Under unsaturated conditions, both moisture flow and the transport of ions strongly depend on the degree of saturation in concrete. In the current literature, most theories and empirical models describe moisture flow and the transport of ions in concrete based on the assumption that concrete is fully submerged in a liquid phase. This simplistic assumption often leads to a systematic underestimation in the amount of ions, such as chlorides, especially in the case of concrete applications subjected to cyclic wetting and drying conditions. In this study, an experimental program was established to determine the key hydraulic parameters needed for modeling the moisture flow and the transport of ions in five types of concrete mixes under unsaturated conditions. The required hydraulic parameters of the five concrete mixes include the saturated hydraulic permeability, the moisture retention function, and the dependency of the relative diffusion coefficient on degree of saturation. A centrifuge technique was used to determine the saturated hydraulic permeability of the five concrete mixes. The moisture retention data of all concrete mixes were determined using a vapour equilibrium technique. The moisture retention data were then used to determine the van Genuchten empirical parameters for an analytical characterization of the capillary pressure-degree of water saturation and the relative permeability-degree of saturation relationships. The dependency of the relative diffusion coefficient on the degree of water saturation was characterized for each type of concrete mix indirectly using an electrical resistivity technique. The experimental results of this study were used in different empirical models that have been originally developed for soils to examine whether they could be applied for concrete The five concrete mixes used in this study were characterized by the usage of a different proportion of dry densified silica fume in each concrete mix. Those mixes were used to determine the effect of silica fume on the experimental and the empirical key hydraulic parameters considered in this study.

Thesis (MAppSc)--University of South Australia, 1995

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xv, 235 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 212-216).

The thermal plasma production of fumed silica in a transferred arc consists of the decomposition of quartz to SiO (g) and oxygen followed by an oxidizing quench back to SiO2. The particles formed have diameters of the order of 10 to 20 nm and are linked in a three dimensional branched chain aggregate. Previous work by Addona and Munz (1999) demonstrated the technical feasibility of producing fumed silica using this method, but was unable to demonstrate the special rheological properties of the powder. The most important characteristic of fumed silica is the presence of hydroxyls on the surface of the particles, in the form of isolated hydroxyl groups, hydrogen-bonded hydroxyl groups and siloxane groups. / In the present work, we studied the changes in the powder quality by varying the quench conditions used for the production of the powder and by agglomerating the obtained particles. The fumed silica was agglomerated by conveying in a length of tubing with sharp bends. The powder was characterized using BET, Viscosity tests, FT-IR, TEM, SEM and XRD. The product was compared to both a commercial product (Aerosil 200) and the material previously produced by Addona. Tests were done before and after the agglomeration experiments. / The experimental results showed that the agglomeration had no effect on the powder's rheological properties. We concluded that the smaller viscosity values obtained for the plasma produced fumed silica were due to the lack of the free hydroxyl groups from the surface of the particles.

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Supplementary cementitious materials (SCMs), are beneficial when used as partial replacement of cement in concrete mixtures for coastal concrete structures, blended with Portland cement (binary or ternary mixes), i.e., high-performance concrete provides improved properties when exposed to marine harsh environment. In order to characterize selected durability properties of different concrete mixtures, a testing program was established. The intent of this study consists of testing 10cm diameter x 20cm long concrete specimens prepared with a range of different mix designs. 1) to evaluate the rate of water absorption due to capillary suction, referred to as sorptivity, 2) to evaluate the concrete surface resistivity, 3) to evaluate and compare the total porosity of specimens with different mixes, and 4) to obtain correlations between resistivity and sorptivity. All of these experimental tests were carried out according to ASTM International Standards (Sorptivity, Porosity) and Florida Method of Test (Resistivity). The tests were performed on concrete samples at various ages. Moreover, The results provided a fast and reasonable approximation of the concrete durability over time. Ordinary portland cement was partially replaced with supplementary cementitious materials including: fly ash (20%), silica fume (8%) and blast furnace slag (50%). These SCMs are highly effective in creating more durable concrete design mixtures. The water-to-cementitious (w/cm) ratios of 0.41 and 0.35 were investigated. The concrete that contains pozzolanic materials has demonstrated progress in extending the time for initiation of corrosion. The test results obtained indicate that the concurrent inclusion of fly ash and silica fume greatly reduced water penetration. The mixes containing slag also showed lower porosity and water absorption result, when compared to specimens containing fly ash only. Ternary concrete mixtures specimens showed much higher surface resistivity values than binary mixture specimens. These results suggest that reducing w/cm ratio, adding SCMs to concrete mixtures improved the concrete durability. The possibilities for the risks of corrosion initiation would be minimized (delayed) by prescriptive and then performance-based concrete blends with SCM materials optimized for service exposure in aggressive environments. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

Specimens from 27 batches of concrete with water to cementitious (cement plus silica fume) ratio of 0.25 to 0.32, with and without entrained air, were tested for freeze-thaw durability in accordance with ASTM C666, procedure A (freezing and thawing in water). In addition, another set of similar specimens were moist cured for 28 days instead of 14 days and tested in accordance with ASTM C666 , Procedure A to determine the effect of curing time on the freeze-thaw durability of high strength concrete. Results show that non air-entrained high strength concrete with water cementitious ratio of less than 0.30, regardless of the length of curing time, is frost resistant. Non-air-entrained concrete with water-cement ratio of 0.32 is also durable if silica fume is not used. / Ph. D.