Modification and reinforcement of dispersive loess through bio-carbonated reactive magnesia cement

Abstract

This study investigates the effectiveness and underlying mechanisms of bio-carbonation of reactive magnesia cement (RMC) for the improvement and stabilization of dispersive loess. A comprehensive experimental program, including pinhole tests, crumb tests, unconfined compressive strength tests, and multiple microstructural characterization techniques, was conducted to systematically evaluate the soil dispersivity, mechanical performance, and water stability under varying urea concentrations and RMC contents. The results demonstrate that bio-carbonation treatment can rapidly and significantly reduce soil dispersivity. The unconfined compressive strength of the treated soil increased dramatically, accompanied by pronounced enhancements in stiffness and water stability. Microstructural analyses reveal that the carbonation products are dominated by hydromagnesite, which predominantly occurs in the form of platy crystals. These hydromagnesite crystals effectively cement and encapsulate soil particles, fill interparticle pores, and promote the formation of a dense and well-bonded soil structure. Furthermore, the results indicate that urea concentration and RMC content jointly govern the efficiency of dispersivity mitigation and mechanical reinforcement achieved through the bio-carbonation process. This study confirms the effectiveness of bio-carbonation as a high-efficiency and low-carbon technique for the stabilization and reinforcement of dispersive loess, providing valuable insights and practical guidance for engineering ground improvement and ecological protection in loess regions.

Graphical abstract

Keywords

bio-carbonation / dispersive soil / loess / mechanism / RMC

References

[1] Tang C S , Pan X H , Cheng Y J , Ji X L . Improving hydro-mechanical behavior of loess by a bio-strategy. Biogeotechnics, 2023, 1(2): 100024

[2] Zhao X B , Ma J J , Du J , Jiang L , Ma Y H , Wang Y L . Dynamic response and microstructural mechanism of biodegradable Fiber-MICP reinforced loess for earthquake resistant stabilization. Soil Dynamics and Earthquake Engineering, 2026, 201: 109992

[3] Petry T M. Identification of Dispersive Clay Soils by a Physical Test. Dissertation for the Doctoral Degree. Stillwater: Oklahoma State University, 1974

[4] Dean J. Dispersive clay embankment erosion—A case history. In: 54th Highway Geology Symposium. Burlington: Highway Geology Symposium, 2003, 306–320

[5] Fan H H , Kong L W . Empirical equation for evaluating the dispersivity of cohesive soil. Canadian Geotechnical Journal, 2013, 50(9): 989–994

[6] Li X Y , Fan H H , Xie F H , Lei B F , Ren G Z . The role of soil dispersivity and initial moisture content in splash erosion: findings from consecutive single-drop splash tests. Biosystems Engineering, 2024, 243: 27–41

[7] Zhao G W , Wu T , Ren G Z , Zhu Z , Gao Y , Shi M , Ding S J , Fan H H . Reusing waste coal gangue to improve the dispersivity and mechanical properties of dispersive soil. Journal of Cleaner Production, 2023, 404: 136993

[8] Liu H L . Biogenic construction: the new era of civil engineering. Biogeotechnics, 2025, 3(1): 100130

[9] Xiao Y , Fan W J , Cui H , Wu B Y , Zhao H H , Fu G Y . Drained shear strength and dilatancy of biocemented soil by biostimulation. Acta Geotechnica, 2025, 20(6): 2683–2693

[10] Ni W B , Ren G Z , Zhao C Z , Fan H H , Gao Y , Wang P W , Pang S , Meng M Q . Sandy soil reinforcement using carbonic anhydrase-producing bacterium with crude soybean urease system: crystallinity optimization and extracellular polymeric substance function. Journal of Rock Mechanics and Geotechnical Engineering, 2026, 18(7): 5789–5802

[11] Ren G Z , Peng Y , Wu S J , Sun Z C , Fan H H , Zhou M Y . Rheological behavior of biogenic calcium carbonate from high-concentration enzyme-induced calcium carbonate precipitation and the mechanical properties of treated soil. Journal of Rock Mechanics and Geotechnical Engineering, 2026, 18(4): 2945–2959

[12] Fu T Z , Saracho A C , Haigh S K . Microbially induced carbonate precipitation (MICP) for soil strengthening: A comprehensive review. Biogeotechnics, 2023, 1(1): 100002

[13] Xiao Y , Zhang Z C , Stuedlein A W , Evans T M . Liquefaction modeling for biocemented calcareous sand. Journal of Geotechnical and Geoenvironmental Engineering, 2021, 147(12): 04021149

[14] Xiao Y , He X , Stuedlein A W , Chu J , Evans T M , Van Paassen L A . Crystal growth of MICP through microfluidic chip tests. Journal of Geotechnical and Geoenvironmental Engineering, 2022, 148(5): 06022002

