International Concrete Abstracts Portal

Conditioning coal-burning power-plant flue gases with ammonia reduces the emission of nitrous oxide compounds. But the ammonia often combines with available sulfur and other compounds that attach to the fly ash. If the ammoniated fly ash is then used in concrete, the high-pH environment causes a release of ammonia and a strong, objectionable ammonia smell. This can make the fly ash unmarketable. What’s the solution? Fly ash beneficiation processes that can remove ammonia and also reduce the unburned carbon content. Some of the processes are described in one of the 54 papers included in ACI SP-199, Seventh CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete. Other papers deal with effects of fly ash and admixture combinations on setting time, use of slag concrete to reduce corrosion of reinforcement, and the role of chemical and mineral admixtures in concrete made with recycled concrete as aggregate. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP199

Svnopsis:--This paper presents information on the leachability of trace metal elements from a number of fly ashes from Canadian and the U.S. sources, and from the concrete incorporating the fly ashes. The concentrations of all regulated elements Ag, As, B, Ba, Cd, Cr, Cu, Hg, Pb, and Se in the leachates from the nine fly ashes tested were within the limits of the United States Environment Protection Agency and the Transportation of Dangerous Goods Act Regulations of Canada. The leaching of As, B, Ni, and Se from the fly ashes appeared to increase with an increase in their content in the fly ash; however, there were some exceptions. In general, the concentration of As leached from the fly ashes derived from the bituminous coals was much higher than that from the lignite or sub-bituminous coals. Regardless of the type and percentage of the fly ash used, w/cm of the concrete, and curing condition, none of the trace metals in the leachates from the fly ash concrete samples exceeded the regulated concentration limits by the United States Environment Protection Agency and the Transportation of Dangerous Goods Act regulations of Canada. The concrete incorporating the fly ashes is, therefore, considered environmentally stable.

The Japan Industrial Standard (JIS) of “Fly Ash for Use in Concrete, JIS A 620 1 ” was revised in 1999 in order to widen the utilizable amount of fly ash as a mineral admixture. The featured points in this revision were that; [l] fly ash with high loss on ignition (LOI) ranging from 5.0% to 8.0% is specified as Class-III, [2] fly ash with low Blaine fineness ranging from 15OOcm’/g to 2500cm’ig is specified as Class-IV, [3] high quality fly ash with LO1 less than 3.0% and Blaine fineness more than 5000cm2/g was specified as Class-I. Most of the fly ash qualified in JIS A 6201-1996 would be specified as Class-II. Class-III and Class-IV fly ash wouldn’t meet the requirement of JIS A 6201-1996. This paper describes the background and the contents of the revision of JIS A 6201.

Synopsis: The amount of ash, produced from the coal fired thermal power plants and its hazardous impact on the environment is continuously increasing. This poses a challenging task of safe handling, proper disposal and utilisation of the ash. The huge quantity of ash produced from these power plants calls for a special attention in terms of its proper utilisation, either directly, or conversion into a value-added product. Chemical activation of the coal ash is being practised for synthesising ash zeolites. These zeolites are being used for various environmental protection schemes and other industrial processes. With this object in view, an effort has been made in this paper to study the effect of chemical activation of a typical class F lagoon ash. This chemical activation is achieved under controlled conditions, in the laboratory, with different concentrations of alkali (NaOH) and for different durations of activation.

Svnomis: This paper presents a study on the mechanical properties and durability of concrete made with a high-volume fly ash (HVFA) blended cement. The results were compared with those of the HVFA concrete in which unground fly ash had been added at the concrete mixer, and the control portland cement concrete. Two control mixtures were made, one with a commercially available ASTM Type I cement, and the other with a normal-portland cement produced in the laboratory that met the requirements of ASTM Type I cement. The properties of the fresh concrete determined included the slump loss, air content, bleeding, and setting time; those of the hardened concrete investigated included the compressive strength, flexural - and splitting-tensile strengths, Young’s modulus of elasticity, drying shrinkage, air void parameters, and resistance to abrasion, chloride-ion penetration, freezing and thawing cycling, and de-icing salt scaling. The results show that the mechanical properties and durability characteristics of the concrete made with the HVFA blended cement and the concrete in which the unground fly ash and the portland cement had been added separately at the mixer were comparable or superior to those of concrete using commercially available ASTM Type I cement. The only exception was the deicing salt scaling resistance in which the HVFA concretes performed poorly compared to portland cement concrete. The mechanical properties of the concrete made with the HVFA blended cement were found to be superior to those of concrete in which the unground fly ash and cement had been added separately at the mixer. The durability characteristics of these two concretes were found comparable.