Hydraulic binder obtained from recycled cement and sand powder

Abstract Environmentally eco-efficient concrete is currently a popular choice of construction material. Reviewing relevant literature indicates that heating of cement paste can remove hydrating water, and that quartz sand of appropriate granulometry can act as a supplementary cementitious material; however, there have been virtually no reports on the reuse of these materials as alternative binders. This work evaluates the phases present in cementitious compounds produced with binders obtained by thermomechanically treating cement pastes with and without a 15% substitution of quartz sand powder (specific surface area 37.4 m²/g), referred to as RCQ and recycled cement RC, respectively. Testing included thermogravimetric analysis (performed with stripped gases), X-ray diffraction, and scanning electron microscopy with phase identification. The obtained data indicated RC cement paste possesses a predominantly ettringite microstructure, whereas the presence of calcium hydroxide and hydrated calcium silicate predominates in RCQ paste.摘要：生态环保型高效混凝土是当前主流的建筑材料之一。相关文献调研结果显示，水泥浆体经加热可脱除水化水，且粒度适宜的石英砂可作为辅助胶凝材料（supplementary cementitious material）；但目前几乎尚无将此类材料作为替代胶凝材料回用的公开报道。本研究对两种胶凝复合材料的物相展开表征：分别以经热机械处理的水泥浆体制备的胶凝剂——其中一组掺加15%替代量的石英砂粉（比表面积为37.4 m²/g，记为RCQ），以及未掺石英砂粉的热机械处理水泥浆体制备的胶凝剂（记为再生水泥RC）。测试手段包括脱气热重分析、X射线衍射（X-ray diffraction）分析，以及具备物相鉴定功能的扫描电子显微镜（scanning electron microscopy）分析。所得测试数据表明，RC水泥浆体的微观结构以钙矾石为主，而RCQ水泥浆体则以氢氧化钙和水化硅酸钙为主要物相。