Ученые определили оптимальную дозировку биоугля для усиления поглощения CO₂ в известковых растворах

Natural hydraulic lime is increasingly used in heritage conservation because it is compatible with traditional masonry, requires lower production temperatures than cement, and absorbs atmospheric CO₂ as it hardens. Biochar, a carbon-rich porous material produced through biomass pyrolysis, can provide additional adsorption sites and gas-transport channels within building materials. Previous studies have mainly examined biochar in cement-based composites, however, and its influence on NHL remains poorly understood. In particular, the relationships among biochar dosage, particle size, carbonation behavior, pore structure, and strength have not been systematically established, making it difficult to identify a formulation that improves carbon uptake without compromising structural performance. A study (DOI: 10.48130/bchax-0026-0017) published in Biochar X on 04 June 2026 by Yue Gu's team, Hohai University, reports that incorporating 2% of 325-mesh biochar provides the most favorable balance between accelerated carbonation and improved compressive strength. The researchers prepared NHL pastes and mortars containing coconut-shell biochar in three particle sizes—100, 200, and 325 mesh—and at dosages ranging from 1% to 5%. Paste specimens were used to measure CO₂ uptake and examine microstructural changes, while mortar specimens were assessed for compressive strength, pH, and water-saturated porosity. After demolding, the samples underwent accelerated carbonation at 20 ± 2 °C, 70% ± 5% relative humidity, and 20% ± 2% CO₂. Compressive strength was measured after three, seven, and 28 days. The researchers also used quantitative X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy to identify changes in mineral composition and microstructure. The results showed that finer biochar generally produced greater strength gains. At a 2% dosage, 325-mesh biochar increased compressive strength by 35.7%, 42.1%, and 10.9% after three, seven, and 28 days, respectively. Strength initially rose with biochar dosage but declined when the dosage exceeded 2%, as excessive biochar increased porosity and disrupted the continuity of the NHL matrix. Carbon uptake followed a different pattern: higher dosages generally promoted greater uptake, although they could weaken mechanical integrity. The selected 2% formulation increased CO₂ uptake by 14.6% after six hours, 7.4% after 12 hours, and 11.9% after 24 hours, while increasing the apparent uptake rate by 3.2%. Mineralogical testing showed that adding 2% of 325-mesh biochar raised crystalline calcium carbonate content from 60.2% to 63.9%. Microscopy revealed a denser carbonated structure containing more calcium carbonate and fewer large pores. Together, the analyses indicated that biochar adsorbed and locally concentrated CO₂, created pathways for gas diffusion, and accelerated reactions that converted calcium hydroxide into calcium carbonate. The resulting carbonate particles filled microvoids and strengthened the material, but only when biochar content remained appropriately controlled. Overall, the study demonstrates that biochar performance in NHL depends on carefully balancing particle size and dosage. Fine biochar can facilitate CO₂ transport and promote carbonate formation, while excessive amounts introduce pores that offset the benefits of carbonation. The optimized 2% formulation therefore offers a practical starting point for designing lime-based materials that combine carbon uptake with adequate strength. Further research under a wider range of environmental conditions and over longer service periods will be needed before biochar-modified NHL can be broadly applied in conservation and sustainable construction. ### References DOI Original Source URL https://doi.org/10.48130/bchax-0026-0017 Funding information This work was supported by the Natural Science Foundation of Jiangsu Province (Grant No. BK20231464) and the National Natural Science Foundation of China (Grant No. 52471288). About Biochar X Biochar X (e-ISSN 3070-1686) is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.