International Concrete Abstracts Portal

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.

Reports data from a comparative, long-term study of several blended cements. The study compared the performances of five different binder systems for strength and for properties related to durability. It was found that both ground granulated blast furnace slag (ggbs/slag) and silica fume (microsilica) were very efficient in improving durability and impermeability. The two materials combined with OPC in a triple blend showed better performance than either on its own, and in this combination, silica fume compensated for much of the delayed strength development in slag cement concretes. Paper gives a thorough summary of the results obtained during the first 30 months of the project.

A high-performance concrete may posses satisfactory performance in many aspects other than compressive strength. In the context of in situ strength development, the performance of concrete at an early age is important. The temperature development, resistance to thermal cracking, early age engineering properties, and in situ strength development may all play a significant role in insuring satisfactory long-term performance. Describes the engineering properties of some very high-strength and high-performance concretes containing blast furnace slag with compressive strengths in excess of 80 Mpa under simulated "in situ" conditions of restricted moist curing and high-hydration temperatures. The influence of blast furnace slag content and the implications of the in situ development of engineering properties on performance are discussed.

Describes the development of a new type of high-performance concrete incorporating large volumes of ASTM Class F fly ash. Briefly, this concrete incorporates about 56 percent fly ash by weight of cement, and has a water-to-cementitious materials ratio of about 0.32. The portland cement and fly ash contents are of the order of 155 and 215 kg/m 3 of concrete, respectively. The flow slumps are achieved by the use of large dosages of superplasticizers. Because of the low cement content, the temperature rise in this concrete is low, and this concrete is ideally suited for concrete structures where excessive temperature rise is a concern. Also, the high-volume fly ash concrete has all the attributes of a high-performance concrete. It has excellent mechanical properties and demonstrates superior resistance to freezing and thawing cycling, chloride-ion penetration, sulfate attack, carbonation, and marine environment. Also, it has low permeability, and shows excellent performance in reducing potential expansion due to alkali-aggregate reaction.