THE KINGSTON, ONTARIO EXPOSURE SITE FOR EFFECTIVENESS OF PREVENTIVE MEASURES FOR ALKALI-SILICA REACTION

The selection of measures to prevent alkali-silica reaction in concrete requires confidence that the selected measure will work over the life of the structure. It is crucial that the results of short-term laboratory tests be correlated to long-term performance of concrete in structures. An outdoor exposure site was established in Kingston, Ontario in 1991. Beams and pavement slabs on grade were cast with Spratt reactive aggregate and various cementing materials. The expansion of the beams and slabs has been measured for nine years and correlated with laboratory expansion of mortar bars and concrete prisms. The concrete made with high-alkali cement cracked at an age of five years. Where various amounts of supplementary cementing materials were used, expansion has been considerably less and only very minor cracking has occurred. The following materials have been shown to be more or less effective: 50% and 25% ground granulated blast-furnace slag, 18% type F fly ash, and low-alkali cement (< 0.6% Na2Oe). The most effective measure that also had adequate freeze-thaw scaling resistance was a ternary blend of 25% slag and 3.8% silica fume interground in a high-alkali Portland cement.