Effect Of Slag On The Resistance To Seawater Corrosion Of The Ordinary Portland Cement-Aluminate Cement-Gypsum Cementitious System

Building under the marine environment occurred corrosion of reinforcement,concrete expansion due to the erosion of the ions in the seawater for a long time,which severely shortens the life of building in the marine environments.But if the beginning of concrete cracking is to be effectively patched,the durability of building in marine environment can be extended.A ternary system,ordinary Portland cement-aluminate cement-gypsum,mixed according to a certain percentage,can be produced the performance of rapid hardening and high strength and used as a building repair materials.In order to improve the resistance to seawater corrosion of the ternary system,different contents of slag were added and replaced part of the ternary system.This paper studied on the the ternary system with different dosages of slag in the corrosive environment,and expect to provided a proper repair material in marine environment.Firstly,this paper determined the mass proportion of ordinary Portland cement-aluminate cement-gypsum is 76%:16%:8%according to existing research results.Different dosages of slag（5%,15%,25%,and 35%）were added to the ternary system.Next,the ternary and quaternary systems were cured in tap water for 28 days and then immersed in the seawater for 360 days.Compressive strength,mass change,porosity,and chloride content were studied.Once again,in order to speed up the erosion process and study the interaction between chloride and sulfate,the different systems cured in tap water for 28 days were immersed in 5%（by mass）NaCl solution,5%（by mass）Na₂SO₄ solution,5%（by mass）NaCl+5%（by mass）Na₂SO₄ solution for 180 days.The changes of compressive strength,mass change,porosity,etc were measured.In the end,the X-ray diffraction analysis was used to test and analyse the reaction products.The results are described as follows:（1）25%-35%dosage of slag significantly enhances the resistance to corrosion of the ternary system when immersed in seawater,5%NaCl solution,5%Na₂SO₄ solution,and 5%NaCl+5%Na₂SO₄ solution.（2）The addition of slag significantly reduces of free chloride content in the system.（3）The existence of chloride in the system can decrease the formation of ettringite,slow down the sulfate attack.The existence of sulfate reduced the free chloride and total chloride contents in the system,limited the formation of Friedel’s salt.（4）By comparison of the test parameters,the optimum amount of slag in seawater,5%NaCl,5%Na₂SO₄,and 5%NaCl+5%Na₂SO₄ environments were determined as 25 wt.%,35 wt.%,25 wt.%,and 25 wt.%,respectively.