Investigating Supplementary Cementing Materials for Alkalis and Pore Fluid Properties

Dwindling supplies of quality fly ash inmany parts of the world necessitates an expeditious search for supplementary cementing materials (SCMs) to conform to the growing demand for sustainable materials in partially substituting for Portland cement in concrete. In recent years finely-ground waste glass, landfilled/ponded coal ashes and natural pozzolans have (re)drawn the attention of researchers and the industry to become potential SCMs. In this study a wide range of such SCMs were characterized for water-soluble and available alkalis using ASTMC114 and ASTMC311. Inductively coupled plasma emission spectroscopy (ICP-ES) was employed to determine the amounts of alkalis. Cementitious pastes containing Portland cement and SCM were prepared at a 0.5 water-to-cementing materials ratio and stored in airtight containers at 23 degrees C. The pore solution of these pastes at 28 and 91 days was analyzed for hydroxyl ion (OH-) concentration, and strengths of alkali ions (Na+ and K+) using ICP-ES. The results indicate that all alkali oxides of SCMs are generally neitherwater-soluble nor available. Except for the high-alkali ground glass and high-calcium fly ash, the use of all other reactive SCMs considerably decrease the presence of the hydroxyl and alkali ions in the pore solution in the long-term.