I am working on the topic "Acid attack in concrete". I found that cement mortar specimens on exposure to sulphuric acid solutions, on leaching, pH of the solution is decreasing. Is it possible that gypsum formed due to the attack will decrease the pH of sulphuric acid solution?
Honestly, I do not see how gypsum precipitation would make the pH of the solution decrease. What would be the mechanism explaining this pH change? On the contrary the precipitation of ettringite could have this impact.
Sir, leaching of hydroxyl ions generally increases the pH of the acid solution. In case of sulphuric acid, pH increase is very lesser when compared to acetic acid. Yes, gypsum may not influence pH change. Could you pls inform how ettringite can impact pH? Ettringite is unstable in acidic solution and could not be present in degraded layers.
Indeed, hydroxyl ion release partially neutralize the acid.
Ettringite precipitation has sometimes been seen during sulfuric acid attack (see §3.2.2 in attached file).
Do you have a published comparison of degradation kinetics of cement in sulfuric and acetic acid?
Sir, thanks for the file. My research is on both sulfuric and acetic acid attack. We are yet to publish our results.
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