Mechanical Properties of Fly Ash-Based Geopolymer Concrete Incorporation Nylon66 Fiber

This study was carried out to investigate the effect of the diamond-shaped Interlocking Chain Plastic Bead (ICPB) on fiber-reinforced fly ash-based geopolymer concrete. In this study, geopolymer concrete was produced using fly ash, NaOH, silicate, aggregate, and nylon66 fibers. Characterization of fly ash-based geopolymers (FGP) and fly ash-based geopolymer concrete (FRGPC) included chemical composition via XRF, functional group analysis via FTIR, compressive strength determination, flexural strength, density, slump test, and water absorption. The percentage of fiber volume added to FRGPC and FGP varied from 0% to 0.5%, and 1.5% to 2.0%. From the results obtained, it was found that ICBP fiber led to a negative result for FGP at 28 days but showed a better performance in FRGPC reinforced fiber at 28 and 90 days compared to plain geopolymer concrete. Meanwhile, NFRPGC showed that the optimum result was obtained with 0.5% of fiber addition due to the compressive strength performance at 28 days and 90 days, which were 67.7 MPa and 970.13 MPa, respectively. Similar results were observed for flexural strength, where 0.5% fiber addition resulted in the highest strength at 28 and 90 days (4.43 MPa and 4.99 MPa, respectively), and the strength performance began to decline after 0.5% fiber addition. According to the results of the slump test, an increase in fiber addition decreases the workability of geopolymer concrete. Density and water absorption, however, increase proportionally with the amount of fiber added. Therefore, diamond-shaped ICPB fiber in geopolymer concrete exhibits superior compressive and flexural strength.     

Improving the Mechanical Properties of Fly Ash-Based Geopolymer Composites with PVA Fiber and Powder

In this work, polyvinyl alcohol (PVA) fiber and powder were added to geopolymer composites to toughen fly ash-based geopolymer, and their different toughening mechanisms were revealed. Firstly, different contents of active granulated blast furnace slag (GBFS) were added to the geopolymer to improve the reactivity of the GBFS/fly ash-based geopolymer, and the best ratio of GBFS and fly ash was determined through experiments testing the mechanical properties. Different contents of PVA powders and fibers were utilized to toughen the geopolymer composites. The effect of the addition forms and contents of PVA on the mechanical properties, freeze–thaw cycle resistance, and thermal decomposition properties of geopolymer composites were systematically studied. The results showed that the toughening effect of PVA fiber was better than that of PVA powder. The best compressive strength and flexural strength of geopolymer composites toughened by PVA fiber were 41.11 MPa and 8.43 MPa, respectively. In addition, the composition of geopolymer composites was explored through microstructure analysis, and the toughening mechanisms of different forms of PVA were explained. This study provided a new strategy for the toughening of geopolymer composites, which can promote the low-cost and efficient application of geopolymer composites in the field of building materials.     

Influence of Bentonite on Mechanical and Durability Properties of High-Calcium Fly Ash Geopolymer Concrete with Natural and Recycled Aggregates

In this study, bentonite (a naturally occurring pozzolana) was incorporated as a partial replacement (up to 20%) for high-calcium fly ash (HCFA)-based geopolymeric natural aggregate concrete (GNAC) and geopolymeric recycled aggregate concrete (GRAC). The mechanical (compressive strength and splitting tensile strength), durability (chloride migration coefficient, water absorption, and acid attack resistance), and rheological properties (slump test, fresh density, and workability) were investigated. The results revealed that incorporation of bentonite (10 wt % with ordinary Portland cement) showed appreciable improvement in the strength and durability of both the GNAC and GRAC, though its effect is more significant for GRAC than the GNAC.     

The Influence of Short Coir,Glass and Carbon Fibers on the Properties of Composites with Geopolymer Matrix

