International Concrete Abstracts Portal

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.

The overall objective of this paper is to establish the engineering properties of concrete containing combinations of fly ash/silica fume and slag/silica fume. Six concrete mixtures were tested, with total cementitious materials content of 350 kg/m3 and 450 kg/m3, and a constant water/cementitious materials ratio of 0.45. The effect of three curing conditions was investigated, and the tests were performed up to about 260 days. The results reflect conclusively that cement replacement materials reduce slightly the engineering properties of portland cement concrete, and that the exposure conditions have a strong influence on flexural strength, dynamic modulus, and ultrasonic pulse velocity. Slag was generally found to be slightly superior to fly ash in the development of these engineering properties. The key to developing fly ash/silica fume and slag/silica fume concretes without suffering a reduction of strength gain when exposed to drying environmental conditions is to incorporate within the mixtures adequate amounts of portland cement and water to ensure the continuation of pozzolanic reactivity and hydration.

In order to investigate the influence of aggregate on autogenous shrinkage and drying shrinkage in high-fluidity, high-strength concrete containing ground granulated blast-furnace slag(GGBFS), a study was made of the water-binder ratio (W/B), quality of coarse aggregate and replacement ratio of GGBFS(replacement ratio of slag) at different levels. In this test, W/B was 23, 28, 33 and 43%, replacement ratio of slag was 0, 50 and 75%, five types of coarse aggregates were used. The authors investigated the relationships between W/B and autogenous shrinkage or drying shrinkage, physical properties of aggregate and, concrete shrinkage, and replacement ratio of slag and concrete shrinkage. Particularly in this study, the authors paid attention to aggregate crushing value of physical properties of aggregate. The aggregate crushing value was measured by method which was defined in British Standard. The following findings were obtained. (a) The smaller the W/B, the greater the percentage of autogenous shrinkage in drying shrinkage. (b) The aggregate crushing value is a critical factor in concrete shrinkage. (c) An increase in replacement ratio of slag leads to an increase in the percentage of autogenous shrinkage in drying shrinkage. (d) The practical significance of these data is that we should consider the aggregate crushing value in evaluating autogenous shrinkage of high-strength, high-fluidity concrete.