[15] Fang C L , Achal V . Enhancing carbon neutrality: a perspective on the role of Microbially Induced Carbonate Precipitation (MICP). Biogeotechnics, 2024, 2(2): 100083

[16] Zhang Y , Hu X L , Wang Y J , Jiang N J . A critical review of biomineralization in environmental geotechnics: Applications, trends, and perspectives. Biogeotechnics, 2023, 1(1): 100003

[17] Xiao Y , Fan W J , Fang Q Y , Cui H , Fu G Y , Zhao H H . Undrained shear behaviors of biocemented sand treated through biostimulation approach. Acta Geotechnica, 2025, 20(6): 2573–2582

[18] Liu L , Liu H L , Stuedlein A W , Evans T M , Xiao Y . Strength, stiffness, and microstructure characteristics of biocemented calcareous sand. Canadian Geotechnical Journal, 2019, 56(10): 1502–1513

[19] Xiao Y , Zhang L , Shi J Q , Hu J , Evans T M . Liquefaction of EICP-treated sand with fabric anisotropy. Journal of Geotechnical and Geoenvironmental Engineering, 2026, 152(1): 04025180

[20] Wang D L , Tang C S , Pan X H , Wang R , Dong Z H , Li L , Chen W B , Shi B . Durability of the bio-carbonated reactive MgO cemented construction and demolition waste: effect of wetting–drying cycles. Journal of Rock Mechanics and Geotechnical Engineering, 2026, 18(3): 2328–2338

[21] Wang R , Tang C S , Pan X H , Wang D L , Dong Z H , Shi B . Stabilization of dredged sludge using bio-carbonation of reactive magnesia cement method. Acta Geotechnica, 2023, 18(3): 1529–1541

[22] Wang R , Tang C S , Pan X H , Dong Z H , Lu X C . Mechanical behavior of biocarbonizing reactive magnesia-stabilized soft soil: strength control and prediction framework based on effective carbonate-to-magnesia ratio. Journal of Geotechnical and Geoenvironmental Engineering, 2025, 151(11): 04025135

[23] Ma G L , Xiao Y , He X , Wu S F , Chu J . Comparison of biomineralization kinetics induced by bacteria, bacterial enzyme, and soybean enzyme. Acta Geotechnica, 2025, 20(5): 2185–2200

[24] Zhou P , Wang H Y , Xu C J , Fang T , Ma G L , Liu H L . Geopolymers for stabilizing soils with diverse compositions. Science China Technological Sciences, 2026, 69(3): 1320701

[25] Chen Z , Fang X W , Long K Q , Shen C N , Yang Y , Liu J L . Using the biocarbonization of reactive magnesia to cure electrolytic manganese residue. Geomicrobiology Journal, 2021, 38(8): 709–718

[26] Wang R , Tang C S , Pan X H , Wang D L , Dong Z H , Zhang X Y , Lu X C . Efficient stabilization of dredged sludge with high water content using an improved bio-carbonation of reactive magnesia cement method. Journal of Rock Mechanics and Geotechnical Engineering, 2024, 16(9): 3760–3771

[27] Wang D L , Tang C S , Pan X H , Wang R , Li J W , Dong Z H , Shi B . Construction and demolition waste stabilization through a bio-carbonation of reactive magnesia cement for underwater engineering. Construction and Building Materials, 2022, 335: 127458

[28] Ma G L , Xiao Y , Chu J , Yin Z Y , Zhou B , Liu H L . Pore-scale investigation of MICP in simplified pore structures through microfluidic tests. Water Resources Research, 2025, 61(2): e2024WR037807

[29] Whiffin V S , van Paassen L A , Harkes M P . Microbial carbonate precipitation as a soil improvement technique. Geomicrobiology Journal, 2007, 24(5): 417–423

[30] ASTM. Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort, ASTM D698-12(2021). West Conshohocken, PA: ASTM, 2021

[31] Ren G Z , Ji Y Y , Fan H H , Gao Y , Wu T , Zhu Z , Zhao G W . Exploring the influence and predictive role of waste acidic calcium on the water stability and mechanical behavior of strongly alkaline dispersive subsoil. Journal of Environmental Management, 2024, 372: 123290

[32] ASTM. Standard Test Methods for Identification and Classification of Dispersive Clay Soils by the Pinhole Test, ASTM D4647/D4647M-13(2020). West Conshohocken, PA: ASTM, 2020

[33] ASTM. Standard Test Methods for Determining Dispersive Characteristics of Clayey Soils by the Crumb Test, ASTM D6572-21. West Conshohocken, PA: ASTM, 2021

[34] ASTM. Standard Test Method for Unconfined Compressive Strength of Cohesive Soil, ASTM D2166/D2166M-16. West Conshohocken, PA: ASTM, 2016

