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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 40 Abstracts search results
April 1, 2007
Editor: V.M. Malhotra
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.
H.-S. Peng, H.-J. Chen, C.-W. Tang, and H.H. Pan
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.
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 mixtures of normal portland cement with fly ash from black coal combustion in classic installation and fly ash from brown coal combustion in fluidized bed were examined; the silica fume additive was used as a hydration process modifier. The hydration kinetics was followed by means of calorimetry. Then the calcium hydroxide content was determined by TG method and the electric conductivity of hydrating suspensions was measured. The course of so-called pozzolanic reaction between the additives and calcium ions was investigated and a selective consumption of calcium ions by silica fume was deduced from the data thus obtained. The use of silica fume as an additive brings about the acceleration of hydrolysis of cement components and acceleration of the formation of hydration products, usually by intensive consumption of Ca ions from the liquid phase. It has been found that silica fume, by quick consumption of calcium ions has a retarding effect in the beginning, but soon after, within a few hours, an intensive hydration, with the formation of dense C-S-H, takes place.
R.K. Panchalan and V. Ramakrishnan
This paper presents the results of an experimental study to develop a new accelerated Rapid Chloride Permeability Test (RCPT). This research was conducted as part of a project for the South Dakota Department of Transportation (SDDOT). The present ASTM C1202 test method "Electrical Indication of Concrete’s Ability to resist Chloride Ion Penetration" recommends that concrete specimens shall be cured for 56 days prior to testing them for chloride permeability. This curing period would have to be further extended to 90 days for high performance concretes made with fly ash and silica fume. Curing concrete specimens for 90 days would allow the internal microstructure of concrete to fully develop due to conclusion of the hydration process. Therefore it is essential to wait for 90 days to determine accurately the chloride permeability of concrete, unless there is another method, which can be used to accelerate the curing process. This study aims to use an accelerated curing process to determine the chloride permeability values within a shorter duration. Two identical batches of concrete specimens were made with various quantities of silica fume and fly ash. One batch was subjected to standard curing for 90 days and the other was subjected to accelerated curing for 7 days prior to testing them for Rapid Chloride permeability using ASTM C 1202 test method. A mathematical equation was developed to establish a relationship between permeability values of standard and accelerated cured specimens. Statistical analysis was done to validate the obtained relationship. This relationship can be used to predict the 90-day chloride permeability values within a time frame of 7 days.
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