الفهرس 
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Abstract
After many decades, concrete remains to be the most important construction material in the globe. Therefore, improving its properties, to make it more durable and eco-friendly material, is vital. So, adding pozzolanic and/or waste materials to concrete blends can play this role. Also, using nanotechnology in processing these materials can add superior characteristics to them. Pozzolanic materials such as slag, fly ash, metakaolin and silica fume, and waste (non-pozzolanic) materials such as, marble, granite and limestone powder can be utilized as a partial replacement of the conventional cementing materials in the concrete mix. For instance, kaolinite-based Nano Clay (NC) and Marble Powder (MP) are abundant in the Egyptian environment, which represents a motive for the Egyptian research community to use such materials.
The present study focuses on the behavior of columns made from reinforced concrete, either normal or high strength, with optimum ratios of NC and MP. This is meant to take a wide step toward testing concrete elements instead of only testing concrete material itself. Therefore, the experimental work incorporates two distinctive studies; material and structural behavior studies. The study of material behavior focused on the feasibility of producing environmentally friendly concrete with NC and MP additives. In addition, for obtaining economically feasible concrete mix, the amount of NC particles in the mix was reduced by MP as a cheap waste material. This reduction of NC particles also facilitated its dispersion in partial amount of mixing water and superplasticizer by practical techniques such as, stirring and sprinkling. At first, concrete samples were prepared with hybrid additions of NC and MP; NC and MP replacement ratios were 3% and 5% of cement and 5%, 10% and 15% of sand by weight, respectively. After that, concrete physical properties; permeability, and mechanical properties; compressive, flexural, splitting and bond strength were investigated. Moreover, stress- strain response of optimum performance mixes was monitored. Finally, the microstructure of these mixes was studied using Scanning Electron Microscopy analysis (SEM) and Thermogravimetric Analysis (TGA).
For the structural behavior study, the influence of the optimum NC and MP ratios as hybrid additives on the structural behavior of reinforced concrete (RC) columns is analyzed, in terms of ultimate capacity, axial strain, lateral strain, toughness, and failure pattern. The structural experimental program was organized to ten RC columns specimens made of either normal strength concrete (NSC) or high strength concrete (HSC) that were tested under axial compressive loading to examine the parameter of hybrid additives presence on the column performance.
It can be concluded from the material behavior study that the best physical/mechanical performance of concrete mixes can be achieved by using 3% NC and 10% MP additives ratios by weight of cement and sand, respectively. Also, the microstructure of these mixes shows less voids due to filling effects of MP and the share of NC in the hydration process.
The experimental results of the structural behavior study showed that, in both NSC or HSC RC columns, the presence of optimum ratios of the hybrid materials (NC&MP) promote more ductile behavior with enhancement in column axial capacity. In particular, additional confinement in RC columns was offered by the presence of NC that achieves highly increment in the lateral strain and toughness. Briefly, Higher axial load capacity, better ductile performance, greater reduction in the ties ratio and larger dissipation of energy can be achieved by using hybrid additions in the RC columns.