A reply to the discussion by Mingshu Tang of the paper “Laboratory assessment of alkali contribution by aggregates to concrete and application to concrete structures affected by alkali–silica reactivity”

Incidence of Alkali Release in Concrete Dams. Evaluation of Alkalis Releasable by Feldspars

“…In these cases, the increase in alkalis in the solution or in the porous phase would be related to the ionic exchange of Na and K with Ca. Furthermore, part of the leached alkalis is incorporated into the reaction products, even though the types of products formed depend on the * Correspondence to: emm@ietcc.csic.es composition of the solution and on the amount of Ca [12]. In accordance with the results, the Na of feldspars in alaskite is stable in alkaline solutions of K (0.5N) and saturated Ca.…”

“…However, different authors are critical as regards the incidence of the alkalis leached from the aggregates in the development of the silica-alkali reaction. The alkalis liberated by the cement are produced under the conditions of an elevated presence of CaO, which is why the Na + and the K + are not fixed [6,12]. Also, [13] indicate that in the case of potassium feldspar, K is liberated, but Al2O3 and SiO2 remain.…”

“…According to [6,12] it is difficult to bring about decomposition of the feldspars in solutions of saturated KOH, NaOH and Ca(OH)2. In these cases, the increase in alkalis in the solution or in the porous phase would be related to the ionic exchange of Na and K with Ca.…”

Effects of Soak Solution Type on Alkali Release from Volcanic Aggre-gates − Is Alkali Release Really Responsible for Accelerating ASR Expansion? −

“…These results emphasize that measuring only the amount of alkalis in the solution is insufficient when trying to determine the relationship between the amount of alkalis released and the potential risk of long-term ASR expansion. Bérubé et al (2004aBérubé et al ( , 2004b argued that there is competition between the consumption of alkalis via silica dissolution and the supply of alkalis being released from the aggregate. In fact, it was observed in these experiments that the amount of dissolved silica was higher than that of the alkalis released by one to two orders of magnitude.…”

“…Following a publication by Bérubé et al (2002), Tang (2004) and Shi (2004) raised a discussion regarding whether or not alkalis released from aggregates can increase hydroxide ion concentration and thus the pH of the pore solution. Bérubé et al (2004aBérubé et al ( , 2004b argued that this was possible, but did not measure hydroxide ion concentration or pH. They believed that the underlying mechanism was the precipitation of the reaction in the presence of lime.…”