| Abstract: |
; Admixtures are used to modify the properties of concrete or mortar tomake them more suitable for the work at hand. In many instances (e.g., very highstrength), admixtures may be the only feasible means of achieving the desiredresult. Lately, some attention has been given to the use of the pozzolan, silicafume as a possible partial replacement for cement to obtain high strengthconcrete to be used in many application such as high-rising buildings, long spanbridges, off shore structures .. etc.In this work, the effect of incorporating different percentages of silica fumeto concrete at two cement contents namely 450 and 350 kg/m’ with gravel orbazalt as coarse aggregate on the properties of fresh and hardened concrete wasstudied. The properties of fresh concrete such as workability and air content aswell as the properties of the hardened concrete such as compressive strength,tensile strength, modulus of elasticity and fracture toughness were investigated.In the present work, it was found that the workability of fresh concretegreatly decreases with increasing silica fume content and decreasing cementcontent. This DROP in workability was more noticeable in the case of crushedcoarse aggregate (Basalt). So it was necessary to use superplasticizers in silicafume mixes to maintain the workability constant without increasing water content.The enhancement in the mechanical properties of silica fume concrete suchas compressive, tensile strength and modulus of elasticity was found to dependgreatly on the properties of the mix ingredients.The effect of silica fume is more obvious in improving the compressivestrength more than in case of tensile strength and modulus elasticity.Also, it was found that silica fume improves the fracture toughness ofconcrete. This improvement increases with increasing cement content androughness of coarse aggregate.
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