Effect of the Pretreatment on the Properties of Cement-Based Recycled Powder

Abstract

Three pretreatment methods including calcination, carbonization, and a carbonization-calcination combined pretreatment were studied to understand the pretreatment mechanisms for cement-based recycled powder (CRP). The mineral and microstructure of the CRP sample were investigated through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermal gravity (TG) analysis, and scanning electron microscopy (SEM) after exposure to different thermal temperatures (400 °C, 600 °C, and 800 °C), carbonization times (6 h, 1 d, and 3 d), and pre-carbonization for 1 d followed by heating at 800 °C. The results showed that the optimal thermal pretreatment temperature was approximately 720–800 °C. Through the process of calcination, the C-S-H, Ca(OH)2, and CaCO3 minerals in the CRP sample underwent decomposition to produce CaO or C2S. During carbonation, the pretreatment not only results in the increased production of CaCO3 owing to the reaction of the C-S-H gel and Ca(OH)2 with CO2, but also enhances its properties and the strength of chemical bond between CaCO3 and the post-hydration products. Both CaCO3 and CaO were present after the combined pretreatment, which indicates that the CaCO3 mineral formed superior stability after it had been pre-carbonated. Due to fewer impurities in CRP, the positive effect of the pretreatment on CRP was significantly better than that on recycled powder derived from construction and demolition waste.

Compressive Behaviors of High-Strength Geopolymeric Concretes: The Role of Recycled Fine Aggregate

“…Recently, research on the use of recycled aggregates in cementitious materials has been conducted. Xiao et al [18], Silva et al [19], and Guo et al [20] summarized the research status of recycled aggregates and noted that recycled aggregates degrades the durability and mechanical properties of concrete. Achieving high strength with 100% recycled aggregates requires additional cement, which is detrimental to both the economy and carbon reduction measures [21].…”

“…In cement-based concrete, as the amount of recycled aggregate increases, the concrete exhibits poor mechanical properties [18,21,28,29]. In particular, the size of the recycled aggregate significantly affects the concrete strength.…”