Microstructure evolution and carbon footprint evaluation of ground activated recycled powder / multi-component composite cementitious materials

In order to replace ordinary Portland cement (OPC) as an supplementary cementitious material (SCM) for large-scale application of recycled powder (RP). The purpose of this study is to construct RP/multi-component composite cementitious material (MCCM). The strength development, phase structure evolution and microstructure of RP/MCCM were studied by compressive strength test and microscopic test methods such as XRD, FT-IR, SEM, BSE-EDS and TEM. The life cycle assessment (LCA) method was used to analyze the carbon emission reduction benefits of RP/MCCM. It indicates that after grinding activation, the 28 d compressive strength increased by 7.6% on the basis of unactivated value when the RP content was 30% (R30). After RP incorporation, the Al—OH is enhanced, the C—O and $\text{CO}_{3}^{2-} $bond peaks are narrowed, and the S element is evenly distributed, which is beneficial to the formation of ettringite (AFt) and CaCO₃ phases. The CaCO₃, Ca(OH)₂ and SiO₂ nanostructures are tightly bonded together in the ternary system without obvious faults appear when RP and fly ash (FA) are mixed with 15% (R15F15) respectively. Hence, the compactness and strength of the structure are improved. Moreover, the results of carbon emission analysis show that the incorporation of RP can reduce carbon emissions during raw material extraction and transportation, and achieve emission reduction targets.