The aim of the article is to analyze the influence of short coir, glass and carbon fiber admixture on the mechanical properties of fly ash-based geopolymer, such as: flexural and compressive strength. Glass fiber and carbon fibers have been chosen due to their high mechanical properties. Natural fibers have been chosen because of their mechanical properties as well as for the sake of comparison between their properties and the properties of the artificial ones. Fourth series of fly ash-based geopolymers for each fiber was cast: 1, 2, and 5% by weight of fly ash and one control series without any fibers. Each series of samples were tested on flexural and compressive strength after 7, 14, and 28 days. Additionally, microstructural analysis was carried out after 28 days. The results have shown an increase in compressive strength for composites with fibers—an improvement in properties between 25.0% and 56.5% depending on the type and amount of fiber added. For bending strength, a clear increase in the strength value is visible for composites with 1 and 2% carbon fibers (62.4% and 115.6%). A slight increase in flexural strength also occurred for 1% addition of glass fiber (4.5%) and 2% addition of coconut fibers (5.4%). For the 2% addition of glass fibers, the flexural strength value did not change compared to the value obtained for the matrix material. For the remaining fiber additions, i.e., 5% glass fiber as well as 1 and 5% coconut fibers, the flexural strength values deteriorated. The results of the research are discussed in a comparative context and the properties of the obtained composites are juxtaposed with the properties of the standard materials used in the construction industry.     

Mechanical and Thermal Properties of Phosphoric Acid Activated Geopolymer Materials Reinforced with Mullite Fibers

This article investigates several important properties, such as thermal resistance, mechanical properties, and phase evolution, of geopolymer ceramics reinforced with mullite fibers. This particular fiber reinforcing geopolymer composites was prepared from kaolinite and mullite fibers with phosphoric acid as activator. X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry, Fourier-transform infrared spectroscopy, and scanning electron microscopy were used to determine the phase evolution and strengthening mechanisms. With the addition of mullite fibers, the mechanical properties increased by at least 20%. The optimum flexural strength exceeded 13 MPa. It was found that mullite fibers had desirable interface bonding with this type of geopolymer, promoting both crack deflection and fiber pullout strengthening mechanisms. This was correlated with a significant strengthening effect of the fibers. The linear shrinkage after heat treatment at 1150 °C~1550 °C was investigated and correlated with XRD analyses. The addition of mullite fibers reduced the linear shrinkage significantly up to 1350 °C. The large linear shrinkage above 1450 °C was correlated with the decomposition and melting of the AlPO₄ phase.     

Survey of Mechanical Properties of Geopolymer Concrete: A Comprehensive Review and Data Analysis

Mechanical properties and data analysis for the prediction of different mechanical properties of geopolymer concrete (GPC) were investigated. A relatively large amount of test data from 126 past works was collected, analyzed, and correlation between different mechanical properties and compressive strength was investigated. Equations were proposed for the properties of splitting tensile strength, flexural strength, modulus of elasticity, Poisson’s ratio, and strain corresponding to peak compressive strength. The proposed equations were found accurate and can be used to prepare a state-of-art report on GPC. Based on data analysis, it was found that there is a chance to apply some past proposed equations for predicting different mechanical properties. CEB-FIP equations for the prediction of splitting tensile strength and strain corresponding to peak compressive stress were found to be accurate, while ACI 318 equations for splitting tensile and elastic modulus overestimates test data for GPC of low compressive strength.     

Effects of Steel Fiber and Specimen Geometric Dimensions on the Mechanical Properties of Ultra-High-Performance Concrete

Ultra-high-performance concrete (UHPC) is an advanced concrete with superior mechanical strength, ductility and durability properties. However, the influence of steel fiber on its constitutive laws and the specimen geometric dimension effect on its strength had not been paid enough attention. To investigate the effect of steel fibers on the properties of UHPC, specimens with different fiber volume contents and fiber types were tested. Meanwhile, the mechanical properties of UHPC at different ages from 3 days to 28 days were conducted. Moreover, specimens with various geometric dimensions were also prepared to study the effect of specimen geometric dimensions (dog-bone-shaped, prism and cylinder specimens) on the properties of UHPC. The results indicated that elastic modulus, tensile peak stress and the corresponding strain increased as the fiber volume content and curing age increased. Specimens with hooked-end fibers exhibited better tensile performance than those with straight fibers. Furthermore, different geometric dimensions of specimens significantly influenced the tensile properties of UHPC. Based on the experimental results, conversion factors were suggested for the transformation of strength obtained from specimens with different geometric dimensions to reference specimens. In addition, both compressive and tensile constitutive laws were proposed to generate the stress–strain relationship of UHPC.     

