Macro-microscopic Characteristics Of Silt Solidified Soil Mixed With Nanometer Powder In Different Environments

The solidification method is one of the common methods for dealing with high water content sludge.With the expansion of the application range of solidified soil,the project often encounters environmental factors such as surface sewage,acid rain,landfill leachate,and seawater on the solidified soil,resulting in deterioration of the strength of the solidified soil and durability problems.Therefore,seeking suitable curing agents or admixtures to improve the erosion resistance of solidified soils has always been a hotspot in academia and engineering.This paper analyzed the strength and deformation characteristics of solidified soil under the conservation environment of tap water,seawater,magnesium sulfate solution and acidic solution,based on the high water content silt of a certain beach in Ningbo,using cement and mixed nano-silica powder and nano-aluminum powder as curing agents,and discussed the resistance to sulfate erosion and freeze-thaw characteristics of solidified soil.Moreover,the influence mechanism of environmental factors and the action mechanism of nanometer mineral powder was investigated through microscopic tests,which aims to provide theoretical guidance for solving the solidification problem of high water content sludge in different environments.The specific research content and the conclusions obtained are as follows:1.The influence of nanometer mineral powder dosage and age on the macroscopic properties of solidified soil under tap water curing was studied.The results show that nanometer mineral powder can significantly increase the unconfined compressive strength of the solidified soil.Compared with the solidified soil without nanometer powder,the maximum growth rates of the strength of the solidified soil at 7d,28 d,and 60 d were 41.1%,35.9%,and 36.8%,respectively.Meanwhile,the compressibility was greatly improved,and the maximum decrease rate of the compression index of the 28 d solidified soil was 50.9%.2.Macro-microscopic tests of solidified soil under seawater curing environment indicate that seawater leads to deterioration of the properties of solidified soil.Compared with tap water curing,the strength of 7 d,28 d,and 60 d solidified soils decreased by 10.7%,17.5%,and 6.1%,respectively.After adding nanometer mineral powder,the maximum increase in strength of 7 d,28 d,and 60 d solidified soils reached64.0%,44.7%,and 15.5%,respectively.Besides,the compression index fell by a maximum of 42.4%.The microstructure of solidified soil is significantly affected by seawater.Scanning electron microscope(SEM)images of the 28 d solidified soil shows that the fractal dimension of porosity was reduced from 2.03(a_w=0%)to 1.98(a_w=4.5%),and the microstructure was significantly improved.The main reasons are the volcanic ash effect of nano mineral powder,the effect of promoting cement hydration,and the effect of filling on solidified soil.3.The macro-microscopic tests of the solidified soil under the curing of magnesium sulfate solution show that the erosion effect of the magnesium sulfate solution is very obvious.The strength of ordinary solidified soil decreased by 5.4%and30.1%on 7d and 28d respectively,while the strength of solidified soil which was mixed with nanometer mineral powder increased by 34.1%and 38.9%,and the compression index decreased by 45.8%.SEM images of the 28 d solidified soil show that the fractal dimension of porosity of the solidified soil reduced from 2.46(aw=0%)to 2.08(aw=4.5%),implying that the microstructure of the solidified soil is significantly improved by nanometer mineral powder.4.In the acid curing environment,regardless of whether or not the solidified soil with nanometer ore powder is added,the strength of the solidified soil at all ages is higher than that of ordinary curing.The reason is related to the salt content of the test soil itself and the concentration of H~+during the entire maintenance process.In the acid curing environment,with the addition of nanometer mineral powder,the strength of the solidified soil increased by 37.1%,32.2%,and 13.7%at 7 d,28 d,and 60 d,respectively.5.The freeze-thaw cycle tests were carried out on the 90 d solidified soil under the conditions of tap water curing and seawater curing.The results show that when the amount of nanometer mineral powder is 4.5%,the effect of freeze-thaw on the solidified soil is significantly reduced,whether it is tap water or seawater curing.The 28 d anti-sulfate erosion tests of the solidified soil show that when the amount of nanometer mineral powder is 4.5%,the ability of the solidified soil to resist sulfate erosion is enhanced.