Biochar-cement concrete toward decarbonisation and sustainability for construction: Characteristic, performance and perspective

Biochar has been increasingly used in the production of cementitious materials due to its low cost, low-carbon emission, and environmental benefits. This study provides a comprehensive review on the effect of biochar on the performance of cementitious composites, focusing on mechanical properties, durability properties, and carbon-sequestration capacity. It has been observed that the use of biochar can improve the mechanical strength, thermal, and electromagnetic performance of hardened biochar-cement composites. The optimum cement replacement with biochar is 1–2 wt% (by weight) for enhancing the compressive and flexural strength. Additionally, the addition of biochar can improve the resistance to sulphate attacks, chloride-induced corrosion, shrinkage, and permeability of biochar-cement composites. Biochar also has the potential to reduce the permeability of concrete, and no significant differences were observed in permeability reduction for biochar processed at different pyrolysis temperatures. The positive effect of biochar (up to 5 wt%) on durability improvement is attributed to enhanced hydration and physical filling, resulting in a denser microstructure that prevents the penetration of ions and water. This study also discusses the impact of biochar on carbon sequestration capacity, demonstrating its ability to enhance the carbon-sequestration capacity of biochar-based concrete. In conclusion, while the mechanical properties of concrete with biochar have been extensively investigated, future research is needed to explore the long-term durability properties under different environmental conditions. Moreover, there is a growing demand for low-carbon concrete that utilizes carbon-negative materials to enhance performance and resilience.This accepted article is published as Lin, X., Li, W., Guo, Y., Dong, W., Cstel, A., Wang, K., Biochar-cement concrete toward decarbonisation and sustainability for construction: Characteristic, performance and perspective. Journal of Cleaner Production. 419(Sept 2023);138219.;https://doi.org/10.1016/j.jclepro.2023.138219. Posted with permission

A comprehensive review on self-healing cementitious composites with crystalline admixtures: Design, performance and application

Crystalline admixture (CA) has garnered attention as a promising self-healing agent for cementitious composites. This paper aims to provide a compressive review on the effects of CA on the self-healing behaviours and durability properties of cementitious composites. CA is in powder form, consisting of Portland cement and special chemicals as self-healing stimulants. Since the powder-form CA was directly mixed with the cementitious mixture, CA addition has no significant impact on the properties of fresh concrete but enhances the compressive strength of CA-cementitious composites. Furthermore, self-healing is activated by moisture, resulting in the production of calcium-based self-healing products. In terms of crack closure efficacy, CA-cementitious specimens cured under wet/dry cycle demonstrated a higher crack closure ratio than those cured under water immersion or air exposure. Specimens cured in chloride solution exhibited the best healing recovery. However, reduced mechanical recoveries are observed in specimens exposed to freeze–thaw cycles and those in chloride solution, while better mechanical recoveries are found in specimens exposed to wet/dry cycles. Overall, CA can reduce the sorptivity, permeability, chloride penetration, and the depth of sodium ions penetration, offering favourable protection for cementitious composites. Although some durability properties of CA-cementitious composites have been explored, further studies are required to investigate potential effects on shrinkage, ingress of aggressive ions, carbonation, and alkali-silica reaction (ASR). The application of CA in cementitious composites could be considered as a cost-effective approach for inducing self-healing capability, given its affordable and straightforward construction process.This article is published as Lin, Xuqun, Wengui Li, Arnaud Castel, Taehwan Kim, Yuhan Huang, and Kejin Wang. "A comprehensive review on self-healing cementitious composites with crystalline admixtures: Design, performance and application." Construction and Building Materials 409 (2023): 134108. doi: https://doi.org/10.1016/j.conbuildmat.2023.134108. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Fracture behaviours of sustainable multi-recycled aggregate concrete under combined compression-shear loading

The mechanical properties and strength failure criteria of natural coarse aggregate and multiple recycled coarse aggregate concrete under the combined compression and shear loading states are investigated in this study. The failure pattern, peak shear strength, and peak shear displacement are compared in terms of the number of regeneration cycles and normal compressive stress ratios. The results reveal that both the peak shear strength and peak shear displacement of concrete increase with the enlarged normal stress ratio. The shear failure pattern with higher severity corresponds to more spalling powder and debris deposited on the shear fracture surface. When the times of coarse aggregate regeneration increase, the peak shear strength decreases, and the descending trend becomes more evident with the increased vertical compressive stress ratio, whereas the peak shear displacement significantly fluctuates, regardless of the regeneration time and the normal compressive stress ratios. With normal compressive stress, the contact friction strength becomes the dominated component of peak shear strength consisting of cohesive strength, contact friction strength, and shear dilation strength. Based on the different stress expressions, three compression-shear failure criterion models considering the times of coarse aggregate regeneration under planar stress state were established for concrete. Despite the strong correlation with the correlation factors (R2) larger than 0.96 for all the models, the failure criterion model based on stress invariance and failure criterion model based on octahedral stresses in the quadratic parabolic functional forms provides the highest predictive accuracy. The related outcomes are expected to fill the gap of the related research on recycled aggregate concrete.This is a manuscript of an article published as Lei, Bin, Hongchen Yu, Yipu Guo, Wenkui Dong, Rui Liang, Xiaonan Wang, Xuqun Lin, Kejin Wang, and Wengui Li. "Fracture behaviours of sustainable multi-recycled aggregate concrete under combined compression-shear loading." Journal of Building Engineering (2023): 106382. DOI: 10.1016/j.jobe.2023.106382. Copyright 2023 Elsevier Ltd. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission