Beneath the futuristic silver-blue aluminum and glass skin of a skyscraper is a core structure built with steel-reinforced concrete. The high-strength concrete allowed architects of Hong Kong's Bank of China Tower and other modern skyscrapers to build habitable structures that often reach heights of more than 1,000 feet. However, today's concrete is much more than the centuries-old recipe of cement, aggregate, and water. Super-plasticizers, including sulfonated naphthalene-formaldehyde condensates and polycarboxylate derivatives, are added to the concrete mix to reduce the amount of strength-diminishing water. Although mechanisms may vary, dispersion of cement particles by super-plasticizers results in a low-water concrete that is more fluid when fresh and stronger and more durable when cured. Such characteristics are essential for the next generation of skyscrapers when large volumes of fresh concrete will be pumped to construction sites more than half a mile above ground.
Park, S. B.; Tia, M. The effects of superplasticizers on the engineering properties of plain concrete. Transp. Res. Rec. 1986, 1062, 38-46. Superplasticizers (sulfonated naphthalene condensates (NP-10), sulfonated melamine condensates (NP-20), and combined sulfonated naphthalene and sulfonated lignin condensates (Sanflo FB and Sanflo FBF)) had an appreciable fluidifying action in fresh concrete. They permitted a significant water redn. while maintaining the same workability. Bleeding of superplasticized concrete was much lower than that of conventional concrete of the same consistency. The compacting factor and Vee Bee value of superplasticized concrete were not significantly different from those of conventional concrete of the same consistency. This indicates that the use of superplasticizers did not affect the tendency of segregation of fresh concrete. The compressive, tensile, and flexural strengths of superplasticized concrete were significantly higher than those of conventional concrete. The permeability and drying shrinkage of superplasticized concrete were significantly less than those of conventional concrete, but there were no significant differences between base and superplasticized concrete. Compared with base concrete, nonair-entrained superplasticized concrete had slightly higher freeze-thaw durability, and superplasticized concrete with an appropriate amt. of entrained air gave even better freeze-thaw resistance.