[35] Pang S , Yang J Y , Liu G Y , Zhang H R , Ni W B , Fan H H , Meng M Q . Shear strength and solidification mechanism of EICP-solidified waste sand to improve loess. Journal of Environmental Chemical Engineering, 2026, 14(3): 122355

[36] Pang S , Li M J , Chen S F , Wu Y Q , Fan H H , Yang X J , Li J Z , Zhang X D . Study on flexural properties of multi-length fiber-reinforced geopolymer cemented aeolian soil. Engineering Fracture Mechanics, 2025, 329: 111625

[37] Fan H H , Li H L , Zhao G W. . Relation among dispersive mechanism, physical-chemical and mineral properties of clayey soil.. Chinese Journal of Geotechnical Engineering, 2012, 34(9): 1740–1745

[38] Ren Z L , Pisch A , Georget F , Matschei T , Pesce C , Reeves-McLaren N , Hanein T . The role and fate of magnesium oxide in Portland cement clinker: mineralogy and thermodynamics. Cement and Concrete Research, 2026, 204: 108187

[39] Yang Y , Ruan S Q , Wu S F , Chu J , Unluer C , Liu H L , Cheng L . Biocarbonation of reactive magnesia for soil improvement. Acta Geotechnica, 2021, 16(4): 1113–1125

[40] Ni W B , Ren G Z , Liu C H , Fan H H , Meng M Q , Gao Y , Pang S , Sun Z C , Yang X J . Mechanism of enhanced bio-carbonation in sandy soils through urea pre-hydrolysis: A more efficient optimisation approach. Journal of Environmental Chemical Engineering, 2026, 14(1): 120568

[41] Wang R , Tang C S , Pan X H , Wang D L , Dong Z H , Lu X C . An efficient bio-stabilization technology with bio-carbonation of reactive magnesia for soil improvement in cold regions. Engineering Geology, 2024, 343: 107779

[42] Yi Y L , Liska M , Unluer C , Al-Tabbaa A . Carbonating magnesia for soil stabilization. Canadian Geotechnical Journal, 2013, 50(8): 899–905

[43] Saldi G D , Jordan G , Schott J , Oelkers E H . Magnesite growth rates as a function of temperature and saturation state. Geochimica et Cosmochimica Acta, 2009, 73(19): 5646–5657

[44] Königsberger E , Königsberger L C , Gamsjäger H . Low-temperature thermodynamic model for the system Na₂CO₃−MgCO₃−CaCO₃−H₂O. Geochimica et Cosmochimica Acta, 1999, 63(19-20): 3105–3119

[45] Yao D F , Wu J , Niu S , Gu Z R , Zheng J J , Yan J Y , Xu L , Yang M , Yan Y J . An anionic biopolymer γ-polyglutamate enhanced the microbially induced carbonate precipitation for soil improvement: mechanical behaviors and underlying mechanism. Acta Geotechnica, 2022, 17(10): 4485–4496

[46] Wang D L , Tang C S , Pan X H , Wang R , Shi M , Dong Z H , Zhang Y C , Shi B . A novel bio-carbonation method of reactive magnesia with urea pre-hydrolysis for geomaterial stabilisation. Géotechnique, 2024, 74(13): 1634–1648

[47] Zhang Z P , Zheng Y J , Ni Y W , Liu Z M , Chen J P , Liang X M . Temperature- and pH-dependent morphology and FT−IR analysis of magnesium carbonate hydrates. The Journal of Physical Chemistry B, 2006, 110(26): 12969–12973

[48] Kangal O , Fïrat C , Güney A . Flotation properties of unusual carbonates: Huntite and hydromagnesite. Minerals Engineering, 2005, 18(6): 631–634

[49] Hopkinson L , Kristova P , Rutt K , Cressey G . Phase transitions in the system MgO–CO₂–H₂O during CO₂ degassing of Mg-bearing solutions. Geochimica et Cosmochimica Acta, 2012, 76: 1–13

[50] Njegić-Džakula B , Brečević L , Falini G , Kralj D . Calcite crystal growth kinetics in the presence of charged synthetic polypeptides. Crystal Growth & Design, 2009, 9(5): 2425–2434

[51] Gautier Q , Bénézeth P , Mavromatis V , Schott J . Hydromagnesite solubility product and growth kinetics in aqueous solution from 25 to 75 °C. Geochimica et Cosmochimica Acta, 2014, 138: 1–20

[52] Wang J F , Li Z B . Crystallization and agglomeration kinetics of hydromagnesite in the reactive system MgCl₂–Na₂CO₃–NaOH–H₂O. Industrial & Engineering Chemistry Research, 2012, 51(23): 7874–7883

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