International Concrete Abstracts Portal

It is now established that the incorporation of industrial byproducts, such as fly ash (FA), ground granulated blast furnace slag (GGBFS) and silica fume (SF), in concrete mixtures as partial cement replacement materials (CRMs) significantly enhances the durability related properties of concrete, besides improving its mechanical properties.. Such concretes are termed as High Performance Concretes (HPCs). In HPC mixtures, it is possible to have low W/C with reduced cement content by judicious choice of mineral and chemical admixtures. The assessment of the flexural behavior of reinforced HPC beams is a subject of ongoing research. Standards and codes of practice differ in the definition of compressive stress block parameters of reinforced HPC beams. Hence, investigations were undertaken at the Structural Engineering Research Centre (SERC), Chennai, to investigate the behavior of reinforced HPC beams under flexural loading. The beam specimens for the test programme were designed as under reinforced, balanced and over reinforced sections as per the guidelines given in the Indian code of practice for reinforced concrete, IS:451 978. The influence of supplementary cementitious materials (SCMs) used as cement replacement materials (CRMs), viz., fly ash (25% as CRM) and GGBFS (40% as CRM), on the flexural behavior of reinforced HPC beams was studied. The paper presents the details of the investigations and discusses the results obtained.

Two silica-manganese slags containing about 11 % MnO were ground to Blaine finenesses of 360 to 600 m*/kg. Their C/S (CaO/SiO2) modulus was very low (0.47 to 0.58) and, for this reason, these slags were considered likely to be unsuitable for use in the preparation of blended cements. They were therefore introduced in concrete instead of either fly ash or silica fume. The cement content of these concrete mixtures was in range of 2 1 0 kg/m3 t o 4 5 0 kg/m3. The quantity of each supplementary cementing material was adjusted according to the French standards and varied from 50 to 80 kg/m3. The slags behaved as well in concrete as fly ash or silica fume: no decrease in strength was observed and the water permeability was the same.

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.