Ex situ leaching measurement of concrete alkalinity

A new technique involving ex situ leaching (ESL) of concrete particles in deionized water and chemical analysis of the resulting leachant was developed to determine the concrete pore water alkalinity. A water-to-concrete powder ratio no higher than 1 and a leaching time no less than 3 days were mostly used. The concrete pore water hydroxide ion concentration ([OH−]pore) was then calculated based upon a protocol that included several assumptions. It was found that [OH−]pore was proportional to the cement equivalent alkali content but relatively insensitive to the concrete water-to-cement ratio. Determinations of [OH−]pore were compared with (1) results from parallel, conventional pore water expression (PWE) experiments using concrete from the same batch, (2) a theoretical estimate of this parameter based upon mix design and cement chemistry of the concretes employed for ESL, and (3) data from the literature. All of these comparisons either directly or indirectly confirmed the validity of the proposed method. However, applicability of the ESL method, as proposed, to concrete containing pozzolans or highly soluble inorganic salts (or both) needs to be further explored.