International Concrete Abstracts Portal

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.

The purpose of this study was to evaluate selected transport properties (resistance to chloride-ion penetration and rate of water absorption) of ternary concrete mixtures containing fly ash and silica fume using different test methods. The resistance to chloride-ion penetration was evaluated using two non-steady, electric field migration tests: rapid chloride permeability (RCP) (AASHTO T 277) test and rapid migration procedure (AASHTO TP 64). The rate of water absorption was evaluated using the ASTM C 1585 sorptivity test and the non-standard absorptivity (ponding water absorption) test. Four mixture compositions (with varying contents of fly ash and silica fume) and five different curing conditions were used in the study. The test results were statistically analyzed (using regression method) to explore the relationships between composition, age of concrete and transport properties. In addition, the existence of possible interrelationships between the transport properties themselves was examined. For continuously moist cured specimens (Series 1 mixtures) the migration-type tests were found to be more reproducible than the absorption-based methods. However, the repeatability of absorptivity test was greatly improved if specimens were dried for certain period of time prior to testing (Series 2 mixtures). Although the curing method was found to have a very significant impact on the RCP and initial absorptivity values of all tested concrete mixtures, at later age much of the observed differences in those properties diminished.

The production of lightweight aggregates entails heating a silica-rich raw material, which is usually shale, clay or slate to about 1150°C. This heat treatment appears to activate the surface of the expanded aggregates so as to produce pozzolanic properties that reduce expansion due to alkali-aggregate reaction. When these heat-treated aggregates are incorporated into a concrete mixture, beneficial effects result that enhance the properties of the concrete. These effects are similar to, but of a significant lower magnitude, than when a pozzolan such as fly ash or silica fume is added to a concrete mixture. This is to be expected because expanded shale, clay and slate that have been ground to a fineness somewhat greater than that of portland cement have been supplied to the concrete industry as a pozzolan for some time. Also, it has been shown in micrographs that the vesicular nature of lightweight aggregates provides a space for any reactants that might form to precipitate without causing expansion.

The application of building rubble collected from damaged structures has become an important issue in Taiwan. The reuse of construction wastes not only conserves the finite raw materials and reduces energy consumption, but also can be a solution for environmental protection. Among the wastes, bricks and tiles were produced under high temperature sintering, which is similar to the producing process of pozzolanic materials like fly ash or slag. Such material might lead to the pozzolanic reaction in concrete. This research intends to investigate the probability to replace the natural sand or cement by using waste bricks and tiles. First, the gradient of fine aggregate was fixed. Four replacement percentages (25%, 50%, 75%, and 100%) were selected to replace part of natural sand in the mortar mixtures. Then the influence to the proporties of mortars was estimated according to the test results. The bricks and tiles were ground into powder with the same fineness of cement. Three replacement percentages (10%, 20%, and 30%) were selected to replace part of cement. The influence to the proporties of mortars was estimated as well. Test results show that the strength of mortars using waste bricks and tiles as fine aggregate is slightly lower than that of the control batch. However, the strength efficiency is good. On the other hand, the mortar containing brick or tile powder possesses higher long-term compressive strength because of the pozzolanic reaction.