Study On Effect Of Common Inorganic Salts On The Property Of Interfacial Transition Zone And Pore Structure Of Concrete

Inorganic salt admixtures are often used in concrete engineering because of their economic suitability for early strength,anti-freeze,quick setting and so on.As the addition of salts can participate in cement hydration reaction,it will have a certain impact for the cement stone with early and late internal structure.In this paper,we mainly tested and observed the interfacial transition zone,pore structure,air voids strcture of concrete admixed with inorganic salt and fly ash.The microhardness and thickness of the interfacial transition zone of the concrete after the mixed with inorganic salt were observed by microhardness tester,It was found that the addition of Na Cl and Ca?NO₃?₂ increased the microhardness,Ca?NO₂?₂ and Na NO₂ will reduce it,low content of Na₂SO₄ have little effect on the microhardness,high content will significantly reduce the microhardness.Ca?NO₃?₂?Na₂SO₄ will increase the thickness of the interface area,but others have little effect on the interface thickness.When mixed with fly ash,the microhardness of the interface area is reduced,others make the interface thickness increase but Na₂SO₄ will make it reduce.The change of pore structure after inorganic salt admixed was measured by nitrogen adsorbometer and mercury porosimeter,it was found that the addition of Na Cl and Na₂SO₄ could refine the early pore structure,Ca?NO₂?₂ and Ca?NO₃?₂ have a coarsening effect,inorganic salts will make the late pore structure development slowly.The inorganic salt had no obvious effect on the early pore structure after adding fly ash,but when concrete cured for 28 d,Na Cl effectively reduces the number of the most distribute pores,the addition of Na NO₂ a and Ca?NO₂?₂ make same effect.Other inorganic salts reduce the number of the most distribute pores and smaller pore size,but the addition of Ca?NO₃?₂ increases the most distribute pores.Observing the air voids structure of hard concrete by microscope,Na₂SO₄ could increase the gas content,other inorganic salts has a more or less reducing effect on the gas content of the concrete;Na Cl had little effect for the average radius of pores,Ca?NO₂?₂,Ca?NO₃?₂ and Na₂SO₄ increases it,Na NO₂ will reduce it;Na Cl,Ca?NO₂?₂,Ca?NO₃?₂,Na₂SO₄ will increase the air void spacing coefficient at varying degrees,Na NO₂ reduces the air void spacing coefficient.When the fly ash is mixed,the gas content of concrete mixed Ca?NO₂?₂,Ca?NO₃?₂,Na₂SO₄ and Na NO₂ increased with the increase of fly ash,Na Cl showed a decrease first and then increase.With the increase of fly ash content,the average pore radius and air void spacing coefficient are decreasing.