| The chloride-induced corrosion is an important issue for the durability ofreinforceing steel in concrete. Chloride ions exist in two ways in the concrete: one isthe free chlorides in the pore solution; the other is bound chlorides combined with thehydration products. It is generally recognized that only free chloride ions penetratethrough the pore solution and reach the surface of the steel, and then corrosionprocess begins. The free chloride ions within the pore solution of cement-basedmaterials are the main cause of premature deterioration of reinforced concretestuctures. Pore solution expression is the common method of obtaining free chlorideion concentration of pore solution. Recent studies report free chloride ionconcentration in pore solution obtained by pore solution expression is significantlyhigher than that of the exposured solution. This is known as the chloride condensationphenomenon.This work investigates the effects of NaCl soaking concentration, soaking time,curing time, sample thickness, soaking temperature, pore solution expression pressure,water-cement ratio and mineral admixtures on the free chloride ion condensation inpore solution of cement-based materials. This work’s achievements mainly focus onas follows: free chloride ion concentration in pore solution exhibits a good linearrelationship with the chloride ion concentration in soaking solutions after56-dayimmersion. The free chloride ion concentration is40%greater than that of theexposured solution when the chloride ion concentration in the exposed solution is lessthan0.3mol/L，and is slightly higher than that of the exposured solution when thechloride ion concentration in the exposed solution was greater than0.3mol/L. Thefree chloride ion concentration increases with soaking time before an immersionperiod of63days. This is due to that specimen does not achieve its maximumadsorption level. Thereafter, free chloride ion concentration decreases with soakingtime, but it is still higher than that of exposure solution.The total and free chloride ion concentration decrease as the curing timeincreased after an immersion period of56days. And the total and free chloride ionconcentrations of curing28days are much lower than that of curing3days. That is tosay, chloride ion concentration of pore solution decreases with curing time.Thespecimen of thicker thickness has a lower chloride condensation index. The freechloride ion concentration increases with soaking temperature and pressure. But they do not have a marked effect on condensation index. Sample thickness, soakingtemperature and pressure do not affect free chloride ion concentration.Chloride ion concentration of pore solution decreases with w/c ratio of0.3?0.6after56-day immersion. Condensation index for specimens of low water-cement ratio(W/C≤0.35) increased with soaking time. For high water-cement ratio (W/C〉0.35)，condensation index is reduced.The higher the proportion of fly ash, slag and silicafume, the lower condensation index. The partial replacement of cement with15%silica fume causes a significantly lower condensation index than other specimen. Forthe specimen containing fly ash and slag, results show that the free chloride ionconcentration is between the specimens containing fly ash or slag only. All thespecimens have a higher free chloride ion concentration than PC except PC with slag(20%replacement level) after the specimens are immersed for56days in the sodiumchloride solution. After immersion in the sodium chloride solution for91days, for thespecimens containing mineral admixture, the condensation index is lower than that ofPC.The theoretical analyse indicates that the electric double layer, zeta potential ofsampleand change of pore structure caused by pressure could be due to the freechloride ion condensation.The results of this project will provide scientific base formeasurement and explanation of chloride ion migration and binding in concrete, andfor service life design and prediction of reinforced concrete structures in chlorideenvironments. |
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