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.
Highlights
Corrosion is responsible for numerous structurally deficient concrete bridge decks as a result of deicing salts [1]
The above results indicate that using as low as 0.5 wt.% COOH-multiwalled carbon nanotubes (MWCNTs) well dispersed in the vinyl ester matrix prior to pultrusion of the Glass fiber-reinforced polymer (GFRP) bar could significantly improve the tensile strength by 20% and horizontal shear strength by 111% and change the GFRP modes of failure
Viscosity measurements and scanning electron microscope (SEM) investigations were first conducted to define the suitable content for MWCNTs dispersed in the vinyl ester resin that can be used in the pultrusion process
Summary
Corrosion is responsible for numerous structurally deficient concrete bridge decks as a result of deicing salts [1]. Despite the advantages offered by the corrosion-resistant material, GFRP reinforcing bars have a relatively low interfacial bond between the glass fibers and the polymer matrix [2] This weak interfacial bond results in several potential limitations of GFRP reinforcing bars, including limited horizontal shear strength, relatively low creep rupture strength, and low fatigue strength [4]. Laminated FRP composites manufactured using vinyl ester dispersed with carbon nanotubes demonstrated an improved interfacial bond between the resin matrix and the fiber reinforcement [21]. It is hypothesized that incorporating a small amount of COOH-MWCNTs in the vinyl ester resin system prior to its use in the pultrusion process will enhance the bond between the vinyl ester matrix and the glass fibers, leading to the improved pultruded GFRP reinforcing bars. Chemical analysis using Fourier-transform infrared spectroscopy (FTIR) was performed to explain the effect of MWCNTs
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