Research On Service Performance Of Buried Concrete Components In Qinghai Saline Soil Area

As the state continues to increase its support for new infrastructure policies,Qinghai Province responded positively and vigorously promoted infrastructure construction.But saline soil is widely distributed in Qinghai Province,and the engineering mechanical properties of saline soil in different regions are obviously different,in the process of infrastructure construction in this area,the special properties of saline soil,such as corrosiveness and salt-expansion,have a relatively unfavorable effect on the service performance of buried concrete components.Therefore,a systematic study of the service performance of buried concrete components in Qinghai saline soil area has important guiding significance for the construction of the area.This paper takes sulfate saline soil in Pingan District,Haidong City,Qinghai Province as the research object.On the basis of determining its salt-expansion property,the field test of the buried reinforced concrete slab subjected to salt-expansion and the sulfate corrosion resistance of the fly ash concrete test block were carried out around its salt-expansion and corrosiveness.At the same time,through the indoor full immersion test of concrete specimens,the influence of sodium sulfate erosion on the deterioration of concrete under different temperature conditions was studied.Combined with SEM electron microscope scanning test,EDS energy spectrum analysis test,matlab software data fitting,orthogonal test method,BP neural network model and other analysis methods,the evaluation index of the service performance of buried concrete components in Qinghai saline soil area was investigated preliminarily and the main conclusions are as follows:（1）The saline soil in Pingan District,Haidong City,Qinghai Province belongs to sulfate saline soil,its salinization degree is medium saline soil,and contains a small amount of chloride salt.The highest percentage of anion is SO4^2-,cation is Na⁺,and the soil presents medium salt-expansion.（2）Based on the field tests of buried reinforced concrete slab in the sulfate saline soil area in Pingan District,Haidong City,Qinghai Province,the concept of salt-expansion stress was proposed.Considering the influence of temperature,the variation of salt-expansion stress with the temperature inside and on the surface of reinforced concrete slabs was investigated.Based on the observational data,an empirical formula was proposed to calculate the salt-expansion stressα_y using the sum of sine model.The variation ofα_y with time can be divided into three stages including developing stable,and decline stages.The developing stage is from October of each year to February of the following year.During this period,the temperature range is between10°C and 0°C.Within this temperature range,as the temperature decreases,theα_ycontinues to increase which demonstrates that the salt expands becomes more significant.Based on the results of this research,suggestions were provided to minimize the damage of saline soil to buried structures in Qinghai Saline soil area.（3）Based on the field test of sulfate erosion resistance of fly ash concrete test blocks in the sulfate saline soil area of Haidong,Qinghai,by studying the change law of the compressive strength of the concrete test block cubes with time.The results showed that the cubic compressive strength of the fly ash concrete test block increased after 240 days of erosion,and the cubic compressive strength of the fly ash concrete test block decreased significantly after 540 days of erosion.The optimal amount of fly ash is 10%.The SEM results show that the expansion of the ettringite crystals formed by the chemical reaction caused micro-cracks in the fly ash concrete test block after540 days of erosion.Orthogonal test and BP neural network model prediction results show that erosion time is the main factor affecting the service performance of fly ash concrete components.After 540 days of field erosion,the fly ash concrete components had initial deterioration,but no damage occurred.（4）Based on indoor concrete components immersion test,the effect of Na2SO4erosion on the concrete deterioration performance under different temperature conditions（i.e.,-35℃,20℃and-15℃）was studied.Three indicators were analyzed including the uniaxial cube compressive strength,the elastic modulus and the corrosion resistance coefficient K.The results show that the uniaxial cube compressive strength,the elastic modulus and the corrosion resistance coefficient K of the concrete test block are decreased as the constant immersion temperature drops.Besides,SEM results show that the generation and number of ettringite crystals are affected by temperature and immersion time.The crystallization pressure caused during the process of ettringite crystals growth and the fine acicular crystals generate internal stress in the hardened cement paste upon absorbency swelling.In consequence,micro-cracks are witnessed in the concrete structure,leading to a strength reduction in the concrete.（5）Based on the results of field test and indoor test,the service performance evaluation index F of buried concrete components in Qinghai saline soil area is initially proposed,and the determination of the empirical coefficient a related to the evaluation index requires a longer period of testing to obtain more abundant test data to determine.