الفهرس 
AbstractOnly 14 pages are availabe for public view
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Abstract
Earth is suffering from global warming phenomena in which carbon dioxide plays a major role. One of the main aims of this study is to minimize the cement industry’s CO2 emissions by reducing the dependence on Portland cement in the concrete industry, as is the case in geopolymer concrete. Geopolymers show enhanced mechanical and durability properties compared with cementitious products, while ductility, energy absorption, and impact resistance tend to be relatively low. Moreover, the thermal properties of construction materials are important in terms of energy efficiency and sustainability. So, the need to develop these properties in geopolymer composites is a persistent need as a contribution to filling the research gap in this area. On the other hand, one of the most widespread environmental problems nowadays is the tons of used tyres left annually in landfills without adequate recycling. Currently, Crumb Rubber (CR) from used rubber tyres can be used as a partial replacement for concrete aggregates, providing valuable properties for concrete such as impact resistance, energy absorption, and improved thermal and sound properties. To achieve these targets, firstly, CR was reused as a partial replacement of sand by volume in geopolymer mortar with (10%, 20%, and 30%) replacement ratios with different CR particle sizes (less than 1.0 mm, 1–3 mm, 4 mm, and less than 1.0 mm to 4 mm). Parallel with using CR, polypropylene (PP) fibres with different volume fractions (0.5%, 1.0%, and 1.5%) were implemented. The effect of CR content and size and the effect of incorporating PP fibres on the physical, mechanical, and thermal properties of geopolymer mortar has been investigated. Secondly, reusing CR as a partial replacement of sand by volume in geopolymer concrete was investigated with (3%, 6%, and 9%) replacement ratios. Additionally, PP fibres with different volume fractions (0.25%, 0.5%, and 0.75%) were implemented. The effect of using CR, PP fibres and a mix of both on the physical, mechanical, impact, and microstructure properties of the geopolymer concrete has been studied. Finally, prestressed monoblock railway sleepers have been prepared on a full scale as a structural application that is subjected to impact and dynamic loads and exposed to harsh environmental conditions requiring fibrous Rubberized Geopolymer Concrete (RGC). All the proposed sleepers were prepared and tested statically according to international specifications. The main results of the rubberized geopolymer mortar show that a ductile mode of failure and a higher toughness index have been recorded for rubberized geopolymer mortar mixes compared with the control geopolymer mix; however, the main mechanical properties tend to be lower. For instance, using 30% CR in geopolymer mortar increases the toughness index I10 by an average of 66.2%; however, it decreases the compressive strength by an average of 44.3%. Moreover, using CR with PP fibres is better than using fibres only in terms of toughness and energy absorption considerations. More and above, using 30% CR decreases the thermal conductivity and the thermal diffusivity by 39.7% and 51.2%, respectively, which sheds light on using such material in applications that require thermal insulation. Furthermore, regression models capable of predicting both the main mechanical and thermal properties of fibrous rubberized geopolymer mortar are introduced, which are valid for use up to a 75% CR replacement ratio with reasonable accuracy. The main results of the RGC indicated that despite the mechanical properties of RGC tending to be relatively low, the mode of failure, toughness, performance under flexural loads, and impact resistance have been improved remarkably. For instance , using 6% CR with 0.75% PP fibres raises the toughness index I20 by about 338% if compared to a 282% increase when 0.75% PP fibres are only used. Moreover, the flexural impact resistance results show that incorporating CR with PP fibres significantly affects the absorbed energy to failure hitting a 240% increment. Finally, all results of the fibrous rubberized geopolymer-based prestressed sleepers passed the performance requirements of the international specification, providing a sustainable, economic, and more durable alternative if compared to the traditional cement concrete and the ultrahigh performance concrete sleepers.