Collaborative recycling of red mud and FGD-gypsum into multi-shell cold bonded lightweight aggregates: Synergistic effect, structure design and application in sustainable concrete. (23rd May 2023)

• Record Type: Journal Article
• Authors: Zhang, Chao; Hu, Zhijuan; Cheng, Guanyu; Wu, Changliang; Li, Jingwei; Jiang, Wen; Wang, Xujiang; Yang, Shizhao; Wang, Wenlong
• Is Part Of: Construction & building materials. Volume 379(2023)
• Publication Date: 2023-05-23
• Subjects: CLAs cold bonding lightweight aggregates -- RM red mud -- FGD flue gas desulfurization gypsum -- LWC lightweight aggregate concrete -- GBFS granulated blast furnace slag -- SSC solid-waste based sulphoaluminate cement -- OPC Ordinary Portland Cement -- SP superplasticizer -- NAs natural coarse aggregates -- OWA organosilicon waterproof agent -- EPS expanded polystyrene -- EPP expanded perlite -- PE pelletizing efficiency -- CS cylinder compressive strength -- AD apparent density -- 1h WB 1h water absorption -- LBD loose bulk density -- XRD X-ray diffractometer -- XRF X-ray fluorescence spectrometer -- FTIR fourier transform infrared spectrometer -- SEM scanning electron microscope -- ICP-OES inductively coupled plasma optical emission spectrometry -- MIP mercury intrusion porosimetry; Red mud -- FGD-gypsum -- Cold bonded lightweight aggregates -- Structure design -- Performance optimization -- Lightweight aggregates concrete; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2023.131134
• Languages: English
• ISSNs: 0950-0618

Abstract

Graphical abstract: Highlights: Multi-shell CLAs was innovatively prepared by synergistically using RM and FGD. The synergistic effect between RM and FGD as well as the multi-shell structure design mechanism were illustrated. The viable CLAs with high CS of 7.3 MPa, LBD of 940 kg/m 3 and 1 h WB of 6.91 % were obtained. The sustainable concrete with lower carbon emission and cost was prepared by using the CLAs as aggregates. Abstract: In this study, novel multi-shell CLAs were prepared by synergistically using red mud (RM) and flue gas desulfurization gypsum (FGD). The performance optimization, mineral compositions, microstructures, and pore size distributions of the CLAs were investigated in detail. The results indicated that the synergistic using of RM and FGD significantly improved the strength of the CLAs, and that the multi-shell structure design by encapsulating, incorporating, and coating EPS, EPP, and hydrophobic shell effectively reduced the density and water absorption of the CLAs. Based on the synergistic effect between RM and FGD, the ettringite, C(N)-A-S-H and U-phase were the main minerals of the CLAs, which jointly contributed to the strength development of the CLAs. The multi-shell structure including lightweight core, intermediate shell and the hydrophobic outer shell further reduced the density and water absorption of the CLAs. Hence, viable CLAs with loose bulk density of 940 kg/m 3, compressive strength of 7.3 MPa and 1 h water absorption of 6.91 % were obtained. The environmental impact and durability of the CLAs were evaluated acceptable. Furthermore, the prepared CLAs were employed as aggregates for lightweight aggregate concrete (LWC) preparation. The workability and mechanical strength of the LWC were investigated, and the LWC with density of 1880–2100 kg/m 3, compressive strength of 39.8–54.5 MPa, and splitting tensile strength of 2.44–2.95 MPa was obtained. Finally, the carbon emissions and cost of the LWC were calculated as 288.5 kgCO2 /m 3 and 335.31Yuan/m 3 (¥), respectively, which were 36.2 % and 23.1 % lower than those of traditional concrete. Overall, this research may provide a green approach for converting RM and FGD into value-added CLAs, with a potential application in sustainable concrete.