Biochar as construction materials for achieving carbon neutrality

Biochar is a waste-derived material that can sequester carbon at a large scale.The development of low-carbon and sustainable biochar-enhanced construction materials has attracted extensive interest.Biochar,having a porous nature and highly functionalised surface,can provide nucleation sites for chemical reactions and exhibit compatibility with cement,asphalt,and polymer materials.This study critically reviewed the state-of-the-art biochar-enhanced construction materials,including biochar-cement composites,biochar-asphalt composites,biochar-plastic composites,etc.The efficacies and mechanisms of biochar as construction materials were articulated to improve their functional properties.This critical review highlighted the roles of biochar in cement hydration,surface functional groups of engineered biochar for promoting chemical reactions,and value-added merits of biochar-enhanced construction materials(such as humidity regulation,thermal insulation,noise reduction,air/water purification,electromagnetic shielding,and self-sensing).The major properties of biochar are correlated to the features and functionalities of biochar-enhanced construction materials.Further advances in our understanding of biochar’s roles in various composites can foster the next-generation design of carbon-neutral construction materials.

Carbon-negative cement-bonded biochar particleboards

Biochar from bio-waste pyrolysis presents excellent CO_(2) sequestration capacity.This study innovated the design of cement-bonded particleboards utilizing a substantial amount of 50-70 wt.%pre-soaked biochar to render the products carbon-negative.We investigated the roles of biochar in magnesium oxysulfate cement(MOSC)system and demonstrated good mechanical and functional properties of biochar cement particleboards.In the presence of biochar,the amounts of hydration products were enriched in the cement systems as illustrated by the thermogravi-metric analyses(TGA)and X-ray diffraction(XRD).We further incorporated supplementary cementitious materials(SCMs)and generated 5 Mg(OH)_(2)⋅MgSO_(4)·7H_(2)O(5-1-7)phase in the MOSC system.As a result,our designs of biochar particleboards satisfied the standard requirements for flexural strength(>5.5 MPa)and thickness swelling(<2%).Moreover,our biochar particleboards presented a low thermal conductivity as the biochar pores disrupted thermal bridging within particleboards.We illustrated that the high dosage ratio of biochar could significantly offset the CO_(2) emissions of the particleboards(i.e.,carbon-negative)via life cycle assessment.Noticeable economic profits could also be accomplished for the biochar particleboards.For instance,the 50BC-MOSC bonded particleboard(with 50 wt.%pre-soaked biochar as aggregate,50 wt.%MOSC as binder)with promising mechanical properties could store 137 kg CO_(2) tonne^(−1) and yield an overall economic profit of 92 to 116 USD m^(−3) depending on the carbon prices in different countries.In summary,our new designs of carbon-negative biochar particleboards could curtail carbon emissions in the construction materials and promote the realization of carbon neutrality and circular economy.