Fiber-reinforced Cement Research Articles

Bond and cracking behavior of tailored limestone calcined clay cement-based composites including bicomponent polypropylene fibers with enhanced mechanical interlocking

This study examines the potential of combining tailored binder formulations with engineered polypropylene (PP) fibers to develop a range of Fiber-Reinforced Cementitious (FRC) systems with enhanced ductility and strain-hardening properties, while encompassing sustainability and economic viability. The experimental investigation compares the surface microstructure of novel bicomponent PP fibers, produced using a pilot fiber spinning device, with that of standard PP fibers. Micro-scale single-fiber pull-out tests are conducted to ascertain the extent to which this surface modification contributes to enhanced energy absorption. The effectiveness of these novel fibers at the composite scale is assessed when embedded into two limestone calcined clay cement (LC3) binder systems, in terms of the fresh and hardened properties of the resulting FRLC3, with low cement content (35% of the total binder). The effect of incorporating super absorbent polymer (SAP) on tailoring the internal porosity of the matrix, thereby promoting the potential for stress transfer via multiple crack pathways, is assessed. A Finite Element Method (FEM) analysis, calibrated with the materials and bond laws retrieved experimentally, is conducted to simulate the tensile and cracking behaviour of the optimal material combination investigated in this study, demonstrating a high degree of correlation with the tensile tests.

Rheology of flexible fiber-reinforced cement pastes: Maximum packing fraction determination and structural build-up analysis

The maximum packing fraction (φfm) of flexible fibers is an essential parameter for understanding the rheological behavior of flexible fiber-reinforced cement paste (FFRCP). However, direct measurement of φfm of flexible fibers is still lacking. In this study, a shear rheology-based method for direct measurement of φfm was proposed and the assumption of fiber conformation under shear was verified by micro-CT. Based on this, a yield stress model for FFRCP was constructed to explain the entanglement and friction effects in the fiber network. Finally, static yield stress tests and small amplitude oscillatory shear (SAOS) tests were carried out to explore the structural build-up of FFRCP. It was found that the proposed method enables direct determination of φfm through only a few viscosity-fiber content data for a given FFRCP. Furthermore, the proposed model can describe the static yield stress of FFRCP well. Finally, the relative structural build-up rate of FFRCP follows a similar trend as the relative yield stress, with a critical relative fiber volume fraction (0.299) as the boundary. Subsequently, the relative structural build-up gradually deviates from the relative yield stress due to the limiting effect of the fibers.

Performance and microstructural characterization of fiber-reinforced cement-based grout incorporating waste tailing sand and fly ash

A fiber-reinforced cement and tailing sand-based grout (FRCTG) was proposed to improve the utilization of solid waste in construction. Different grout specimens were prepared using various proportions of ordinary Portland cement, iron tailing sand (ITS), fly ash (FA), basalt fibers (BFs), and water as raw materials. Used single-factor test, orthogonal test and artificial neural network model that provided a comparative analysis of the change in the rheological and mechanical properties of different grout mixes according to their component ratios. Furthermore, microscopic characterization techniques were used to reveal the intrinsic physicochemical mechanisms underlying the structural evolution of the considered grouting materials. The results indicate that ITS significantly increases the rheological properties of the grouting material. The maximum strength of the grouting material is achieved when the length of BF is 6 mm and the dosage is 0.2 %. An 8 % dosage of FA can effectively improve the rheological properties of the grouting material and enhance its flexural strength. Microscopic tests reveal that SiO2 in ITS exists in the form of quartz with low reactivity, thereby inhibiting the hydration reaction of the binder material. Different distribution patterns allow BF to serve both as reinforcement for the matrix and as a framework for hydration products, effectively enhancing the density between the BF and the surrounding matrix. The surface of FA is covered in layers by hydration products, forming a chain-like structure that improves bonding strength with the material. The results of this research offer a high-performance, low-cost, and environmentally friendly grouting material for construction grouting projects, which is of significant importance for promoting innovation in comprehensive utilization of solid waste.

Assessment of the Mechanical and Microstructural Performance of Waste Kraft Fibre Reinforced Cement Composite Incorporating Sustainable Eco-Friendly Additives

