International Concrete Abstracts Portal

The performance of a beneficiated fly ash (BFA), with very low carbon and very fine particle size (5 µm as mean size) was compared with silica fume in superplasticized high strength concretes. The silica fume content of concrete was 40 kg/m3 and the amount of BFA was 80 kg/m3 to obtain approximately the same cost as that of silica fume (SF). When the two concrete mixtures are compared at the same water-binder ratio (0.39) and at a given slump (about 165 mm), the dosage of superplasticizer was much higher for the SF concrete (2.6 kg/m3) than for the concrete with BFA (1.2 Kg/m3). The compressive strength of the SF-concrete was higher than that of the BFA-concrete, particularly at early ages, and this effect could be related to the better space filling capability of SF, as compared to BFA. However, when the same dosage of superplasticizer was used, the water-binder ratio of the BFA-concrete turned out to be lower (0.31) than with SF concrete (0.39). The strength increase in the BFA-concrete with respect to the SF-concrete has been recorded in specimens cured at room temperature as well as with steam-cured. In a second set of tests, BFA was used to manufacture high strength self- compacting concrete (SCC) in comparison with a corresponding SCC where untreated fly ash (FA) was used. In such a case the most important advantage in using BFA rather than FA was the self-leveling properties needed particularly in placing slabs or ground- floors. Due to the higher cost of BFA with respect to FA, there is no significant advantage in using the former in manufacturing SCC when the above mentioned self-leveling properties are not needed.

Alkaline activation of granulated blast furnace slags by highly concentrated solutions of sodium or potassium ions has been a subject of numerous investigations for many decades. Irrespectively of the type of activator used, the so-called C-S-H phase formed is very compact, of low C/S ratio, rich in sodium, aluminium and magnesium and is predominant hydration product. Properties of AAS pastes, mortars and concretes strongly depend on the chemical and phase composition of the slag. This paper presents the properties of the alkali activated pastes and mortars produced on the base of synthetic alumino-silicate glasses of gehlenite type. Setting time, mechanical properties and heat of hydration of the gehlenite-glass pastes are presented. Detailed studies of phase composition, microstructure and structure of alkali-activated gehlenite glasses are presented in the paper. Alkaline activation of gehlenite slag glasses is influenced by molar ratio Al2O3/SiO2 of the slag and concentration of NaOH. The hydration process is much quicker in the case of gehlenite type glasses than for typical industrial melilite granulated blast furnace slags. The results of XRD and SEM/EDS examinations show that in gehlenite type pastes amorphous C-A-S-H phase containing high amount of sodium, silicon and aluminium are the dominating hydration product.

This publication contains the proceedings from the Ninth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete, held in Warsaw, Poland, in May 2007. The 36 papers include topics related to silica fume in high-quality concrete, temperature attack and freezing-and-thawing cycles on durability of high-strength concrete with silica fume, measuring shrinkage of self-consolidating concrete incorporating fly ash and silica fume, and development of alkali-activated slag concrete for practical use, among others. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-242

The purpose of the research program was to investigate how the addition of new-generation wastes produced in the coal-fired power plant, fluidized-bed type installations, impact mechanical properties and chemical durability of cements. Tests were made on cements derived from two portland cement clinkers containing widely different amounts of C3A. With addition of the fluidized-bed material from the brown and black coal combustion systems blended portland cements were made. The properties of these blended cements were compared with those of the reference portland cements. The composition of all cements was adjusted to achieve the maximum permissible amount of SO3 i. e. 3.5%. Three different curing procedures were used for mortar specimens: normal temperature and humidity conditions, low pressure steam curing, and autoclaving. Durability to sulfate attack was studied using two methods: one method involved monitoring of linear dimensions of 20 x 20 x 160 mm mortar prisms cured under different conditions and exposed to aqueous solutions of Na2SO4 and MgSO4, with 16±0.5 g/l concentration of SO42- anions. The other method involved investigation of changes of mechanical properties of 25x25x100 mm mortar prisms cured under different conditions and subjected to prolonged sulfate exposure. The strength of samples was measured after different times of exposure in sulfate. Five percent aqueous solutions of Na2SO4 and MgSO4 were used for sulfate immersion test. Compressive and flexural strength tests were measured after 90, 180, 365, and 730 days of exposure. SEM and EDS techniques were used for microstructure studies.

The changes in the procedures of solid fuel combustion and application of different methods of sulfur removal from combustion gas in electric and thermal-electric power stations have resulted in fly ashes from fluidised-bed combustion. There are available in the market for addition cement beside fly ashes. In Poland, there are frequent cases of combustion of hard coal in conventional and fluidised-bed combustion installations, which have been derived from the same mine. It allows comparing the properties of different types of ashes obtained from the same coal. This paper presents chemical composition (basic and traces components) and phase composition, and properties of both kinds of fly ashes from combustion of Silesian coals. Also presented are comparison between properties of hydration products of cements and mortars made from two and three-component blended cements with different type and quantity of ashes. Fly ash from fluidised-bed combustion installations was incorporated in blended cements as the pozzolana component and sulfate ions carrier (modulus of gypsum). Beside standard methods of testing of functional quality of ashes and cements, different types of analysis have been used.