Are we ready to accept high-volume fly-ash concrete in cold-weather climates? A number of practitioners in Canada's largest city, Toronto, think so. They are betting that a 50/50 fly-ash-to-portland-cement mix for a four-story 120,000-square-foot computer sciences building on the campus of York University will prove their point.

Although fly ash has been used extensively for underground concrete projects—subway tunnels in Toronto are a case in point—high-volume mixes (50% or more) are relatively unheard of in above-ground applications where cold weather slows curing and hampers workability. For concrete purposes, cold weather is defined as 3 consecutive days averaging below 40° F in which the temperature never rises above 50° F for more than half of any 24-hour period.