Research Of Concrete Durability In Saline Soil Environment

This thesis studies the deterioration mechanism of highway concrete with saline soil in Hetao,Inner Mongolia.Two field researches were conducted in spring and autumn.The saline soil samples were collected from G6-W,110-W,110-D respectively,and environmental conditions were simulated in the laboratory.The compound salt solution（NaCl,Na₂SO₄,NaHCO₃,Na₂CO₃）in Hetao saline soil environment and the single salt solution（Na₂SO₄）for comparison were prepared.5kinds of concrete with different elements（reference concrete;concrete mixed with 10%and 20%fly ash;concrete mixed with 10%and 20%metakaolin）were prepared for experimental studies on concrete durability.The compound salt-wetting-drying cycle test,single salt-wetting-drying cycle test,compound salt-freeze-thaw cycle test,single salt-freeze-thaw cycle test were carried out.In the wetting-drying cycle test,the compressive strength value as the concrete deterioration evaluation index,and in the freeze-thaw cycle test,the relative dynamic modulus as valuation index.The outcome shows:（1）The saline soil in Hetao is carbonate soil,total soluble salts in spring is greater than that in autumn,and the pH value of soil in spring is greater than that of soil in autumn.（2）In this paper,the concrete wetting-drying cycle was divided into four stages:crystal compaction stage,damage development stage,strength deterioration stage,and residual strength stage.Compound salt-wetting-drying cycle test caused greater destruction to concrete than single salt-wetting-drying cycle test.Fly ash and metakaolin enhanced concrete’s ability to resist wetting-drying circle.（3）Compound salt-freeze-thaw cycle test caused greater destruction to concrete than single salt-freeze-thaw cycle test.Metakaolin concrete’s ability to resist freeze-thaw cycle is better than fly ash concrete.The best proportion of metakaolin and fly ash is between 10%²0%.（4）Deterioration prediction model of compressive strength of salt-wetting-drying cycle and deterioration prediction model for relative dynamic elastic modulus of salt-freeze-thaw cycle were respectively verified in the test,and average fitting degrees were respectively 0.92 and 0.93.