Liu Mengtong, Liu Hui, Hua Minqi, Chen Chunhong, Wang Xinjie, Guo Xiang, Ma Tianyu
School of Urban Construction, Changzhou University, 21 Gehu Middle Road, Wujin District, Changzhou 213164, China.
School of Civil Engineering & Architecture, Wuhan University of Technology, Wuhan 430070, China.
Materials (Basel). 2024 Apr 23;17(9):1944. doi: 10.3390/ma17091944.
Geopolymer concrete (GPC) represents an innovative green and low-carbon construction material, offering a viable alternative to ordinary Portland cement concrete (OPC) in building applications. However, existing studies tend to overlook the recyclability aspect of GPC for future use. Various structural applications necessitate the use of concrete with distinct strength characteristics. The recyclability of the parent concrete is influenced by these varying strengths. This study examined the recycling potential of GPC across a spectrum of strength grades (40, 60, 80, and 100 MPa, marked as C40, C60, C80, and C100) when subjected to freeze-thaw conditions. Recycling 5-16 mm recycled geopolymer coarse aggregate (RGAs) from GPC prepared from 5 to 16 mm natural coarse aggregates (NAs). The cementitious material comprised 60% metakaolin and 40% slag, with natural gravel serving as the NAs, and the alkali activator consisting of sodium hydroxide solution and sodium silicate solution. The strength of the GPC was modulated by altering the Na/Al ratio. After 350 freeze-thaw cycles, the GPC specimens underwent crushing, washing, and sieving to produce RGAs. Subsequently, their physical properties (apparent density, water absorption, crushing index, and attached mortar content and microstructure (microhardness, SEM, and XRD) were thoroughly examined. The findings indicated that GPC with strength grades of C100, C80, and C60 were capable of enduring 350 freeze-thaw cycles, in contrast to C40, which did not withstand these conditions. RGAs derived from GPC of strength grades C100 and C80 complied with the criteria for Class II recycled aggregates, whereas RGAs produced from GPC of strength grade C60 aligned with the Class III level. A higher-strength grade in the parent concrete correlated with enhanced performance characteristics in the resulting recycled aggregates.
地聚合物混凝土（GPC）是一种创新的绿色低碳建筑材料，在建筑应用中为普通硅酸盐水泥混凝土（OPC）提供了一种可行的替代方案。然而，现有研究往往忽视了GPC未来使用的可回收性方面。各种结构应用需要使用具有不同强度特性的混凝土。母体混凝土的可回收性受这些不同强度的影响。本研究考察了强度等级范围为40、60、80和100兆帕（标记为C40、C60、C80和C100）的GPC在冻融条件下的回收潜力。回收由5至16毫米天然粗骨料（NA）制备的GPC中5至16毫米的再生地聚合物粗骨料（RGA）。胶凝材料由60%的偏高岭土和40%的矿渣组成，天然砾石用作NA，碱激发剂由氢氧化钠溶液和硅酸钠溶液组成。通过改变Na/Al比来调节GPC的强度。在350次冻融循环后，对GPC试件进行破碎、清洗和筛分以生产RGA。随后，对其物理性能（表观密度、吸水率、压碎指标、附着砂浆含量）和微观结构（显微硬度、扫描电子显微镜和X射线衍射）进行了全面检查。结果表明，强度等级为C100、C80和C60的GPC能够承受350次冻融循环，而C40则不能承受这些条件。强度等级为C100和C80的GPC衍生的RGA符合II类再生骨料标准，而强度等级为C60的GPC生产的RGA符合III类水平。母体混凝土中较高的强度等级与所得再生骨料中增强的性能特征相关。
