The feasibility of using natural rice husk ash in structural concrete (part II): durability

Abstract Waste incorporated in construction materials should be used, whenever possible, without processing in order to avoid environmental impact and additional costs. Rice husk ash (RHA) is a pozzolan that must be ground before use in order to increase its fineness and reactivity with Portland cement when it is used as a cementitious material. This study investigates natural rice husk ash (NRHA), without processing, replacing 15% of Portland cement, in mass. The NRHA was ground together with the aggregates in the mixer drum. Part I of this study presented the test results regarding microstructure, mechanical strength and shrinkage, including 25% content; Part II presents durability test results (carbonation, chloride penetration, electrical resistivity, water absorption, oxygen permeability and alkali-silica reaction - ASR), compared with a reference concrete with 100% cement and with ground RHA (GRHA). The results showed that it is feasible to use 15% NRHA in concrete, as it presents higher performance when cement with pozzolans is used, and near or even better performance than GRHA mixtures for most of the variables analysed. The study concludes that 15% of NRHA in structural concrete is feasible and produces a more sustainable material.

摘要 用于建筑材料中的废弃物应尽可能不经处理直接利用，以规避环境影响与额外成本。稻壳灰（Rice Husk Ash, RHA）是一种火山灰材料，作为胶凝材料使用时，需经粉磨以提升其细度与对硅酸盐水泥的反应活性。本研究针对未经处理的天然稻壳灰（Natural Rice Husk Ash, NRHA）展开试验，以其按质量占比15%替代硅酸盐水泥，且将NRHA与集料一同在搅拌筒内进行粉磨。本研究第一部分报告了微观结构、力学强度与收缩性的试验结果，其中包含25%掺量的NRHA；第二部分则以100%水泥的基准混凝土及磨细稻壳灰（Ground RHA, GRHA）混凝土为对照，给出耐久性试验结果，涵盖碳化、氯离子渗透、电阻率、吸水率、氧气渗透性及碱-硅酸反应（Alkali-Silica Reaction, ASR）。试验结果表明，在混凝土中掺加15%的NRHA具备可行性：当使用掺有火山灰材料的水泥时，NRHA混凝土表现出更优的性能，且在绝大多数测试指标上，其性能接近甚至优于GRHA混凝土组配。本研究最终得出结论：在结构混凝土中掺加15%的NRHA具备可行性，且可制备出更具可持续性的建筑材料。