Chemical,Physical, and Mechanical Properties of 95-Year-Old Concrete Built-In Arch Bridge

This research aimed to determine the durability and strength of an old concrete built-in arch bridge based on selected mechanical, physical, and chemical properties of the concrete. The bridge was erected in 1925 and is located in Jagodnik (northern Poland). Cylindrical specimens were taken from the side ribs connected to the top plate using a concrete core borehole diamond drill machine. The properties of the old concrete were compared with the present and previous standard requirements and guidelines. The laboratory testing program consisted of the following set of tests: measurements of the depth of carbonated zone and dry density, water absorption tests, determination of concrete compressive strength and frost resistance, determination of modulus of elasticity, measurement of the pH value, determination of water-soluble chloride salt and sulfate ion content, and X-ray diffraction analyses. Large variations in the cylindrical compressive strength (14.9 to 22.0 MPa), modulus of elasticity (17,900 to 26,483 MPa), density (2064 to 2231 kg/m³), and water absorption (3.88 to 6.58%) were observed. In addition to the experiments, a brief literature survey relating to old concrete properties was also conducted. This paper can provide scientists, engineers, and designers an experimental basis in the field of old concrete built-in bridge construction.     

An Investigation of the Ground Walnut Shells’ Addition Effect on the Properties of the Fly Ash-Based Geopolymer

The development of geopolymers is in line with the requirements of sustainable development. Creating a new type of material from various industrial and bio-based wastes and by-products can lead to reduced energy consumption, reduced waste generation, reduced global CO₂ emissions, as well as reduced resource extraction of natural resources. In this study, geopolymer composites based on class F fly ash with the addition of fine quartz sand and ground walnut shells used as a substitute for sand were examined. The study focused on investigating the effects of different weight percentages of ground walnut shells and quartz sand on the density and strength properties, including compressive and flexural strength, thermal conductivity, efflorescence formation, and water absorption of the fly ash-based geopolymer composites. The microstructure of the studied geopolymers was also analyzed using a scanning electron microscope (SEM). It was observed that the addition of ground walnut shells contributes to the decrease in density and mechanical properties, increase in absorption properties, and decrease in porosity of fly ash-based geopolymers. Furthermore, the addition of ground walnut shells allows for a significant reduction in efflorescence on the surface of the tested geopolymer composites. Moreover, partial or complete replacement of sand by ground walnut shells in geopolymer composites based on fly ash allows for a significant reduction in their thermal conductivity, which makes it possible to use these composites as insulation materials.     

Effect of Size of Coarse Aggregate on Mechanical Properties of Metakaolin-Based Geopolymer Concrete and Ordinary Concrete

Geopolymer binders are a promising alternative to ordinary Portland cement (OPC) because they can significantly reduce CO₂ emissions. However, to apply geopolymer in concrete, it is critical to understand the compatibility between the coarse aggregate and the geopolymer binder. Experimental studies were conducted to explore the effect of the size of the coarse aggregate on the mechanical properties and microstructure of a metakaolin-based geopolymer (MKGP) concrete and ordinary concrete. Three coarse aggregate size grades (5–10 mm, 10–16 mm, and 16–20 mm) were adopted to prepare the specimens. The microstructure of the concretes was investigated with scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and mercury intrusion porosimetry (MIP). Results showed an opposite coarse aggregate size effect between OPC and MKGP specimens in terms of compressive strength. SEM/EDS analysis indicated that the MKGP concrete has a weaker microstructure compared to OPC concrete induced by a higher porosity. The differences in mechanical properties and pore structure between the MKGP and OPC concrete are attributed to the greatly differing shrinkages triggered by the large surface area and penny-shaped particles of metakaolin. The findings in this work help tailor the mechanical properties and microstructure of MKGP concrete for future engineering applications.     

Investigation on Fracture Behavior of Cementitious Composites Reinforced with Aligned Hooked-End Steel Fibers

Aligning steel fibers is an effective way to improve the mechanical properties of steel fiber cementitious composites (SFRC). In this study, the magnetic field method was used to prepare the aligned hooked-end steel fiber cementitious composites (ASFRC) and the fracture behavior was investigated. In order to achieve the alignment of steel fibers, the key parameters including the rheology of the mixture and magnetic induction of electromagnetic field were theoretically analyzed. The results showed that, compared with SFRC, the cracking load and the ultimate load of ASFRC were increased about 24–55% and 51–86%, respectively, depending on the fiber addition content. In addition, the flexural tensile strength and residual flexural strength of ASFRC were found to increase up to 105% and 100%, respectively. The orientation of steel fibers also has a significant effect on energy consumption. The fracture energy of ASFRC was 56–70% greater than SFRC and the reinforcement effect of hooked-end steel fiber was higher than straight steel fiber. The fibers in the fracture surface showed that not only was the number of fibers of ASFRC higher than that of SFRC, but also the orientation efficiency factor of ASFRC was superior to SFRC, which explains the improvement of fracture behavior of ASFRC.     

