Influence Mechanism of Phosphogypsum on Mechanical Properties and Impermeability of Soft Clay Solidified with Slag-Cement Cementitious System

doi:10.16552/j.cnki.issn1001-1625.2025.0541

Abstract

Abstract: Soft clay has a high moisture content, high plasticity and extremely low strength, which can easily cause engineering hazards such as foundation instability and settlement. This study used a stabilizer composed of phosphogypsum, slag and ordinary Portland cement to solidify high moisture content soft clay. By gradually replacing the inert stone powder in the soil stabilizer with equal amounts of phosphogypsum, a univariate study of phosphogypsum was conducted to investigate its role in the system. Firstly, the microstructure evolution of solidified soil was studied based on pH test, X-ray diffraction test, scanning electron microscopy test and thermogravimetric test to determine the solidification mechanism. Secondly, the effect of phosphogypsum mass proportion in the stabilizer on the mechanical properties and impermeability of the solidified soil was studied through unconfined compressive strength test, direct shear test and permeability test. The results show that the main hydration products of the stabilizer are calcium (alumino) silicate hydrate (C-(A)-S-H) gel and ettringite. Phosphogypsum increases the hydration degree of the stabilizer and promotes the formation of ettringite in the system by stimulating the sulfate excitation effect on slag. The cementation of gel and the expansion and filling of ettringite jointly improve the mechanical properties and impermeability of solidified soft soil. With the gradual increase in the mass proportion of phosphogypsum in the stabilizer, the unconfined compressive strength and shear strength of the solidified soil are significantly enhanced. Under the optimal ratio conditions, it meets the usual acceptance criteria for soft soil foundation reinforcement, and the permeability coefficient is decreased by an order of magnitude (from 10^-7 to 10^-8).

Key words: soft clay, phosphogypsum based soil stabilizer, mechanical property, impermeability, solidification mechanism

CLC Number:

TU447

SUN Tao, LIU Yue, WANG Ziyan, OUYANG Gaoshang, QIN Tingxuan. Influence Mechanism of Phosphogypsum on Mechanical Properties and Impermeability of Soft Clay Solidified with Slag-Cement Cementitious System[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2025, 44(12): 4480-4491.

References

[1] ZHAO C H, ZHAO D J. Application of construction waste in the reinforcement of soft soil foundation in coastal cities[J]. Environmental Technology & Innovation, 2021, 21: 101195.
[2] AYUB F, KHAN S A. An overview of geopolymer composites for stabilization of soft soils[J]. Construction and Building Materials, 2023, 404: 133195.
[3] 李琴, 孙可伟, 徐彬, 等. 土壤固化剂固化机理研究进展及应用[J]. 材料导报, 2011, 25(9): 64-67.
LI Q, SUN K W, XU B, et al. Progress and application on curing mechanism of soil stabilizer[J]. Materials Review, 2011, 25(9): 64-67 (in Chinese).
[4] GARTNER E. Industrially interesting approaches to “low-CO₂” cements[J]. Cement and Concrete Research, 2004, 34(9): 1489-1498.
[5] LEI Y, ZHANG Q, NIELSEN C, et al. An inventory of primary air pollutants and CO₂ emissions from cement production in China, 1990—2020[J]. Atmospheric Environment, 2011, 45(1): 147-154.
[6] FARROUKH H, MNIF T, KAMOUN F, et al. Stabilization of clayey soils with tunisian phosphogypsum: effect on geotechnical properties[J]. Arabian Journal of Geosciences, 2018, 11(23): 760.
[7] ZENG L L, BIAN X, ZHAO L, et al. Effect of phosphogypsum on physiochemical and mechanical behaviour of cement stabilized dredged soil from Fuzhou, China[J]. Geomechanics for Energy and the Environment, 2021, 25: 100195.
[8] 张大捷, 田晓峰, 侯浩波, 等. 矿渣胶凝材料固化软土的力学性状及机制[J]. 岩土力学, 2007, 28(9): 1987-1991.
ZHANG D J, TIAN X F, HOU H B, et al. Mechanical behavior and mechanism of stabilizing soft soil by slag cementitious material[J]. Rock and Soil Mechanics, 2007, 28(9): 1987-1991 (in Chinese).
[9] SARGENT P, HUGHES P N, ROUAINIA M. A new low carbon cementitious binder for stabilising weak ground conditions through deep soil mixing[J]. Soils and Foundations, 2016, 56(6): 1021-1034.
[10] HUANG Y, LIN Z S. Investigation on phosphogypsum-steel slag-granulated blast-furnace slag-limestone cement[J]. Construction and Building Materials, 2010, 24(7): 1296-1301.
[11] WANG Z Y, SHUI Z H, SUN T, et al. An eco-friendly phosphogypsum-based cementitious material: performance optimization and enhancing mechanisms[J]. Frontiers in Physics, 2022, 10: 892037.
[12] FU J Y, JONES A M, BLIGH M W, et al. Mechanisms of enhancement in early hydration by sodium sulfate in a slag-cement blend-insights from pore solution chemistry[J]. Cement and Concrete Research, 2020, 135: 106110.
[13] JIN W, ZHANG C L, ZHANG Z M. Study on the pH variation and regulation measures during the cement solidification treatment of dredged material[J]. Procedia Environmental Sciences, 2011, 10: 2614-2618.
[14] SUN G W, ZHANG J J, YAN N. Microstructural evolution and characterization of ground granulated blast furnace slag in variant pH[J]. Construction and Building Materials, 2020, 251: 118978.
[15] BARZGAR S, TARIK M, LUDWIG C, et al. The effect of equilibration time on Al uptake in C-S-H[J]. Cement and Concrete Research, 2021, 144: 106438.
[16] BEN HAHA M, LE SAOUT G, WINNEFELD F, et al. Influence of activator type on hydration kinetics, hydrate assemblage and microstructural development of alkali activated blast-furnace slags[J]. Cement and Concrete Research, 2011, 41(3): 301-310.
[17] GAVIRIA X, BORRACHERO M V, PAYÁ J, et al. Mineralogical evolution of cement pastes at early ages based on thermogravimetric analysis (TG)[J]. Journal of Thermal Analysis and Calorimetry, 2018, 132(1): 39-46.
[18] SUN T, XIAO X Y, OUYANG G S, et al. Utilization of waterglass coatings to improve the carbonization resistance of excess-sulphate phosphogypsum slag plastering mortar[J]. Construction and Building Materials, 2023, 408: 133644.
[19] YUAN S, LI Y J, HAN Y X, et al. Effects of carbonaceous matter additives on kinetics, phase and structure evolution of coal-series kaolin during calcination[J]. Applied Clay Science, 2018, 165: 124-134.
[20] YU C Y, CUI C Y, ZHAO J Y, et al. Enhancing mechanical properties of dredged sludge through carbonation stabilization employing steel slag: an eco-friendly and cost-effective approach[J]. Construction and Building Materials, 2024, 412: 134748.
[21] LIU S H, WANG L, YU B Y. Effect of modified phosphogypsum on the hydration properties of the phosphogypsum-based supersulfated cement[J]. Construction and Building Materials, 2019, 214: 9-16.
[22] 郑振. 水泥-膨润土复合固化污泥的强度及重金属迁移特性研究[D]. 抚州: 东华理工大学, 2022: 34-35.
ZHENG Z. Study on the strength and heavy metal migration characteristics of cement-bentonite composite solidified sludge[D]. Fuzhou: East China Institute of Technology, 2022: 34-35 (in Chinese).