The use of recycled aggregate concrete (RAC) is undoubtedly on the increase and further research is required for more appropriate mix design methods. This paper presents the result of investigations into the mix design of RAC. The study examined experimentally two conventional and one unconventional mix design methods. The conventional methods include the absolute volume approach according to the American Concrete Institute (ACI) standard and the Department of Environment (DoE) concrete mix design method given by the British specification. The unconventional method is a new technique dubbed “Equivalent mortar volume (EMV)” method developed to incorporate both fine and coarse recycled aggregates for RAC production. A total of four mixes were designed as follows: (1) natural aggregate concrete regarded as the reference mix using the ACI guide, (2) RAC using the ACI guide, (3) RAC using the DoE guide and (4) blended aggregate concrete using the EMV guide. Fresh concrete properties were tested, and twenty concrete cubes and eighteen cylinders were produced accordingly and tested after curing by water immersion for density, compressive strength, tensile splitting strength and water absorption. The results showed that the EMV mix design method used significantly lesser amount of cement to achieve a RAC of higher strength than those obtained from its comparable conventional methods even with original natural aggregates. This is the first work on mix design of RAC incorporating both coarse and fine crushed concrete aggregates carried out using the EMV method. This research highlights that the ACI and DoE mix design method guides should be reviewed and amended appropriately, before adopting them for RAC mix design.

中文翻译：

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再生骨料混凝土常规和等效砂浆体积配合比设计方法的评价

再生骨料混凝土 (RAC) 的使用无疑在增加，需要进一步研究更合适的配合比设计方法。本文介绍了对 RAC 混合设计的研究结果。该研究通过实验检验了两种常规和一种非常规混合设计方法。常规方法包括根据美国混凝土协会（ACI）标准的绝对体积法和英国规范给出的环境部（DoE）混凝土配合比设计方法。非常规方法是一种新技术，被称为“等效砂浆体积 (EMV)”方法，开发用于将细粒和粗粒再生骨料混合用于 RAC 生产。总共设计了四种混合料，如下所示：(1) 使用 ACI 指南将天然骨料混凝土作为参考混合料，(2) RAC 使用 ACI 指南，(3) RAC 使用 DoE 指南和 (4) 混合骨料混凝土使用 EMV 指南。对新拌混凝土性能进行了测试，相应地制作了二十个混凝土立方体和十八个圆柱体，并在水浸固化后测试了密度、抗压强度、抗拉劈裂强度和吸水率。结果表明，即使使用原始天然骨料，EMV 混合设计方法使用的水泥用量明显少于其可比传统方法获得的更高强度的 RAC。这是使用 EMV 方法进行的混合粗碎和细碎混凝土骨料混合设计的第一项工作。本研究强调应适当审查和修改 ACI 和 DoE 混合设计方法指南，