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Concrete durability has become a matter of great practical significance. It is particularly critical to reinforced and prestressed structures where lack of concrete durability can lead to lack of structural stability and integrity through steel corrosion. The two significant factors affecting and controlling concrete durability are permeability and porosity. While nonadmixture low w/c concrete can be durable, this paper puts forward the thesis that it is superplasticizers that can insure long-term durability of concrete and concrete structures. For too long, water-reducing agents, plasticizers, and superplasticizers have been looked upon as workability/pumping agents with possible savings in cement and increases in compressive strength. It is suggested that this concept of these admixtures is misleading and ill-informed. While good workability is recognized as an essential component of placing and compacting, the more critical role of superplasticizers should be seen to reduce the porosity and sorptivity of concrete through water reduction. Paper presents test data on concrete and mortar mixes with blended cements and superplasticizers and having water-binder ratios of 0.35 to 0.40. The properties of these concretes are presented and discussed in terms of strength development, permeability, pore structure, carbonation, and microstructure. It is shown that superplasticizers should be seen as agents of concrete durability rather than as agents of concrete workability.

Steel is used widely in reinforced concrete for its structural properties and because the alkaline environment normally protects the steel from corrosion. However, this alkalinity does not protect steel in the presence of chloride ions. Furthermore, in environments subjected to freezing and thawing, durability can also be affected severely. The corrosion resistance of embedded metals can be improved by the use of concrete admixtures. Calcium nitrite improves corrosion resistance by promoting passivity of metals in concrete. Superplasticizers reduce chloride ingress by allowing the use of lower water-cement ratios. Microsilica (silica fume) substantially increases concrete resistivities as well as lowering permeability to chloride. In this paper it is demonstrated how various combinations of these admixtures improve the corrosion resistance of steel in concrete, while giving greatly improved strengths, necessary freeze-thaw resistance, and handling properties conducive to rapid placement and consolidation.

The influence of alkali sulfate on the viscosity of cement paste containing a superplasticizer was studied by using rotational viscometer. The mechanism of the action of superplasticizer on the fluidity of cement paste was also investigated. A larger amount of superplasticizer was rapidly adsorbed onto C3A and C4AF compared to that on C3S and C2S. The presence of alkali sulfate inhibited the adsorption of superplasticizer on C3A and C4AF, thus permitting increased adsorption on C3S and C2S. The reduction of viscosity of cement paste by superplasticizer is dependent mainly on its adsorption onto C3S and C2S. Therefore, an increase in alkali sulfate leads to an increase in the adsorption of superplasticizer on C3S and C2S, and results in reduced viscosity of cement paste. Excessive amount of alkali sulfate, however, compressed the electric double layer, providing an increase in viscosity of cement paste. Based on the results, it was concluded that there was an optimum alkali sulfate level with respect to the fluidity of cement paste containing the superplasticizer.

Purpose was to optimize the type and dosage of superplasticizer in concretes incorporating ASTM Class F fly ash, so that compressive strengths as high as those of superplasticized silica fume concretes could be obtained. Two types of high-range water reducers based on sulfonated naphthalene polymer (SNP) and sulfonated melamine polymer (SMP) both as 40 percent aqueous solution have been used in the presence of fly ash or silica fume to manufacture superplasticized flowing concretes containing ASTM Type I or Type III portland cements. The superplasticizer dosage and the pozzolan addition ranged from the 2 to 4 percent and from 12 to 20 percent, respectively, by weight of cement. The cement factor varied from 255 to 400 kg/m3. The results of the investigation work indicate that only in the presence of ASTM Type III portland cement, superplasticized fly ash concrete can be as strong as the corresponding silica fume concrete, particularly at relatively high cement factors ( ò 300 kg/m3).

To design and build state-of-the-art concrete structures, you need access to the latest information on materials and materials research. Bringing together the combined expertise of the chemical admixtures, cement, and concrete industries, Superplasticizers and Other Chemical Admixtures in Concrete will provide the answers you need on these important concrete admixtures. A collection of 33 papers, this ACI publication presents the latest findings on topics such as: superplasticizers--a global review with emphasis on durability and innovative concretes; reuse of returned concrete by hydration control; superplasticizers and concrete durability; evaluation of superplasticizers in concrete; chemical admixtures in concrete platforms; superplasticized concrete containing blast furnace slag; slump control with reactive polymeric dispersant; and physiochemical characterization of superplasticizers. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP119