Carbon capture efficiency of ultrafine cementitious substituents and fine aggregate alternatives subjected to accelerated CO2 curing

Abstract

This manuscript examines the quantification of CO<inf>2</inf> uptake, calcium hydroxide (Ca(OH)<inf>2</inf>, CH) and calcium carbonate (CaCO<inf>3</inf>, CC) formed for processed recycled concrete fines (RCF), supplementary cementitious materials (SCMs) and various sustainable fine aggregate alternatives subjected to accelerated carbonation process. A thermogravimetric (TG) analyser was used to enumerate the mass loss consequential from these compounds' breakdown at particular temperature range (400–500 °C for CH, 600–800 °C for CC, and CO<inf>2</inf>). The increased areas of peaks from fourier transform infrared spectroscopy (FTIR) analysis confirmed the presence of calcite and vaterite polymorphs for carbonated RCF and SCMs at 875 cm?1 and 714 cm?1 respectively whereas the formation of calcium silicate hydrate (Ca<inf>2.25</inf>[Si<inf>3</inf>O<inf>7.5</inf>(OH)<inf>1.5</inf>].8H<inf>2</inf>O or CSH gel) is confirmed by the increased stretching vibrations of Si-O bond at 970 and 1030 cm?1. The X-ray diffraction (XRD) found the presence of useful compounds such as aragonite, calcium silicate hydroxide (Ca<inf>4</inf>Si<inf>5</inf>O<inf>13.5</inf>(OH)<inf>2</inf>) and portlandite that further confirmed the carbonation of RCF, SCMs and various fine aggregate alternatives. The formation of these compounds in carbonated specimens resulted in a significant fall in Ca/Si atomic ratio to a maximum of 98 % that further signifies the denseness in microstructure owing to precipitation of CaCO<inf>3</inf> and CSH gel deposition. The filled cracks and pores represented by scanning electron microscopy (SEM) images in carbonated specimens demonstrates the suitability of adopted carbonation regimes. The physical performance of RCF, SCMs and various fine aggregate specimens post accelerated carbonation highlights the increase in bulk density, specific gravity and reduced water absorption levels and volume changes that is an area of grave concern for incorporating recycled materials in construction sector. In addition, the CO<inf>2</inf> uptake of various carbonated specimens is found using TG analysis demonstrates the highest uptake for RCF at 32.4 % surpassing various other utilised SCMs and fine aggregate alternatives used in the research work. It is to be noted that metakaolin and ultrafine fly ash shows minimal CO<inf>2</inf> uptake owing to the manufacturing process. The findings of this study recommend the use of processed RCF and various other SCMs and fine aggregate alternatives for potential carbon dioxide sequestration through accelerated carbonation technology. © 2024 Elsevier Ltd