International Concrete Abstracts Portal

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.

Because of increasing annual production volumes of fly ash, large volume applications, such as aggregate production, are beneficial in solving the disposal problem of fly ash while making economical use of a mineral resource. Aggregates have been produced from high calcium fly ash of Soma Thermal Power Plant and their engineering properties measured. For high volume utilization of fly ash, aggregate production involving pelletization and pressing into specially designed molds has been carried out successfully. Mechanical property and durability tests were conducted on the cured lightweight fly ash aggregates; five percent by weight lime addition to fly ash showed the best performance. It was also shown that different shapes of aggregates can be produced using the pressing technique.

Presents results of five-year exposure tests on the long term properties of concretes containing fly ash (FA), blast furnace slag (BFS), and silica fume (SF). Four kinds of concretes with and without a mineral admixture (OPC concrete, FA 30 percent concrete, BFS 50 percent concrete, and SF 10 percent concrete) were prepared. After 28 days of initial curing, they were exposed to different environments for five years. Compressive strength, pulse velocity, depth of carbonation, and chloride ion penetration of concrete were determined at various intervals of exposure time. From the results, it was found that under the indoor exposure condition, influences of initial curing conditions on the long term strength development of concrete were especially pronounced for FA 30 percent concrete and BFS 50 percent concrete, but that under the outdoor exposure conditions, its influence was considerably reduced due to the supply of rainfall during the outdoor exposure. On the other hand, SF 10 percent concretes showed some reduction in compressive strength when they were initially cured in water for seven days and then continuously air-dried indoors for a long period. The depth of carbonation of BFS 50 percent concrete and FA 30 percent concrete was much greater than that of the corresponding OPC concrete and SF 10 percent concrete when they were exposed indoors or outdoors for five years. Furthermore, all mineral admixtures used in this study were found to be equally efficient in preventing chloride ions from intruding into concretes under a marine environment.

It is necessary for concrete engineers to get more information on the ion movement through and in concrete for the development of new technologies, such as cathodic protection, desalination, and re-alkalization for reinforced concrete members. In concrete members with these treatments, various ions should be moved through and in concrete members. The movement of ions could influence concrete properties and steel reinforcing bars. Ground granulated blast furnace slag, fly ash, and silica fume have been recognized as high quality mineral admixtures for concrete. Since structures built with these materials might eventually be subjected to electro-migration processes, a set of experiments to assess the effects of these pozzolans were devised. In this study, considering the conditions mentioned above, the movement of several kinds of ions through hardened mortar with mineral admixtures was investigated. As ions, Na +, K +, and Cl - were selected because the ions were closely related to alkali-aggregate reaction or chloride attack. As mineral admixtures, ground granulated blast furnace slag, fly ash, and silica fume were used. Also, the influences of water-to-binder ratio on the movement of ions were investigated. Electrochemical cells were used for the experimental work; the current was applied to a cell in the range between 0.1 A/m 2 and 10.0 A/m 2. Analyzing the data from the experimental work, the following conclusions were obtained. 1. The electromigration of ions through mortar are reduced with the addition of admixtures. 2. The electromigration of ions increases with the water-to-binder ratio. 3. The electromigration of ions is closely related to the pore size distribution of mortar and paste.

Bagasse is the fibrous residue of sugar cane, which is burned for energy leaving various types of ashes as waste residue, of which grate ash is found to be the most suitable for use in concrete. Grate ash shows poor chemical reactivity with portland cement, making it not very effective as a pozzolan. It can, however, be used as a fine aggregate constituent of concrete. Five grades of concrete were tested, ranging from 20 to 60 MPa, to compare the performance of grate ash concrete with that of normal concrete. The use of the ash alone as fine aggregate gave harsh concrete with low workability and poor cohesion. This was improved by blending about 25 percent normal concrete sand with the ash. Bleeding was comparable with, if not generally less than, that of normal concrete. Grate ash concrete, in particular the lower strength mixes, had 10 to 18 percent higher initial drying rates and would, therefore, require more stringent curing precautions than normal concrete. Rates of strength development were comparable in the two concretes. Compressive strengths of over 80 MPa were achieved after one year with the high-strength ash concrete mixtures. But, for a given strength, the grate ash concrete requires more cement than normal concrete. In comparison with normal concrete, grate ash concrete had similar shrinkages, slightly lower modulus of elasticity, and about 40 percent lower creep deformations. For equivalent strengths, the two concretes showed similar durability properties, in terms of their resistances to mechanical abrasion, water absorption, chloride diffusion, and carbonation. However, due to the porosity of the grate ash particles, the concrete had a much better resistance to freezing and thawing attack than normal concrete, even though all concretes were non-air-entrained.