Tensile Performance of GFRP Bars after Being Sprayed with Shotcrete

Shotcreting involves pneumatically spraying concrete at high velocities of approximately 100 km/h, yielding efficient construction, but raises concerns that the high-velocity spray can damage glass fiber–reinforced polymer (GFRP) rebars. This study is the first to investigate shotcrete’s potential to harm the tensile performance of GFRP bars by subjecting 48 bars to wet-mix shotcrete, using conventional industry practices and equipment, for spray durations of 5, 15, or 25 s. Two common types of 15.9 mm diameter GFRP rebar with different surface profiles were used, comprising ribbed or sand-coated bars. Two shotcrete mixes were used with either round (pea gravel) or angular (crushed limestone) aggregate. After shotcreting, all 48 abraded and 16 control bars were 3D-scanned to quantify the damage, if any, and measure their minimum cross-sectional area before tension testing the bars. Shotcrete damage to the bars was caused primarily by abrasion rather than impact damage from high-velocity aggregate impacts. Varying abrasion severity was observed. Common observations include removed sand-coating and local fiber erosion in one bar type and partially worn-away ribs in the other. Prismatic sand-coated bars were more susceptible to shotcrete abrasion than ribbed bars and showed nonlinearly increasing abrasion with spray duration. The average and maximum cross-sectional area losses were approximately 7% and 18% for sand-coated bars sprayed for 25 s with angular aggregate shotcrete. This area loss resulted in average and maximum reductions in tensile capacities of 11% and 22%, respectively; however, the bars still exceeded their guaranteed tensile capacity. The damage to ribbed rebars from shotcrete abrasion was negligible, with the ribs seeming to act as a sacrificial layer. The round aggregate mix produced negligible damage to both bar types. A model is developed to predict bar abrasion duration during construction based on member geometry and nozzle parameters, which is then used to predict cross-sectional area loss and force reduction. The model was verified against another experimental study and predicted exposure time within an 11% difference. While this study offers a first look at shotcrete abrasion of GFRP bars, further research is needed to predict abrasion damage conservatively.