This study investigates the influence of limestone powder and metakaolin as sustainable eco-friendly additives on the properties and behavior of cementitious composite boards, with a focus on mechanical strength, physical properties, and microstructural characteristics. The experimental investigation begins with the characterization of the raw materials, including limestone powder, and metakaolin, to assess their particle sizes, elemental composition, and microstructural features. Cement composite boards were fabricated using an innovatively developed lab-simulated vacuum dewatering process, by varying the proportions of limestone powder and metakaolin as partial replacements for cement, along with waste kraft fibres as reinforcement. Mechanical testing was conducted to evaluate the flexural strength and behaviour of the composite boards according to standardized procedures. A microstructural analysis was performed using scanning electron microscopy (SEM) to examine the effect of additives on the cementitious matrix, fibrematrix interaction, and hydration products. The findings from the experimental study reveal insights into the influence of limestone powder and metakaolin on the mechanical properties and microstructure of waste kraft fibre-reinforced cement composite boards. Our analysis of the results shows that adding 9% limestone powder as partial cement replacement produces a 24% and 50% enhancement in flexural strength at 7 and 28 days of hydration, while that of metakaolin as partial cement replacement was optimum at 6% with an enhancement of 4% and 36%, respectively, at 7 and 28 days of hydration. The implications of these findings for the development of sustainable cementitious composite are discussed, including the potential benefits of using limestone powder and metakaolin as supplementary cementitious materials in waste kraft fibre-reinforced cement composite boards. Finally, recommendations for optimizing additive proportions are also provided to enhance the understanding and application of these materials in the construction and building industries.

Development of Sustainable and Innovative Manhole Covers in Fibre-Reinforced Concrete and GFRP Grating

In several countries, manhole covers made of steel are being stolen, with significant economic losses for private and public entities, and even causing accidents. In this work, a new manhole cover is developed using fibre-reinforced cementitious (FRC) materials and glass fibre-reinforced polymer (GFRP) gratings. Since the GFRP gratings are immune to corrosion, and FRC is a relatively low-cost material, manhole covers in FRC reinforced with GFRP gratings are durable and not so appealing to be stolen as those made from steel. An experimental program with manhole cover specimens made with two types of FRC and two types of GFRP gratings was executed by investigating the strength, stiffness and post-cracking tensile capacity of the FRCs and the stiffness and flexural capacity of the two GFRP gratings. It was demonstrated that the developed manhole cover concept can be of class A15 up to D400 according to the recommendations of BS EN 124:1994.

Mechanical performance study of PVA fiber-reinforced seawater and sea sand cement-based composite materials

Due to the swift progress in the construction sector, there is a global concern about the potential scarcity of river sand and freshwater resources. The development of new construction materials is considered an inevitable trend for industry growth. PVA fibers, known for their strong corrosion resistance, cost-effectiveness, and high toughness, have the potential to enhance the corrosion resistance and seismic performance of structures in marine environments. However, their mechanical properties and durability in the seawater and sea sand environment are not well understood. Therefore, the investigation of the impact of seawater and sea sand on the mechanical properties and durability of PVA fiber-reinforced cement composites is considered crucial. A mechanical performance analysis of PVA fiber-reinforced seawater and sea sand fiber cement composites was conducted in this study. PVA fiber volume fractions of 0%, 0.75%, and 1.5%, cement composite matrix strength grades of C30 and C50, and curing periods of 28 days, 90 days, and 180 days were examined, investigating their influence on the bending toughness of PVA fiber-reinforced seawater and sea sand cement composites. Specific conclusions include the addition of fibers increased the peak bending load, had a less corrosive effect in seawater, and improved the flexural toughness of the material. The most significant improvement was observed at 1.5% fiber content, where the load-deflection curve was fuller and the energy absorption capacity of the material increased by 33–109%, maintaining good bending toughness. Furthermore, higher fiber contents are required for high-strength cementitious composites to improve flexural toughness and durability. The formulation of calculation formulas for predicting bending strength and corresponding deflection, which fit well with the experimental results; and the development of a calculation model for the bending toughness index of PVA fiber-reinforced seawater and sea sand cement composites, providing an effective prediction of material bending toughness.

Combined effect of fiber and degree of stabilization on the early age behavior of cement bound granular mixtures

Abstract An investigation has been undertaken to study the effect of fiber-reinforcement and different degrees of stabilization on the early age mechanical behavior of cement bound granular mixtures intended to be used as a base layer within pavement structure. Waste plastic fibers (WPF) recycled from soft drink bottles were used at 1% by the mass of aggregate to reinforce cemented mixtures. To stabilize different mixtures, cement content of 3%, 5%, and 7% by the mass of aggregate and by the weight of aggregate and fiber were used for conventional and fiber-reinforced cement bound granular mixture (CCBGM& FRCBGM), respectively. The examined properties include unconfined compressive strength (UCS), indirect tensile strength (ITS), bulk density, and ultrasonic pulse velocity (UPV). The results showed a significant improvement in UCS and ITS as the cement amount increased for both types of mixtures. Incorporating PET fibers at cement content of 5% and 7% resulted in a noticeable improvement of ITS compared to the conventional mixtures while a marginal enhancement in the UCS occurred due to fiber-reinforcement. Both bulk density and UPV were increased as cement content increased, while both were decreased due to the inclusion of waste plastic fibers (WPF). Hence, utilizing waste plastic fiber has a positive and promising effect on the pavement structure from sustainability, integrity, and economic points of view.

