Mechanical characterization of SRG composites according to AC434

In the last decades, technologies and materials such as fiber reinforced polymer (FRP) have been used to strengthen different types of existing structures. More recently, composites have been developed consisting of reinforcement fabrics embedded in an inorganic mortar. These composites are known as fabric reinforced cementitious matrix (FRCM), when the fabric is made of aramid, glass, basalt, polyparaphenylene benzo-bisoxazole (PBO) or carbon fibers, and steel reinforced grout (SRG), when the fabric is made of twisted high-strength steel cords. In the United States, the characterization of FRCM/SRG systems is conducted in accordance to Acceptance Criteria AC434. According to AC434, the tensile properties of FRCM/SRG are obtained through a direct tensile test on coupons using clevis grips. The objective of this research is to discuss the applicability of the AC434 test method to determine the mechanical properties of SRG as a function of the length of the anchoring plates. SRG panels were cast and stored in a humidity chamber. After a 28-day curing period, they were cut to size and metal plates of different lengths adhered to their extremities. Results show that not all the assumptions currently made in AC434 are applicable to this type of composite. The experimental response was characterized by a trilinear stress-strain behavior. Furthermore, the cracked modulus calculated based on stress values between 60 and 90% of the ultimate stress does not accurately represent reality. Re-evaluation of this provision is of importance since the cracked modulus is used in design.