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Conflicting information on the freeze-thaw resistance of superplasticized concrete is given in the literature. For this reason, the Research Centre of the German Cement Industry instigated an extensive research program. Superplasticizers based on melamine and naphthalene sulfonates were used in the main program and lignosulfate-based products in a subsidiary program. Some of these contained de-airing agents. The air-void distribution and the spacing factor were measured as well as the freeze-thaw resistance with deicing chemicals. When superplasticizers were used in a high-workability air-entrained concrete, the number of pores with a diameter up to 300 æm decreased, while the content of pores larger than 500 æm and the bubble spacing factor increased. Small pores coalesced and formed larger pores. Although the air content of the fresh concrete was sufficient, the superplasticized concrete sometimes had a spacing factor above 0.20 mm. For this reason, concrete with superplasticizers did not always have adequate freeze-thaw resistance. An influence due to the type of superplasticizer could not be detected, while the de-airing agents of the superplasticizers had a considerable effect. Some additional tests with plasticizers and retarders show that these admixtures also alter the air-void distribution or air-entrained concrete.

The basic principle of preventing the deterioration of reinforced concrete structures is to inhibit the wet corrosion of reinforcing bars. According to the principle, the effective inhibition of the penetration of carbon dioxide, oxygen, water, and chloride ions is required to make highly durable concrete. Mortars are prepared with various contents of chemical admixtures and cement modifiers to meet such requirements, and tested for strength, water absorption, chloride ion penetration, and carbonation. From the test results of the mortars, effective admixtures are selected for concrete mixes. The strength, chloride ion penetration, carbonation, and drying shrinkage of concretes containing the selected admixtures are examined. In conclusion, the simultaneous addition of polymer dispersions and alkyl alkoxy silane at a polymer-cement ratio of 0.5 percent is recommended for the highly durable concrete.

Highway structures ranging in age from 4 to 12 years and constructed from concretes incorporating high-range water reducers were surveyed for extent of surface scaling. Core samples were obtained from selected areas. Samples were subjected to petrographic analysis and linear traverse measurements. Air-void systems were characterized using standard ASTM C 457 parameters, chord distribution analysis, "Philleo" factors, and modal chord lengths. Statistical models relating degree of surface scaling to various combinations of parameters were tested. A three-parameter linear model incorporating spacing factor, water-to-cement ratio, and alteration of air voids in near-surface regions was found to yield the highest level of correlation with observed scaling.

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.