Seismic Performance of a Single-Story Timber-Framed Masonry Structure Strengthened with Fiber-Reinforced Cement Mortar.

Timber-framed masonry structures are widely used around the world, and their seismic performance is generally poor. Most of them have not been seismically strengthened. In areas with high seismic fortification intensity, there are great potential safety hazards. And it is urgent to carry out effective seismic reinforcement. However, due to the complicated construction process of the existing reinforcement technology, the poor durability of the reinforcement materials, and the significant disturbance to the life of the original residents, an efficient single-story timber-framed masonry structure reinforcement technology suitable for comprehensive promotion and application has not been explored. In this paper, a fiber-reinforced cement mortar (FRCM) material was proposed. A 1/2 scale model of a single-story timber-framed masonry structure was taken as the research object. The method of strengthening a single-story timber-framed masonry structure with FRCM layer was adopted. And the shaking table test of the model before and after reinforcement was carried out in turn. The dynamic characteristics, failure modes, acceleration response and displacement response of the FRCM layer-strengthened structure were analyzed through comparisons of the two cases. The experimental results showed that the FRCM layer significantly improved the seismic performance of the seismic-damaged single-story timber-framed masonry structures. The X- and Y-direction natural frequencies of the model structure were increased by 31.30% and 30.22%, respectively, after the structure was strengthened with FRCM. During a rare eight-degree earthquake, the inter-story displacement angles in the X- and Y-direction of the unreinforced model reached 1/98 and 1/577, respectively, and the structure was destroyed, while the inter-story displacement angle of the FRCM-reinforced model was only 1/2 of that the unreinforced model. During a rare nine-degree earthquake, the X-direction inter-story displacement angle of the model strengthened with FRCM reached 1/78 and the Y-direction inter-story displacement angle reached 1/178. At this time, the reinforced model structure was destroyed, but there was no collapse of the structural components, which met the seismic design objectives of "operational under the design minor seismic intensity, repairable damage under the design seismic precautionary intensity, and collapse prevention under the design rare seismic intensity", which proved that the FRCM layer was an effective and feasible way to strengthen the existing single-story wood-masonry rural building.

Meso-scale Study of Bond Behavior between Ribbed Steel Rebar and Fiber-reinforced Cementitious Composite Considering Rebar Rib Geometry

This study aims to develop a meso-scale finite element approach to investigate the pull-out behavior of ribbed steel rebar and fiber-reinforced cement composites. We considered separately the three phases of steel fibers, cement composite matrix, and rebar within the meso-scale finite element model. A random distribution of fibers was generated in the matrix based on the geometric characteristics of the fibers and their volume fraction. By employing the interfacial transition zone (ITZ) model, the interaction between rebar and fibers with cement composite was simulated. Experimental pull-out tests were conducted to determine the parameters of the model. A meso-scale finite element model was validated and the effect of rebar diameter and fiber volume fraction on the bond behavior of rebar with fiber-reinforced cement composites was examined. In accordance with the experimental results, the bond-slip curve obtained with the meso-scale finite element model can be divided into five areas: non-slip, slight slip, splitting, decreasing, and residual. Additionally, it can be observed that fiber-free cement composites fail by splitting, whereas specimens containing fibers fail by sliding. This numerical model is therefore able to predict and estimate the influence of a variety of parameters on the pull-out response between fiber-reinforced cement composite and ribbed bar and failure mechanisms without the need for expensive and time-consuming testing.

Molecular investigation on interfacial toughening between silane coupling agent treated glass fiber and cement

Silane coupling agents (SCAs) are widely used as adhesion promoters to tightly bond glass fiber (GF) and cement matrix (CM) for developing sustainable and high-performance glass fiber-reinforced cementitious (GFRC) composites. This study uses molecular dynamics (MD) simulation to examine the effect of 3-aminopropyltriethoxysilane (APS) on CM/GF interfacial properties. Pure cement and nine cement models bonded to APS-modified GF with APS concentrations of 0.00%, 12.50%, 25.00%, 37.50%, 50.00%, 62.50%, 75.00%, 87.50%, and 100.00% are constructed. It is shown that pure CSH system experiences interfacial delamination. With increasing APS from 0.00% to 37.50%, the failure mode transits from interfacial delamination to CSH delamination, and with increasing APS to 100.00%, it transits to interfacial delamination. Meanwhile, it is measured that with increasing APS from 0.00% to 37.50%, the tensile strength increases from 0.48 to 0.58 GPa and the adhesion energy increases from 0.71 to 0.90 J⋅m−2. Comparatively, with increasing APS to 100.00%, the tensile strength decreases to 0.26 GPa, and the adhesion energy decreases to 0.23 J⋅m−2. Moreover, the interfacial structure and chemical bond analysis demonstrate that with increasing APS from 0.00% to 37.50%, the peak of H2O molecules decreases, which denotes stronger interfacial bonding. With increasing APS from 37.50% to 100.00%, the peak of the H2O molecules increases, which induces low interfacial bonding. These findings provide a basis for optimizing APS concentrations for specific performance enhancements of GFRC materials.

