A pressurized fluidized-bed combustion power plant (PFBC) is a coal-fired thermal power plant specially developed for the enhancement of generating efficiency and the reduction of environmental loads. The physico-chemical properties of coal ash produced from this type of power plant (PFBC ash) are different from those of ordinary fly ash, because coal is mixed with pulverized limestone and burnt at a lower temperature than that in the conventional power generation system. This study explores the feasibility of utilizing PFBC ash as a concrete mineral admixture. It has been found that the coal ash from a secondary cyclone dust collector enhances the strength of concrete although it cannot improve the fluidity. A series of tests, including those for durability and changes in length, show that the durability of concrete containing the coal ash so produced is adequate for practical applications.

Concrete containing fly ash has been used in many parts of the world for several decades. Various standards and codes have generally limited the use of ASTM Class F fly ash from 20 to 25 percent. Laboratory studies and field demonstration projects sponsored by CANMET during the last 12 years have shown that concrete containing 55 to 60 percent fly ash has excellent structural and durability characteristics when proportioned with superplasticizers and at low water to cementing materials ratios. This paper presents some results of research performed under contract to CANMET and some of the practical uses for which the high-volume fly ash concrete system has been utilized in Eastern Canada. The applications discussed include structural concrete, relatively massive machinery foundations, a roller compacted dam, environmental applications such as impermeable shotcrete covers and encapsulation/solidification, and design of mine backfills. The high-volume fly ash system has proven to be an economical construction material which can be mixed, placed and consolidated with conventional concrete construction equipment. Some unique properties such as very low heat generation, low cost, and the possibility to use large quantities of fly ash will expand the future use of the high volume fly ash system.

This paper describes the results on the chloride penetration into concretes incorporating mineral admixtures such as fly ash, blast-furnace slag and silica fume in a marine environment. OPC concretes, FA 30% concretes, BFS 50% concretes and SF 10% concretes were prepared. After 7 years of the exposure time in a marine environment, concrete cores of 50 mm or 100 mm in diameter were drilled from the cubes. Concrete cores were sliced into discs of 10 mm in thickness, and then analyzed. Using chloride distribution profiles of concretes with and without mineral admixtures from the exposed surface to the interior, diffusion coefficients for chloride ions were calculated. The chloride permeability of concretes with and without mineral admixtures was also determined by the rapid chloride permeability test (RCPT). The relationship between the diffusion coefficient for chloride ions in exposure test on seashore and the charge passed in RCPT in concretes with and without mineral admixtures was discussed. From experimental results, it was found that concretes incorporating mineral admixtures were much less permeable to chloride ions than the corresponding OPC concretes, and that the chloride penetration into concretes incorporating mineral admixtures was effectively reduced, which was limited-to a surface layer only 40 mm after 7 years of the exposure time. The results also showed that the diffusion coefficient for chloride ions correlated well with the charge passed in the RCPT test for all concretes.

In many standard specifications there is a limit for the maximum amount of unburnt carbon of fly ashes often referred to as LOI. In particular, according to the European norm EN 450, this limit is 5% on the continental basis of the European Unity, or 7% on the domestic national basis. Therefore, fly ashes with LO1 over 7% should be rejected as a supplementary cementitious material in concrete mixtures. Four fly ashes from coal-fired electric generating plants, with LO1 content of about 4, 7, 9, and 1 l%, were used to manufacture concrete mixtures. They had the water-cement (W/C) ratio of 0.68, corresponding to a water-binder ratio of 0.48 and a fly ash/binder ratio of 0.30. A small amount of superplasticizer (0.3- 0.4% by cement mass) was required to compensate the slump decrease caused by fly ash with higher LOI (> 7%). Two reference concrete mixtures, without fly ash, were also produced with a w/c of 0.68 and 0.48. The performance of all these concrete mixtures was assessed in terms of compressive strength at early and later ages (l-l 80 days), water-permeability, chloride diffusion, and carbonation rate. There was no evidence available which indicated that the LO1 content of the fly ash affected negatively any of the properties studied. In particular, due perhaps to its peculiar pozzolanic activity, the fly ash with the highest LO1 content (11.30%) performed better than that with the smallest amount of LO1 material, (4.19%). This occurred in terms of higher compressive strength, lower water-permeability, slower chloride diffusion, and decreased carbonation rate in the corresponding concretes. Therefore, the conformity criteria adopted by some standard specifications in rejecting fly ashes only on the basis of the relatively high LO1 content, without determining the corresponding concrete performance in terms of strength and durability, appear to be technologically inadequate and

The reduction in the useful-service life of reinforced concrete structures in the coastal areas of the Arabian Gulf is of major concern to the construction industry. The harsh climatic conditions, high level of chloride and sulfate contamination in the environment, low quality and contaminated aggregates, and substandard construction practices constitute the major causes of deterioration of reinforced concrete structures in less than 10 years in this part of the world. Since the concrete deterioration phenomena are strongly permeability dependent, mineral admixtures and industrial by-products, such as natural pozzolan, fly-ash, blast-furnace-slag, and silica-fume are increasingly used to improve its durability. Among the mineral admixtures and industrial by-products, fly-ash and silica-fume are considered to be more beneficial due to their superior performance in improving concrete durability. However, to attain beneficial properties, pozzolanic concrete needs early and extended curing compared with normal portland cement concrete. This is of particular concern in the Arabian Gulf environment, where the high ambient temperatures, solar radiation and blowing winds make curing a difficult process. Therefore in this study, the effect of temperature and drying as well as different curing conditions on the compressive strength development in normal Portland, silica-fume and fly-ash cement concretes was evaluated. The test specimens were cured in the laboratory and under field conditions, and tested 1,3,7, 14,28, 60 and 90 days after casting to evaluate the compressive strength development. The results indicated an increase in the compressive strength, in both the normal, fly-ash and silica-fume cement concrete specimens with the period of curing. Field curing had more negative effect on the strength development in concrete specimens containing fly-ash and silica-fume than in the plain concrete specimens. High temperature casting and curing increased the compressive strength in both plain and fly-ash concretes. Drying during curing produced the highest strength the silica-fume concrete specimens compared to plain and fly-ash concretes.