International Concrete Abstracts Portal

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.

High-strength concrete tends to mean small water-cement rations, implying poor workability. This tendency becomes more pronounced when much higher strength is required, and conventional concreting processes cannot sufficiently guarantee high-quality work. In current construction work, therefore, maximum use has been made of precast concrete (guaranteeing quality and minimizing the need for concrete cast in situ) and a new high-performance, air-entraining, and plasticizing admixture has been used for the necessary in situ concrete. The concrete prepared in this way exhibited a mix strength of 55 MPa at best. This value, in itself, is by no means high, but meaningful efforts to establish methods of concreting that insure still greater strength have been made. This construction work has demonstrated that combining the reinforced concrete (RC) layer method (which uses a large proportion of precast members) with high-strength concrete obtained from mixing with the new high-performance, air-entraining, plasticizing admixture is an extremely effective way to secure quality structures. Since this admixture is a novel product, the physical properties of the resulting concrete have been thoroughly checked to supplement the results of laboratory experiments and preliminary field tests.

Briefly reviews five joint industry-research programs pertaining to offshore concrete structures. These programs were sponsored by the oil and gas industry and related construction industries. These studies, conducted in both North America and Norway, included the use of high-strength, lightweight aggregate concretes in both material and structural evaluations. Selected characteristics of the high-strength, lightweight aggregate concretes used in these studies (such as ductility in reinforced concrete elements, punching shear behavior, and fatigue characteristics) are summarized. Future research needs are discussed.

Pore structure, density, and strenght may vary within a wide range for different types of lightweight aggregate. Hence, not all types of lightweight aggregate are suitable for production of high-strength concrete. In the present work, the significance of various lightweight aggregates on the concrete strenght and density was studied. Twenty-eight-day compressive strengths up to 102 MPa, corresponding to a density of 1865 kg/m3, were obtained. The type of lightweight aggregate appears to be the primary factor controlling both the density and the strength. For high-strength lightweight concrete, it is difficult to predict the 28-day strengths from early strengths because of the influence of the aggregate.

In Norway, almost every car is equipped with tires that have small steel studs to improve the traction between the tire and the road for driver control during the winter season. These studded tires have an enormous wearing effect on ordinary asphalt pavement. Roads with the heaviest traffic near the major towns need to be resurfaced at intervals of 1 to 2 years. To improve the abrasion resistance, application of high-strength concrete instead of asphalt has been started. The national Norwegian cement producer has performed a large-scale investigation to determine the relation between concrete composition and abrasion resistance. The results prove that a 100 MPa concrete might approach the same properties as massive granite. The paper describes a number of projects performed by an independent company, where this high-quality material has been utilized in practical construction.