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The utilisation of biochar, the carbon negative product of pyrolysis, reduces the carbon footprint of the cementitious composites as it possesses the potential to replace the consumption of Portland cement. In a systematic investigation, biochar was used as a partial cement replacement for up to 20 wt% in both cement pastes and mortars. A comprehensive experimental framework was conducted to evaluate the impact of biochar replacement on the performance of (i) cement paste in terms of hydration kinetics, rheology, strength development, porosity, and (ii) mortars in terms of mechanical, thermal, and transport properties. In addition, the durability of developed mortars, including freezing and thawing resistance, thermal resistance, acid (corrosion) resistance, flammability, and smoke production, were examined. The results revealed that lower replacement rates of cement with biochar (up to 5 wt%) do not substantially change the performance of cementitious composites. However, incorporating biochar in higher dosages (i.e., 20 wt%) influenced the hydration process, reduced flexural and compressive strengths by 49% and 29%, respectively, and increased the water absorption coefficient by 60% compared to control specimens. The same cement mortar demonstrated the most promising freeze-thaw (i.e., 98% relative residual compressive strength), acid resistance as well as considerably lower thermal conductivity. In addition, regardless of biochar content, mortars did not exhibit flammability. Therefore, this study demonstrated that despite specific technical issues, biochar can be successfully incorporated into high dosage to cementitious composite as an alternative binder with minimum environmental impacts to improve durability and insulating performance of mortars. • Biochar was used to replace up to 20% of the cement in the paste and mortar. • Biochar increases yield stress and decreases workability of cement-based composites. • Biochar lowers mechanical properties in ambient and elevated temperature conditions. • Oven-dry density and thermal conductivity of mortars were substantially decreased. • Improved durability e.g. freeze-thaw and acid resistance was reported. [ABSTRACT FROM AUTHOR]

Utilising wheat straw reinforced OPC-free composites in the construction industry requires efficient, eco-friendly pre-treatment coupled with surface functionalisation methods to turn it into a high-performance material. Herein, alkali-activated material (AAM) was used as an OPC-free matrix, while eco-friendly hybrid pre-treatment and surface functionalisations were applied to mitigate the surface quality deficiencies of wheat straw and improve its compatibility with low-carbon binders. Wheat straw particles were subjected to a mild physical pre-treatment (hot-water followed by steam) and surface functionalisation using attapulgite nanoclay and graphene nanoplatelets to improve their capacity as an effective reinforcing material in AAM. Comprehensive characterisation verified successful pre-treatment and surface functionalisation, which led to the improved interfacial bond between wheat straw and AAM. The best results were obtained for the AAM samples reinforced with pre-treated straw that was functionalised with attapulgite nanoclay (i.e., H+S-AT), in which the volume of permeable voids decreased by 18%, while compressive and flexural strength at 90 d increased by 41% and 27%, respectively, compared to the control sample. However, the effect on the thermal properties of the resulted composites was not significant. • Hybrid pre-treatment and functionalising method using nanomaterials is presented. • Surface functionalising methods with AT nanoclay and G nanoplatelets were tested. • The deterioration mechanisms of wheat straw reinforced AAM were explained. • Improved compatibility of straw particles in the alkali-activated matrix was found. • Attapulgite functionalisation of straw improves compressive and flexural strengths. [ABSTRACT FROM AUTHOR]

An eco-friendly pre-treatment coupled with surface functionalisation were developed to enhance the quality of wheat straw particles to be used for development of high-performance polylactic acid (PLA) compressed strawboard. Eco-friendly hybrid pre-treatment (i.e., hot water followed by steam, H+S) and surface functionalisation processes employing attapulgite nanoclay (AT) and graphene nanoplatelets (G) were used to obtain an appropriate wheat straw surface quality while increasing its compatibility with the PLA matrix. The successful pre-treatment and surface functionalisation of wheat straw particles was verified through characterisation techniques, including SEM, FTIR, XRD, Raman spectroscopy, and TGA. Tensile strength and water absorption properties of compressed strawboards were examined to investigate the influence of pre-treatment and surface functionalisation of wheat straws. The maximum tensile strengths of 28 MPa and 27 MPa were recorded for 10 H+S-AT and 10 H+S-G samples, respectively, which are considerably higher than the value (i.e., 9.7 MPa) registered for the sample without pre-treatment and surface functionalisation (i.e., 10UN). The lowest water absorption after 24 h of immersion was registered for 10UN-G (i.e., 1.6%), which is 11% and 31% lower than the 10UN and 10 H+S samples, respectively. The effect is attributed to an improved interfacial bond between wheat straw and PLA matrix due to the graphene surface functionalisation, as evidenced by the SEM. • Dual enhancement of pre-treatment and surface nano-functionalising was proposed. • Pre-treatment and functionalising effects on the straw's structure were verified. • Crosslinking effect of surface functionalising agents is confirmed. • Maximum tensile strength of 28 MPa was registered for 10 H+S-AT. • The developed composites can be used in several applications, e.g., construction and automotive industry. [ABSTRACT FROM AUTHOR]