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.

Heavy damage due to alkali-aggregate reaction has been observed in concrete structure in and along the sea. An accelerated test is performed on mortar to evaluate effectiveness of fly ash for controlling alkali-aggregate reaction in the marine environment. Mortar bars using Pyrex as aggregate and cements with 0.6 and 1.1% of equivalent sodium oxide are made. The alkali content in the mixture is adjusted by adding NaOH or NaCl. Specimens are stored in distilled water, NaCl solution, and under more than 95% of relative humidity. The controlling effect of fly ash and the effect of internal and intruded chloride ion in mortar on alkali-aggregate reaction is studied by measuring the expansion of mortar. Expansion of mortar depends on the type of cement and chemical reagents used for alkali adjustment, the amount of fly ash used and the exposure condition. Even with the same equivalent sodium oxide in the mixture, mortar using NaCl for alkali adjustment shows higher expansion than mortar using NaOH. The highest expansion is revealed for mortar cured in NaCl solution. The controlling effect of fly ash also depends on the type of cement and the exposure condition.

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.

The changes in physical and chemical properties of rice husk ash (RHA) fired at several temperatures from 400 to 800 C at 50 C increments were studied. The noncrystalline of RHA fired below 600 C could not be determined by x-ray diffraction (XRD), but it could be expressed by Luxan's method, which determines the variation in electric conductivity in a saturated solution of calcium hydroxide containing RHA. The effect of RHA on the properties of mortar, such as strength, drying shrinkage, resistance to acid attack, freeze-thaw resistance, and carbonation, was also determined. It was found that the compressive strength of RHA blended mortar with respect to that of plain mortar corresponded to the variation in conductivity. The RHA in mortar improved resistance to acid attack and developed the same degree of resistance to freeze-thaw action as that with silica fume, while it increased the drying shrinkage.