International Concrete Abstracts Portal

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 development of high-volume fly ash (HVFA) blended cements. The blended cements were made by combined grinding 45% of ASTM Type III cement clinker, 55% of ASTM class fly ash, a small percentage of gypsum, and 0.7% of superplasticizer by weight of the cement including clinker, fly ash, and gypsum. Several concrete mixtures were made with the control and the blended cements; also, concrete mixtures were made in which high volumes of fly ash had been added at the concrete mixer. A large number of test specimens were cast for determining the mechanical properties and durability characteristics of the hardened concrete. The results of the investigations indicated that the mechanical properties of concrete made with the HVFA blended cement are superior to that made with laboratory-produced portland cement and where the fly ash had been added as a separately batched material at the mixer. The durability characteristics of these two concretes are comparable except that the de-icing salt-scaling resistance of concrete made with the HVFA blended cement is considerably inferior to that of the concrete in which fly ash had been added as a separately-batched material at the mixer. The coarse Genesee fly ash that fails to meet the fineness requirements of ASTM C 618 has been used successfully to produce a HVFA blended cement. The mechanical and durability properties of concrete made with this blended cement (BCGS), are comparable to the concrete made with the HVFA blended cement produced with the finer Sundance fly ash. Thus, the production of HVFA blended cements offers a possible way for the utilization of coarse fly ashes. T h e intergrinding of the dry superplasticizer with clinker, fly ash and gypsum to produce HVFA blended cements did not pose any problems; however, for equal performance as regards to slumps, the amount of the superplasticizer needed in the blended cements was higher compared to that needed when superplasticizer was added separately at the mixer.

This paper describes the repair of a high-strength silica FUME concrete structure using a high-strength repair material which also contains silica FUME The repair represented the largest single application of this material and the largest single use of low-pressure spraying of the repair material. Information is provided on the repair procedures, proficiency of the nozzlemen, acceptance criteria applied to this type of operation. Because of the lack of actual in-situ bond and compressive strength data on high strength concrete in the literature, all of the actual in-situ test results are provided for this repair. Approximately 1,300 m3 of the repair material was used to repair 24,000 sq. meters of concrete surface damaged during a slipform operation. The damaged concrete had compressive strengths in the range of 78 to 82 MPa. The repair material had a target compressive strength of 80 MPa and an in-situ bond strength requirement (minimum) of 1.5 MPa. Using low-pressure spraying techniques because of confined working areas, the repairs were successfully completed over a 24 week period. Compressive strengths of cores from sprayed production test panels averaged 85 MPa at 28-DAYS. The in-situ bond strength of the repairs did not appear to increase with age and averaged 1.87 MPa for all ages evaluated.

This article outlines an experimental and numerical study of the long-term interaction between silica fume and Portland cement in concrete subjected to air, water or sealed curing. For this purpose about 2000 kg of eight qualities of concrete were studied at 4 different ages each over a period of 90 months. Half of the concretes contained silica fume. Parallel studies of strength, hydration and internal relative humidity were carried out. The article contains a great deal of valuable data based on comprehensive testing and data analysis. New and original results and analyses of the interaction between Portland cement and silica fume related to compressive strength, splitting tensile strength, hydration and internal relative humidity are presented. The project was carried out between the years 1989 and 1996.This article outlines an experimental and numerical study of the long-term interaction between silica fume and Portland cement in concrete subjected to air, water or sealed curing. For this purpose about 2000 kg of eight qualities of concrete were studied at 4 different ages each over a period of 90 months. Half of the concretes contained silica fume. Parallel studies of strength, hydration and internal relative humidity were carried out. The article contains a great deal of valuable data based on comprehensive testing and data analysis. New and original results and analyses of the interaction between Portland cement and silica fume related to compressive strength, splitting tensile strength, hydration and internal relative humidity are presented. The project was carried out between the years 1989 and 1996.