Ceramics-Silikáty 49, (2) 109 - 114 (2005)

The study deals with the investigation of changes of sodium and potassium hydroxide concentrations in the mortar pore solution and related material expansion. The experiments following the alkali-silica reaction were carried out on a model mixture of opal as reactive aggregate component and cements having different alkali content. The pore solution was obtained by extraction of the crushed mortar with hot water. The molar sodium-potassium hydroxides ratio in the mortar pore solution is similar to the sodium-potassium ratio in cement. The decrease of alkali concentration in the solution with time and the increase of mortar expansion are proportional. Mortar expansion increases as a result of expansion pressure generated by products of the alkali-silica reaction. The time change of the alkali concentration in the solution is not affected by C₃A content in cement.