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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.

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.

Study examines the microstructure properties of cement-based grout consisting of Type II rapid-hardening portland cement, Saskatchewan fly ash, and brine. The liquid brine is composed mainly of salts of sodium, calcium, potassium, and magnesium obtained from an underground potash mine. A scanning electron microscope (SEM), with an electron probe x-ray microanalyzer, was used to study the mechanism by which fly ash and brine alters the microstructure characteristics of cement grouts under confining pressures of 0, 3.4, and 6.9 MPa (0, 500, and 1000 psi). The SEM examination was conducted at 7, 14, and 365 days. This examination revealed that grout mixes containing brine had a gel-like substance covering the entire surface of the hydrated products. The probe x-ray microanalyzer identified the gel-like substance as consisting mainly of sodium chloride salt. Fly ash cement particles were also found to be encapsulated by the sodium chloride gel-like substance. This encapsulation may decrease the rate of pozzolanic reaction between fly ash particles and the lime available in the cement. Microscopic examination of specimens mixed with brine also showed the presence of long fibrous crystals with diameters ranging from 3 to 20 æm growing on the surface of the gel-like substance. Generally, at 7 and 14 days, the fly ash-cement grouts were found to have more such fibers than the grout containing no fly ash. This trend reversed at 365 days.

The interface between the cement matrix and aggregate is mostly regarded as a weak link in concrete with respect to durability and strength. It is shown that the positive effects of pozzolans on the permeability of concrete are partly related to a decrease in the thickness of the weak, lime-rich, interfacial zone. Results for various mineral admixtures, such as ground granulated blast furnace slag, powder coal fly ash, silica fume, a synthetic colloidal silica, and metakaolinite are presented. It is shown that in the presence of mineral admixtures, the calcium hydroxide content in the interfacial zone is reduced substantially.