Study On Erosion Failure Types Of Concrete In Saline Soil Area Of Tumushuke City, Xinjiang

Saline soil is widely distributed in Tumushuke City,Xinjiang.SO₄^2-in saline soil seriously affects the durability of concrete.Concrete buildings are also damaged by freeze-thaw cycles,which aggravates the durability damage of concrete.In view of this,the study of saline soil in Tumushuke City was carried out,the spatial distribution characteristics of soil salt ions in Tumushuke City were analyzed,and the spatial distribution map of soil salt ions in the study area was drawn.According to the actual content of sulfate,the sulfate erosion and freeze-thaw cycle tests were carried out,and the macroscopic indexes such as appearance morphology,mass,compressive strength,dynamic elastic modulus of the specimens were measured.This thesis analyzes the performance deterioration of concrete specimens in different environments,and analyzes the types of concrete erosion products under different test conditions,so as to classify the erosion failure types of concrete.The main research results are as follows:（1）Tumushuke City,Xinjiang,is a sulfite saline soil with uneven horizontal distribution of salinity and strong spatial heterogeneity.Soil salinity shows strong spatial autocorrelation at all horizontal levels,and environment is the main factor influencing its spatial distribution.Salinity at the soil level shows a pattern of"high in the east and low in the west"and"high in the north and low in the south".Moreover,the concentration of soil salts decreases with increasing depth,with the highest concentration of soil salts in the surface layer.（2）In the concrete sulfate total immersion test,the mass loss rate showed a decreasing and then increasing trend with the increase of erosion age.The greater the sulfate concentration,the greater the initial mass growth of the erosion and the greater the rate of mass change of the concrete specimen.The compressive strength increases with the age of erosion and then decreases,reaching a maximum at 120 d of the age of erosion.The higher the concentration of sulfate,the faster the rate of decline in compressive strength,and the compressive strength is more sensitive to sulfate attack.（3）In the sulfate-freeze-thaw cycle test,the mass loss rate of concrete specimens gradually increased with the number of freeze-thaws.The greater the concentration of the sulfate solution,the greater the mass loss of the specimen.The compressive strength firstly increased and then decreased with the increase of the number of freeze-thaw cycles.The relative dynamic elastic modulus generally shows a downward trend.The relative dynamic modulus of elasticity and compressive strength of concrete are more sensitive than mass loss.In other words,under the action of sulfate-freeze-thaw cycle,the internal damage of concrete is greater than the damage of concrete surface spalling.（4）The erosion products in the environment of total sulfate immersion are mainly calcium alumina and gypsum.When the concentration is lower than 10000mg/kg,the main erosion product is calcium alumina,and the concrete specimen shows calcium alumina type erosion.At concentrations of 10,000 mg/kg and 15,000 mg/kg,calcium alumina and gypsum were present simultaneously,showing calcium alumina-gypsum type erosion.When the concentration is greater than 20000mg/kg,it mainly shows gypsum type erosion.Under the coupled sulfate-freeze-thaw action,concrete specimens microformation in addition to the erosion products needle-like calcium alumina and columnar gypsum appear.It is also accompanied by microcracking caused by hydrostatic and osmotic pressures generated during freeze-thaw,which accelerates the expansion and structural loosening of microcracks in concrete specimens.Also,at low temperatures,carbon sulfur silica-calcium crystals are generated and the specimens exhibit carbon sulfur silica-calcium type erosion.（5）The results of microscopic test analysis,combined with the salt distribution map,can be used to derive the zoning of concrete sulfate erosion damage types in Tumushuke City.The sulfate concentration is low in the southwestern part of Tumushuke City and some areas in the northeastern part of the city,which mainly shows the type of caliche erosion damage.The central northern region with higher sulfate concentration is mainly characterized by calcite-gypsum type and gypsum type erosion damage.