High-temperature mechanical properties and microscopic analysis of nano-silica steel fibre RC

Abstract

This paper investigated the high-temperature mechanical properties of nano-steel fibre-reinforced concrete (NSFC), steel fibre-reinforced concrete (SFRC) and normal concrete. The mechanical properties were compressive strength, splitting tensile strength and flexural strength. The microstructure and interfacial transition zone of steel fibre at different temperatures were also examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanical properties of NSFC are found to be better than those of SFRC and normal concrete at all test temperatures, particularly at 4008C, where the maximum values are reached. Compared with normal concrete, the compressive, splitting tensile and flexural strengths of NSFC increase by 27 . 0%, 63 . 3% and 54 . 1%, respectively, at room temperature, and by 35 . 1%, 84 . 6% and 87 . 2%, respectively at 4008C. SEM and XRD analysis show the existence of a permeable diffusion layer on the steel fibre surface because of the solid-state reaction in the interfacial transition zone of steel fibre and concrete. This layer is white, bright and serrated, and mainly consists of iron disilicide (FeSi 2 ) as well as the complex hydrated calcium silicate. The compounds of this layer change the interfacial transition zone structure, enhance the bonding capacity of the steel fibre and matrix, and also increase the hightemperature mechanical properties of concrete. IntroductionIn recent years, frequent fire accidents have inflicted damage to the stability and safety of buildings. Thus, many researchers are focusing on the loss of mechanical properties of ordinary concrete at high temperatures (Long and Carino, 1998;Schneider, 1988;Zhang et al., 2000). The application of nanotechnology in concrete has enabled improvements in its performance and multifunctionality. Given the unique effects of nanomaterials (e.g. small-size, quantum, surface and interface effects), there are many distinctive features in structure, physical and chemical properties (Xu, 2004). Several studies (Senff et al., 2010;Ye et al., 2007) on the mechanical properties of nanoconcrete at normal temperature have obtained interesting results. For example, mixing 1-3% nano-silica (nano-SiO 2 ) noticeably improves the compressive and splitting strengths of concrete at the early period, reduces the amount of calcium hydroxide (Ca(OH) 2 ) on the interface between the cement paste and aggregate, results in grain refinement and also improves the microstructure of concrete. The influence of lithium silicate sol mixed with nano-silica particles on the later period of concrete hydration has also been studied (Guo et al., 2010). Adding nano-silica particles to the lithium silicate sol doubles the number of pores between C-S-H gel layers. Consequently, the number of pores is greatly reduced and concrete hydration in the later period becomes more noticeable. However, the mechanical properties of nano-steel fibre-reinforced concrete (NSFC) at high temperatures has not been reported. Therefore, this paper investigates the mecha...

The Influence of Nanomaterials on the Thermal Resistance of Cement-Based Composites—A Review

“…In distinction to the abovementioned works, other studies have reported rather negligible effects of NS on flexural strength [ 28 , 49 , 51 ]. Yan et al [ 51 ] have analyzed the effect of NS on the flexural strength of steel-fiber reinforced concrete (SFRC), exposed to temperatures of up to 800 °C. They reported an increment in the initial flexural strength of concrete containing NS, as well as a slightly higher flexural strength after exposure to 200 °C, compared to plain SFRC.…”

“…It is difficult to draw any clear conclusions, regarding the effects of NS on the flexural strength of cementitious composites, from the works cited above. While some authors have reported flexural strength improvements [ 44 , 45 ] in the presence of NS under elevated temperatures, others have reported only negligible effects [ 28 , 49 , 51 ]. As such, further work is required.…”

Effect of nanosilica on durability and mechanical properties of high-strength concrete

“…Several kinds of nanoparticles are often used in concrete, such as nanoparticles of silicon dioxide (SiO 2 ), calcium carbonate (CaCO 3 ), aluminium oxide (Al 2 O 3 ), titanium dioxide (TiO 2 ), zinc peroxide (ZnO 2 ) and zirconium dioxide (ZrO 2 ), and there are many research reports on the implementation of nanoparticles in cement-based building materials. Among these nanoparticles, nanosilica seems to be the most popular, since it has pozzolanic activity in addition to a filler effect in a concrete matrix (Givi et al, 2011;Ltifi et al, 2011;Nazari and Riahi, 2011;Yan et al, 2013).…”

Experimental Research on Acoustic Emission Characteristics of High Performance Concrete Beam with Nano SiO2

“…Nanomaterials have small size, quantum, surface, and interface effects, characteristics which are absent in macro objects, and provide nanomaterials with special structures and physical and chemical properties [6][7]. Similar to the AE mechanism of other materials, the AE of concrete is the consequence of dislocation motion of crystals, relative slippage between crystals, elastic and plastic deformations, crack development and extension, and friction [8].…”