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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.

Waste disposal has become a major concern in most industrial countries because of limited sites and strict environmental standards for landfilling. The common cementing material, widely available and used, are normal portland cement, lime and high-calcium fly ashes from coal combustion. Ground granulated blast-furnace slag is also a component in binder formulation of general interest because of its potential for metal immobilization, based on its physical and chemical properties. The present work analyses the immobilization of toxic wastes containing Cd, Pb and Cr in portland cement matrices with 80 % of blast-finnace slag in comparison with plain portland cement matrices. The results show that lower levels of toxic ions in pore solution are obtained for blast-&mace blended cements due to differences in phases formed and the reduction of species to less toxic ones that occurs at the redox potential of slags. Differences in porosity also cause a reduction in metal leaching from slag-blended cements.

The behavior of superplasticizers has been studied in highly alkaline suspensions of magnesium hydroxide and silica fume, which can be considered as good model system for cementitious systems containing silica fume. Rheology showed that as superplasticizer dosage is increased, suspensions pass from behaving as Bingham fluids to Newtonian fluids. Beyond a critical concentration large dispersed particles sediment due to the absence of yield stress. The critical concentrations required to obtain Newtonian fluids has allowed to elucidate the dependence between adsorption and dispersion. Indeed, dispersion appears to be only linked to adsorbed polymers and can therefore be attributed either to electrostatic or steric repulsion mechanisms. On the other hand, superplasticizer requirement increases with silica fume fraction in particular with the less ionic polymer. This indicates important electrostatic interactions with the surface in the process of adsorption.

Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM) and Chemical Analysis investigations lead to a fine characterization of Reactive Powder Concretes elaborated under different conditions as pressure application during setting and post-set heat treatment. An abrasive thinning method followed by ionic etching allowed for the preparation of 100 nm thick specimens with wide observation surface areas while still avoiding any water or CO2 contact which may cause their alteration. Silica fume distribution and reactivity versus curing processes are studied. The Si diffusion interfacial zone between hydrated products and silica time, clinker particles or crushed quartz is measured in different curing cases. The Ca/Si ratio spatial distribution in hydrated products and its evolution with the curing processes are then analysed and shown to be strongly microheterogeneous.