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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.

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.

This study concerns the possibility of reusing two industrial by-products from combustion processes (MSWIFA -- Municipal Solid Waste Incineration Fly Ash and SSA -- Sewage Sludge Ash) in cement-based materials containing metakaolin. The experimental program included tests on mortars to evaluate the impact of ternary binders (cement, metakaolin and residue) on the technological and environmental properties of concrete intended for non-structural applications. The binders were composed of 75% cement, 22.5% metakaolin and 2.5% residue. Results on the technological and environmental behaviour of mortars showed that the mechanical, dimensional and leaching properties were not affected by the residues. The use of metakaolin especially led to a significant decrease in soluble fractions and heavy metals released from the binder matrix.

Sections of high strength concrete (target mean strength of 100 MPa) column elements were cast in the laboratory and cured in a temperature-controlled environmental room at conditions representing average summer or winter temperatures in the UK. In each case, the room was programmed to cycle with a 24-hour period between a minimum and a maximum temperature representing day and night variations. The elements were instrumented with embedded thermocouples and pull-out test inserts, for measurement of in situ strength. Temperatures were continuously recorded for at least seven days after casting. Strength development was assessed by means of both pull-out tests and compressive strength testing of drilled cores at ages up to 28 days. Temperature-matched curing of 100 mm cubes was also carried out using the thermocouple output measured from the column elements. In summer conditions, the temperature rise was observed to be lower in slag concretes than in portland cement concrete but despite this the measured strength development was significantly enhanced compared to standard cured (20 °C) control cubes. The in situ strength improvement was sufficient to allow slag concrete to be used in construction in summer without causing delays to fast-track construction schedules.

In Japan, sea sand is used frequently as fine aggregate for concrete. The mining of sea sand has been more difficult year by year for environmental reasons. This would be a serious problem in manufacturing concrete. The amount of fly ash has been increasing gradually in Japan, therefore the utilization of fly ash as the substitution of fine aggregate has a significant advantage. In this study, bending fatigue test of roller compacted concrete was carried out, in which all fine aggregate was replaced with fly ash. The obtained S-N curve was compared with that of normal concrete and general roller compacted concrete. Scatter of fatigue strength was also determined.