Ferrochrome slag (FCS) is one of the main by-products generated from the smelting of ferrochrome alloy. Its utilization as aggregate can reduce the mining of natural aggregate and cost of ultra-high performance concrete (UHPC). The morphology of aggregate, maximum size (Dmax) and particle gradation are key factors that affect the properties of concrete. Herein, the morphology of FCS compared to river sand was quantitatively characterized. Aggregate gradation was optimized according to the MAA model. Influence mechanisms of aggregate morphology, Dmax, and optimized gradation on the properties of UHPC were clarified. The results indicated that large-size FCS above 2.36 mm had higher circularity and roughness, which was beneficial for enhancing the interface bonding and restraining shrinkage. Grading optimization improved the mechanical properties of UHPC (up to 14.1 % at 7 days), interface hardness by 8.6 % and reduced the autogenous shrinkage by 6.0 %. This shrinkage was further reduced by 12.0 % at larger sand-binder ratio of 1.4 due to the enhanced restraint capacity of compactly stacked aggregates. Plastic viscosity of fresh mixture increased with the decrease of Dmax, which resulted in a poor workability. Moreover, small-size FCS below 1.18 mm had less roughness and more needle-like particles, which was detrimental to the mechanical properties. The finer particles in FCS also accelerated the hydration process and led to a larger autogenous shrinkage. Thereby, it is not appropriate to adopt more small-sized porous aggregates in UHPC manufacturing. This study provides a theoretical basis for the mixing design and property improvement of UHPC with porous aggregate.

中文翻译：

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多孔骨料形态、最大尺寸和优化级配对含铬铁渣的超高性能混凝土的影响机制


铬铁渣 （FCS） 是铬铁合金冶炼产生的主要副产品之一。将其用作骨料可以减少天然骨料的开采和超高性能混凝土 （UHPC） 的成本。骨料的形态、最大尺寸 （Dmax） 和颗粒级配是影响混凝土性能的关键因素。在此，对 FCS 与河沙相比的形态进行了定量表征。根据 MAA 模型优化骨料级配。阐明了聚集体形态、Dmax 和优化级配对 UHPC 性能的影响机制。结果表明，2.36 mm 以上的大尺寸 FCS 具有较高的圆度和粗糙度，有利于增强界面结合和抑制收缩。级配优化提高了 UHPC 的机械性能（7 天时提高了 14.1%），界面硬度提高了 8.6%，自体收缩率降低了 6.0%。由于紧密堆叠骨料的约束能力增强，在更大的砂-粘合剂比 1.4 下，这种收缩率进一步降低了 12.0%。新鲜混合物的塑料黏度随着 Dmax 的降低而增加，导致加工性差。此外，小于 1.18 mm 的小尺寸 FCS 粗糙度较低，针状颗粒较多，这对机械性能不利。FCS 中较细的颗粒也加速了水合过程，并导致更大的自体收缩。因此，在 UHPC 制造中采用更多的小尺寸多孔骨料是不合适的。本研究为多孔骨料 UHPC 的混合设计和性能改善提供了理论依据。