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Showing 1-10 of 40 Abstracts search results

Document: 

SP242-39

Date: 

April 1, 2007

Author(s):

J. Matolepszy, M. Gawlicki, and R. Mroz

Publication:

Special Publication

Volume:

242

Abstract:

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.

10.14359/18738


Document: 

SP242-38

Date: 

April 1, 2007

Author(s):

Z. Pytel

Publication:

Special Publication

Volume:

242

Abstract:

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.

10.14359/18737


Document: 

SP242-37

Date: 

April 1, 2007

Author(s):

T.W. Bremner, S.R. Boyd, T.A. Holm, and J.P. Ries

Publication:

Special Publication

Volume:

242

Abstract:

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.

10.14359/18736


Document: 

SP242-36

Date: 

April 1, 2007

Author(s):

M. Radlinski, J. Olek, and T.E. Nantung

Publication:

Special Publication

Volume:

242

Abstract:

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.

10.14359/18735


Document: 

SP242-35

Date: 

April 1, 2007

Author(s):

R.E. Rodriguez Camacho, B. Martinez Sanchez, J.J. Flores Martinez, R.U. Afif, and H.J. Montano Roman

Publication:

Special Publication

Volume:

242

Abstract:

The purpose of this study was to examine the effect of a Class F fly ash on mechanical and durability properties of concrete. The fly ash used in this study, from a Mexican source, was characterized by chemical and mineralogical analysis, and by its pozzolanic activity. Concrete mixtures were prepared with 20, 25, and 30% fly ash by mass of total cementitious material. Concrete specimens were cast and tested to determine the durability of fly ash concrete; the tests used included water, rapid chloride permeability tests (RCPT), migration test, acid resistance and abrasion resistance tests. Also the compressive strength was determined. Mortar specimens were used to evaluate sulfate resistance and alkali-silica reaction. The results of this study confirmed that the Mexican Class F fly ash was suitable in improving the durability characteristics of concrete when used at 25% or higher dosage of cement replacement.

10.14359/18734


Document: 

SP242-34

Date: 

April 1, 2007

Author(s):

H.-S. Peng, H.-J. Chen, C.-W. Tang, and H.H. Pan

Publication:

Special Publication

Volume:

242

Abstract:

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.

10.14359/18733


Document: 

SP242-33

Date: 

April 1, 2007

Author(s):

H.H.C. Wong, I.Y.T. Ng, P.L. Ng, and A.K.H. Kwan

Publication:

Special Publication

Volume:

242

Abstract:

Concrete-polymer materials that include polymer-impregnated concrete (PIC), polymer concrete (PC) and polymer-modified concrete (PMC), have been developed within the past 50 years. PIC, which started out with great promise, has essentially disappeared from the scene. PC has been widely used for repairs, floor and bridge overlays, and precast components, but has not achieved the volume of use that had been projected. PMC has been widely used for overlays and repairs, including spray-on applications. There are many potential applications for the future related to materials processing and applications, which will ensure these materials will continue to be important in the construction field.

10.14359/18732


Document: 

SP242-32

Date: 

April 1, 2007

Author(s):

A.-S. Cheng, T. Yen, Y.-N. Sheen, and K.-C. Jane

Publication:

Special Publication

Volume:

242

Abstract:

This research aims to investigate the pore structures of fly ash concrete and the relation between porosity and compressive strength, and accordingly to establish a strength prediction model. In the study, three water-to-binder ratios (0.35, 0.50, 0.70) and three substitution ratios of cement with fly ash (10%, 20%, 30%) were selected for preparing concrete specimens. These specimens were tested at six ages from 1 day to 91 days for compressive strength and MIP porosity measurement. Test results show that the fly ash concrete consisted of more micro-pores that were larger than 0.05µm at an early age (7 day),but this portion of micro-pores evidently decreased after 28days. It was also found that the capillary pore volume had the closest relation with the strength of fly ash concrete, and the correlation coefficient reaches to 0.954. To establish the strength prediction model, a prediction equation of capillary porosity in fly ash concrete was firstly developed. The proposed prediction model is shown as the following: f'c=a·ln(W/B)+b·ln(R)+c·ln(age)+d·ln(Vc)+e. The calculated results show that the proposed model compared favorably with the other prediction model.

10.14359/18731


Document: 

SP242-31

Date: 

April 1, 2007

Author(s):

S.K. Antiohos, G. Tzouvalas, and S. Tsimas

Publication:

Special Publication

Volume:

242

Abstract:

Reject fly ash (rFA) represents a significant portion of the fly ashes produced from coal or lignite-fired power plants. Due to the high carbon content and large mean particle diameter, rFA is not used in the construction sector (for example as a supplementary cementing material) and is currently dumped into landfills, thus representing an additional environmental burden. In order to maximize the use of solid wastes, there is a need to investigate potential applications for rFAs. The benefits, however, of the inclusion of recycled materials will only be realized if they result in improved performance and economic savings for the final product. In this work, critical mechanical and hydration properties of blended cements made by blending the coarse fraction (after grinding) of a lignite high-calcium fly ash with ordinary cement were measured and compared with the respective properties of a good quality fly ash-cement blend. The results reveal that a relatively cheap, two-step classification-grinding method is able to enhance the pozzolanic behaviour of the rFAs, so that the overall performance of rFA containing cement is significantly improved.

10.14359/18730


Document: 

SP242-30

Date: 

April 1, 2007

Author(s):

V. Bilek, M. Urbanova, J. Brus, and D. Kolousek

Publication:

Special Publication

Volume:

242

Abstract:

Alkali-activated slag concretes (AASC) are relatively well-known composites. For practical application various different problems must be solved. For example, they are the optimum content of alkaline activator and its nature; the composition of the activator for optimum setting and hardening time; the design of concrete for good workability, for the reaching of the smallest volume exchanges, and for maximum strength and for high durability. These problems are discussed in the present paper. Water glass and/or natrium hydroxide were chosen as the best type of activator and the optimum ratio Na2O and SiO2 were found. Calorimetry, MAS NMR (27Al and 29Si), SEM and other methods were used for the characterisation of the mixes. The concrete mixes are designed as self compacting for easier introduction of these materials into practice. Strengths, volume changes and their time development were measured during the aging of the mixes. Some elements will be produced from the concretes in 2005 and 2006 (elements for cable pipe-lines).

10.14359/18729


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