International Concrete Abstracts Portal

As part of a series of experiments designed to develop binary and ternary blended cements for use in structures exposed to freezing and thawing cycles in the presence of deicer salts, 39 mortar mixtures were made. Five different portland cements (two Canadian Type 10 cements, two ASTM Type I cements, and one Canadian Type 30 cement), seven fly ashes (three Class F fly ash, one Class CF fly ash, and three Class C fly ash), and two blast furnace slags were used as cementitious materials. The water-cementitious material ratio of all mixtures was fixed at 0.40; the amount of supplementary cementitious material (as a percentage of the total mass of binder) was zero percent for the five portland cement reference mixtures, 20 percent for nine mixtures, and 40 percent for the other 25 mixtures. The compressive strength of all mortars was measured after seven, 28, and 90 days of curing in water. The pore size distribution (with mercury intrusion porosimetry) and the chloride ion permeability of all mortars were determined after 28 days of curing. The results of the tests carried out to analyze the portland cements, the fly ashes, and the slags are also given in this paper. It was found that certain mixtures containing 40 percent of supplementary cementitious material had an excellent 28-day strength, a very low chloride ion permeability, and a very small average capillary pore size.

Partial replacement of a moderately sulfate-resistant cement with a high-calcium fly ash may result in either increased or decreased sulfate resistance for concrete. These effects of fly ash have been related to, among other factors, changes in the permeability of concrete and changes in the stability of hydrated calcium aluminates in the presence of sulfate-bearing solutions. The objective of this study was to investigate the effects of using anhydrous sodium sulfate as a chemical admixture in concrete made with Class C fly ash. The sodium sulfate admixture was expected to influence the sulfate resistance of concrete by increasing the availability of sulfate ions during the hydration of calcium aluminates. The admixture was also expected to increase the rate of pozzolanic reactions by increasing the concentration of alkali ions in solution. In addition to studying the effects of the sodium sulfate admixture on sulfate resistance, its effects on mixing water requirements, compressive strength, and permeability were also examined. The fly ash was introduced into the concrete by two methods: partialre placement of portland cement with fly ash at the time of mixing concrete and intergrinding of fly ash with portland cement clinker and gypsum, as in the production of blended cements. A commercially available ASTM C 150 Type II cement and five ASTM C 618 Class C fly ashes were used. The fly ashes replaced the portland cement (or the cement clinker plus gypsum) at a level of 35 percent by volume. For each source of fly ash, 14 concrete mixtures were produced; seven mixtures included Type II cement and fly ash with various amounts of the sodium sulfate admixture and seven mixtures included blended fly ash cement with various amounts of the sodium sulfate admixture. The use of sodium sulfate as a concrete admixture, in amounts ranging from two to five percent by mass of cement, resulted in improved sulfate resistance for concrete containing Class C fly ash. In many cases, sulfate resistance exceeded that of Type II cement concrete without fly ash. Additional effects of the sodium sulfate admixture included increased compressive strengths at early ages and lower permeabilities at early ages.

The effectiveness of fly ash (FA) in suppressing concrete expansion due to alkali-silica reactivity (ASR) is thought to be largely affected by its particle size distribution and composition, in particular, the glass and alkali contents. This study is particularly concerned with the effect of particle size. A low alkali Type F fly ash was screened to obtain different size fractions. The fly ash was also ground to obtain different Blaine fineness, from 3100 (natural fly ash) to 8800 cm 2/g. The activity index of the various fly ash samples, including the bulk fly ash, was determined on mortar samples made with 25 percent fly ash by mass as cement replacement. The effectiveness of the same samples was investigated through the Accelerated Mortar Bar Method ASTM C 1260 (or CSA A23.2-25A), in the presence of a well known alkali-silica reactive aggregate from Canada, a siliceous limestone (Spratt Quarry, Ottawa, Ontario), at a 30 percent cement replacement by mass. High-performance concrete was also made with the same fly ash samples at a 25 percent cement replacement level, using a high-range water-reducing admixture (HRWRA), with an alkali-silica reactive aggregate from France (Tournesis Quarry), then stored in air at 100 percent relative humidity and 60 C. Such an accelerated expansion test is currently under investigation in France to test the potential for ASR expansion of job concrete mixtures. This study indicated that, irrespective of the procedure used to get a finer sample (screening or grinding), the finer the fly ash under investigation, the higher its activity index and the greater its effectiveness in suppressing expansion due to ASR.

Presents the results of exploratory experiments using AFBC ash to produce a new kind of expansive cement. The principles for design of the compositions and theoretical consideration are discussed. The tests were carried out to examine the XRD pattern and the pozzolanic activity of the AFBC ash used. The expansive properties of this cement and its effects on porosity, pore structure, heat evolution, setting time, resistance to chemical attack, leaching effect, and strength of hardened cement paste are analyzed in detail. A kind of warm-pressed AFBC ash expansive cement product is also presented. The present results indicate that the sulfoaluminate of AFBC ash can be used as an expansive component. This kind of expansive cement could be used to chemically induce compressive stress in the mortar and thereby reduce the size and amount of shrinkage cracks that frequently occur in portland cement concrete during drying. The results suggest an economically and environmentally acceptable approach.

As focus increasingly shifts to protecting the environment through recycling of industrial byproducts and wastes, as well as conserving energy and resources, corresponding restructuring of conventional production technology and practices has become imperative. Because of these considerations, mixtures of kiln dust and fly ash were hydrothermally treated and calcined to produce a new type of beta-C 2S rich cement. Fly ash, which is the most abundantly generated industrial byproduct, is still largely disposed of as waste; kiln dust is the waste product of the cement industry, vast quantities of which are discarded due to its high alkali content. The former is composed of alumino-silicate glass, while the latter has a composition similar to that of partially calcined cement raw meal. This study demonstrates that it is possible to produce C 2S cement of dequate 28-day strength by suitably proportioning fly ash and kiln dust. The results of variations in factors such as the CaO:SiO 2 ratio and two different precalcination treatments are presented. Prehydration-dehydration (sintering at 950 C) processes were specially applied for the production of this cement, in contrast to the direct calcination method in the presence of a mineralizer. The cement was constituted of beta-C 2S and calcium aluminates. The formation of these minerals in relation to the clinkering sequence is discussed. The cement is sufficiently hydraulic, and its strength development largely depended on the CaO:SiO 2 ratio of the raw mix and the precalcination process.