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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.

A considerable amount of natural zeolite has been used as an admixture for portland cement in the People's Republic of China. Paper first deals with a comprehensive characterization of inorganic admixtures such as natural zeolites with different mineralogical compositions, a fly ash, a fine blast furnace slag, and a silica fume. Binders, such as ordinary portland cement and a quick lime for the substitution of portland cement, were also subjected to the characterization. Next, bending and compressive strength and drying shrinkage of the test mortars were measured under the constant flow value. Standard test mortars were prepared by making use of the ordinary portland cement and quick lime-substituted portland cement, and blended cement mortars were also tested with the inorganic admixtures previously mentioned. As a result, natural zeolite was proven to be of sufficient applicability as an admixture for cement.

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.

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.