Validation of the alkali contribution by aggregates to the concrete pore solution

Abstract

Mortar and concrete specimens were made with six reactive and non-reactive aggregates from Eastern Canada, with different alkali contents, to determine their alkali contribution to the pore solution. Two methods were used to determine the alkali content of samples over time: the high pressure extraction method and the espresso extraction method. Also, an alkali leaching test was conducted directly on the same aggregate materials. One aggregate was clearly identified as a potential source of Na+ to the pore solution. Results obtained after one year at 60°C showed that rich alkali-bearing aggregates, which can be identified in an alkali leaching test by immersion in alkaline solutions, can release up to 1.75kg Na2O/m3 of concrete if used as fine fraction and up to 0.24kg Na2O/m3 of concrete if used as coarse fraction. However, no clear K+ contribution from aggregate was observed.