International Concrete Abstracts Portal

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.

Examines the utilization of ultra-fine particles originated from fly ash, when a part of cement is replaced with the particles. The ultra-fine particles mainly consist of amorphous silica and alumina, and specific surface area of these particles can be changed from 200,000 cmý/g to 1,300,000 cmýg. To study the pore structures of mortar containing those fly ash particles, water-cement ratio, replacement ratio of the particles, and period of standard curing were varied. The properties, such as rate of hydration, rate of strength development, chemical components dissolved out to various alkali solutions during early ages, and pore-size distribution were measured. These properties were compared with properties of the cement mortar containing silica fume, meta kaolin, or fly ash for similar mortar specimens. It is shown that compressive strength of mortar containing the ultra-fine particles developed with age, and the pore structure of the mortar was like that of mortar with fly ash. Chemical components dissolved out to the particles were different from those dissolved out by other mineral admixtures.

To remove coarse PFA particles from bulk fly ash batches, a pilot plant air classifier was built and tested. This plant also enabled the production of fly ash gradings with various particle size distributions. The effect of upgrading by air classification on mortar and concrete properties was investigated in an extended research program. For that purpose, the PFA particle size distribution was expressed by the grading modulus, which proved to correlate well with fresh mortar and fresh concrete properties, as well as with strength and efficiency factors of the hardened materials. A simplified model for packing the dry components (fly ash, cement, and sand) of mortar was derived and applied. For the combinations investigated, mixes with coarser sized cement showed the highest packing density. A dense packing proved to be favorable for fresh mortar and hardened mortar properties.

The economic problem of energy consumption in the cement industry obliges many countries to produce blended portland pozzolan cements. These pozzolans have different origins and mineralogical structures influencing the qualities of the concrete. The criterion of mechanical strength of standard cement mortars is generally judged sufficient for marketing theblended cement. Samples of 15 natural pozzolans used by cement factories inTurkey were investigated in this research. Petrographic and mineralogical characteristics were determined by microscopic and x-ray diffraction examination. Their properties--including density, water absorption, specific surface; article size distribution, ability to be ground, pozzolanic activity, and chemical compositions--were studied. Blended cements were prepared in the laboratory by mixing 15 percent of pozzolan with 85 percent of normal portland cement; water requirements and times of setting were determined. Flexural and compressive strengths, workabilities, drying shrinkages, and freeze-thaw resistance, determined by cycles of immersion in magnesium sulfate and oven drying were examined on standard mortar specimens. The pozzolans used were fresh or altered pyroclastic tuffs representing rhyolite, basalt, trachyte, andesite, and dacite. Some of them contained phenocrysts, clay minerals, zeolites, and calcium carbonates. They exhibited different properties as powders, in pastes, and in mortars. Reliable and distinct relations between petrographic types and engineering properties cannot be proposed on the basis of current data. Further systematic and detailed research is needed.

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.