PSI - Issue 64

Sadeq Mo. Annooz et al. / Procedia Structural Integrity 64 (2024) 1565–1572 Annooz, Williams, and Myers / Structural Integrity Procedia 00 (2024) 000–000

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1. Introduction Concrete is highly resistant to compression forces, but has very low capacity to carry tension forces, which is why it was efficiently used for simple arch structures early on similar to masonry arches bonded with mortar. Mild steel rebars were later developed to enhance the tension resistance of concrete, and reinforced concrete (RC) with mild steel rebars developed into a primary construction option for many years. RC relies on the interaction between steel rebars and the surrounding concrete matrix to provide structural strength and durability. One crucial aspect of this interaction is the formation of a passive layer of protection on the surface of the steel rebar. This passive protection is a thin layer of oxide that naturally forms in highly alkaline environments, such as those found in concrete pore solutions. However, aggressive substances such as chloride and sulfate ions can infiltrate the concrete in natural environments, especially those characterized by marine or Salt Lake exposure. These aggressive ions have the ability to penetrate through the concrete matrix and reach the surface of the steel rebar. When aggressive ions come into contact with the passive protection on the steel rebar, they can disrupt or destroy it. This process is often referred to as de-passivation. Once the passive film is compromised, the steel rebar becomes vulnerable to active electrochemical corrosion (Köliö et al. 2015). Many solutions were considered to overcome the problem of steel corrosion, such as galvanization and powder resin coating (Nanni et al. 2014). Since the beginning of the fiber-reinforced polymer (FRP) rebar industry in the mid 1900s, engineers have shown interest in using FRP materials (Bank 2006). Basalt FRP (BFRP) is the most recent type of FRP composite. Basalt fibers are manufactured directly by melting volcanic rocks (Militký, Kova č i č , and Rubnerová 2002). Compared to carbon fibers, they are less expensive and have abundant sources of raw materials. Basalt fibers are non-toxic, environmentally friendly, non-magnetic, have a high working temperature, and excellent fatigue resistance (Dong et al. 2016). The bond behavior between FRP rebars and concrete is essential to using FRP as a reinforcement material. In this study, two diameters of BFRP and steel rebar were tested, and ten specimens with an embedment length of 5d b were prepared to investigate the bond strength of BFRP. 2. Test matrix and material used For the concrete mixture, Portland cement ASTM type 1, 19 mm (3/4 in.) size limestone aggregate and natural sand were used. The cement’s properties are shown in Table 1. Two diameters of steel rebars complied with ASTM A615 09 (ASTM A615 2018), (#4) 13 mm (1/2 in.), and (#6) 19 mm (3/4 in.) grade 60 were used. The rebar shape and deformation (ribs) conformed to ACI 408R-03 (ACI Committee 408 2003). Two diameters of BFRP (#4) 13 mm (1/2 in.) and (#6) 19 mm (3/4 in.) made by a Canadian manufacturer were used. The properties of the BFRP rebars tested conformed to ASTM D7205 (ASTM D7205 2021) are shown in Table 2. An embedment length of 5 times the rebar diameter (d b ) was utilized.

Table 1. Cement Properties Material

Units

Amount

SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO SO 3 Na 2 O

18.7 3.98 3.00 63.3 1.70 3.20 0.53 5.40 98.3 62.5 5.10 95.0 180 3.10

%

Loss in ignition

Fineness (+325 Mesh)

C3S C3A

Vicat set time, initial Vicat set time, final. Specific gravity

Minutes

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