Browsing by Author "Omar Saeed Baghabra Al-Amoudi"

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Studies on soil-foundation interaction in the sabkha environment of Eastern Province of Saudi Arabia
(Saudi Digital Library) Omar Saeed Baghabra Al-Amoudi
The large, extremely flat, saline, evaporative areas situated either along the coasts or farther inland of many arid, semi-tropical countries are known by the word 'sabkha'. The main distinguishing features of sabkha are its heterogeneous matrix and its highly concentrated ground-water. These characteristics of sabkhas contribute to many unresolved geotechnical problems which could hamper the performance of foundations. In an attempt to assess the safety and serviceability of foundations in eastern Saudi sabkha environments, a full-scale research was conducted to: (i) study the sabkha, its load-bearing and compressibility characteristics as well as other relevant geotechnical properties to assess the safety of foundations; and (ii) investigate the interaction between foundation materials and chloride and/or sulfate salts in the sabkha to evaluate the performance of plain and blended cements in resisting reinforcement corrosion and sulfate attack to assess the durability of foundations. Results of this research indicate that the surficial sabkha soil is very loose and possess low strength. Some standard techniques, such as sieve and hydrometer, permeability and consolidation, are shown to be inappropriate. The collapse potential of sabkha, as determined by a modified oedometer, rather than its compressibility, is classified as 'very severe trouble'. Silica fume and BFS blended cements exhibited deterioration to a higher degree than other cements in both pure sulfate and high sulfatechloride environments. The chloride beneficiation for these two cements is only marginal because of the excessive magnesium decomposition of C-S-H due to the lower CH content, which is shown to be unhampered by the presence of chloride ions. However, reinforcement corrosion, as determined by time to initiation of corrosion and corrosion current density, is much lesser in silica fume and BFS cements due to their denser structure. The concomitant presence of sulfate ions aggravat
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Studies on the evaluation of permeability and corrosion resisting characteristics of Portland pozzolan concrete
(Saudi Digital Library) Omar Saeed Baghabra Al-Amoudi
The service conditions of Eastern Saudi Arabia necessitate the production of concrete which is dense and impervious, so that it inhibits penetration of salts which are effective in setting up corrosion of rebars and chemical deterioration of hardened cement paste. Pozzolan is considered a potential admixture. This investigation evaluated the effect of using pozzolan on the permeability, porosity and general quality of concrete made with typical local aggregates consisting of finely graded sands and crushed limestone. I varied possolan substitution from 0 to 40% and water cement ratio in the range of 0.35 to 0.55. The performance of pozzolans from four different sources was also evaluated. The effects of hydration reaction of pozzolan on the properties of concrete was studied for one year, by measuring water permability, porosity, pulse-velocity and compressive strength. Accelerated corrosion tests were carried out in the laboratory to determine the effectiveness of pozzolan in inhabiting rebar corrosion. Exposure-site tests were carried out to evaluate the corrosion resistance characteristics of pozzolan concrete made with salt contaminate mixing water. The exposure-site samples were monitored to determine the time to cracking. Carbonation depth, weight loss of rebars, and pH were measured after 11 months. Results show that 20% fly ash improves the general quality of concrete. Pozzolan concretes show better performance than straight portland cement concrete in terms of resistance against rebar corrosion. Pozzolan concrete contaminated with salts do not show any noticeable aggravation, in rebar corrosion due to the presence of fly ash. Reaction between fly ash and calcium hydroxide (Ca(OH)$sb2$) of the hydrated cement paste does not reduce pH below that observed for the no-fly ash concretes. Carbonation depths of about 1.0 cm were observed in 11 months of exposure. The best performance was exhibited by French fly ash. (Abstract shortened by UMI.)
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