Mechanical and Microstructural Characterization of Quarry Rock Dust Incorporated Steel Fiber Reinforced Geopolymer Concrete and Residual Properties after Exposure to Elevated Temperatures

The purpose of this research is to study the effects of quarry rock dust (QRD) and steel fibers (SF) inclusion on the fresh, mechanical, and microstructural properties of fly ash (FA) and ground granulated blast furnace slag (SG)-based geopolymer concrete (GPC) exposed to elevated temperatures. Such types of ternary mixes were prepared by blending waste materials from different industries, including QRD, SG, and FA, with alkaline activator solutions. The multiphysical models show that the inclusion of steel fibers and binders can enhance the mechanical properties of GPC. In this study, a total of 18 different mix proportions were designed with different proportions of QRD (0%, 5%, 10%, 15%, and 20%) and steel fibers (0.75% and 1.5%). The slag was replaced by different proportions of QRD in fly ash, and SG-based GPC mixes to study the effect of QRD incorporation. The mechanical properties of specimens, i.e., compressive strength, splitting tensile strength, and flexural strength, were determined by testing cubes, cylinders, and prisms, respectively, at different ages (7, 28, and 56 days). The specimens were also heated up to 800 °C to evaluate the resistance of specimens to elevated temperature in terms of residual compressive strength and weight loss. The test results showed that the mechanical strength of GPC mixes (without steel fibers) increased by 6–11%, with an increase in QRD content up to 15% at the age of 28 days. In contrast, more than 15% of QRD contents resulted in decreasing the mechanical strength properties. Incorporating steel fibers in a fraction of 0.75% by volume increased the compressive, tensile, and flexural strength of GPC mixes by 15%, 23%, and 34%, respectively. However, further addition of steel fibers at 1.5% by volume lowered the mechanical strength properties. The optimal mixture of QRD incorporated FA-SG-based GPC (QFS-GPC) was observed with 15% QRD and 0.75% steel fibers contents considering the performance in workability and mechanical properties. The results also showed that under elevated temperatures up to 800 °C, the weight loss of QFS-GPC specimens persistently increased with a consistent decrease in the residual compressive strength for increasing QRD content and temperature. Furthermore, the microstructure characterization of QRD blended GPC mixes were also carried out by performing scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS).     

Improvements of Flexural Properties and Thermal Performance in Thin Geopolymer Based on Fly Ash and Ladle Furnace Slag Using Borax Decahydrates

This paper elucidates the influence of borax decahydrate addition on the flexural and thermal properties of 10 mm thin fly ash/ladle furnace slag (FAS) geopolymers. The borax decahydrate (2, 4, 6, and 8 wt.%) was incorporated to produce FAB geopolymers. Heat treatment was applied with temperature ranges of 300 °C, 600 °C, 900 °C, 1000 °C and 1100 °C. Unexposed FAB geopolymers experienced a drop in strength due to a looser matrix with higher porosity. However, borax decahydrate inclusion significantly enhanced the flexural performance of thin geopolymers after heating. FAB2 and FAB8 geopolymers reported higher flexural strength of 26.5 MPa and 47.8 MPa, respectively, at 1000 °C as compared to FAS geopolymers (24.1 MPa at 1100 °C). The molten B₂O₃ provided an adhesive medium to assemble the aluminosilicates, improving the interparticle connectivity which led to a drastic strength increment. Moreover, the borax addition reduced the glass transition temperature, forming more refractory crystalline phases at lower temperatures. This induced a significant strength increment in FAB geopolymers with a factor of 3.6 for FAB8 at 900 °C, and 4.0 factor for FAB2 at 1000 °C, respectively. Comparatively, FAS geopolymers only achieved 3.1 factor in strength increment at 1100 °C. This proved that borax decahydrate could be utilized in the high strength development of thin geopolymers.     

