International Concrete Abstracts Portal

Fluidized bed coal combustion produces a new kind of fly ash by-product. Fluidized bed fly ashes have different chemical composition and physical properties than conventional fly ashes. They can be used as complex addition to cement where they play simultaneously the role of sulphate setting time controlling agent and high active pozzolanic admixture as well. This gives the possibility to reduce the consumption of portland cement clinker and gypsum. Thus, it may also contribute to the reduction of CO, emission. In the paper the results of the laboratory investigations of fluidized bed fly ashes as cement additive and the effects of their industrial implementation will be presented.

European countries have a great deal of experience in the use of Portland Limestone Cements (PLC). In Latin American, most of the cement plants use limestone as a raw material and an increase in cement production is expected in the next few years. The manufacture of this cement would represent a rapid increase of production without environmental consequences. This paper synthesizes data from a research program carried out over two years to determine the effects of limestone filler on concrete and mortar behavior. At early age, the influence of limestone filler on workability, bleeding, initial curing and mechanical behavior (modulus of elasticity, compressive and tensile strength) was studied. Sulfate resistance and chloride penetration, the most important durability problems related with PLC, were also studied. The addition of slag was also investigated to improve the long-term strength and the durability of PLC. Results show that cements containing around 10% of limestone filler provide similar or better mechanical behavior than portland cement concrete, without compromising their durability properties where low chloride diffusion and high sulfate resistance is required, In this case, the environmental impact of cement manufacture decreases because the energy consumption and the CO2 emission are reduced per ton of cement and the combination with other supplementary cementing materials (slag, fly ash or natural pozzolan) can improve these aspects.

The aim of this study is the valorization of magnesium slags in order to recycle them in construction block form. Two kinds of slag with hydraulic properties are obtained according to a l/3-2/3 ratio: powdered slag similar to cement, and granulated slag similar to sand. A previous laboratory study was curried out in order to obtain sufficient mechanical strength for construction blocks and setting kinetics compatible with an industrial process. The present paper deals with the consecutive implementation of life size tests on an industrial scale. Two pre-industrial tests were carried out in extremely different temperature conditions 7°C for the first test and 22°C for the second one. Furthermore, the second test benefited from the new casting conditions resulting from updating of the manufacturing unit. The first test showed that the laboratory study permitted to adjust the set kinetics to a level adequate for industrial casting, whereas the mechanical strength obtained was lower than expected when the powdered slag was used as a substitute for cement. The second test enabled us to obtain enough mechanical strength for mixtures entirely composed of magnesium slags and proved the possibility of total and simultaneous enhancing value of magnesium slags as construction blocks. More generally, these industrial tests show how difficult the transfer to the industrial scale is.

Environmental about the high energy consumption and huge emissions of CO2 associated with the production of portland cement are leading to the search for more environmentally viable alternatives to portland cement. One of these alternative materials isalkali-activated slag (AAS) in which ground, granulated blast furnace slag is used not as a partial replacement to cement but as a binder in itself in the production of concrete. This paper presents results of tests carried out to study the performance of alkali-activated slag concrete using sodium silicate (water-glass) as an activator in NazO dosages of 4 and 6%. The fresh concrete properties (setting time, workability and air content) were examined in addition to the engineering properties (compressive strength, splitting tensile strength, drying shrinkage, dynamic modulus of elasticity and ultrasonic pulse velocity). Hydration products were identified using XRD.

Sustainable development in the concrete and cement industry is achievable in the near future. This paper proposes the viability of a factor 10 reduction in the negative environmental effects of current cement/concrete production through the use of cement blends with minimum portland cement and maximum pozzolanic loading. Such cement blends substantially extend the longevity of concrete and avoid the enormous cost of several repair and replacement cycles. ‘l’he transition to sustainable concrete technology will be driven not by environmental imperative but rather by market forces pursuing economic advantage through more durable concrete. Market driven economics already in place will soon prove that concrete durability is worth a high premium but is available at a bargain. There is enormous leverage in improving concrete quality as a doubling of the price of highest quality cement would add only 2% to overall construction project costs while the extended service life of the structure would offer a many-fold return on the additional investment. In coming years, the consideration of CO2 emissions regulations and increasingly valuable internationally traded CO2 credits will assume an economic importance equal to or greater than capital and operating costs among cement producers. Those who do not move to sustainable concrete technologies will run the risk of losing substantial market share or business failure.