The effect of using supplementary cementitious materials on damage development due to the formation of a chemical phase change in cementitious materials exposed to sodium chloride

摘要

It has been reported that concrete can chemically interact with high-concentrated sodium chloride solution to form a new chemical phase change at temperatures between 0 degrees C and 10 degrees C. The formation of the chemical phase change has been found to be destructive and can cause damage in concrete. The chemical phase change appears to be the result of reactions between the sodium chloride, the tricalcium aluminate and the calcium monosulfoaluminate hydrate in the concrete matrix. This paper reports results of a study conducted to determine the effects of using supplementary cementitious materials as a partial replacement of the cement on reducing the chemical phase change amount and the associated damage development. Class C fly ash, class F fly ash, slag, and silica fume were used in this study. The amount of the chemical phase change was quantified using low-temperature differential scanning calorimetry. The damage development was monitored and quantified using a low-temperature longitudinal guarded comparative calorimeter equipped with acoustic emission technique. The results indicated that the addition of silica fume, class F fly ash, and slag can reduce the chemical phase change amount and the associated damage development while the addition of class C fly ash showed the opposite effect. X-ray diffraction analysis coupled with thermogravimetric data were also used to estimate the chemical compositions of cementitious pastes in order to determine the relationship between the amounts of the chemical phase change and the chemical constituents present in the cementitious systems. It was found that the formation of the chemical phase change is well correlated with the amounts of tricalcium aluminate and calcium monosulfoaluminate hydrate while a poor relationship existed for other chemical constituents available in cementitious systems. The beneficial aspects of supplementary cementitious materials based on their replacement levels, such as dilution effect and pozzolanic activity were also discussed. The best mitigation strategy to limit the formation of the chemical phase change and the associated damage is to utilize Type V cement or partially replace the Type I cement with silica fume, slag, or class F fly ash. The use of class C fly ash was found to increase the chemical phase change and the associated damage. Therefore, it should not be recommended in concrete exposed high-concentrated NaCI solution. (C) 2019 Elsevier Ltd. All rights reserved.