Experimental Study On Corrosion Of Cement-Soil In Peat Soil Environment

The durability of peat soil strengthened by cement has attracted much attention.The reason is that the cemented cement-soil is still in the original peat soil environment,and the humic group(humic acid and fulvic acid)contained in this environment seriously impacts cement-soil’s durability.Therefore,it is of great significance to study the regularity of peat soil environment’s corrosion on cement-soil for the durability of peat cement-soil and the follow-up anti-corrosion work.In this paper,humic acid was added to alluvial mucous soil with low organic matter content to make peat soil,and then the cement sample was infiltrated into cement by mixing method,and then soaked in fulvic acid solution and deionized water(soaking method)to simulate the actual working environment of cement-soil.After immersion and corrosion of cement-soil,the apparent phenomenon observation,acid consumption test,ion leaching test,unconfined compressive strength test,scanning electron microscope(SEM)test,mercury intrusion porosimetry(MIP)test,Particles(Pores)and Cracks Analysis System(PCAS),and X-ray diffraction(XRD)tests are carried out to reveal the corrosive law and mechanism of peat soil environment on cement-soil.(1)The apparent phenomenon shows that struvite crystals precipitate on the surface of cement-soil in a peat soil environment,and the crystals produce expansive erosion on cementsoil.Acid consumption and ion leaching tests show that cement-soil has a certain consumption effect on fulvic acid in the soaking process,leading to a large amount of dissolution of Ca2+,Mg2+,Al3+,and Fe3+,namely,another erosion type of cement-soil in peat soil environment is dissolution erosion type.(2)The effect of the humic group on the strength and microstructure of cement-soil.The results show that adding humic acid can weaken cement-soil’s structure and greatly reduce cement-soil’s strength.Fulvic acid has a filling effect on the pores in cement-soil.In addition,Fulvic acid has a filling effect on pores in cement-soil.In addition,fulvic acid also has a gelling effect on solid particles in cement-soil,which increases the strength of cement-soil with a partial cement incorporation ratio in the short term.When the soaking time is 28 d,fulvic acid has an enhancement effect on the strength of cement-soil mixed with each amount of humic acid,and the lower the pH value of fulvic acid soaking solution(the higher the concentration),the more obvious the enhancement effect is.However,when the soaking time increases to 90 d,fulvic acid only has an enhancement effect on the strength of cement-soil with a higher amount of humic acid(about 20%),and the lower the pH value of the fulvic acid soaking solution(the higher the concentration),the more obvious the enhancement effect is.The change of microstructure of cement-soil under the action of humic group shows that fulvic acid’s adsorption,filling,and gelation can fill some pores and cement clay particles.The lower the pH value of fulvic acid(the higher the concentration),the more obvious the filling effect,the full play of the gelation,and the strength of cement-soil is relatively enhanced.The higher the amount of humic acid,the stronger the absorption capacity of fulvic acid,and the more obvious the strength enhancement.The increase in the cement mixing ratio can weaken the negative effect of the humic group on the strength of cement-soil,but whether the increase in the cement mixing ratio is reasonable or not needs to be considered in combination with economic and environmental protection factors.(3)The strength characterization test of cement-soil corrosion law in peat soil environment shows that when the cement-soil is not mixed with humic acid,its strength gradually decreases with the increase of soaking time.However,when adding humic acid,cement-soil strength increases first and then decreases greatly.The stronger the enhancement effect in the early stage of fulvic acid soaking(28d to 90d),the stronger the corrosion effect in the later stage of soaking(after 90d).When the soaking time is about 180d,the strength of cement-soil soaked in fulvic acid solution is lower than that of deionized water.The lower the pH value of the soaking solution(the higher the concentration),the lower the strength.The long-term effect of peat soil environment on cement-soil is obviously corrosive,and the corrosion effect of humic acid and fulvic acid on cement-soil has obvious synergy.In order to explore the erosion mechanism of peat soil environment on cement-soil,firstly,the changes of the microstructure of cement-soil under peat soil environment corrosion were studied by SEM test.The results show that the corrosion of the peat soil environment consumes cement hydration products.With the increase of soaking time,the solid particles in cement-soil are gradually dispersed,and the structure of cement-soil is weakened.Then,the MIP test of cement-soil was carried out.The results show that the pore size distribution with the largest proportion of pore volume in cement-soil without fulvic acid soaking is 0.003～0.1 μm.After soaking in fulvic acid solution,the pore size distribution range with the largest proportion of pore volume in cement-soil becomes 0.3～100μm,and the proportion of pore volume in this pore size range gradually increases with the increase of soaking time.In addition,with the increase of soaking time,cement-soil’s permeability and conductivity coefficient(calculated value)gradually increases,and the corrosion effect becomes more obvious.The changing trend of PCAS analysis results is consistent with MIP.Finally,the XRD test shows that the main phases in cement-soil are silicon dioxide and calcium silicate hydrate.The diffraction peak value of hydration products decreases with the increase of soaking time,and even some diffraction peaks corresponding to the diffraction angle of hydration products disappear.