Pultruded GFRP Reinforcing Bars Using Nanomodified Vinyl Ester

Abstract

Glass fiber-reinforced polymer (GFRP) reinforcing bars have relatively low shear strength, which limits their possible use in civil infrastructure applications with high shear demand, such as concrete reinforcing dowels. We suggest that the horizontal shear strength of GFRP bars can be significantly improved by nanomodification of the vinyl ester resin prior to pultrusion. The optimal content of functionalized multiwalled carbon nanotubes (MWCNTs) well dispersed into the vinyl ester resin was determined using viscosity measurements and scanning electron micrographs. Longitudinal tension and short beam shear tests were conducted to determine the horizontal shear strength of the nanomodified GFRP reinforcing bars. While the tensile strength of the GFRP reinforcing bars was improved by 20%, the horizontal shear strength of the bars was improved by 111% compared with the shear strength of neat GFRP bars pultruded using the same settings. Of special interest is the absence of the typical broom failure observed in GFRP when MWCNTs were used. Differential scanning calorimetry measurements and fiber volume fraction confirmed the quality of the new pultruded GFRP bars. Fourier-transform infrared (FTIR) measurements demonstrated the formation of carboxyl stretching in nanomodified GFRP bars, indicating the formation of a new chemical bond. The new pultrusion process using nanomodified vinyl ester enables expanding the use of GFRP reinforcing bars in civil infrastructure applications.

Nano-hybridization effects of nano-silica and nano-graphene platelet on mechanical properties of E-glass/epoxy nanocomposites

“…Therefore, this may be a sign of interaction between epoxy matrix and nanofillers. 44,45,52 It can be interpreted that the decrease in peak density for nanofillers added samples reduces the autocatalytic effect due to agglomeration during curing proceses. 40,53 As seen in Figure 5, new band formation, which indicates the Si-O bending stretching groups was observed at 463 cm −1 in nano-silica and nano-hybrid added samples.…”

“…Chennareddy et al 44 achieved a high increment in tensile strength by adding MWCNTs to GFR-laminated epoxy composites. Vemuganti et al 45 determined that MWCNTs addition into pultruded GFR/vinyl ester bars provided a 20% increase in tensile strength. Demirci et al 23 determined that nano-hybridization of nano-silica and MWCNTs showed an adverse effect compared to SiO 2 nanoparticle added Basalt Fiber-Reinforced (BFR) nanocomposites for the tensile and low-velocity impact responses.…”

“…3,21,23,27,59–61 In addition, the increasing intensity of peak and new band formation in FTIR analysis can also be a sign of the interfacial adhesion of fiber/matrix. 44,45…”

“…It may be seen from the different fracture planes in the SEM images that the nanoparticles were embedded and closed to each other in the epoxy resin at the partial regions of the fracture surfaces. Vemuganti et al 45 reported that as the additive amount of nanoparticles increases in the matrix, the increased viscosity of the matrix could affect the dispersibility.

Figure 16.SEM fractography images of nanoscale fracture mechanisms of nano-silica (a), nano-graphene platelets (b) and nanohybrid filled (c) nanocomposites.

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Recent Development in the Processing, Properties, and Applications of Epoxy-Based Natural Fiber Polymer Biocomposites

“…As the method relies on the pulling of continuous roving through a resin bath/impregnator, care must be taken during production using natural fibers due to their yarn’s low pull strength. As a result, pull speeds are usually limited to 100–200 mm/min, which is low when compared to the pull speeds used during glass fiber/epoxy processing [ 80 ].…”