High Temperature Performance of Concrete Confinement by MWCNT Modified Epoxy Based Fiber Reinforced Composites.

The conventional method of fiber reinforced polymer (FRP) wrapping around concrete columns uses epoxy as the binder along with synthetic or natural fibers such as carbon, glass, basalt, jute, sisal etc. as the reinforcement. However, the thermal stability of epoxy is a major issue in application areas prone to fire exposure. The current work addressed this major drawback of epoxy by modifying it with a nanofiller, such as multiwalled carbon nanotubes (MWCNT), and reinforcing it using basalt and sisal fibers. The effect of exposure to elevated temperature on the behavior of concrete cylinders externally confined with these FRP systems was analyzed. Three types of specimens were considered: unconfined; confined with sisal fiber reinforced polymer (SFRP); and confined with hybrid sisal basalt fiber reinforced polymer (HSBFRP) specimens. The test samples were exposed to elevated temperature regimes of 100 °C, 200 °C, 300 °C and 400 °C for a period of 2 h. The compressive strengths of unconfined specimens were compared with various confined specimens, and from the test results, it was evident that the mechanical and thermal durability of the FRP systems was substantially enhanced by MWCNT incorporation. The reduction in the compressive strength of the FRP-confined specimens varied depending on the type of the confinement. After two hours of exposure at 400 °C, the compressive strength corresponding to the epoxy-HSBFRP-confined specimens were improved by 15%, whereas a 50% increase in strength corresponding to MWCNT-incorporated epoxy-HSBFRP-confined specimens was observed with respect to unconfined unexposed specimens. The MWCNT-modified epoxy-incorporated FRP-confined systems demonstrated superior performance even at elevated temperatures in comparison to unconfined specimens at ambient temperatures.

Modification of epoxy binder with multi walled carbon nanotubes in hybrid fiber systems used for retrofitting of concrete structures: evaluation of strength characteristics.

The rapid development in infrastructural facilities necessitates an efficient approach for the repair and retrofitting of concrete structures and, confinement method using fiber reinforced polymer is a promising one. The commonly used carbon and glass fibers for confinement poses environmental and performance issues. The present study addresses these two major aspects by considering natural fibers along with modification of epoxy binder to impart ductile behavior ie., to investigate the effectiveness of multiwalled carbon nanotubes (MWCNT) incorporated synthetic and natural fiber reinforced polymer (FRP) systems as the external confinement. MWCNT is incorporated in 0.5-1.5wt.% in epoxy nano and epoxy multiscale and there is significant enhancement in tensile and fracture properties of the composites up to 1wt.%, beyond which it declined due to agglomeration. Various strength tests were performed with sisal, basalt, carbon and hybrid sisal-basalt FRP systems with different FRP layer thickness on plain concrete cylinders. From the test results it is outlined that external confinement with MWCNT incorporated FRP improved the axial load-carrying capacity, energy absorption and ductility of concrete with respect to that of control specimens. Compared with unconfined specimens, those strengthened with MWCNT modified hybrid FRP wraps containing sisal and basalt fibers recorded increments of 114% and 87% in their load-carrying capacity and energy absorption, due to the intrinsic rigidity of hybrid fibers and epoxy modification. Furthermore, the outcomes indicate that MWCNT incorporated hybrid sisal-basalt FRP confined specimens exhibited superior properties and the low strength of natural FRP confinement compared to artificial FRP can be improved by epoxy modification. The outer jacketing resisted abrupt and catastrophic failure to a great extent.

Non-isothermal crystallization kinetics of polypropylene/short glass fibre/multiwalled carbon nanotube composites.

The non-isothermal crystallization kinetics of polypropylene (PP) reinforced with multiwalled carbon nanotubes (MWCNTs) and short glass fibres (GF) was studied by differential scanning calorimetry (DSC). The glass fibre concentration was maintained at 20 wt% and the MWCNT content ranged from 1 to 5 wt% in the PP matrix. The crystallization studies performed by DSC showed an increase in crystallization rate and a decrease in half time of crystallization of PP in the presence of micro and nano fillers. The Avrami, Ozawa, and Mo models were applied to analyze the non-isothermal crystallization behavior of PP multiscale composites. The Avrami model could very well describe the crystallization behavior of PP to 70% of the completion of crystallization. Beyond that level, it deviated significantly for all composites. On the other hand, the kinetics of crystallization could be well described by the Mo model. The strongest nucleating effect and the lowest activation energy were obtained for the composite with 2 wt% MWCNT and 20 wt% glass fibre. The X-ray diffraction analysis showed a significant reduction in the average crystal size in accordance with the amount of MWCNTs added.