Study On The Interaction Of Cementitious Materials And Various Aggressive Media In The South China Sea Environment

Many aggressive media in the South China Sea environment destroy concrete structures.With the development and utilization of marine resources,solving the durability of marine concrete becomes urgent particularly.In addition,concrete produced by seawater directly or seawater through simple treatment is expected in engineering applications due to a shortage of freshwater resources on the South Island Reef.Most current studies on the durability of concrete in the marine environment focus on investigating the effects of aggressive ions diffusing from the external environment?extravasated aggressive ions?under a single environment factor on the performance of the concret.Therefore,simulating different environmental conditions in the South China Sea to explore the complex interaction between cementitious materials and two aggressive ions of Cl^-and SO₄^2-introduced in the ways of incorporation and extravasation and to prove the mechanism,which can provide theoretical guidance and data support for marine construction and concrete produced by seawater and are of important theoretical significance and engineering application value.Firstly,in order to reveal the interaction mechanism between the two aggressive ions,phase analysis,ion titration and thermal analysis were the main means used and the chloride ion binding capacity of cementitious materials was used as the evaluation index to investigate the effects of the aggressive ions penetrating into the cement paste,ie,Cl^-and SO₄^2-,on cement hydration products at ambient conditions.The study finds:whether aggregate and sulfate ions are added or not,the isotherm adsorption curves of Cl^-in the cementitious materials follow the law of linear variation;there is a complex competitive relationship between the two ions in the process of diffusion migration and chemical combination when the two ions exist in the erosion solution at the same time.Then,the vertical semi-immersion method was used to place the test specimens in the environmental chambers that the concentration of sea water and temperature and humidity in the South China Sea were simulated.According to analyse the changes in the distribution of Cl^-,physical properties,microcosmic composition and morphology at different depths in saturated and unsaturated regions of the specimen to investigate the effects on the influence law and mechanism of action of aggressive media and cementious materials under the combined effects of multiple factors.The results indicate that:diffusion of Cl^-is affected by SO₄^2-through two different interactions:promotion and inhibition,which are affected by the ambient temperature,promotion of SO₄^2-in the time period is shortened and the inhibition is correspondingly prolonged when the ambient temperature increases when the two ions exist in the erosion solution at the same time.This law also exists in the unsaturated.Because the capillary adsorption capacity increases with the decrease of relative humidity,the content of free chloride and bound chloride at different heights in the unsaturated zone of the specimen increases with decreasing ambient humidity.When Cl^-and SO₄^2-coexist in the erosion solution,SO₄^2-occupies the transmission channel of Cl^-,thereby the transmission channel of Cl^-is inhibited.Finally,simulating the concentration of seawater ions in the South China Sea,introducing aggressive ions in different ways?incorporation and incorporation-extravasation?and using phase analysis,hydration heat test and microscopic morphology analysis to study the influence of chloride ions introduced in incorporation way on the hydration process of cement and the stability of corrosion products.The results show that Cl^-and SO₄^2-in the mixing water participate in the cement hydration process and have the effect of accelerating hydration,Cl^-is especially obvious.When Cl^-are introduced into the cementitious materials as mixing water:the Cl^-accelerates the dissolution of C₃A to produce ettringite to accelerate the cement hydration in the cement hydration of 10h.Friedel salt can be detected in 1d hydration,ettringite gradually turns into Friedel salt as the hydration proceeds.Because the ettringite and aluminum phase can form AFm and Cl^-can replace the anion in AFm to produce Friedel salt while the introduction of SO₄^2-can promote the formation of Friedel salt.Friedel salt can basic stablility exist in 28d hydration.At the cement hydration of90d,part of the Friedel salt can be converted to Kuzel salt.In order to study the stability of Friedel salt,the cementitious materials 28d hydration mixed by seawater were selected and immersed in an erosion solution with Cl^-.It is found that the seawater-mixed cementitious materials still have the capacity of chloride ion,but the capacity is significantly less than purewater-mixed cementitious materials;In the erosion solution,Cl^-promotes the formation of Friedel salt while SO₄^2-promotes the decomposition of the Friedel salt.The following innovations have been made in this paper:different environmental conditions in the South China Sea were simulated and vertical half-soaking testing system was used to verify the effect of extrapolated Cl^-and SO₄^2-and the combined effects of different temperature and humidity on the corrosion of cementitious materials and to reveal the mechanism of interaction among cementitious materials and extra-corrosive media in the South China Sea.Cl^-and SO₄^2-were introduced in different ways to study the stability and conversion relationship of Friedel salt and ettringite in the hydration process,to reveal the impact of Cl^-and SO₄^2-on the hydration process and the interaction mechanism of cementitious materials and aggressive ions introduced in different ways.It is of great significance for the study of environmental marine structures and seawater mixing concrete in the South China Sea.