الفهرس 
CHAPTER I: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The objective of this study is to investigate the possibility of utilizing bagasse ash and silica fume to improve the cement immobilization of chromium (VI). The thesis is written in 99 pages and contains 30 tables, 56 illustrative figures, list of 187 of most recently published reviews and English as well as Arabic summaries. The thesis was divided into four chapters as follows:
1- Chapter I is the introduction which summarizes the following items; production of ordinary Portland cement, properties of major clinker phases, cement hydration process, definition of heavy metals, cement immobilization of heavy metals and chromium through cement-based solidificationnstabilization treatment technology, criteria and effectiveness of the immobilization process, definition of pozzolana and the history of some Egyptian industrial wastes (bagasse ash and silica fume).
2- Chapter II is the literature survey which summarizes the following items; the pozzolanic activity of bagasse ash, theory of cement immobilization of heavy metals including precipitation and adsorption mechanisms, influence of cement hydration products such as C-S-H, ettringite and gypsum in the cement immobilization of heavy metals, leachability of heavy metals from solidified cement pastes, survey of recently published reviews dealing with cement immobilization of chromium (III) and (VI) as well as industrial chromium wastes, role of silica fume on cementitious materials and the aim of the work.
3- Chapter III is the experimental techniques which discuss in details the origin of selected raw materials, proposed mix compositions of blended cements, solutions and hydrated cement paste preparation as well as different laboratory and instrumental techniques used in this investigation.
A- Part I deals with the characterization of raw materials by XRF, XRD, TGA, FTIR and SEM techniques.
B- Part II studies the calcination and pozzolanic activity of bagasse ash by XRD, TGA, FTIR and SEM techniques.
C- Part III investigates the hydration characteristics of bagasse ash and silica fume blended cement pastes by setting time, combined water content, bulk density, total porosity and compressive strength measurements as well as XRD, TGA, FTIR and SEM techniques.
D- Part IV investigates the immobilization of Cr (VI) in bagasse ash and silica fume blended cement pastes by setting time, combined water content, bulk density, total porosity, compressive strength and toxicity characteristic leaching procedure (TCLP) measurements as well as XRD, TGA, FTIR and SEM techniques.
Summary and Conclusions
The main conclusions of this study are:
XRD, FTIR, TGA and SEM techniques illustrate that bagasse ash contains amorphous silica and unburned carbon which adversely affects its pozzolanic activity while silica fume composes of amorphous silica particles.
2- XRD, TGA, FTIR and SEM techniques illustrate that the optimum calcination conditions that enhances the pozzolanic activity of bagasse ash is 700-800°C for 3 hrs. Calcination at higher temperature and/or longer periods enhances the crystallization of silica and reduces the pozzolanic activity as well as the adsorption capacity of bagasse ash.
3- At the early ages of hydration bagasse ash acts as a filler whereas at later ages it acts as pozzolana. Increasing bagasse ash content make a dilution effect, require higher water demands and forms a layer of bagasse ash particles around anhydrous cement grains which delays the hydration of cement.
4- Partial replacement of bagasse ash by silica fume enhances the hydration of cement and improves the microstructure of blended cement paste. With increasing its content, silica fume agglomerates and requires high water demand and delays the hydration of cement.
5- The addition of low concentrations of Cr (VI) accelerates hydration reactions due to precipitation of calcium chromate and the increased demand for Ca2+ ions in the cement pore solution which was satisfied by hydration of unhydrated cement grains. Hence, combined water content and compressive strength increase while total porosity decreases. The addition of higher concentrations of Cr (VI) retard hydration reactions as a result of calcium chromate which coat around anhydrous calcium aluminate and silicate phases retarding cement hydration hence the situation is reversed, i.e. combined water content and compressive strength decrease while total porosity increases.
6- The rate of strength development of OPC paste hydrated in presence of Cr (VI) enhanced at later ages of hydration. This indicates that Cr (VI) affects the pore formation mechanism.
7- The incorporation of bagasse ash may improve the hydration of cement in presence of Cr (VI) due to that addition of Cr (VI) may accelerate hydration reactions in presence of pozzolana due to precipitation of calcium chromate and the increased demand for Ca2+ ions in the cement pore solution. Hence, setting time and total porosity of OPC paste hydrated in presence of Cr (VI) are lower whereas combined water content is higher than that hydrated with water. The situation is reversed with increasing bagasse ash content which may be due to increasing the amount of mixing water, decreasing clinker content as well as the formation of a layer of bagasse ash particles around anhydrous cement grains which delays the hydration of cement.
8- Cement immobilization of Cr (VI) in presence of silica fume was improved because of the pozzolanic activity of silica fume which accelerates hydration reactions and refines the microstructure of hydrated cement paste as confirmed by SEM results.