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Presents results of an investigation dealing with the long-term strength of silica fume concrete. Three series of concrete mixtures with and without silica fume were made with water-cementitious ratios from 0.25 to 0.40. The replacement level of portland cement with silica fume was kept constant at 10 percent. Test specimens were cast from each mixture to determine the compressive and flexural strengths of concrete at up to 3.5 years under both water-curing and air-drying conditions. The test specimens were also subjected to the determination of microstructure, carbonation, and weight changes with time. It is concluded that, under water-curing conditions, both the control and silica-fume concretes show gain in strength with age, with both concretes reaching similar strength levels after 3.5 years. However, continuous air-curing adversely affects the long-term compressive strength development of both types of concrete. This effect is considerably more marked for silica-fume concrete than for the control concrete, especially at w/c + sf of 0.30 and 0.40.

It is well known that curing concrete at elevated temperatures reduces the final compressive strength. The reduction depends on the temperature regime as well as the concrete composition. This program was based on recent data indicating that concrete containing condensed silica fume suffers less strength loss if a strength of about 10 MPa is reached at 20 C before heating. In this investigation, concrete characteristics were w/c + s = 0.30, 0.45, and 0.60 with and without 8 percent condensed silica fume. The temperature regime was to transfer specimens at 40 and 60 C, after delay times at 20 C. The delay times corresponded to strengths of about, 0, 3, 6, 9, 12, and 16 MPa. After 6 days, all specimens were cooled to 20 C and tested at 28d. The results show that the delay period had no significant influence on the final strength, except for the specimens with zero delay. The rest suffered some strength reduction compared to 20 C references, about 15 percent for w/c + s = 0.60, and less than 10 percent for the others. The reductions at 60 C were slightly greater than at 40 C. Concretes containing condensed silica fume generally suffered the smallest strength reductions.

There is an increasing tendency worldwide toward using cements blended with fly ash, silica fume, blast furnace slag, and natural pozzolans. Incorporation of these materials in concrete makes it dense and impermeable. While the effect of chloride and sulfate ions on the durability of blended cements is well documented, meager data are available on the synergistic effect of high concentrations of these salts on the durability performance of these cements. Since the structural components, especially foundations in the coastal areas in some parts of the world, are subjected to high concentrations of these salts, it is imperative to investigate the performance of blended cements in such environments. In this investigation, mortar and concrete specimens made with Type I cement blended with fly ash, silica fume, and blast furnace slag were exposed to a highly concentrated chloride-sulfate (2.1 percent SO4-- and 15 percent Cl- solution for a period of 540 days. The performance of these cements in resisting reinforcement corrosion was evaluated by monitoring half-cell potentials and measuring corrosion rates at periodic intervals. Deterioration due to sulfate ions was evaluated by visual survey, and measuring loss in compressive strength. Results indicate that surface deterioration and loss in strength was greater in blast furnace slag and silica-fume cement specimens compared to fly ash and plain cement specimens. Severe surface scaling and considerable reduction in strength (55 to 75 percent) was observed in the former cements. Moderate surface deterioration and loss in strength of about 25 percent was observed in fly ash and Type I cements. Corrosion of steel in silica fume and blast furnace slag was, however, much lower than in fly ash blended and Type I cements.

Gypsumless Portland cements (GPC) are inorganic binders, which may be described aas system of: ground Portland clinker (specific surface of 400-500 m2/kg - Blaine), a surface-active agent with hydroxyl groups and a hydrolyzable alkali metal salt (carbonate, bicarbonate, silicate). New cements, developed in recent years, are able to reach both higher strengths and fracture toughness than ordinary Portland cement (1,2,3). New developments in the making of very strong cements have resulted from modifying cement compositions and manipulating the microstructures (4).

In High-Strength Concrete in general high-quality aggregate is used. This aggregate has a high compressive strength and often a high modulus of elasticity. This high modulus of elasticity of the aggregate strongly influences the deformation behaviour of high-strength concrete. Results show that there is a direct and linear relationship between the shrinkage value and the modulus of elasticity of the concrete. The highest modulus of elasticity of concrete was 85 GPa. The compressive strength at the age of 28 days was in the range from 102 to 182 MPa. A design aid is given to show the interrelation between modulus of elasticity and shrinkage strain of the concrete on one side and modulus of elasticity of the aggregate, modulus of elasticity of the matrix and matrix content on the other side.