Crack-free concrete for outside industrial floors in the absence of wet curing and contraction joints

Shrinkage-compensating concrete can be manufactured by using an expansive agent provided that an adequate wet curing is carried out after demolding: the surface treatment should be wet cured for at least one week.In the present work a special superplasticized shrinkage-compensating concrete has been studied which does not need any wet curing, provided that it is protected for 1 day by a polyethylene sheet from rain or sunny weather, when an outside industrial floor is cast. The superplasticizer (PA/SRA) is still based on a polyacrylate superplasticizer (PA), but it also contains a special chemical group acting as shrinkage-reducing admixture (SRA) incorporated in its molecular structure. Due to the increase in the pH of the aqueous phase caused by the cement hydration, the SRA chemical group is liberated from the molecular structure of the superplasticizer and is then capable of reducing the surface tension of the pore. This change in the surface tension of the pore water increases the restrained expansion of the concrete containing a CaO-based expansive agent.Due to this additional effect, a superplasticized shrinkage-compensating concrete can be successfully placed even in the absence of a wet curing. In this paper a practical application is shown where this crack-free concrete is used for an outside industrial floor of 800 m2 without contraction joints and in the absence of any wet curing.