有硬化砂浆浸泡在5%的硫酸中长达12周。此外，对养护91天的CM和CM-FNJ样品进行了快速氯离子渗透性试验，以评估煅烧FNJ抑制氯离子扩散到CM中的能力。结果表明，所有含有FNJ900的样品均表现出比对照样品更好的物理和力学性能，而含有NFJ760的CM表现出与CM-NFJ900几乎相似的性能。相比之下，CM-FNJ620混合物的性能低于其他混合物。除了煅烧黏土的火山灰反应性外，煅烧黏土中赤铁矿的存在通过形成铁硅酸钙水合物结合相，对提高硬化砂浆的力学性能有很大贡献，这一点通过X射线衍射得到证实。此外，赤铁矿的存在提高了CM对硫酸侵蚀的抗性，因为它可作为酸性介质的缓冲剂。与CM-FNJ900相比，推荐使用CM-FNJ760，因为它具有更高的强度活性指数，在加速氯离子扩散和抗硫酸方面具有相当的抗性，同时能源需求更低，二氧化碳排放量更低，实现了“可持续性”的概念。