Influence of Fiber Addition on the Properties of High-Performance Concrete

High performance fiber-reinforced concrete (HPFRC) has been frequently investigated in recent years. Plenty of studies have focused on different materials and types of fibers in combination with the concrete matrix. Experimental tests show that fiber dosage improves the energy absorption capacity of concrete and enhances the robustness of concrete elements. Fiber reinforced concrete has also been illustrated to be a material for developing infrastructure sustainability in RC elements like façade plates, columns, beams, or walls. Due to increasing costs of the produced fiber reinforced concrete and to ensure the serviceability limit state of construction elements, there is a demand to analyze the necessary fiber dosage in the concrete composition. It is expected that the surface and length of used fiber in combination with their dosage influence the structure of fresh and hardened concrete. This work presents an investigation of the mechanical parameters of HPFRC with different polymer fiber dosage. Tests were carried out on a mixture with polypropylene and polyvinyl alcohol fiber with dosages of 15, 25, and 35 kg/m³ as well as with control concrete without fiber. Differences were observed in the compressive strength and in the modulus of elasticity as well as in the flexural and splitting tensile strength. The flexural tensile strength test was conducted on two different element shapes: square panel and beam samples. These mechanical properties could lead to recommendations for designers of façade elements made of HPFRC.     

Experimental Research on Flexural Mechanical Properties of Ultrahigh Strength Concrete Filled Steel Tubes

Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength (f_cu) of the core concrete reached 80.3–115.2 MPa. The effects of concrete strength on flexural bearing capacity, deformation characteristics, and failure modes of UHSCFST specimens were discussed. Test results showed that the bending failure modes of UHSCFST specimens were the same as those of ordinary ones. The failure of UHSCFST specimens was attributed to excessive deflection, and local buckling occurred in the compression zone. Moreover, the bending capacity of the specimens did not decrease, even if they had yielded. Although ultrahigh strength concrete was poured, all of the specimens displayed outstanding bending ductility. The main function of core concrete was to provide radial restraint for the steel tube to avoid premature buckling. When the steel content of the specimen section was constant, the strength increases of core concrete had a slight impact on the bending failure mode, bearing capacity and ductility of UHSCFST specimen. The research results can deepen the understanding of the mechanical behaviors of the UHSCFST composite truss structure.     

Influence of Polypropylene Fibre Factor on Flowability and Mechanical Properties of Self-Compacting Geopolymer

The possibility of using geopolymer instead of Portland cement could effectively reduce carbon dioxide emissions from cement manufacturing. Fibre-reinforced self-compacting geopolymers have great potential in civil engineering applications, such as chord member grouting for concrete-filled steel tubular truss beams. However, to the best of the authors’ knowledge, the quantitative relationship between FF and the properties of the fibre-reinforced geopolymer has been rarely reported. In this research, 26 groups of mixtures were used to study the influence of the polypropylene fibre factor (FF) on the flowability and mechanical properties and also the compactness of the fibre-reinforced self-compacting geopolymer. At the same volume fraction, geopolymers with long fibres present worse flowability than those having short fibres due to the easier contacting of long fibres. By growing the FF the influence of fibre addition on the V-funnel flow rate is more significant than the slump spread. This can be ascribed to the consequence of fibre addition and friction by the V-funnel which estimates the restrained deformability. For FF lesser than critical factor Fc = 100, influence of fibres is negligible and fibres are far apart from each other and, thus, they cannot restrict cracking under load and transfer the load to improve the mechanical properties. For FF between the Fc = 100 and density factor Fd = 350, a noteworthy enhancement of mechanical properties was obtained and the geopolymer was still adequately workable to flow by weight of self, without any symbols of instability and fibre clumping. Under this condition, better fibre dispersal and reinforcing productivity can lead to better hardened properties. For FF higher than Fd = 350, fibres tend to come to be entwined together and form clumping resulting from the fibre balling, resulting in worse hardened properties. This research offers a sensible basis for the application of the workability regulator of the fresh properties of fibre-reinforced geopolymer as an operative way to basically obtain ideal mechanical properties.     

