The concrete industry's response to society's need for immediate gratification is concrete that can be put into service early—in less than a day in some cases! To meet this demand, cement producers have adjusted the composition and fineness of the cement, concrete producers have lowered the w/c, precasters have raised curing temperature, and concrete contractors have taken on fast-track building, bridge, and pavement contracts. In these and other ways concrete has shown itself to be up to the challenge, and high early strength is an option almost anywhere there is an owner who is willing to pay for it. But is there a downside?
One common side effect is that whenever the mixture is modified or the construction procedures configured to increase the early-age rate of strength gain, there is a reduction in later-age strength. “Slow and steady” hydration is portland cement's preference for optimal performance, as long as you have the time to wait for it.
Another aspect of this is that even though strength gain may be accelerated effectively, associated properties such as abrasion resistance, frost resistance, or resistance to corrosion may not be equally accelerated. Thus a structure can be put into service without its full complement of environmental protection. If we are going to pay the price and deal with the side effects of accelerated concrete performance, let's make sure that it matters in the context of the overall project schedule. Does the owner get an equivalent concrete earlier, or an inferior concrete earlier?
Read more highlights from 50 Years of Concrete Construction Progress.