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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.

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.

The reduction in the useful-service life of reinforced concrete structures in the coastal areas of the Arabian Gulf is of major concern to the construction industry. The harsh climatic conditions, high level of chloride and sulfate contamination in the environment, low quality and contaminated aggregates, and substandard construction practices constitute the major causes of deterioration of reinforced concrete structures in less than 10 years in this part of the world. Since the concrete deterioration phenomena are strongly permeability dependent, mineral admixtures and industrial by-products, such as natural pozzolan, fly-ash, blast-furnace-slag, and silica-fume are increasingly used to improve its durability. Among the mineral admixtures and industrial by-products, fly-ash and silica-fume are considered to be more beneficial due to their superior performance in improving concrete durability. However, to attain beneficial properties, pozzolanic concrete needs early and extended curing compared with normal portland cement concrete. This is of particular concern in the Arabian Gulf environment, where the high ambient temperatures, solar radiation and blowing winds make curing a difficult process. Therefore in this study, the effect of temperature and drying as well as different curing conditions on the compressive strength development in normal Portland, silica-fume and fly-ash cement concretes was evaluated. The test specimens were cured in the laboratory and under field conditions, and tested 1,3,7, 14,28, 60 and 90 days after casting to evaluate the compressive strength development. The results indicated an increase in the compressive strength, in both the normal, fly-ash and silica-fume cement concrete specimens with the period of curing. Field curing had more negative effect on the strength development in concrete specimens containing fly-ash and silica-fume than in the plain concrete specimens. High temperature casting and curing increased the compressive strength in both plain and fly-ash concretes. Drying during curing produced the highest strength the silica-fume concrete specimens compared to plain and fly-ash concretes.

This paper describes the approach for customization of fly ash, focused on the proportioning of concrete mixtures for applications where specific performance is needed such as strength, durability and workabili-ty. In order to tailor these specific concrete mixtures, bulk fly ashes can be selected and upgraded to fulfil the requirements with respect to for instance, grain size distribution and carbon content (LOI). By customizati-on of fly ash its value will increase, which is beneficial inspite of the cost for upgrading. For customization, basic knowledge and relationships are needed about the decisive influential factors of the total system of concre-te components and design. To this end, descriptive models have been evaluated and applied with the emphasis on models for fly ash fineness and packing. These models have been used as a background for classifica-tion and micronization of fly ash. In experimental work, a relation was found between the dry pac-king of the solid constituents of mortar and the workability after the addition of water. Then fine and ultra-fine fly ashes were processed throu-gh air-classification and grinding (micronization). These processed fly ashes were added to concrete and the strength development was compared to concrete with silica fume and with reference concrete. In full scale tests the suitability of micronized fly ash for the production of very workable concrete, was confirmed.