Influence of Polypropylene and Steel Fibers on the Performance and Crack Repair of Self-Compacting Concrete

The research reported in this paper aims to evaluate the epoxy injection technique used to strengthen fiber-reinforced self-compacting concrete (FRSCC) with high strength. This method is carried out on ruptured concrete specimens to assess the efficiency of the epoxy resin adhesive injection retrofitting technique for strength and stiffness. Five FRSCC mixes were designed and placed using different types (steel and polypropylene) and contents (0%, 0.25%, and 0.45% by volume) of fibers. The fresh and mechanical properties in addition to the microstructure of produced mixes were evaluated to assess the impact of fibers on the behavior of FRSCC. Results showed that the workability of FRSCC is reduced by increasing steel or polypropylene fiber content; however, the rheological characteristics of placed mixes satisfied the European Guidelines for Self-Compacting Concrete recommendation for fresh concrete. Also, splitting tensile, flexural, and shear strengths were enhanced by increasing fiber content. The simultaneous application of epoxy injection in FRSCC for repairing damaged concrete beams was shown to be highly effective.     

Experimental Study on the Flexural Properties of Concrete Beams Reinforced with Hybrid Steel/Fiber-Belt-Bars

Reinforcement corrosion poses a great threat to the safety of reinforced concrete structures, and the fiber-reinforced polymer is the ideal material to partially replace steel bars due to the high strength, light weight and good durability. However, the selection of appropriate fiber materials and a reasonable ratio of fiber bar to steel bar is not clear. Here, we measured the mechanical properties of fiber bars containing aramid fiber and carbon fiber. The deflection deformation, crack distribution and maximum crack width of the concrete upon various loads were experimentally and theoretically investigated. The predictions of the maximum crack width and deflection of reinforced concrete beams under various loads were proposed in ACI standard, which may provide guidance for further applications of fiber-belt-bar-containing concrete beams.     

Setting Time,Microstructure, and Durability Properties of Low Calcium Fly Ash/Slag Geopolymer: A Review

Ordinary Portland cement (OPC) is known for its significant contribution to carbon dioxide emissions. Geopolymer has a lower footprint in terms of CO₂ emissions and has been considered as an alternative for OPC. A well-developed understanding of the use of fly-ash-based and slag-based geopolymers as separate systems has been reached in the literature, specifically regarding their mechanical properties. However, the microstructural and durability of the combined system after slag addition introduces more interactive gels and complex microstructural formations. The microstructural changes of complex blended systems contribute to significant advances in the durability of fly ash/slag geopolymers. In the present review, the setting time, microstructural properties (gel phase development, permeability properties, shrinkage behavior), and durability (chloride resistance, sulfate attack, and carbonatation), as discussed literature, are studied and summarized to simplify and draw conclusions.     

Experimental Study on the Mechanical Properties,Water Absorption,and Fiber Degradation of Naturally Aged Glass Fiber and Polypropylene Fiber-Reinforced Concrete

The main objective of this study is to better understand the performance changes of naturally aged glass fiber-reinforced concrete (GFRC) and polypropylene fiber-reinforced concrete (PPFRC), especially the degradation of fibers, which is of great significance for evaluating the durability of structures using these two types of composite materials. The mechanical properties, water absorption, and microstructures of GFRC and PPFRC at a curing age of three years, including their compressive strength, full curves of water absorption, fiber-matrix interaction, and fiber degradation, were systematically studied, and the related properties were compared with those at the curing age of 28 days. The degradation of fibers after freeze-thaw cycles was also studied. The results revealed the following. The water/binder ratio (w/b) affects the rate of increase of the long-term compressive strength of naturally aged concrete. In general, the water absorption of fiber-reinforced concrete (FRC) at the curing age of three years was found to be significantly reduced, but with the increases of w/b and the fiber content to the maximum values, the water absorption of the specimens cured for three years was higher than that of the specimens cured for 28 days. Moreover, with the increase of the curing age, the optimal glass fiber (GF) contents for reducing the water absorption decreased from 1.35% to 0.90% (w/b = 0.30), and from 0.90% to 0.45% (w/b = 0.35), respectively. The GF surface was degraded into continuous pits with diameters of about 200 to 600 nm, and the surface of the pits was attached with spherical granular C-S-H gel products with diameters of about 30 to 44 nm. The freeze-thaw cycles were found to have no significant effect on the pits on the GF surface and the granular C-S-H gel products attached to the pits, but caused a portion of the cement matrix covering the GF to fall off. The interfacial bonding between the polypropylene fiber (PPF) and the cement matrix exhibited almost no change in the PPFRC after three years of curing as compared with that after 28 days of curing. Furthermore, the cement hydration gel on the PPF surface was not significantly damaged by 150 freeze-thaw cycles.