Synthesis and characteristic of decomposed products from recycled concrete fines by acetic acid decomposition treatment

In this work, an acetic acid decomposition method was proposed to synthesize amorphous nano-silica and calcium acetate rich solution from the recycled concrete fines (RCF), waste concrete with the aggregates removed, which realized the conversion of RCF into high value-added products by separating and purifying the phases of calcium and silicon. Characterization was carried out by means of thermogravimetry, Fourier transformation-infrared spectroscopy, electron microscope, 29 Si Solid-state nuclear magnetic resonance and BET method to better investigate the phases assemblage evolution and their microstructure development during decomposition systematically. The results indicated that the RCF was decomposed rapidly to generate amorphous silica bearing gel. A purified amorphous nano-silica gel was successfully prepared with high porosity, high polymerization degree and high purity up to 99.3%. And a calcium acetate rich solution was obtained as well. Both decomposed products have proved to be beneficial to the cementitious material system. The work provides technical and theoretical support for the complete and efficient reuse of the recycled cementitious material system during the later stages.