No abstract

This study represents an extension work to investigate the role of ultra fine sand (UFS) in enhancing the mechanical properties of fiber reinforced cementitious compounds. The micro-structural origins were identified by scanning electron microscope (SEM). About 50% of UFS had a diameter of less than 20 m. Ordinary Portland Cement (OPC) was partially substituted by UFS at 3, 5, 7 and 10% by weight of binder. It was found that as UFS loadings increase, the flexural, compressive, and tensile strengths increased up to about 5% UFS loading by 12.9, 15.7 and 30.1%, respectively, thereafter, a decrease in these properties was observed. This can be attributed to the pozzolanic effect besides the filling effect of UFS resulting in enhancing the interfacial bonds between the sand grains and hydration products that makes the paste more homogeneous and dense. The effect of both short natural and artificial fiber loadings on the structural performance of compounds was also studied. Loadings of 2%, by weight, of short natural date palm leaves' midribs fibers (DP) and artificial polypropylene fibers (PP) were added to the 5% UFS blended mix. An increase in both flexural and tensile strength was achieved, while a decrease in the compressive strength was observed.

This study aims at evaluating the influence of low cost nano materials including; nano silica (NS) and nano clay (NC) and various industry by-products including; silica fume (SF), Fly ash (FA), and fine Air-Cooled Slag (FACS) as cement replacements on the compressive strength, flexural strength and rheological properties of cement mortars. The results revealed that, the investigated industrial by-products contribute to the strength development by various ratios at various replacement percentages. The best mechanical performance was obtained for the mortar incorporating 15 wt. % SF; remarkable enhancements by about 30.8 and 26.8 were obtained for the compressive and flexural strengths respectively as compared with the plain ordinary mortar. FACS showed insignificant contribution to both compressive and flexural strengths. Even at low levels of replacement; the nano-materials provide better enhancements of the mechanical strength. Incorporation of 3 wt. % NS into the cement mortar has increased the compressive strength by about 38.5%; while, the incorporation of 5 wt.% of activated NC has considerably increased the flexural strength by 59% as compared to the ordinary cement mortar at 28 days of hydration. The workability of the blended mortars decreases with the loading of silica fume, fine air cooled slag nano-silica and nano-clay while increases with using fly ash and marble dust. The nano materials showed noticeable improvement of the structural integrity and microstructure, confirming the enhanced durability characteristics.