International Concrete Abstracts Portal

The troll GBS platform is the world's largest concrete offshore concrete platform. The platform is designed for an operational lifetime of 70 years and will be installed in the North Sea during 1995. To improve the buoyancy of the platform during tow-out to the field, a concrete mixture with reduced density has been developed, providing a characteristic 28-day cube compressive strength of at least 75 MPa and an in situ density of 2250 kg/m 3. The weight reduction has been obtained by partly replacing the natural coarse aggregates by high-quality lightweight aggregates. The concrete is denoted as modified normal density (MND) concrete. The modification was expected to reduce both compressive strength, Young's E-modulus, and material ductility to some extent. A comprehensive testing program comprising laboratory tests and full-scale tests has been performed to investigate and to document all relevant concrete properties related to mechanical, durability, and constructibility performance of the concrete. A secondary purpose of the investigations has been to evaluate the possibility of retaining the mechanical properties of the original normal density concrete by replacing the remaining coarse granite aggregate with a more rigid quartz-diorite aggregate. The laboratory investigations included the determination of the following concrete properties: fresh concrete properties, compressive strength development, compressive strength at sustained load, compressive E-modulus, tensile strength and E-modulus, stress-strain in compression, fatigue, fracture energy and characteristic length, shrinkage, creep, water intrusion, and alkali-silica reactivity.

The chemical and petrochemical industries that process chemical and petrochemical products manufacture, store, and transfer a number of liquids that are hazardous to the environment and particularly to the groundwater. In Germany, uncoated concrete may be used only as a secondary barrier for handling water-hazardous materials. Development and optimization studies were carried out to reduce the permeability and increase the ductility of concrete for this application. Concretes with styrene-butadiene-based polymer dispersions and silica fume were produced to reduce the permeability, and concretes with limestone or expanded clay instead of Rhine gravel to improve ductility. The mechanical behavior of the concretes was characterized by determining the stress-strain curves under tensile and compressive loading and the stress crack-opening curves. Resistance to environmentally hazardous liquids was tested using a special penetration test standardized in Germany. Various organic liquids, each representing a main chemical group and of differing water solubilities and viscosities, were used as test media.

One of the techniques proposed to improve the durability performance of concrete in aggressive environments is to use quality concrete. Much research has shown that cement composition also has a significant effect on concrete durability in sulfate-bearing soils/groundwaters and in chloride-corrosive situations. High C 3A cements have been found to be superior in terms of protection against corrosion of reinforcement, although they have a lower sulfate-resistance performance. In many situations, such as marine and Sabkha environments, chlorides and sulfates occur concomitantly and operate against concrete durability simultaneously. This study has been carried out to evaluate the sulfate resistance and chloride penetration performance of high-strength concrete. Two high-strength concrete mixes in the range of 60 to 75 MPa were designed first by using a superplasticized concrete of 0.36 water-cement ratio (w/c) and second by replacing 10 percent cement by silica fume. The control for comparison is a 25 Mpa concrete made with a 0.58 w/c. Type I portland cement has been used to provide higher chloride-binding capacity and, hence, better corrosion protection. A mixed sodium and magnesium sulfate environment has been used to evaluate sulfate resistance. High-strength concrete made with silica fume blending showed the best sulfate resistance in a sodium sulfate environment and the worst performance in a magnesium sulfate environment. Also, the normal 0.58 w/c ratio of 300 kg/m 3 cement content mix showed 1.5 times better performance than the 0.36 w/c ratio 450 kg/m 3 cement factor mix in magnesium sulfate environment. High-strength concrete showed three to four times better performance against chloride penetration compared to normal strength concrete. Use of 10 percent silica fume further improved resistance against chloride penetration.

A significant proportion of Australian infrastructure is located in a zone that is close to or in direct contact with seawater. At most of these locations, the coastal environment is coupled with high ambient temperatures and large diurnal temperature ranges, conditions that are conducive to promoting corrosion of steel reinforcement in concrete structural elements. Users of concrete are thus always looking for ways to maximize concrete performance for long-term use under these aggressive conditions. The options available in terms of binder systems for concretes in a marine environment have increased in recent years. There are currently available a range of cements and blended cements that include fly ash, slag, and silica fume, which have a place in specifications for marine concrete applications. To provide technical data for potential specifiers and users of such concrete types, a collaborative CSIRO-CSR research and development project was initiated to consider the performance of a range of concretes for marine environments. Concretes considered had a water-binder ratio of 0.35 and included both portland and blended cements. Paper reviews current standards on specifications of concrete for marine environments and goes on to present some recently produced Australian data for different concretes reflecting potential performance. Techniques considered include chloride-ion penetration of concrete based on charge transfer measurements, chloride-ion penetration through concrete, and some mechanical properties of concrete. Conclusions are drawn as to the suitability of certain concrete types under marine conditions.

The combined use of chemical and mineral admixtures has resulted in a new generation of concrete called high-performance concrete (HPC). Understanding the roles of mineral admixtures, such as silica fume, fly ash, and slag depends on in-depth microstructural investigation of HPC at different ages. What is of major interest concerning these materials is their contrasting hydraulic behavior. Whereas silica fume and fly ash are pozzolanic, slag is strictly cementitious. The early strength of concrete increases when silica fume is incorporated, but the activity of slag and fly ash starts much later, and therefore, manifestation of changes in concrete properties, such as strength enhancement, also appears to be delayed. It is in this light that the roles of these admixtures, both individually and in combination, are described in terms of the development of HPC moisture.