Abstract
In 1980 a sidewalk was built at Bécancour, Québec, with condensed silica fume concretes containing highly reactive aggregates. Eleven concrete mixes were used with cement quantities from 140 to 405 kg of cement per m3 and condensed silica fume substitutions varying from 10 to 40%. In spite of the great reactivity of the aggregates, the alkali-aggregate reaction is still under control. Microstructural studies of four particular concretes have been made after the first and third winters. No silicate gel has been observed in the two leaner mixes but some has been found in a few locations encircling coarse aggregate particles in the two richer mixes. The severe scaling problem observed in one of the concrete is characterized at the microstructure level by frequent unbonding of coarse aggregates and presence of converging cracks around the aggregates.