International Concrete Abstracts Portal

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.

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.

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.

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.

This paper utilizes electrical methods to follow the early hydration characteristics of a range of materials activated with calcium hydroxide at room temperature (20°C). The electrical response is measured in terms of the in-phase (i.e. resistance) and quadrature (i.e. capacitance) components of the sample admittance. A number of presentation formalisms are exploited in identifying the stages of hydration and studying reaction kinetics in alkali-activated systems. It is also shown that the electrical response of the material displays a frequency dependence, which is particularly evident in the measured capacitance. The work highlights the applicability of the electrical method as a non-invasive, non-destructive technique in evaluating the reactivity of supplementary materials.