Abstract
The paper deals with the verification of the effect of the addition of inorganic SiO2 nanofibers to cement composites. In the first stage, a stable suspension of SiO2 nanofibers was prepared in an aqueous medium. It is important to distribute nanofibers so that the nanofibers do not appear in the form of clumps and at the same time do not get damaged during the dispersion process. The ultrasonification process was used for dispersion. The dispersed suspension of SiO2 nanofibers and water was dosed together with the superplasticizing admixtures into the dry components of the cement composite and the components were homogenized. The properties of the cement composite with SiO2 nanofibers have been tested – compressive strength, flexural strength, density. Composites with the addition of SiO2 nanofibers at a dose of 0.008 % by weight of cement exhibited an increased compressive strength of up to 33 % and a 19 % greater flexural strength at doses of 0.016 and 0.032 % of cement weight than the reference sample without nanofibers. The presence of SiO2 nanofibers in the composite was monitored by scanning electron microscopy (SEM).
Highlights
Concrete is the most widely used building material worldwide
This can largely be prevented by the application of fibers that act as dispersed reinforcement in the cement matrix and, if the fibers have a greater modulus of elasticity than the matrix, they capture a portion of internal stress [1,2,3,4]
Due to their small dimensions and the large ratio between the length and the diameter, large aggregates are formed, which have to be disassembled before being used in the matrix. Another condition without which nanofibers would not fulfil their purpose is the strength of the fiber-matrix transit zone (ITZ – interfacial transition zone). This zone is analogous to the transit zone at the aggregate-matrix interface and, as is known, that is the weakest place in the concrete structure
Summary
Concrete is quasi-brittle material with high compressive strength, low tensile strength and low toughness, which in the end can result in cracks, especially in the stretched areas of concrete structures This can largely be prevented by the application of fibers that act as dispersed reinforcement in the cement matrix and, if the fibers have a greater modulus of elasticity than the matrix, they capture a portion of internal stress [1,2,3,4]. It is possible that a great deal of these pitfalls can be circumvented by at least suppressing the use of ultraviolet concrete due to its dense structure, lower content of portlandite, higher content of C-S-H gel and better transit zone properties Another reason to use ultra high strength concrete is purely economic. The research work focused on the use of nanofibers for high strength cement composites
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