| Saline soil is widely distributed in China,which is mainly divided into five saline soil areas,namely coastal area,Huang Huai Hai Plain,semi desert inland area,Songnen Plain and Qinghuanxin extremely arid area.Because there are a lot of permafrost in this area,in order to study the erosion mechanism of sulfate erosion of concrete under constant negative temperature environment,further solve the occurrence of such problems,research excellent physical and mechanical properties Concrete with good durability and engineering adaptability is very important.Considering the negative temperature concrete construction and maintenance environment in permafrost and saline soil areas where Lanzhou–Xinjiang railway passes,comparative tests of concrete with different maintenance environment temperatures,body surface ratios,and stone powder content were carried out,and the sulfate corrosion resistance of machine-made sand concrete with equal strength under constant negative temperature was studied.The experimental conditions simulate the typical environment of the permafrost saline soil area on the Lanxin Line,and analyze the constant curing temperature(-5 ℃,20 ℃),body surface ratio(1.67 cm,1.17 cm,0.67cm),and micro indicators of concrete(porosity,pore size distribution)from the macro indicators of concrete(compressive strength,mass loss rate,relative dynamic modulus,and morphology change)and the micro indicators of concrete(porosity,pore size distribution)The influence of stone powder content(5%,10%,15%)on the strength development and sulfate corrosion resistance of concrete.(1)The mechanical sand concrete cured for 35 days at negative temperature has the same strength value as the concrete cured for 28 days under the same conditions,which means that the negative temperature concrete reaches equal strength.Based on experimental analysis,the development law of concrete compressive strength is obtained.The results show that the 10%stone powder content is more effective in optimizing the concrete pore structure and increasing compressive strength compared to 5% and 15% stone powder content.At the same time,the 15% stone powder content has better performance than the 5% stone powder content;The body surface is negatively correlated with compressive strength values and positively correlated with porosity.Although the negative temperature curing mechanism sand concrete achieves equal strength,its pore structure is different from that of standard cured concrete after 28 days.A concrete strength prediction model was established based on the relationship between the compressive strength of concrete during the development stage of equal strength and the variation of pore structure with the increase of curing age.(2)According to the experimental principle,negative temperature and equal strength concrete should be subjected to a dry wet cycle test in an environment of-5 ℃.However,in order to conduct the test and analyze the rules within a limited time,the dry wet cycle test was placed in an environment of 20 ℃ room temperature with an erosion age of 360 days.According to the results of the dry wet cycle test,it was found that under the same conditions except for the curing temperature,the internal pore structure of negative temperature cured concrete deteriorates significantly compared to standard cured concrete,indicating that the sulfate corrosion resistance of equal strength concrete decreases with the decrease of temperature;As the surface ratio of concrete decreases,the macroscopic indicators of concrete deteriorate more significantly,and the corrosion resistance of concrete also decreases accordingly;The amount of stone powder added can improve the corrosion resistance of concrete,but there is a certain limit to the gain effect of the amount of stone powder added.Among the three types of stone powder added concrete under the same conditions,10% stone powder added mechanical sand concrete has better corrosion resistance than 5% and 10%stone powder added concrete.(3)Based on the loss of dynamic elastic modulus of concrete at different ages,the loss of dynamic elastic modulus of concrete was obtained.A concrete damage degree model was established by comprehensively considering the relationship between curing temperature(-5 ℃,20 ℃),body surface ratio(1.67 cm,1.17 cm,0.67cm),and stone powder content(5%,10%,15%)and the loss degree of machine made sand concrete.(4)Analyze the effects of curing temperature(-5 ℃,20 ℃),body surface ratio(1.67 cm,1.17 cm,0.67cm),and stone powder content(5%,10%,15%)on the corrosion resistance of concrete from a microscopic perspective(porosity,pore size distribution).According to the microscopic experimental results,it was found that as the age of concrete erosion increases,the porosity of concrete under the same conditions decreases in the early stage,and increases with age in the later stage;The experimental results show that adding an appropriate amount of stone powder to concrete can improve its sulfate resistance performance,and among the three types of stone powder dosages(5%,10%,and 15%),the optimal effect is the 10%dosage;A decrease in curing temperature and a decrease in body surface ratio will have a negative impact on equal strength concrete,making it more susceptible to corrosion.(5)Based on the macroscopic relative dynamic elastic modulus index and erosion age of sand concrete in sulfate corrosion stage under equal strength mechanism,a concrete loss degree model under sulfate corrosion environment is used to predict concrete life.According to the deterioration equation,the corrosion life distribution of experimental concrete is between 68.49 years and 86.42 years;Through analysis,it was found that there is a positive correlation between the body surface ratio and the average life of machine-made sand concrete.As the body surface ratio increases,the average life also increases;As the curing temperature decreases,the average lifespan of machine-made sand concrete also decreases;Among the three types of stone powder admixtures(5%,10%,15%),the machine-made sand concrete with 10% stone powder admixtures has the longest average lifespan. |
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