Study On Solidification Of Acid Soil By Inorganic-organic Composite Materials And Its Road Performance

With the rapid development of highway construction and the increasing requirements for environmental protection in China,the shortage of natural sand and stone resources has become a bottleneck in the supply of important road fill materials.The use of soil stabilization technology to improve the engineering soil,enhance its strength and service performance,is considered an advanced technology with practical value.In the construction of the Xuanhui Expressway in Yunnan Province,a large amount of tunnel waste soil can be utilized as a substitute for natural sand and stone as roadbed material,significantly reducing transportation costs and the consumption of natural sand and stone resources,while generating economic and environmental benefits.This paper proposes an inorganic-organic composite stabilizer suitable for solidifying the abandoned tunel soil（acid soil）of Yunnan Expressway,aiming to improve the adverse properties of high water content and high plasticity in acid soil.The new type of composite stabilizer,through the synergistic effect between stabilizers,can better enhance the performance of engineering soil for road subgrade construction.The main research content and conclusions of this paper are as follows:（1）Investigate the development law of solidified soil strength by cement composite with one or more inorganic additives.The results showed that the addition of Ca（OH）₂,gypsum dihydrate,and anhydrous sodium sulfate as single inorganic additives to cement produced the best strength of solidified soil among all proportions.In addition,under the premise of keeping the cement content constant,compounding with external addition of three inorganic additives can fully leverage the synergistic effect between cement and inorganic additives,resulting in significantly improved strength of solidified soil compared to internal addition method.（2）The proportioning experiments were conducted to study the effects of different dosages of cement and inorganic additives on the soil mixtures.The results showed that the 7-day unconfined compressive strength of the solidified soil had already met the requirement for subgrade of the expressway when the content of cement was 15%of the mass of soil.Additionally,the experiment results indicated that the optimal dosage of inorganic composite additives was 5%of the cement quality.Among them,when the ratio of Ca（OH）₂,gypsum dihydrate,and anhydrous sodium sulfate was 1:3:1,the strength of the solidified soil was the highest.The addition of inorganic additives improved the hydration environment of cement and promoted the formation of hydration products,thereby enhancing the strength and water stability of the solidified soil.（3）Testing and analysis were conducted on the effects of three types of ion additives on the hydration of cement using inductively coupled plasma mass spectrometry,infrared spectroscopy,and isothermal calorimetry.Results showed that all three ion additives contained high-valence cations,with the SZ ionic additive containing a high concentration of Na⁺and the presence of hydrophobic groups observed in the infrared spectrum.Furthermore,the SZ ionic additive significantly promoted the hydration heat release rate and total heat release of cement.Based on these findings,a study was conducted on the compressive strength and water stability of cured soil using four typical ratios:cement alone,cement combined with inorganic additives,cement combined with SZ ionic additives,and inorganic-organic composite stabilizer.The microstructure of the solidified soil was analyzed by XRD,MIP,SEM,and FTIR.The results showed that the ion exchange effect of the SZ ionic additive and the presence of hydrophobic groups improved the hydrophilic properties of clay particles,making them easier to compact.Additionally,the SZ ionic additive promoted cement hydration and exhibited synergistic effects with inorganic composite additives,thereby improving the performance of the cured soil.（4）The road performance of four typical solidified soil mixtures was investigated:cement alone,cement with inorganic additives,cement with SZ ionic additives,and inorganic-organic composite stabilizer.The results showed that the road performance of the inorganic-organic composite solidified soil had significant advantages.With the increase of curing time,the unconfined compressive strength and water stability of the solidified soil were significantly improved.At the same time,the bearing capacity of the inorganic-organic composite solidified soil under adverse load conditions was significantly enhanced,and its CBR and rebound modulus met the road strength requirements of extremely heavy traffic levels.In addition,the unconfined compressive strength of the inorganic-organic composite solidified soil showed a trend of increasing first and then decreasing with the number of dry-wet cycles.