A durability study by three ready mixed concrete producers from Columbus, Ohio has shaken the widely held assumption that concrete exposed to deicers and severe winters will inevitably scale. The three firms subjected a variety of concrete slabs to two winters of repeated deicer applications in order to demonstrate to an audience of local concrete masons and residential builders factors which affect durability of the finished product. What they saw was firm proof that following established guidelines for placing, finishing and curing produces exterior concrete that will not scale no matter how much salt is dumped on it.
The ready mix producers placed two rows of eight 4-inch-thick, 10- by 10-foot slabs on a site. The concrete mix was the same for all slabs and contained no special admixtures with the important exception of an air-entraining agent used in half the slabs. The demonstration was kept as simple as possible so that, besides air entrainment, the only variables that came into play were the slump of the concrete used in each slab and the adequacy of curing, if any. Strength of all hardened concrete, while varying significantly from slab to slab, exceeded 3500 psi by the time the first deicers were applied, more than 6 weeks after placement.
During the first winter deicers were spread over the slabs at the rate of 8 pounds per square yard. (By comparison, the Ohio Department of Transportation applies about 4 pounds per square yard to its highway surfaces in an average season.) Initial scaling began with the first thaw, only 3 weeks after the first deicers went on. This occurred only in the uncured portion of the air-entrained slab placed with an 8-inch slump. As for the moderate- (4-inch) slump slabs, none showed any scaling or deterioration whatsoever after one year, even those placed without entrained air and then left uncured. This confirms the well-known rule that lowering slump by reducing water content produces stronger, more durable concrete.