Effect of drying-rewetting on the alkali concentration of the concrete pore solution

Experience has shown that the pore solution alkalinity of resaturated concrete was lower than expected. Laboratory-concrete specimens were made with reactive aggregates, stored over water at 38 °C, and then broken into two pieces. The pore solution of half-specimens was extracted by high-pressure squeezing. The other half-specimens were dried at ambient air and rewetted in humid air to their initial weight. The pore solution was then extracted and compared with the composition results of the first extraction. The results obtained from this investigation confirmed that a certain part of the alkali ions in pore solution that had become fixed by drying are not subsequently extracted after rewetting. The alkali concentration [Na+K] was reduced from 34% to 61% by the drying and rewetting treatments.