Engineering low-carbon fiber cement with biochar: Understanding its physicochemical properties and their impact on the composite performance and carbon footprint

Abstract

Wood derived biochar as a low – carbon supplementary cementitious material (SCM) for fiber cement (FC) – curbing CO2 emissions whilst enhancing rheo-mechanical properties. To address United Nations sustainable development goals, low CO2 ordinary Portland cement (OPC) blend for composite building materials, like fiber cement (FC) can aid in curbing the CO2 footprint of OPC. However, conventional silicate or aluminosilicate based supplementary cementitious materials (SCMs) possess environmental and health issues, which can be mitigated by exploring biomass-derived char (carbon) materials. Since understanding its role on the physicochemical characteristics on FC are central to material development, in this study we have performed in-depth rheo-mechanical characterization. Static yield stress (rheological) of the FC slurry increased (max. of 52.07 Pa, 98% increase vs control) with biochar content (10 wt.%), whereas the dynamic yield stress did not change substantially. Thixotropic properties of the FC slurry improved with biochar content (vs control) indicating more pronounced shear thinning behaviour and structural rebuilding at rest – crucial to effective handling of the FC slurry (pumping and consolidation of the FC slurry). Flexural strength (mechanical) of the FC increased (40% vs control) with biochar content (8wt.%). Furthermore, combination of spectroscopic studies (XRD,29Si MAS NMR, XPS) and SEM analysis revealed insights on what could be the contributing factors to strength development. Notably, biochar porosity and chemical functionality could facilitate early precipitation hydration products. Finally, upon cradle to gate life cycle analysis (LCA) and Cost to performance analysis (C/P), we learned that 8 wt.% biochar substitution achieved best C/P balance (among all samples) while reducing Global warming potential (GWP) by 18.1% (vs control).