Effect of Synthetic Calcium Silicate Hydrate(C-S-H)on Combination of Chloride Ions with Cementitious Materials
Mixtures of cement-based material with the addition of synthetic calcium silicate hydrated(C-S-H)was prepared,then the effect of internal admixture of C-S-H on the evolution of the combination ofchloride ions with the cement paste during aging process was investigated by means of XRD,TG-DTG,SEM and EDS.The results showed that the quantity of free chloride ions in the test pieces tended to decrease and then increase with aging process.At the ages of 7,14 and 21 d,the quantity of free chlo-ride ions in the cement paste with C-S-H was higher than that without C-S-H.This was due to the relative-ly larger particle size and smaller specific surface area of C-S-H,which reduced the total specific surface area of C-S-H in the cement paste and reduced the combination amount of C-S-H to chloride ions;in ad-dition,the addition of C-S-H to the cement paste could promote the hydration of cement and increase the pH value in the early hydration period,and the high pH value is not conducive to the adsorption of C-S-H on chloride ions;and there is no Friedel's salt generation in the early hydration period of the cement paste mixed with C-S-H,so that weaken the chemical combination ability for chloride ions.At the age of 28 d,Friedel's salt was generated in the cement paste with addition of C-S-H,thus the amount of chemi-cal combination of chloride ions increased,so the free chloride ion quantity of the two groups of cement paste was more similar.Due to more SiO2 existed in the cement paste with C-S-H at 28 d,the pozzolanic reaction to generate C-S-H with low Ca/Si and the decrease in pH value affecting Friedel's salt stability,the amount of free chloride ions increased significantly at 35 d.
cement pastechloride ionscalcium silicate hydrationchloride bindingpH value
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