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To investigate the mechanical properties and durability of nano-SiO2, polyvinyl alcohol (PVA) fiber-modified fly ash (FA), and metakaolin (MK)-based geopolymer mortar (FMGM), tests of compressive strength, electrical flux, freeze–thaw cycles, and sulfate dry and wet cycles were conducted. Based on the experimental results, combined with Dunn’s gray correlation theory analysis method, a mathematical analysis of the effect sensitivity of the contents of the four mixtures on the mechanical properties and durability of FMGM was carried out. The method of gray correlation analysis can solve the mathematical problem with partial unclear and uncertain information, and the method requires less data and less computation compared with other mathematical analysis method. The results showed that the gray correlation degree between the content of MK and the electric flux value is higher than the that of other comparison sequence and each reference sequence, while the gray correlation degree between the PVA fiber dosage and the loss rate of compressive strength is lower than that of other comparison sequence and each reference sequence. The influence of the four mixture contents on the compressive strength and mass loss rate was in the following decreasing order: MK and FA, PVA fiber, and nano-SiO2. In addition, the influence of the four material mixture contents on the electric flux value and compressive strength loss rate was consistent in the following decreasing order: MK and FA, nano-SiO2, and PVA fiber. Furthermore, the mechanical properties and durability reached the optimum when the PVA fiber content was 0.6% and the dosage of nano-SiO2 was 1.0%. The results of this study can provide a new method for the analysis and evaluation of mechanical properties and durability of nano-SiO2 and PVA fiber-reinforced FMGM in future.

In this study, nano-SiO2 (NS) and basalt fiber (BF) were used to improve the quality of recycled aggregate concrete (RAC). The crushing value, water absorption, and apparent density of NS-modified recycled coarse aggregate (RA) were determined, and the effects of BF with different contents and lengths on the slump, compressive strength, splitting tensile strength, and flexural strength of RAC and BF-reinforced RAC containing NS-modified RA were analyzed. Finally, the filling effect of NS, the toughening and crack resistance mechanism of BF, and the micro-composite effect between NS and BF were analyzed based on scanning electron microscope (SEM) and energy-dispersive detector (EDS) measurement. The results show that the optimum modified concentration of NS solution is 2%, the content of BF is the main factor affecting the mechanical properties of concrete, and the optimum length and content of BF are 12 mm and 0.2%, respectively. For BF-reinforced RAC containing NS-modified RA, the 28 day compressive strength, splitting tensile strength, and flexural strength of RAC increase by 34.28, 40.55 and 54.5%, respectively. Based on SEM and EDS measuring, NS can react with Ca(OH)2 crystal to form flocculent C–S–H gel, which makes RAC compact and enhances the bonding properties of the interfacial transition zone (ITZ) between BF and the matrix.

The surface adhesion mortar of recycled coarse aggregate (RCA) is the main factor leading to poor aggregate quality, and it also affects the internal structure and mechanical properties of recycled aggregate concrete (RAC). To improve the quality of RCA and mechanical properties of RAC, self-developed mortar removal equipment was used to strengthen the RCA. Then, the RCA was soaked in 1, 2, and 3% nano-silica solutions, and the vibration-mixing process was used to improve the quality of RAC. In addition, the microstructure of the RAC was examined via scanning electron microscopy to observe its improvement effect on the microstructure of the RAC. The results indicated that the quality of the RCA was improved by mechanical and physical strengthening, and the water-absorption rate and crushing value decreased by 32.9 and 23.9%, respectively. The improvement effect of nano-immersion on the RAC was obvious. The optimal condition was a combination of physical strengthening, 2 days of immersion in 2% NS solution, and vibration stirring. The 28 day compressive strength increased by 31.3%, the splitting tensile strength increased by 23%, and the flexural strength increased by 49%. The proposed strengthening method improves the mechanical properties and microstructure of RAC. The results of this study provided a technical reference for the mechanical strengthening of RAC and promotion of the application and popularization of RAC.

