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The effect of temperature on the acceleration of the pozzolanic reaction rate is well known. In the case of the pozzolanic reaction between MK and calcium hydroxide, the researches have been focused on the hydrated phases and mainly on their stability, taking into account the possible transformation from metastable phases (C2ASH8 and C4AH13) to cubic phase C3ASH6, with the corresponding risk on durability.This paper reports a study to evaluate the influence of temperature on the formation of hydrogarnet (C3ASH6) in metakaolin (MK)/lime matrices subjected to 60°C curing temperature. The MIS and lime were mixed in a ratio of 1 :l by weight, stored and cured at 60°C and up to 123 days of hydration time. The kinetics of the pozzolanic reaction, sequence of appearance of different reaction products, quantities and crystallinity of the hydrogarnet as well as other hydrated phases, has been investigated using thermal (TG and DTA) and diffraction (XRD) analysis. The results showed that under the conditions tested here the hydrogarnet is formed very quickly in the first hours of curing (after 30 hours of hydration). This phase coexists at the same time with C2Ash8 (gehlenite) and C4AH13. The formation and amount of the hydrogarnet was closely related to the calcium hydroxide content in mixtures. There was not any evidence that the hydrogarnet was formed from a transformation reaction, but it was a result of the reaction between MK and lime.

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.