多元固废基胶凝体系固化盐渍土的力学性能

Mechanical properties and mechanism of cement‑based multi‑component solid waste solidified saline soil

【目的】改善宁夏地区工程盐渍土地基的冻胀和腐蚀问题。【方法】采用水泥、粉煤灰、硅灰和硅锰渣作为盐渍土的固化剂,设计四因素三水平正交试验方案,通过无侧限抗压强度试验和三轴试验,探讨不同固化剂掺量(质量分数,下同)对盐渍土抗压强度和抗剪强度的影响;采用扫描电子显微镜(scanning electronic microscopy,SEM)和X射线衍射(X‐ray diffraction,XRD)表征分析固化盐渍土的强度提升机制。【结果】水泥和硅灰提升固化盐渍土的早期强度作用较为显著,随掺量的增加,粉煤灰强度呈先增后减的趋势,硅锰渣结构较为稳定,需要充足的碱性环境来激发胶凝能力;水泥、粉煤灰、硅灰和硅锰渣4种因素对固化盐渍土抗压强度的影响程度由高到低的顺序为水泥、硅灰、粉煤灰、硅锰渣;水泥、粉煤灰、硅灰和硅锰渣掺量分别为3%、5%、5%和3%时固化效果最佳,为最佳配合比;固化盐渍土生成棒状的钙矾石(aluminate ferro-copper-calcium sulfate,AFt)和网状的水化铝酸钙(calcium aluminate hydrate,C-A-H)等水化产物相互联结,微观结构变得致密。协同作用提升了固化盐渍土的强度。【结论】采用水泥、粉煤灰、硅灰和硅锰渣最佳配合比能够使盐渍土地基固化,改善地基的冻胀和腐蚀问题。

Objective To address the frost heave and corrosion issues in engineering saline soil foundation in Ningxia,and to improve the comprehensive utilization of solid waste in the Ningxia Hui Autonomous Region,this study focuses on the analysis of the interaction of a composite curing agent used to solidify saline soil.Methods Every year,industrial areas in Ningxia Hui Autonomous Region produce a significant amount of solid waste,including fly ash,silica fume,and silicon manganese slag.This waste exhibits good pozzolanic activity and can be effectively cured using alkali-activated materials.To this end,this paper employs cement,fly ash,silica fume,and silicomanganese slag as curing agents for saline soil.To comprehensively study the influence of mixed cement,fly ash,silica fume,and silicon manganese slag on the strength characteristics of solidified saline soil,we used an orthogonal test to design a four-factor three-level orthogonal test scheme.This method selects a representative experimental scheme from many experimental conditions,effectively solving the problem of many factors and a large number of tests.The experiment is discussed from two perspectives:macro mechanics and micro mechanism.The mechanical properties of solidified saline soil are verified using the unconfined compressive strength test and triaxial test.The influence of different curing agent content on the compressive strength and shear strength of saline soil is discussed.The strength improvement mechanism inside the solidified saline soil is characterized and analyzed using scanning electronic microscopy(SEM)and X-ray diffraction(XRD).The microstructure of cementitious materials,including particle size,shape,distribution,and surface characteristics,can be observed using the high-resolution ability of SEM.XRD is a powerful tool for identifying various crystal phases in cementitious materials and analyzing their crystal structure and phase composition.The microstructure,composition,and crystal structure information of the material can be analyzed more effectively by combining SEM and XRD.This allows for a better determination of the main components of the cementitious material and the reaction mechanism between the curing agents.Results and Discussion Compared to the 7-day age,the compressive and shear strength of the solidified saline soil significantly improved after 28 days.The compressive strength of the solidified saline soil is influenced by cement,silica fume,fly ash,and silicon manganese slag in that order of importance.The optimal mix ratio for cement,fly ash,silica fume,and silicon manganese slag is achieved when their respective contents are 3%,5%,5%,and 3%.This ratio results in the best curing effect.The hydration reaction time of cement is brief,creating an alkaline environment for silica fume,fly ash,and silicon manganese slag.This reaction produces cementitious materials that effectively enhance the strength of solidified saline soil.Silica fume contains a significant amount of SiO_(2),which reacts with Ca(OH)_(2) produced by cement hydration to form cementitious materials such as C-S-H,thereby improving strength.Cement and silica fume have a significant effect on improving the early strength of solidified saline soil.The strength of fly ash increases initially with an increase in dosage,but then decreases due to the'ball effect'.The structure of silicon-manganese slag is relatively stable,but it requires a sufficient alkaline environment to stimulate its cementitious ability.The cementing material produced by the curing agent improves the mechanical properties of solidified saline soil in two ways:firstly,by enhancing the bonding effect between soil particles through its own cementation,and secondly,by filling the pores and cracks of the saline soil,thereby improving the integrity of the soil structure.The solidified saline soil produces hydration products,such as rod-shaped ettringite(AFt)and reticular calcium silicate hydrate(C-A-H),which are interlinked.This results in a denser microstructure and improved strength of the solidified saline soil due to the synergistic effect.Compared to the 7-day age,the reactions between the curing agents at 28 days,such as hydration,ion exchange,and pozzolanic reactions,are more sufficient,leading to the formation of more cementitious substances.As a result,the compressive and shear strength of the solidified soil are higher at 28 days.Conclusion To solidify saline soil foundation in the channel,it is recommended to use a mix ratio of 3%cement,5%fly ash,5%silica fume,and 3%silicon manganese slag.These ratios were determined based on research results and provide a theoretical reference for the synergistic solidification of cement and multiple solid wastes in channel saline soil foundation.