Transforming waste powder into two types of supplementary cementitious materials through a wet carbonation process

Abstract

Recycled fine powder (RFP) derived from construction and demolition (C&D) waste lacks practical upcycling approach due to its various sources and complex mineral compositions. This study transformed RFP into supplementary cementitious materials (SCMs) as value-added products by using a two-step wet carbonation approach. The two main products i) Ca-rich residue and ii) Si-rich gel were collected and utilized as SCMs to reduce cement usage and carbon footprint. The hydration mechanism was analyzed by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and Fourier-transformed infrared spectroscopy (FTIR). A series mixture designs were compared and evaluated by hydration heat tests and mechanical experiments. The activation effect of the chemical activator (NaOH) for Si-rich gel was also evaluated. The experimental results showed that incorporating Ca-rich residue and Si-rich gel effectively improved the hydration of cement. Incorporating 2 %-10 % Ca-rich residue in binder mixture increased the compressive strength by 4.48 %-7.22 %. Meanwhile, the addition of Si-rich gel showed a negative effect on the compressive strength. But increasing the gel content from 5 % to 20 % enhanced the compressive strength. The strength loss can be compensated by adding NaOH in the mixture.