International Concrete Abstracts Portal

Recently, there has been a great demand for high-quality concrete and concrete structures with high performance. In this context, silica fume is one of the most remarkable mineral admixtures that can give concrete high performance, such as high workability, strength, and durability. However, it is unclear as to the types of form silica fume takes in concrete, mortar, and cement paste. Some researchers point out that silica fume may be in high agglomeration. Therefore, it is very important to disperse silica fume in concrete effectively to get high-performance concrete. Consequently, this paper deals with the effect of physical treatment (ultrasonic homogenizer) and chemical treatment (superplasticizer) of silica fume on the properties of mortar. In this study, different silica fumes were used, one Japanese and five imported. The investigated properties of mortar were workability (flow values), compressive strength, and total pore volume. The study resulted in the following conclusions: 1) Silica fumes in the Japanese market were highly agglomerated in the natural state. This agglomeration of silica fume can be broken up by using some treatment methods, such as ultrasonic homogenizer and superplasticizer. 2) Physical treatment (ultrasonic homogenizer) before mixing mortar was useful to improve compressive strength and to decrease total pore volume of mortar containing silica fume. The use of superplasticizer could result in highly workable mortar. 3) The effectiveness of ultrasonic homogenizer treatment and that of superplasticizer treatment are different.

The latest developments in concrete platform concepts for deep water and floating structures have indicated the need for further development in the field of practical concrete technology. Paper presents some of the most significant factors in this challenge such as increased compressive strength, improved workability, and stability of fresh concrete, use of high-strength lightweight aggregate concrete, measures to improve the concrete E-modulus, and utilization of variable concrete density to optimize the platform design. This has been achieved through further development of the constituent materials, refinements of the mix design, and advancements in production methods, as well as the use of high-quality lightweight aggregates.

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.