Complete replacement of mineral raw materials in asphalt concrete by steel & iron slags based on cascade utilization strategy

Abstract

Steel slag and iron slag, generating during steelmaking process, are two typical solid wastes. Currently, only partial steel slag is used to replace coarse aggregates in asphalt concrete. To further increase the reuse efficiency of steel and iron slag, this study evaluated the feasibility of using steel slag and iron slag with different sizes to completely replace the mineral raw materials in asphalt concrete. Two main studies were conducted. First, the material characteristics of steel slag and iron slag were analyzed using some microscopic analysis techniques of materials and test methods of the basic technical indexes of the aggregate. A suitable size combination scheme of steel slag and iron slag to completely replace mineral raw materials in asphalt concrete was proposed. Second, the feasibility of the proposed scheme was verified. All asphalt concretes were designed using the Superpave method. The mixing procedure of the asphalt mixture was modified, and the main engineering performances of the asphalt concrete were checked. The results suggest that the cementitious activity of the steel slag makes steel slag fine aggregate (SSFA) consolidated, and some technical indexes of the iron slag coarse aggregate (ISCA) are not good. Hence, SSFA and ISCA cannot be used to directly replace mineral raw materials in asphalt concrete. Asphalt concrete, with mineral raw materials completely replaced by steel slag coarse aggregate (SSCA), iron slag fine aggregate (ISFA), and steel slag powder (SSP) filler, mixed with SBS-modified asphalt under a modified mixing procedure, shows satisfactory engineering performances. Some performances are significantly better than those of limestone-based asphalt concrete. The high-temperature flow number (Fn) and low-temperature fracture energy are 18% and 23% higher, respectively. This work has proved that the cascade utilization of steel slag and iron slag in asphalt concrete can be done based on their size combination. 钢渣和铁渣是伴随炼钢产生的２种典型固废。目前部分钢渣已被再生用于替代沥青混凝土中的粗骨料。为进一步提高钢渣和铁渣的再利用效率，探讨了采用不同粒径的钢渣和铁渣１００％替代沥青混凝土矿料的可行性。首先基于材料微观分析技术以及集料技术指标测试方法，揭示不 同粒径钢渣和铁渣的材料特征，确定适合其１００％替代沥青混凝土矿料的粒径搭配方案；然后验证方案的可行性，采用Ｓｕｐｅｒｐａｖｅ方法设计沥青混凝土，优化拌和工艺，检验沥青混凝土的主要工程性能。结果表明：钢渣细集料受自身矿物胶凝活性的影响易固结成块，铁渣粗集料的技术指标不佳，因而两者不宜直接替代沥青混凝土矿料使用。采用钢渣粗集料、铁渣细集料和钢渣粉１００％替代常用的石灰石矿料，结合使用高黏度的ＳＢＳ改性沥青和改进型混合料拌和工艺，可制备出性能优良的沥青混凝土，且部分性能指标优势显著：其高温下的流动次数（Ｆｎ）以及低温下的断裂能分 别提高了１８％和２３％。可见，将不同粒径的钢渣和铁渣搭配使用可实现两者在沥青混凝土中的梯级全利用。