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Mortars with and without fly ash are cured initially in distilled water or NaCl solution for 7, 28, 56, and 91 days and then exposed to the accelerated carbonation. The influence of chloride ion on the depth of carbonation is evaluated. Furthermore, mortars initially cured in distilled water are exposed to the accelerated carbonation condition and then immersed in NaCl solution to study the influence of carbonation on penetration of chloride ion. In both cases, electrochemical properties of steel reinforcement embedded in the specimen are measured. The penetration depth of chloride ion in fly ash mortar immersed in NaCl solution is larger at an early age, but becomes almost the same as that of the control mortar later. The depth of carbonation of mortar cured initially in NaCl solution is smaller than that in distilled water, and the same trend is observed, independent of initial curing period and the addition of fly ash. Fly ash mortar shows higher carbonation depth than the control mortar. Corrosion current of steel reinforcement in mortar is affected by both carbonation depth and chloride ion penetration.

The use of high-volume fly ash as a supplementary cementing material in controlling alkali-aggregate reactivity is an attractive solution. Fly ashes are often used in reducing the expansions due to alkali-aggregate reaction in concrete. However, in the past, only smaller quantities of fly ash, less than 30 percent by weight of cement, have been used. This paper presents the results of a study to determine the influence of very high quantities of fly ash in reducing the expansion due to alkali-aggregate reactions. Ten samples of sands collected from various locations in South Dakota were tested for alkali-aggregate reactivity using both standard ASTM C 227 and accelerated test methods. Five of the sands that caused greater expansions than permitted were tested with high fly ash contents, using the accelerated test method. Cements satisfying ASTM Type I and a low-calcium fly ash (ASTM Class F) were used for the entire investigation. The water/fly ash + cement ratio was 0.44 and the fly ash/fly ash + cement ratios expressed as percentages were 40, 50, 60, and 70. Control mortar specimens containing the same Type I cement and alkali content were used for comparison. An accelerated test method proposed by the Canadian Standards Association was used for the detection of potentially deleterious expansion of mortar bars. The test results had shown that high fly ash replacement levels were very effective in reducing the expansion due to alkali-aggregate reaction. The expansions of the mortar bars made with the highly reactive sands and high volumes of fly ash were negligible as measured in the accelerated test method.

Presents results of an investigation dealing with the long-term strength of silica fume concrete. Three series of concrete mixtures with and without silica fume were made with water-cementitious ratios from 0.25 to 0.40. The replacement level of portland cement with silica fume was kept constant at 10 percent. Test specimens were cast from each mixture to determine the compressive and flexural strengths of concrete at up to 3.5 years under both water-curing and air-drying conditions. The test specimens were also subjected to the determination of microstructure, carbonation, and weight changes with time. It is concluded that, under water-curing conditions, both the control and silica-fume concretes show gain in strength with age, with both concretes reaching similar strength levels after 3.5 years. However, continuous air-curing adversely affects the long-term compressive strength development of both types of concrete. This effect is considerably more marked for silica-fume concrete than for the control concrete, especially at w/c + sf of 0.30 and 0.40.

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.