Mix design for concrete specimens per m3.

The intent of this study is to explore the physical properties and long-term performance of concrete made with metakaolin (MK) as a binder, using microsilica (MS) and nanosilica (NS) as substitutes for a portion of the ordinary Portland cement (OPC) content. The dosage of MS was varied from 5% to 15% for OPC-MK-MS blends, and the dosage of NS was varied from 0.5% to 1.5% for OPC-MK-NS blends. Incorporation of these pozzolans accelerated the hardening process and reduced the flowability, consistency, and setting time of the cement paste. In addition, it produced a denser matrix, improving the strength of the concrete matrix, as confirmed by scanning electron microscopy and X-ray diffraction analysis. The use of MS enhanced the strength by 10.37%, and the utilization of NS increased the strength by 11.48% at 28 days. It also reduced the penetrability of the matrix with a maximum reduction in the water absorption (35.82%) and improved the resistance to the sulfate attack for specimens containing 1% NS in the presence of 10% MK. Based on these results, NS in the presence of MK can be used to obtain cementitious structures with the enhanced strength and durability.本研究旨在探究以偏高岭土（metakaolin, MK）作为胶凝材料，搭配微硅粉（microsilica, MS）与纳米二氧化硅（nanosilica, NS）替代部分普通硅酸盐水泥（ordinary Portland cement, OPC）所制备混凝土的物理性能与长期性能。针对OPC-MK-MS复合体系，MS的掺量范围设定为5%~15%；针对OPC-MK-NS复合体系，NS的掺量范围设定为0.5%~1.5%。掺入上述火山灰材料可加速水泥浆体的硬化进程，同时降低其流动度、稠度与凝结时间。此外，该复合体系可形成更为致密的基体结构，进而改善混凝土基体的强度性能，该结论经扫描电子显微镜（scanning electron microscopy, SEM）与X射线衍射（X-ray diffraction, XRD）分析得以验证。试验结果表明，掺入MS可使混凝土28天强度提升10.37%，而掺入NS可使28天强度提升11.48%。同时，该复合基体的渗透性有所降低，其中吸水率的最大降幅可达35.82%；当MK掺量为10%且NS掺量为1%时，试件的抗硫酸盐侵蚀性能得到显著改善。基于上述试验结果，在偏高岭土存在的条件下掺入纳米二氧化硅，可制备出强度与耐久性均得到提升的胶凝结构体。