Influence Of Nano-CaCO₃ On Durability Of Pervious Conrete Against Acid Rain Erosion

In recent years,as my country has actively promoted the construction of"sponge cities",environmental problems such as urban waterlogging and the"heat island effect"have been greatly improved.Pervious concrete is one of the important building materials for the construction of"sponge city",and its physical mechanics properties and durability are one of the important factors that determine the development prospect of"sponge city".The porous structure of pervious concrete increases its contact area with the external environment,which not only leads to its poor mechanical properties and durability against acid rain,but also restricts its application in areas with more acid rain.To improve physical mechanics properties and acid rain corrosion resistance of pervious concrete,this paper researched the effect of nano-CaCO₃ and its powder on physical mechanics properties and acid rain resistance durability of pervious concrete specimens,and analyzed enhancement mechanism of nano-CaCO₃ on acid rain erosion resistance of pervious concrete,and the regression analysis between shock wave velocity,ultrasonic wave velocity and basic performance indicators is carried out by test.The main research conclusions of this article are as follows:（1）With nano-CaCO₃ content increasing,the water permeability of pervious concrete specimens first decreased and then increased,the ability to resist elastoplastic deformation shows the opposite trend.Though adding nano-CaCO₃ will reduce the porosity and water permeability of the specimens,the influence is small;adding nano-CaCO₃ has an excellent effect on compressive and flexural strength of the specimens,and the enhancement effect of flexural performance is better,the best effect is when the dosage is 1%～2%.（2）After acid rain corrosion,the appearance and morphology of each group of specimens showed deformation,missing edges and corners,aggregate shedding and surface pitting,the mass loss and water permeability showed a change law of first decreasing and then increasing;while the dynamic elastic modulus and compressive strength show a trend of first increasing and then decreasing,and flexural performance of the specimen was also damaged.Adding nano-CaCO₃ can slow down the appearance deformation,the amount of aggregate shedding and the surface pitting area of the specimens,reduce the change rate of the mass loss,the water permeability coefficient and the dynamic elastic modulus,and improve the compressive and flexural properties of the specimens,improve the ability of pervious concrete to resist acid rain erosion,the best content is 1%to 2%.The compressive strength,flexural strength and water permeability of each group of specimens showed a linear relationship and an exponential function relationship,respectively.（3）The combined action of dissolution damage to cement stone by H⁺and swelling damage from gypsum,AFt and others formed by SO₄^2-and hydration products is the fundamental reason for acid rain to attack pervious concrete.After corrosion,the specimens without mixing appear cracks,and its structural integrity is reduced,nano-CaCO₃ can form stable products such as 3Ca O·Al₂O₃·CaCO₃·12H₂O and Ca（OH）₂（CO₃）₅ with hydration products,Thereby improving the ability of pervious concrete to resist acid rain erosion.（4）With acid rain erosion days increasing,the shock wave velocity and ultrasonic wave velocity of each group of specimens all increased first and then decreased,adding nano-CaCO₃ can reduce the wave velocity loss.The mass loss,porosity and water permeability of each group of specimens all decrease with the increase of wave velocity,but the dry density,compressive strength,flexural strength and wave velocity are positively correlated.The dynamic elastic modulus calculated by the shock wave method and the ultrasonic method is basically consistent with the test results of the resonance method used in the specification.Therefore,the shock wave method and the ultrasonic method can be used for the non-destructive testing of the dynamic elastic modulus of pervious concrete.