The major reasons for using accelerators are: to accelerate initial set for earlier finishing; to develop high early strength for maximum concrete production; and to minimize length of time required for winter protection. However, growing concern about the effect of chloride-based materials on corrosion of metals in concrete has led to some limitations of their use. Fortunately the nonchloride accelerating admixtures now available have allowed the benefits of acceleration to be achieved without the major concern of corrosion. Some projects using a nonchloride accelerator are outlined in this article.
ONE OXFORD CENTRE, PITTSBURGH, PENNSYLVANIA
During the winter, the contracting company replaced its water-reducing admixture with a nonchloride accelerator which has water-reducing properties also. The typical slab placement in this 48-story office building involved 300 cubic yards per day; the nonchloride dosage was 14 ounces per 100 pounds cement, increased to 21 ounces per 100 pounds cement for the last 100 cubic yards each day. This increase in dosage was to reduce setting time and minimize overtime. In the 10-story parking structure adjacent to the building, the nonchloride accelerator was used in conjunction with a high-range water-reducing admixture (superplasticizer) to place flowable concrete with optimum setting characteristics.