Preparation And Performances Of Nano-scale Silica And Carbon Fibers Filled Cement Mortars

Development of nanotechnology provides a new impetus for sustainable development of cement-based materials. Nanomaterials can modify properties of cement-based materials at nanoscale, which includes both improving the mechanical properties and endowing functional properties. In this paper, the performances and their effect factors of hybrid nano-silica(NS) and carbon nanofiber (CNF) filled cement mortars was studied based on preparation and performances of NS filled cement mortars and CNF filled cement mortars. Main contents are as follows:1 The mechanical mixing and grinding preparation methods of hydrophobic nano-silica (SS) filled cement mortars were compared. The preparation of hydrophilic nano-silica (QS) filled cement mortars included mechanical stirring, grinding and ultrasound methods. Mortars with 0%,0.5%,1.0%,2.0%,3.0%,4.0% and 5.0% of SS or QS were fabricated. Flexural strength, compressive strength, microstructure and properties of these cement mortars were tested. The results indicated that QS can refine calcium hydroxide, promote hydration of cement, reduce the preferred orientation of calcium hydroxide. A suitable dosage of QS can enhance flexural and compressive strength of cement mortars. SS has no enhancement effect to cement mortars.2 The mass ratio of superplasticizer to CNF and ultrasonic time were determined 1 and 30min, respectively, through characterizing flexural and compressive strength of cement mortars at ages of 3 and 28 days. On this basis, the cement mortars with 0.05%,0.10%,0.15%, 0.20%,0.40%,0.60% and 0.80% of CNF were prepared. Their flexural strength, compressive strength, resistivity, and microstructure and properties were tested. The results indicated that CNF can promote hydration of cement but increase the preferred orientation of calcium hydroxide. A suitable dosage of CNF can improve the flexural strength, compressive strength and electrically conductivity of cement mortars.3 Cement mortars containing (2%/3%) QS+(0.05%/0.10%/0.15%) CNF were fabricated. Flexural strength, compressive strength and electrical resistivity variation during bending loads were tested. Hybrid QS and CNF have no mechanical reinforcing effect to mortars compared with single QS or CNF due to big crack and reunited state of CNF in mortars with hybrid QS+CNF. The change rate in electrically resistivity under bending of mortars with hybrid 3% QS+CNF was greater than that of mortars with hybrid 2% QS+CNF. 4 The four factors (including water-cement ratio, sand-cement ratio, content of QS, content of CNF) affecting mechanical and electrical properties of cement mortars with hybrid QS and CNF were analyzed by orthogonal experiment. The results indicated that the most significant factor for mechanical properties was the water to cement ratio. Hybird QS and CNF filled cement mortars with excellent mechanical properties can be fabricated by improving the matrix compactness and using ultrasound, chemical dispersion and silica fume to enhance dispersion of CNF together. The most significant factor for the electrically resistivity was the content of CNF. Finally, the combination of optimum factor level was obtained.