Discussion of “Flexural Behavior of Reinforced Concrete Beams with TRC Tension Zone Cover” by Shiping Yin, Shilang Xu, and Henglin Lv

Abstract

Based on four-point flexural tests conducted on textile-reinforced concrete (TRC) beams, the discussed paper presents an interesting experimental study on the influences of the layers of textile, the surface treatment of textile, and mixing short fibers into fine-grain concrete on the mechanical performance and crack pattern of the beams with a TRC tension zone cover. The authors should be complimented for providing a detailed paper, which reports valuable findings of interest. The discusser would like to thank the authors for this and to also offer some comments and questions for their consideration and response, mainly about aspects related with the experimental results and discussion, such as the crack form of specimens and the load-maximum crack width curves. The authors detail that, during the entire testing process, no visible cracks are observed at the interface between the textile and the fine-grain concrete, and between the concrete and the fine-grain concrete, and that there are at least two or three much smaller cracks on the fine-grain concrete layer below the concrete cracks because textiles play their fiber-bridge role by allowing cracks to be distributed uniformly throughout the tensile zone. The discusser is confused about these apparent contradictory descriptions. Perhaps the authors refer to longitudinal cracks for the former and to flexural cracks for the latter. Can the authors provide confirmation or an explanation about this to offer a better understanding? Regarding the load-maximum crack width relationship, Fig. 5 shows experimental curves in a comparative manner. From Figs. 5(a and b), the authors state that adhering sand on the textile surface helps reduce the maximum crack width. However, in the discusser’s opinion, despite the intention of these figures to depict the influence of surface treatment of textile, it seems there are no significant differences among the four curves for the one layer textile case [Fig. 5(a)], their final points being 60 kN load and 0.7–0.8 mm maximum crack width. In fact, for a similar comparison, as depicted in Fig. 5(c), which includes three curves to analyze the influence of polypropylene fiber and U-shaped hooks, the authors detail that the use of U-shaped hooks has no visible effect on the control of crack width, with the final points of curves being 70 kN load and 0.8–1.0 mm maximum crack width. Furthermore, one can observe differences in the three curves for the two layers textile case [Fig. 5(b)] as their final points range from loads of 65 to 75 kN and from 0.6 to 1.2 mm maximum crack width. Moreover from Figs. 5(a and c), the authors observe that if the same load is carried in the service stage, adding polypropylene fiber to fine-grain concrete can lead to a small maximum crack, crack spacing can reduce and the cooperative load-bearing capability of the textile and the fine-grain concrete can improve. Once again, in the discusser’s opinion, it seems there are no significant differences between the cases with and without polypropylene fibers depicted in Figs. 5(a and c). Despite the different scales used in Fig. 5, one can observe that, except for Fig. 5(d), there are no differences in the initial cracking points, the service stage points (about 30–35 kN load and 0.1–0.2 mm maximum crack width), the yielding points (about 50–60 kN load and 0.2–0.3 mm maximum crack width), and the ultimate points (in the terms explained in the precedent paragraph). Furthermore, crack width is important in service, whereas it seems the authors focus some analyses on the ultimate points, and values of crack width in service are not reported in Table 4. Certainly, crack distribution is also of interest, and the discusser suggests including complementary details on crack spacing and height for the service stage in order to check for any improvements in crack patterns. As observed in Fig. 5(d), when carrying the same load, the crack width of the TRC beams is much narrower than that of the control beam (beam 2). Nevertheless, beam 2 presents a maximum crack width of 1.4–1.5 mm at the ultimate point in Fig. 5(d), whereas 1.2 mm is reported in Table 4 at yielding instead of 0.4 mm. Apart from this inconsistency, a remarkable difference in the crack width at yielding between beams 1 (0.8 mm) and 2 (1.2 mm) is observed. Can the authors confirm the correct data? If this corresponds to variability in the materials properties and/or tested phenomena, the discusser believes that additional determinations with the TRC beams should be made.