Due to the shortage of high-quality fly ash (FA) in Kenya, the successful construction of the Mombasa–Nairobi railway had to rely on the abundant natural pozzolan resources in the country instead. In the work reported in this article, concrete samples produced using 30% FA, 30% fine tuff (FT), 30% fine volcanic slag (FVS), or 10% FA and 20% FVS to replace cement were tested. The hydration activity of the FT was found to be poor. The mechanical properties and durability of the concrete made with FVS were close to those of the FA concrete and optimal performance was obtained from a mixture of FA and FVS. Mercury intrusion porosimetry, X-ray diffraction and differential thermal analysis were used for microanalysis of cementitious systems with 70% cement and 30% FA, 70% cement and 30% FT, and 70% cement and 30% FVS. The results were promising and suggested that the FVS possessed obvious secondary hydration activity and could improve the microstructure of the concrete matrix. It is therefore feasible to use natural pozzolans instead of FA to produce high-performance concrete in railway projects, which would reduce construction costs and help protect the environment.

中文翻译：

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在蒙巴萨-内罗毕铁路的高性能混凝土中使用天然火山灰

由于肯尼亚优质粉煤灰（FA）短缺，蒙巴萨-内罗毕铁路的成功建设不得不依赖该国丰富的天然火山灰资源。在本文报道的工作中，测试了使用 30% FA、30% 细凝灰岩 (FT)、30% 细火山渣 (FVS) 或 10% FA 和 20% FVS 代替水泥生产的混凝土样品。发现FT的水合活性很差。用 FVS 制成的混凝土的力学性能和耐久性与 FA 混凝土接近，并且从 FA 和 FVS 的混合物中获得了最佳性能。压汞孔隙率测定法、X 射线衍射和差热分析用于对 70% 水泥和 30% FA、70% 水泥和 30% FT 以及 70% 水泥和 30% FVS 的胶结体系进行微量分析。结果是有希望的，表明 FVS 具有明显的二次水化活性，可以改善混凝土基体的微观结构。因此，在铁路项目中使用天然火山灰代替 FA 生产高性能混凝土是可行的，这将降低建设成本并有助于保护环境。