Ginghis B. Maranan

Bond stress-slip behavior: case of GFRP bars in geopolymer concrete

The use of geopolymer concrete reinforced with fiber-reinforced polymer (FRP) bars is anticipated to address the concerns on the usage of traditional reinforced concrete structures, such as the corrosion of internal steel reinforcement, costly repair and rehabilitation, and development of sustainable infrastructures. To gain wide acceptance in the construction market, the bond between geopolymer concrete and the FRP bar should be investigated first because it is a critical factor that influences the behavior of structures, specifically its strength and long-term durability. In this study, the bond performance of sand-coated glass fiber-reinforced polymer (GFRP) bars into geopolymer concrete with a compressive strength of 33 MPa was investigated under a direct pullout test. The effects of parameters such as bar diameter (12.7, 15.9, and 19.0 mm) and embedment length (5, 10, and 15 db, where db is the bar diameter) were evaluated. The results showed that the maximum average bond stress obtained is around 23 MPa. As GFRP bar diameter increases, the average bond stress decreases. Similarly, the average bond stress decreases as the bond length becomes longer. The specimens with shorter embedment length failed because of pullout of the bars, whereas those with longer embedment lengths failed because the concrete split. The results further revealed that the geopolymer concrete reinforced with GFRP bars have a bond strength similar to that of steel-reinforced geopolymer concrete. Finally, bond-slip models for the ascending branch up to maximum bond stress of the bond-slip curves for GFRP bars and geopolymer concrete were proposed.

Shear Behavior of Geopolymer Concrete Beams Reinforced with Glass Fiber-Reinforced Polymer Bars

The shear behavior of geopolymer concrete beams reinforced with GFRP bars and stirrups was investigated. Six short beams with a shear-span-to-effective-depth ratio (a/d) of 1.8 were cast: one with no stirrups, three with different stirrup spacing, one with less reinforcement, and one with steel stirrups. In addition, a slender beam (a/d=4.7) with the same cross-sectional area were built to investigate the influence of a/d. Experimental results showed that the GFRP stirrups enhanced both the shear strength and deflection capacity of the beams by approximately 200%. The shear crack initiated at a higher load and with a finer crack width in the beam with narrower stirrups spacing. The short beam yielded higher shear strength than the slender beam with a similar transverse reinforcement ratio. The beams with GFRP stirrups yielded a shear strength and deflection capacity—including an analogous load–deflection response—similar to that of the beam with steel stirrups.