New Admixtures for Eliminating Steam Curing and its Negative Effects on Durability

Heat curing is the most common method used for accelerating the strength development in concrete. Accelerated curing finds large applications in the precast industry for quick turnaround of forms and casting beds. The increase in the initial strengths is simply a result of increased rate of hydration caused by higher temperature. However, later strengths are often lower than those of the same concrete cured at 20C. The causes of the strength loss are of physical and chemical nature. The physical cause results in increased porosity and cracking because the concrete constituents have different thermal expansion, (air has the highest). The chemical causes are the differences in the hydration products, microstructure and degree of hydration. Generally, physical causes are the dominating factors for strength loss in hear cured concrete. Results of extensive laboratory and field tests are presented showing that equivalent compressive strengths at 18 hours are obtained with concrete containing the new generation superplasticizers and heat cured concretes at 60C. The 28 day strengths of concretes with admixtures are substantially higher. Thus, with the use of these new generation superplasticizers it's possible to overcome the negative effects of steam curing such as strength loss, permeability, shrinkage, creep and frost resistance.