The fatigue performance of emulsified asphalt mastics directly affects the long-term service performance of emulsified asphalt cold recycled pavement. Fatigue properties of 24 different mastics before and after short-term aging composed by the combination of 3 different fillers and 4 filler-binder ratios (F-B) were evaluated based on the viscoelastic continuum damage (VECD) model. Atomic force microscopy (AFM) was employed to analyze the surface morphology of the mastics and determine the interaction between filler and asphalt. The results show that increasing the F-B or the aging effect reduce the stress–strain withstand capacity of emulsified asphalt mastic, increase its integrity damage rate, and further reduce the fatigue life. Comparing three mastics, limestone mastic with a low F-B exhibits a better fatigue performance. The limestone mastic is more affected by short-term aging, while cement mastic and coal gangue mastic are significantly affected by F-B. Filler types, F-B and aging can obviously change the surface morphology of mastics. The microscopic morphology change of coal gangue mastic with a low F-B is dominated by the dispersing effect of the filler, whereas the microscopic morphology of mastic with a high F-B is dominated by the adsorption effect. [ABSTRACT FROM AUTHOR]

Based on an analysis of the extant literature, this paper summarizes the research progress on the mechanical properties and long-term behavior of corrugated steel web (CSW) box girder bridges. First, the research results of CSW box girder bridges in terms of the shear buckling performance (local shear buckling, overall shear buckling, and interaction buckling), bending performance, bending capacity, torsional capacity, and coefficient of internal force increase are summarized, along with the main factors affecting the mechanical performance of CSW box girder bridges. Second, based on research on the self-oscillation characteristics and dynamic response of CSW box girder bridges, the influence of structural parameters on the self-oscillation characteristics is analyzed. Finally, the long-term mechanical behavior of the CSW box girder bridges is analyzed in terms of fatigue, creep, and temperature effects. The existing research results demonstrate that there still exist deficiencies in the mechanical properties and long-term behavior of CSW box girder bridges, and this paper thus suggests a future research focus on CSW box girder bridges to provide a reference for further improving their basic theoretical system. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical properties and internal stress condition of the reinforcing bar sleeve connectors with ferro-tailed mineral sand cementitious grout as filler material were analyzed as research objects. Firstly, an experimental study was carried out on the reinforcing bar sleeve connectors of iron tailing sand grout with a 40% substitution rate of mechanism sand to analyze the mechanical properties of different grout types, age, and reinforcement diameters under unidirectional tensile, high stress, and large deformation of repeated tensile and compressive stresses. Next, five groups of sleeve joints with different anchorage lengths were set up for unidirectional tensile tests. The results show that, with the decrease of the diameter of the reinforcement, the grip force and bond strength of the iron tailing sand grout on the internal reinforcement gradually increase. Under conditions of large deformation and high stress due to repeated tensile loading, the residual deformation and total elongation of iron tailing sand grout sleeve joints are satisfactory. Additionally, the restraining anchorage effect of iron tailing sand grout in the end section is small. The utilization rate and integrity of iron tailing sand grout in the initial anchorage section are better. [ABSTRACT FROM AUTHOR]

Marine engineering structures are often faced with complex environmental factors. It is the focus of current research to modify cement-based composites (CBCs) to achieve their high durability in complex environments such as seawater. In this study, the effect of polyvinyl alcohol (PVA) fibers on durability of nano-SiO2 (NS)-reinforced cement-based composites was investigated by simulating seawater environment and taking PVA fiber content as variable. In addition, based on the Weibull probability distribution model, the damage degree of NS and PVA fiber-reinforced cement-based composites (NFRCCs) subjected to wet-thermal and chloride salt-coupled environment (WTCSE) after 300 freeze–thawing cycles (FTCs) was predicted. The test results demonstrated that the NFRCC exhibited the most excellent durability subjected to WTCSE when the content of PVA fibers was 1.2%. Compared with the reference group only doped with NS subjected to WTCSE, its impermeability pressure increased by 150%, the chloride ion electric flux decreased by 31.71%, the compressive strength loss rate decreased by 19.00% after 125 FTC, and the compressive strength corrosion resistance coefficient of chloride salt erosion increased by 9.15% after 25 wetting–drying cycles. The predicted results of the Weibull probability distribution model indicated that the damage degree of NFRCC subjected to WTCSE after 300 FTC would not exceed 0.35. The microscopic test analysis showed that the incorporation of PVA fibers reduced the proportion of large pores and the overall porosity of NFRCC subjected to WTCSE. PVA fibers bridged microcracks while adsorbing NS and its hydration products, thus enhancing the adhesion of the substrate. This study provides a reference for the research of high-performance CBC in complex environment.

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.