International Concrete Abstracts Portal

SP-132 Published in two volumes...The first volume contains papers dealing with fly ash and natural pozzolans. The second volume consists of papers dealing with condensed silica fume and ferrous and non-ferrous slags.

The anchorages of Akashi Kaikyo Bridge are mass concrete having horizontal dimensions of 60 x 85 m, and a height of 45 m. Precooling and pipe cooling of concrete are used to prevent the thermal cracking of these mass concretes. Furthermore, the low-heat cement has been judged to be more effective to reduce the occurrence of thermal cracks. Comparisons have been made of the basic properties of concrete using a variety of low-heat generating cements to select the ones suitable for the project. The new types of low-heat cement have different ratios of finely ground blast furnace slag, fly ash, and portland cement, and can be broadly divided into binary blended types containing large quantities of slag, and ternary blended types containing large quantities of slag and fly ash. Paper gives results of the strength and adiabatic temperature rise in concrete made using these low-heat-type cements, and the influences of the slag and fly ash on the properties of concrete are described. Although low-heat-generating concrete generally shows retardation in the setting time and shows more bleeding, it was found that the use of very finely ground blast furnace slag and finely ground limestone powder improved workability of concrete, reduced bleeding, and is effective for the development of early-age strength.

The lining of underground cavities for storage of natural gas requires a proper cementing paste as does the cementing of casing in boreholes placed in salt beds. The following properties of the cementing pastes are required: high corrosion resistance, minimal shrinkage, even some expansion, high leak tightness, good bond to steel and rock, proper rheology and strength. The following blended cements were investigated: cement "Nowa Huta" 25 with 40% blast-furnace slag (bfs), cement "Rejowiec" 45 for bridge construction and cement with 70% bfs. The cements were mixed with NaCl brine at a concentration 310 g NaCl/L at liquid to solid ration 0.45. The properties of pastes, such as density, rheological, sedimentation and filtration characteristics; time of setting; strength development and shrinkage were determined. The phase composition of pastes was studied by XRD and the microstructure was observed under SEM. The best results were obtained for the pastes with the blast-furnace slag.

This paper gives the results of an investigation on the performance of high-volume fly ash concrete made with ASTM Class F fly ashes from three different sources. Cementitious materials contents of 300, 370, and 430 kg/m3 were used. The percentage of fly ash used was 58 percent of the total cementitious materials content. All the concrete mixtures were air-entrained and superplasticized. A large number of concrete specimens were subjected to the determination of compressive and flexural strengths, Young's modulus of elasticity, creep strain, drying shrinkage, abrasion resistance, deicing salt-scaling resistance, and resistance to chloride-ion penetration. High-volume fly ash concrete with adequate early-age strengths and excellent later age strengths can be produced with cement and total cementitious materials as low as 125 and 300 kg/m3, respectively. The Young's modulus of elasticity, creep, and drying shrinkage of high-volume concrete are comparable to those of the plain portland cement concrete. The high-volume fly ash concrete shows excellent resistance to chloride-ion penetration and outperforms plain portland cement concrete. The total charge in coloumbs at 91 days, a measure of resistance to the chloride-ion penetration, ranges from 278 to 1078. The corresponding values for reference concrete range from 1003 to 2313. Further research is needed to explain the relatively poor performance of the high-volume fly ash concrete under deicing salt scaling and abrasion tests.

Paper is concerned with the compressive strength of flowable mortars containing high-volume coal ash applicable to backfill or base construction. In addition to Type I portland cement, both Class F fly ash and bottom ash were used. The test specimens with flowability ranging from 13 sec to 5 min measured by a flow cone were fabricated by hand-rodding in the paper molds of dimensions 5 x 10 cm. The relationship between 28-day compressive strength and flowability as affected by fly ash content is studied. Compressive strength as a function of cement content is discussed. The effect of tasting condition and of curing condition on compressive strength is also evaluated. A comparison relating to strength gain is made between specimens utilizing tap water and seawater, respectively, as mixing water. Moreover, the influences of other factors such as mix proportion and curing temperature on compressive strength are reported. In this paper, 28-day compressive strength of about 1 MPa can be achieved for the specimens with 6 percent cement, by weight, at the excellent flowability of around 20 sec. For a given flowability, the replacement of fly ash by bottom ash generally can improve compressive strength. Compared to tap water, seawater as mixing water or as curing moisture definitely has more beneficial effect on compressive strength. The test results obtained from this study indicate that flowable mortar containing high-volume coal ash has a great potential as backfill or base construction material, particularly in hot weather regions.