Study On Performance Of High Performance Concrete Paste In Seawater Environment

With the blooming of ocean construction engineering,the influence of seawater on concrete durability draws increasing attentions.A great deal of facts have proved that ordinary concrete cannot meet the requirement of durability in marine environment.High performance concrete?HPC?has been widely used in ocean construction engineering for its stronger resistance to all kinds of deleterious ions than ordinary concrete.This paper investigates the compressive strength and expansion rate of HPC pastes soaked in simulated seawater and different erosive solutions with the development of age.In addition,the mineral composition and microstructure of HPC pastes had been studied at 1320 days.On this basis,the mechanism and protective measures of HPC on resistance to erosive ions in marine environment are investigated.The following conclusions are obtained:For the compressive strength of HPC pastes,the erosive effect of SO₄^2-on the paste at 1320 days is always greater than Cl^-;For pure cement paste,ground granulated blast-furnace slag?GGBS?paste,silica fume?SF?paste and limestone powder?LP?paste,the erosive effect of Cl^-is stronger before 90 days.The reaction between erosive ions and cement hydration products improves the early compressive strength of HPC paste.At the age of 1320 days,the simulated seawater has the strongest erosive effect on the compressive strength of the LP paste.MgSO₄ solution has the strongest erosive effect on the compressive strength of pure cement paste,FA paste,GGBS paste and SF paste.When two erosive ions coexist,Mg²⁺always shows a promotion of SO₄^2-or Cl^-erosion at 1320 days.At the age of 1320 days,the compressive strength of FA paste and GGBS paste is significantly improved.For the expansion rate of HPC paste,the expansion caused by Cl^-at 1320 days is always greater than that caused by SO₄^2-.At the age of 1320 days,the expansion rate of all pastes soaked in simulated seawater is the highest.At 1320 days,for pure cement paste,FA paste,GGBS paste and LP paste,Mg²⁺promotes the expansion of paste caused by SO₄^2-.For SF paste,Mg²⁺inhibited the expansion caused by SO₄^2-.According to XRD analysis,at the age of 1320 days,the content of Ca?OH?₂ in the paste soaked in erosive solution is lower than that in pure water.When the two ions coexist,Mg²⁺prevents SO₄^2-or Cl^-from invading into the paste.The presence of Ca²⁺inhibits the formation of Friedel's salts.According to SEM analysis,at the age of 1320days,there are more holes and cracks of the pastes soaked in the erosive solution.CoMPared with the pure cement paste,the paste mixed with mineral mixture has a more coMPact internal structure.The results of this project are helpful to understand the erosive mechanism of high-performance concrete under the marine environment,and put forward more reasonable anti-erosion measures,so as to improve the durability of marine engineering concrete and provide theoretical basis and technical guidance for the preparation of marine engineering concrete.