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Among the major problems facing the concrete industry at the end of the twentieth century are the enormous infrastructural needs of a rapidly urbanizing world, the premature deterioration of many concrete structures, the need to improve concrete durability in a cost-effective way, and increasing public interest in finding ecological solutions for safe disposal of millions of tons of industrial by-products that might be suitable for incorporation into cementitious materials and concrete. In this paper the author has shown that all these problems are interrelated and can be resolved by adopting a holistic approach.

This paper presents laboratory test results of the use of limestone modified cement for high-performance concretes, namely: self-compacting high-performance concrete and vibrated high-performance concrete. The limestone modified cement consists of portland cement and milled limestone. The test results show that proper selections of fineness and content of milled limestone reduces water demand, drying shrinkage, superplasticizer dosage and portland cement content for mortars as well as for concrete. The use of limestone modified cement containing selected fineness and content of limestone also increases compressive strength of the high-performance concretes.

Hardened concrete contains interconnected pores if, during its production, the quantity of water used is higher than that required to do away with capillary continuity of the paste. These pores contain ions in solution from the chemical reactions that take place. The major ionic components involved in the reactions may vary in concrete affected by ASR, in contrast with concrete with no ASR. By applying the fundamentals of the Longuet et. al. method, the composition of the liquids contained in the pores of specially proportioned mixtures has been studied. This paper presents the results of the research work carried out up to the age of 180 days in order to know the chemical composition of the liquid contained in the pores of hardened mortars, whether affected or not by the ASR, and that of others to which pozzolans had been added so as to prevent excessive expansion due to ASR.

The Siberian State Academy for Mining and Metallurgy (SSAMM) has developed a cementless fine-grained ash-slag concrete consisting of high calcium fly ash and slag sand from thermal power plants and containing silica fume. The also composition and technology of the concrete has been patented. The compressive strength of the concrete is 5 to 20 MPa. It does not contain any natural or artificial aggregates (gravel, sand, claydit, polystiren). High-calcium fly ash combined with silica fume is used as a binder. The influence of the ratio of the above mentioned three components on the compressive strength and density of the concrete developed was studied using a computing technique. As result, a three-dimensional integral scheme was designed for proportioning the concrete of a required strength class (5 to 20MPa) and density (2000 to 2500 kg/m3). The optima1 mixture proportions for concrete of 20 MPa strength class were as follows: Fly Ash 30-40% Slag Sand 3 O-40% Silica Fume 3-4% Water (60-80°C) the rest Concrete with optimum mixture proportions was used to investigate optimization of schedules of concrete heat treatment carried out in an automatic steam-curing chamber. Here, the three-dimensional system was involved as well: previous curing before heat treatment of 3, 6 and 12 hours; three schedules of a heat treatment i.e.,3(6)3, 3(9)3 and 3(12)3 hours cycles where (6), (9) and (12) hours are holding periods; three isothermal temperatures of 60, 80 and 100°C. A computerized analysis of the results of the investigation showed that heating of concrete during 9 to 10 hours at 80 to 1OO’C with 6 to 7 hours of curing provided the best strength characteristics of the concrete.

Cement paste samples incorporating various amounts of silica fume were made and stored in humid air at 23°C and 38°C. Their pore solution was expressed under high pressure at different times, then analyzed for its alkali content. The storage temperature did not significantly affect the alkali concentration in the short term (O-28 days), where most reaction products (hydrates) are formed. However, all control and blended pastes stored at 38°C recycled very significant amounts of alkali in the pore solution between 28 days and 1.5 years, while not those stored at 23°C. Consequently, the longter effectiveness of silica fume against ASR should be better than expected from a number of recent experimental studies all involving concrete expansion tests conducted at 38°C for field concretes exposed at an average lower temperature, e.g. in many regions of the world. This would explain at the same time why satisfactory field performance is reported in Iceland, for instance, while the only one case reported until now relating to poor field performance of silica fume against ASR took place under the hot South African climate. Results from concrete prism expansion tests also indicated that ASR expansion can develop in high-performance concrete, even with moderately reactive aggregates. Other expansion results confirmed that the higher the degree of reactivity of the particular reactive aggregate to counteract, the alkali content in the silica fume, the alkali content in the portland cement used, and the cement dosage, in other words the higher the total concrete alkali content, the higher is the amount of silica fume required to counteract ASR expansion. The study also indicated that pelletizing the silica fume before mixing with the clinker at the grinding stage did not reduce its effectiveness against ASR, provided the grinding process is effective in dispersing the silica fume.