Carbon sequestration in engineered lightweight foamed mortar – Effect on rheology, mechanical and durability properties. (7th March 2022)

• Record Type: Journal Article
• Authors: Gupta, Souradeep; Kashani, Alireza; Mahmood, Aziz Hasan
• Is Part Of: Construction & building materials. Volume 322(2022)
• Publication Date: 2022-03-07
• Subjects: Biochar -- Fly ash -- Silica fume -- Carbonation -- Shrinkage -- Rheology -- Sorptivity; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2022.126383
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Combination of biochar and silica fume enhance carbon sequestration. Enhanced hydration in biochar-foamed mixtures improve strength and sorptivity. Adding biochar reduces yield stress and plastic viscosity of foamed paste mixtures. Biochar-foamed mortar retain higher strength after prolonged carbonation. Adding biochar reduces shrinkage associated with only carbonation. Abstract: Enhancing carbon sequestration in Portland cement-based foamed mortar is a potential means to reduce carbon emissions associated with lightweight building components. This research aims to investigate the influence of biochar, prepared from wood waste, in enhancing carbon sequestration in foamed mortar of three target densities – 1150 kg/m 3 and 1300 kg/m 3 and 1450 kg/m 3 respectively through accelerated carbonation (CO2 concentration of 2%) technique. Effect of biochar on rheology, and influence of carbonation on micro-structure, compressive strength, water absorption and shrinkage are investigated. Based on thermogravimetry analysis, carbon dioxide uptake of 26.80% and 30% by mass of cement are achieved in foamed mortar containing biochar, silica fume and fly ash after 7 days and 28 days respectively, which is higher by 3% compared to control (without biochar). Adding biochar to replace 3% by mass of fly ash (density of 1150 kg/m 3 ) and 20% by mass of silica fume (density 1450 kg/m 3 ) improves the workability of foamed mortar mixtures, evident from the 32% and 44% reduction in yield stress up to 35 min from the time of wet mixing. For density groups of 1300 kg/m 3 and 1450 kg/m 3, addition of biochar reduces water-accessible porosity by 2 – 3%, leading to 17% and 23% higher compressive strength compared to the controls after 28 days of water curing. After carbonation biochar-foamed mortars retain 20–38% higher strength than the respective controls, although reduction in strength by 40 – 60% compared to water curing is observed, ascribed to degradation of hydration products during prolonged carbonation. Addition of biochar results in 10–12% higher shrinkage under an air-drying regime, while it reduces chemical shrinkage associated with carbonation by 15–20% than control. Overall, this study demonstrates a promising potential for developing biochar-enhanced low-carbon lightweight building products.