The effects of polyvinyl alcohol (PVA) fiber content on mechanical and fracture properties of geopolymer concrete (GPC) were investigated in the present study. Mechanical properties include cubic compressive, prism compressive, tensile and flexural strengths, and elastic modulus. The evaluation indices in fracture properties were measured by using the three-point bending test. Geopolymer was prepared by fly ash, metakaolin, and alkali activator, which was obtained by mixing sodium hydroxide and sodium silicate solutions. The volume fractions of PVA fiber (length 12 mm and diameter 40 μm) were 0, 0.2, 0.4, 0.6, 0.8, and 1.0%. The results indicate that the effects of the PVA fiber on the cubic and prism compressive strengths and elastic modulus are similar. A tendency of first increasing and then decreasing with the increase in the PVA fiber content was observed in these properties. They all reached a maximum at 0.2% PVA fiber content. There was also a similar tendency of first increase and then decrease for tensile and flexural strengths, peak load, critical effective crack lengths, fracture toughness, and fracture energy of GPC, which were significantly improved by the PVA fiber. They reached a maximum at 0.8% PVA fiber content, except the tensile strength whose maximum was at 1.0% PVA fiber volume fraction. Considering the parameters analyzed, it seems that the 0.8% PVA fiber content provides optimal reinforcement of the mechanical properties of GPC.

The development and application of nondestructive testing technology for prestressed reinforced concrete structures in the field of infrastructure construction were summarized in this study via the analysis of relevant literature worldwide. The detection methods, detection principles, and detection instruments in quality evaluation of prestressed reinforced concrete structures were analyzed and compared, based on which, acoustic emission detection technology, impact echo detection technology, ultrasonic detection technology, infrared thermography detection technology, ground-penetrating radar detection technology, piezoelectric transducer detection technology, and X-ray detection technology were summarized. Additionally, the advantages, disadvantages, and application scope of each detection method were focused upon and analyzed comparatively. It is indicated that further improvement in the detection visualization, accuracy, and efficiency for most nondestructive testing technologies is available by optimizing the algorithm and combining artificial intelligence technology with neural network deep learning, precise positioning, and imaging analysis of the quality defects in prestressed reinforced concrete structures. The results of this study can provide technical reference for the further application and research of nondestructive testing technologies in the quality inspection of prestressed reinforced concrete structures.

Geopolymer composites can be used as a proper substitute for ordinary Portland cement, which can reduce carbon dioxide (CO₂) emissions and make rational use of industrial waste. In this study, an investigation of the workability and compressive strength of geopolymer composites was carried out through a series of experiments, such as slump flow test, consistency meter test and compressive strength test, to clarify the interaction mechanism among superplasticizer (SP), polyvinyl alcohol (PVA) fiber, Nano-SiO₂ (NS) and geopolymer composites, thereby improving the properties of engineered composites. The results showed that with the increase in PVA fiber content, the flowability of geopolymer composites decreased, while the thixotropy increased. With the increase in the NS content, the flowability of geopolymer composites first increased and then decreased, reaching its best at 1.0%, while the thixotropy was the opposite. With the increase in the SP content, the flowability of geopolymer composites increased, while the thixotropy decreased. A significant correlation between thixotropy and flowability of geopolymer composites was found (R² > 0.85). In addition, the incorporation of single PVA fiber or NS significantly improved the compressive strength of geopolymer composites. Specifically, the compressive strength of geopolymer composites with 0.8% content PVA fiber (60.3 MPa) was 33.4% higher than that without PVA fiber (45.2 MPa), and the compressive strength of geopolymer composites with 1.5% content NS (52.6 MPa) was 16.4% higher than that without NS (45.2 MPa). Considering the synergistic effect, it is found that the compressive strength of geopolymer composites (58.5–63.3 MPa) was significantly higher than that without PVA fiber (45.2–52.6 MPa). However, the flowability and compressive strength of geopolymer composites were only slightly improved compared to that without NS. With the increase in the SP content, the compressive strength of geopolymer composites showed a trend of a slight decrease on the whole. Consequently, the results of this study may be useful for further research in the field of repair and prevention of the delamination of composite structures.