Increase of Crack Resistance of FRC by Optimization of Glass-Composite Macrofiber Shape

The study aims to investigate new types of reinforcing elements in concrete–glass fiber composites (GFCs) – as an alternative to steel and rod reinforcement. This research is relevant due to the need to reduce the material consumption and weight of structures. The complexity lies in the poorly predictable interaction of the fiber with the concrete matrix due to its anisotropy and non-standard geometry. This paper describes the main test methods for assessing the adhesion quality of GFCs to concrete and identifies the main regulatory documents used for the tests. The subject of the study is heavy fiber-reinforced concrete based on GFCs: straight tests with 4 mm and 10 mm windings, as well as a wave test with a periodic profile pitch of 8 mm. Based on the test results, the dependence of fiber adhesion strength on the strength of the concrete matrix is presented. The dependence has an exponentially increasing nature, which can be used to identify the effective application of GFCs in concrete. It was determined that a concrete matrix with a fiber-reinforced concrete bond strength of 30 to 50 MPa is optimal for fiber-reinforced concrete. Fibers with a 4 mm winding pitch achieve 20 MPa in the concrete matrix. Subsequently, tests were conducted to determine the crack resistance of fiber-reinforced concrete with various fiber configurations, where the optimal fiber concentrations and shapes were identified. Fibers with a 4 mm winding pitch demonstrated excellent results, with the specific energy consumption for opening a main crack amounting to 5139.6 J/m2 and a stress intensity factor of 1.26. Crack resistance and pullout strength tests revealed the optimal fiber geometry. These results confirm the feasibility of using fiber-reinforced concrete as a replacement for steel in certain applications where the properties of lighter, corrosion-resistant fiber are essential. The study experimentally demonstrates that adhesion strength is related to the geometry of the fiberglass composite.