Experimental Research On Anti-corrosion Additives Of UFC Cement Soil In Peat Soil Environment

There are a large amount of peat soils distributed around Dianchi Lake and Erhai Lake in Yunnan,and the reinforcement of peat soils with high organic matter content by ordinary cement cannot meet the actual engineering requirements.In the humic acid-rich peat soil environment,cement-based materials are susceptible to corrosion,and how to solve the durability problem economically and effectively is of great significance to us.Combined with the research results of a large number of scholars,it is concluded that the essential reason for the unsatisfactory reinforcement effect is that humic acid in peat soil will undergo a series of physical-chemical reactions with cement and cement hydration products.As a result,the hydration reaction rate,degree of hydration,and quantity of hydration products of cement are reduced,thereby weakening the reinforcement effect of cement,resulting in an unsatisfactory reinforcement effect.For this reason,in this experiment,ultrafine cement(UFC)was added to cement soil to form a composite curing agent with ordinary cement.The purpose is to rely on its excellent characteristics of fast hydration reaction rate,high hydration degree,and large number of hydration products to weaken the adverse effects of humic acid on cement hydration to a certain extent.Therefore,the purpose of increasing the strength of the reinforcing body and improving the durability of the reinforcing body is achieved.In this paper,peat soil was prepared by mixing humic acid reagent into the alluvial and diluvial clay soil with low organic matter content.Cement-soil samples were prepared by adding cement and ultra-fine cement(UFC)by stirring method.It was then soaked in a fulvic acid solution to simulate cement soil in a peaty soil environment.Through the indoor unconfined compressive strength test,combined with the test results of X-ray diffraction test(XRD),scanning electron microscope test(SEM),mercury intrusion test(MIP)and PCAS microscopic quantitative test.To study the durability of UFC cement soil in peat soil environment.The main research contents are as follows:(1)When the influence of humic acid and fulvic acid is not considered,the strength of cement soil can be significantly improved by adding UFC,and the strength growth rate is the largest when the content of UFC is 10%.When the proportion of UFC continues to increase,Its intensity growth rate gradually flattens out.(2)In the peat soil environment,humic acid had a significant weakening effect on the strength of cement soil in both physical and chemical aspects.UFC can appropriately weaken the adverse effects of humic acid on cement soil due to its small particle size,high surface energy and strong binding ability.(3)In the peat soil environment,the infiltration of fulvic acid has a certain effect on the strength of the sample before the soaking time of 90 days.That is,the q_u of the sample increases gradually with the decrease of the p H value of the soaking solution,and the addition of UFC can properly promote the enhancement effect of fulvic acid on the q_u of cement soil.(4)The microscopic test results show that with the increase of the percentage of UFC,the hydration reaction rate of cement accelerates,the relative content of cement hydration products gradually increases,and its filling and cementing effect makes the internal pore morphology and structure of cement soil change.The large pores are gradually transformed to medium and small pores,the distribution of pores is more concentrated and uniform,the chance of pore penetration is smaller,and the pore connectivity is no longer significant.Finally,a denser and better overall microstructure of cement soil is presented.The strength test results have a good correlation with the microscopic test results.(5)In peat soil environment,humic acid and fulvic acid will interact.After the immersion time exceeds 90 days,there is a significant difference in the weakening effect of the strength of cement-soil in the range of 0%-15%and 15%-30%of humic acid reagent;simultaneously,influenced by the synergistic effect of humic acid fulvic acid,the corrosion effect of fulvic acid itself was highlighted with different characterization from the change pattern of strength and p H value.(6)With the growth of immersion time,the q_u curves of the cement soil specimens are the process of gradually increasing to the peak q_u and then decreasing.That is,the strength change curves were presented as two phases,the strength enhancement phase and the corrosion phase.But the soaking time corresponding to the peak strength has significant difference.With the increase of UFC proportion,the strength change per unit time,the strength growth rate per unit UFC ratio,and the strength reduction rate from 90d to 360d of the specimens showed that UFC could significantly reduce the strength reduction rate of the specimens.Thus,the specimens can still maintain high strength under long-term immersion time,and the optimal UFC proportion amount is 10%.It shows that UFC significantly inhibits the erosion effect of fulvic acid solution on the cement soil specimens,thus reflecting the excellent anti-corrosion performance of UFC.(7)The results of SEM and PCAS tests show that the microstructure of cement soil weakens gradually with the increase of immersion time.However,the excellent characteristics of small particle size,narrow particle size distribution,fast hydration reaction rate,high degree of hydration and high number of hydration products of UFC particles somewhat weakened the adverse effects caused by humic acid on the structure of the hydric soil.Although the number of large pores gradually increased,it did not bring about significant changes in the integrity of the cement-soil structure.The cement soil still presents a relatively compact honeycomb overall structure,which still has a strong ability to resist humic acid erosion,and still has a high strength.