Study On Composition Optimization And Performance Of Fluidized Solidified Soil Based On Sand And Sea Sand

With the virtues of in-situ soil extraction,co-disposal of construction waste,high mobility,and pumpability,fluidized solidified soil is gradually being used in back voids of retaining walls,around underground pipeline corridors and backfilling projects in mine quarries.However,during the preparation process of fluidized solidified soil,there are still problems such as difficulty in coordinating fluidity,bleeding rate,and compressive strength,poor consolidation effect of cement on soil,and unclear impact of construction waste incorporation on the performance of solidified soil.Therefore,this article takes sand from Sichuan region and sea sand from Hainan region as raw materials to study three aspects: working characteristics,mechanical intensity and durability capability.(1)The effects of water solid ratio,ash soil ratio,and additives on the working performance of fluidized solidified soil were studied,and the correlation between the two fluidity mold test values was compared and analyzed.The experimental group under optimized composition conditions was subjected for the heat of hydration analysis and Zeta potential analysis.The findings indicated that with the increase of water solid ratio,the fluidity and bleeding rate of fluid solidified soil increased significantly,and increasing the ash soil ratio was helpful to reduce the bleeding rate.There is a good linear correlation between the two fluidity mold test values,and the fitted equation is: y=13.15+1.02 x.The incorporation of HPMC can significantly reduce the bleeding rate of fluid solidified soil,reduce the loss of fluidity after30 minutes,but also significantly reduce its fluidity;The improvement effect of PCE on fluidity is better than that of FDN-C,but when these two water reducing agents are added alone,they will both increase their bleeding rate;Mixing HPMC(0.03%～0.1%)with PCE(0.4%～1%)can prepare a fluid solidified soil that meets the working performance.It can not only improve the fluidity of the fluid solidified soil,but also reduce or maintain the bleeding rate in a lower range,and can also reduce the loss of fluidity over time.However,the peak hydration rate of cement is delayed by both HPMC and PCE.Additionally,PCE also diminishes s the peak hydration rate and hydration heat release.Soil particles will adsorb PCE,reducing the amount of PCE acting on cement particles,and the adsorption of PCE by sandy soil is stronger than that of sea sand.(2)Respectively,the single-factor test was adopted to investigate the effects of water-solid ratio,ash-soil ratio,mineral powder content,fly ash content and the amount of construction waste admixture on the compressive strength and flowability of fluidized solidified soil.As the results show,an increase in the water-solid ratio decreases the strength of the fluidized solidified soil,but the decrease was not significant.When adding pure cement,the ash soil ratios for the sandy soil and sea sand to meet the minimum strength requirement of 0.4MPa for fluid solidified soil are 0.18 and 0.10,respectively.Under the same ash to soil ratio,the strength of the sea sand test block is significantly higher than that of the sand soil test block.The partial replacement of cement with fly ash and mineral powder contributes to the flowability of fluidized solidified soil,which is better with fly ash than with mineral powder;Increasing the amount of mineral powder can help to reduce the strength loss of solidified soil after replacing cement.Mixing construction waste can improve the compressive strength of solidified soil,but it will reduce its fluidity.For sandy soil in Hainan,the optimal mixing amount of construction waste is 20% to 30%.(3)The strength of the fluid solidified soil was optimized by adding water glass,phosphogypsum,and metakaolin.The solidification mechanism of the cementitious material was investigated based on the test results of XRD,FT-IR,and SEM.It was demonstrated that the mixing of sodium silicate,phosphogypsum(PG),and metakaolin(MK)can enhance the strength of fluidized solidified soil significantly.With the optimum admixture of 4% sodium silicate,the 28 d compressive strength of sandy soils and sea sand were increased by 18% and71%,respectively;As the PG mixture increases,the strength of sandy soil gradually decreases and that sea sand increases and then decreases,reaching a peak strength when PG content is5%;MK is the most evident in the improvement of solidified soil strength.The 28 d compressive strength of sandy soil and sea sand increased by 269% and 343% respectively.With the increase of the content of MK,the generation and density of C-S-H gel in the solidified soil increased significantly.(4)The effects of ash soil ratio and construction waste content on the volume stability of fluidized solidified soil under optimized composition conditions were studied through dry shrinkage and dry wet cycle tests.The results show that the dry shrinkage process of fluid solidified soil is closely related to the water loss process.When the water loss rate no longer changes,The drying shrinkage value also does not change,and the water loss rates of sandy soils and sea sand do not change after 21 and 14 days of curing,respectively.The water solid ratio of sandy soil is high,mainly due to dry shrinkage.Increasing the lime soil ratio can reduce the internal pores of solidified soil and reduce the dry shrinkage value;The water solid ratio of sea sand is low,mainly due to chemical shrinkage.Increasing the lime soil ratio will consume more free water and increase the dry shrinkage value of solidified soil.Increasing the amount of construction waste added is beneficial to reducing the dry shrinkage value of fluidized solidified soil.Adding 30% construction waste,the dry shrinkage value of sandy soil and sea sand decreased by 35.0% and 14.9%,respectively.Increasing the ash soil ratio can reduce the strength loss rate of fluid solidified soil during the dry wet cycle.