In the quest for sustainable construction materials, researchers have uncovered a promising synergy between biochar and hemp fiber that could revolutionize recycled aggregate concrete. A study led by Huanyu Li from the Shanghai Key Laboratory for Digital Maintenance of Buildings and Infrastructure at Shanghai Jiao Tong University, in collaboration with the Technische Universität Dresden, has demonstrated significant improvements in the performance of recycled aggregate concrete through the use of activated coconut biochar and hemp fiber.
The study, published in the journal *Resources, Environment and Sustainability* (translated to English as *Resources, Environment and Sustainability*), addresses a critical challenge in the construction industry: the significant drying shrinkage of recycled aggregate concrete, which has hindered its widespread adoption. By incorporating mix-sized biochar and hemp fiber, the researchers were able to enhance both the fresh and hardened properties of the concrete.
“Our findings show that the combination of biochar and hemp fiber not only improves the strength and durability of recycled aggregate concrete but also significantly reduces its carbon footprint,” said Li. The study revealed that the incorporation of biochar reduces fluidity due to water absorption and increased inter-particle friction, but it also enhances both flexural and compressive strengths by up to 34% and 28%, respectively. This improvement is attributed to matrix densification and fiber-bridging effects.
The synergy between biochar and hemp fibers facilitates internal curing by lowering the local water–cement ratio during hardening and promoting cement hydration through both internal curing and nucleation effects. Despite an initial increase in drying shrinkage, the combined addition of biochar and hemp fiber ultimately achieves a remarkable reduction of up to 96%. Additionally, increasing biochar dosage and fiber length enhances matrix compactness, substantially reducing water absorption and improving resistance to chloride penetration.
The commercial implications for the energy sector are substantial. Concrete modified with 30% biochar and 30 mm-long hemp fibers demonstrates significant potential for carbon emission reduction, achieving decreases of 4.4 kg CO2 eq./m3/MPa in compressive scenarios and 23.8 kg CO2 eq./m3/MPa in flexural scenarios. This research offers a scalable pathway for the development of high-performance, low-carbon recycled aggregate concrete, which could have a profound impact on the construction industry’s efforts to reduce its carbon footprint.
As the construction industry continues to seek sustainable and durable materials, the findings of this study provide a compelling case for the adoption of biochar and hemp fiber in recycled aggregate concrete. The research not only advances the understanding of shrinkage mitigation mechanisms but also paves the way for future developments in the field of sustainable construction materials.