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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.

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.

Waste materials may be upgraded to specification standards and occasionally to premium materials for use in the preparation of composites or for use in their own. The treatment for upgrading is a matter of cost and of the potential environmental problems that the treatment can create. The investigation presented in this paper shows an example of the improvements of fly ash properties achieved by a simple physical process, that is, air cyclone separation. This process gives a very line ash with adequate pozzolanic activity and is suitable for producing high performance concrete with excellent durability particularly when exposed to aggressive environments. The paper presents data on the properties of the fine fly ash including lime reactivity, composition, size distribution and shape. The investigation was carried out using two fly ashes obtained by the process of air separation using a prototype small air cyclone separator and an air mini-splitter. The properties of these ashes were compared to the properties of the original raw ash and with the properties of a fly ash processed industrially by the conventional mechanical separation process, which produces a fly ash conforming to the appropriate British specifications for use in the production of structural concrete. In this test programme, high performance concrete made with 0.3 fly ash and 0.7 ordinary Portland cement (by weight) as binder was assessed by measuring strength, porosity, and permeability. These properties were used to evaluate the performance of concrete and potential long term durability.

Structural grade fly ash (FA) concrete and concrete with high volume of fly ash (HVFA) are well accepted and utilized in the Australian construction industry. These are concretes with fly ash (ASTM C 618 type F) making up between 10 and 50 % by weight of the total cementitious material. This paper is intended to demonstrate the importance of the selection of the appropriate amount of FA content for a range of applications. The durability performance of the FA concretes was compared with portland cement concretes of equivalent 28-day compressive strength, in terms of the resistance to carbonation, chloride penetration and sulfate attack. Some mixture design data for both FA and HVFA concretes and their mechanical properties are given. The likely optimum fly ash percentages for a range of applications are highlighted with respect to their properties and construction demands. It was found that a lower fly ash dosage would be more suitable for above-ground structures where a carbonation-related deterioration mechanism applied. However, for structures in aggressive sulfate ground condition or in marine environments, HVFA concrete was found to be much more suitable. Available field performance data have confirmed laboratory evaluated performance.