Superplasticizing Admixtures

Portland cement concrete has clearly emerged as the material of choice for the construction of a large number and variety of structures in the world today. This is attributed mainly to low cost of materials and construction for concrete structures as well as low cost of maintenance. Therefore, it is not surprising that many advancements in concrete technology have occurred as a result of two driving forces, namely the speed of construction and the durability of concrete. During the period 1940-1970, the availability of high early strength portland cements enabled the use of high water content in concrete mixtures that were easy to handle. This approach, however, led to serious problems with durability of structures, especially those subjected to severe environmental exposures.1 Among the recent advancements, most noteworthy is the development of superplasticized concrete mixtures which give very high fluidity at relatively low water contents. The hardened concrete due to its low porosity is generally characterized by high strength and high durability. Macro-defect-free cements and chemically bonded ceramics are examples of alternative technological approaches to obtain low-porosity, high-strength products. For the specific purpose of enhancement of service life of reinforced concrete structures exposed to corrosive environments, the use of corrosion-inhibiting admixtures, epoxy-coated reinforced steel, and cathodic protection are among the better known technological advancements. In addition to construction speeds and durability, there is now a third driving force, namely the environmental friendliness of industrial materials, which is becoming increasingly important in technology assessment for the future. In this article, a critical evaluation of various technologies is attempted using the following three criteria: • cost of materials and construction,