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Author: search.filters.author.Ansari, F.Subject: search.filters.subject.Fine aggregates

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    Carbon capture efficiency of ultrafine cementitious substituents and fine aggregate alternatives subjected to accelerated CO2 curing
    (Elsevier Ltd, 2025) Trivedi, S.S.; Ansari, F.; Karthik Kumar Goud, P.; Joy, S.; Das, B.B.; Barbhuiya, S.
    This manuscript examines the quantification of CO2 uptake, calcium hydroxide (Ca(OH)2, CH) and calcium carbonate (CaCO3, 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 CO2). 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 (Ca2.25[Si3O7.5(OH)1.5].8H2O 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 (Ca4Si5O13.5(OH)2) 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 CaCO3 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 CO2 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 CO2 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
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    Effect of CO2 curing on phase compositions of nano silica blended cementitious mortar partially replaced with carbonated recycled fine aggregates
    (Elsevier Ltd, 2025) Trivedi, S.S.; Ansari, F.; Das, B.B.; Barbhuiya, S.
    This manuscript examines the quantification of CO2 uptake, hydration and carbonation phases such as calcium hydroxide (Ca(OH)2, CH), calcium carbonate (CaCO3, CC), magnesite (MgCO3), hydromagnesite (MgCO3.Mg(OH)2.4H2O, Hmgs), siderite (FeCO3) and subsequent carbonation and hydration degrees (CD, HD) in cementitious mortar (CM) incorporating colloidal nano silica (CNS) and carbonated and uncarbonated recycled concrete fine aggregates (RCF) subjected to accelerated carbonation curing (carbonated RCF- CRCF, Non-carbonated RCF- NCRCF). The RCF was prepared through multi cycle jaw crushing technology followed by repeated abrasion cycles and subsequently treated using accelerated carbonation. The mass loss resulting from the breakdown of these compounds at specific temperature ranges (220–350 °C for Hmgs, 250–400 °C for FeCO3, 400–500 °C for CH, 460–900 °C for MgCO3, and 600–800 °C for CC and CO2) was calculated using a thermogravimetric (TG) analyzer. The main findings of this research work confirms the presence of vaterite, calcite, tobermorite (Ca2.25[Si3O7.5(OH)1.5].8H2O or CSH gel), and magnesite polymorphs for CM incorporating 6–9 % CRCF and 1 % CNS as validated by the increased areas of peaks from fourier transform infrared spectroscopy (FTIR) analysis at 714 cm?1, 875 cm?1, 1007 cm?1, and 1405 cm?1, respectively which is further recognized by the increased peak intensities in X-ray diffraction (XRD) analysis. The important findings from the scanning electron microscopy (SEM) analysis revealed the development of additional C-S-H and calcite phases filling the pores and densifying the matrix in CRN mixes while the Ca/Si atomic ratio significantly decreased up to 67 % for CRN-19 mix as found by the energy dispersive X-ray spectroscopy (EDAX). The fresh and hardened state properties of blended mixes highlight the increase in dry density and compressive strength that are found maximum for CRN-19 mix of 57.9 MPa at 28 days owing to the highest rate of strength contribution of 27.95 % from the mix components such as 9 % CRCF and 1 % CNS. However, the flowability is observed to get reduced for all the mixes with CRN-13 mix illustrating approximately 83 % flow values with reference to the control mix. Furthermore, the durability performance of CRCF based primary mixes and all the secondary blends are found to show lowest ingress of chloride ions and permeable porosity values, illustrating up to 73 % and 39 % fall respectively to that of control mix at 28 and 56 days cured samples. Based on the comprehensive investigation and analysis, it is recommended to use pre-carbonated RCF and CNS for developing sustainable CM and achieving CO2 sequestration. © 2025 Elsevier Ltd