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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.

Binder systems containing large amounts of fly ash have become interesting for the building material industry because of their relatively low cost, the high resistance against aggressive solutions, durability against alkali-silica reaction, low hydration heat and ecological friendliness. The hydration mechanism of these systems differs from that of neat portland cement pastes, mainly in type and amount of solid hydration products and the composition of pore solution. It was the aim of this work to compare the hydration reactions of binder systems containing fly ashes from brown coal combustion and portland cement in mixture proportions of 60% fly ash /40% portland cement with corresponding 70/30, 85/15 and zero-fly ash mixtures. Investigations of the solid hydration products by high resolution solid 29 Si MAS NMR spectroscopy, molybdate method, DTA/DSC and the chemical analysis of the pore solution showed that the pozzolanic reaction of the ash leads to a decrease of the hydroxide ion concentration in the pore fluid and the amount of solid calcium hydroxide, and increased formation of aluminosilicate hydrates. When all the Ca(OH)z is consumed, the sulfate ion concentration in the pore solution begins to rise. The influence of the activity of fly ash, the mixture ratio of fly ash/Portland cement, and the hydration time on the chemical structure of the C-S-H and C-S-A-H phases is discussed.