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Deals with the design of a concrete capable of increasing the airtightness of the primary containment of nuclear power stations. The general context of structures of this type and the types of damage commonly found in them (thermal cracking) are introduced. Then an ideal concrete is described and an attempt is made to approximate it by applying a rigorous formulation process. The result is a high-strength concrete having a low cement content (270 kg/m3), a 28-day strength of about 70 MPa, and a high workability through the use of silica fume and calcareous fillers. This concrete and a more conventional concrete are put through a series of characterization tests which makes it possible to conduct numerical simulations of the temperatures and restrained deformations in the containment. The reduction of the risk of thermal cracking is clearly demonstrated. Finally, all of these laboratory investigations are verified on a full-scale containment element, in which all the benefits of using this new type of high-performance concrete appear (temperature rise cut by 25 percent, near disappearance of cracking, tenfold reduction of airleaks). The advantages of such a concrete are not restricted to the nuclear context, but cover all applications for which a dense, crack-free concrete is desired.

Compressive strength and water penetration of three grades of high-strength concretes with cement contents ranging from 400 to 500 kg/m3 and a proprietary superplasticizer are reported. The control mixes were redesigned by adding a Class F-type fly ash at fly ash/cementitious ratios of 0.15 and 0.35. All concretes were designed for a similar workability. The strength development was monitored in three curing regimes. It is concluded that the superplasticized concrete developed a higher strength than that predicted from a reduction in the water/cement ratio. The curing conditions significantly influenced the strength development and the water penetration of the concretes. An optimum fly ash/cementitious ratio of 0.15 was found to be appropriate for the concretes; larger amounts of fly ash were found undesirable for higher strength development.

Use of silica fume is important to produce high-strength concrete. Possible negative effects on long-term properties are, therefore, of vital interest for the future development of high-strength concrete. It has been reported that silica fume concrete stored in air showed strength loss from 90 days to 5 years, but courses are not discussed. The report was based on a limited number of results. Similar results are not found in high-strength concrete up to 10 years old either in laboratory tests or testing samples from existing structures in Norway. Results from two major research projects showed that, for laboratory-stored specimens, the strength increased or was constant for concrete stored in water or air, respectively. No difference was found between high- and normal strength concretes. The increase was somewhat higher for concretes without silica fume compared to concretes with up to 20 percent silica fume by weight of cement. Furthermore, the strength increase was somewhat higher for water-stored concretes than for air-stored. However, high-strength silica fume concrete was not more sensitive to early drying than concrete without silica fume. High-strength concrete from several existing structures did not exhibit the same consistent pattern in strength development, however. This is probably due to insufficient documentation at an early age. However, the results did not show any significant negative long-term strength development.

This investigation reports on three high-strength concretes produced by low-heat portland cement with silica, blast furnace slag cement, and rapid-hardening portland cement, and a normal strength control concrete produced by rapid-hardening portland cement. The weight losses of creep and shrinkage cylinders are compared to corresponding deformation values at 1 year. The porosities of creep and shrinkage concrete specimens were determined by mercury porosimeters at the age of 7 days when the tests started and, thereafter, at the ages of 14, 35, and 372 days. The microporosity of binder paste specimens was determined by nitrogen adsorption at the ages of 14 and 35 days. The creep and shrinkage values of the high-strength concretes are compared to the values obtained by CEB formulas. It is concluded that the initial creep and shrinkage rate of high and normal strength concretes is governed by the evaporable water amount lost to the external environment. The average pore radii of the test concretes emptied from water during the creep and shrinkage tests were calculated.

Heat of hydration of a selection of high-strength concretes has been investigated by means of a so-called semiadiabatic calorimeter test. The temperature development within a hardening specimen enclosed in an insulated container is used as basis for a simulation of the adiabatic temperature increase and the specific heat development of the cement. The results indicate that the heat of hydration can be affected within a relatively wide range by the utilization of traditional mix design parameters. Heat of hydration is affected not only by the cement content but also by the water/cementitious ratio {w/(c + s)} and the silica fume content. The heat of hydration per cement unit decreases approximately 9 percent when the w(c + s) is reduced form 0.36 to 0.27. At w(c + s) 0.50, the replacement of cement by silica fume on a 1:1 basis induces a significant increase in the heat evolved per cement unit. The increase corresponds approximately to the reduction in cement content. Hence, the temperature rise in the concrete is not significantly affected. The ability of the silica fume to increase the heat evolvement of the cement decreases with decreasing w(c + s), and is negligible at w(c + s) 0.27. Hence, a replacement of cement by silica fume on a 1:1 basis at this w(c + s) leads to a lower temperature rise of the concrete.