Study on bearing capacity of corroded pipes before and after spraying rehabilitation

In recent years, there has been growing interest in trenchless technology, particularly in using centrifugal spraying technology to rehabilitate drainage pipelines. In this study, we evaluated the effectiveness of fiber-reinforced cement mortar spraying materials on pipes using the three-edge bearing test (TEBT) as per ASTM C497 standards. Six conditions of corroded and rehabilitated pipelines were tested: (1) corrosion depths, (2) corrosion widths, (3) corrosion positions, (4) pipe diameters, (5) loading rates, and (6) repair thicknesses. Through the TEBT, the structural bearing capacity and failure form of the pipe before and after repair were compared, and the bearing capacity difference of the pipe under different conditions was studied. Finally, a sensitivity analysis was conducted on the six variables. Among the many factors that affect the reliability of pipe structures, the influence degree of each factor is quite different. Through the parameter sensitivity analysis, the influence degree of each factor on the reliability of the structure can be clarified. The results show that the bearing capacity of the rehabilitated pipes is sufficient to meet the normal pipe bearing capacity requirements. The mortar lining and existing pipes can bear stress jointly, significantly increasing the maximum load of the rehabilitated pipes by up to 55.6 % and correspondingly reducing the circumferential strain. This indicates that the application of the mortar spraying lining layer effectively achieves the purpose of pipeline repair. This study provides valuable guidance for structural design optimization and safe operation.

Experimental study on fiber-reinforced cement tailings sand-based grouting material preparation and factors influencing the grouting effect

To address the problem of permeation of tailings pond initial dams rockfill dams, fiber-reinforced cement tailings sand-based grouting (FRCTG) material, which can be used for rockfill dam reinforcement, was prepared by selecting ordinary portland cement (OPC), iron tailings sand (ITS), basalt fiber (BF), fly ash (FA) and water as the raw materials. Orthogonal tests were used to investigate the effects of the water-binder ratio (w/b) and material mass fraction on the rheological and mechanical properties of FRCTG and determine the optimum mixing ratio. Comparative analyses were performed of the grouting effect of FRCTG and pure OPC grouting materials based on concrete self-compacting tests and COMSOL simulations. Combined X-ray diffraction (XRD) and scanning electron microscopy-energy spectroscopy (SEM-EDS) microstructural characterization were used to reveal the factors influencing FRCTG mechanical properties. The results showed that when the water-binder ratio (w/b) was 0.5, ITS substitution percentage for OPC was 10 %, BF dosage was 0.2 %, BF length was 6 mm, and FA substitution percentage for OPC was 8 %, FRCTG had better rheological properties and flexural strength than pure OPC grouting materials. In addition, FRCTG self-compacting concrete also had stronger compressive strength and splitting strength. FRCTG showed a better filling capacity and diffusion effect, which preliminarily verified the feasibility of rockfill dam grouting. ITS inhibited the hydration reaction of the cementitious material and prolonged the setting time of the slurry. The interlocking structure formed by FA and hydration products indirectly enhanced the flexural strength of the grouting material. BF not only provided FRCTG reinforcement but also acted as the hydration product skeleton. FRCTG demonstrated better economic and environmental performance than traditional cement material while effectively utilizing ITS and FA solid waste.

Enhancing shear strength of RC beams through externally bonded reinforcement with stainless-steel strips and FRCM jacket to mitigate the failure risk

This study aims to assess the efficacy of innovative and sustainable methods in improving the shear performance of Reinforced Concrete (RC) beams lacking shear stirrups. Eleven specimens, including two control specimens and nine strengthened ones, underwent monotonic loading through three-point testing. Various strengthening configurations were investigated, involving the application of Stainless-Steel Strips (SSSs) affixed to the beam surface in the defective zone, along with a Fiber-Reinforced Cementitious Matrix (FRCM) jacket. In the first set of beams, SSSs were vertically applied, while the second set featured beams with SSSs inclined at 60°, and the third set had SSSs inclined at 45°. Each set comprised three beams, allowing for the examination of the impact of SSS thicknesses, set at 1 mm, 1.25 mm, and 1.50 mm. After the installation of SSSs, all strengthened beams received an FRCM jacket, including a 5 mm Engineered Cementitious Composites (ECC) layer with embedded Glass Fiber Reinforced Polymer (GFRP) textile. The study concludes that incorporating SSS strips with an FRCM jacket delays the initiation of the first crack in defective beams. Increasing SSSs thickness contributes to a more favorable crack distribution. The 60° inclined SSSs proves to be the most effective, rectifying the deficiency from the absence of shear stirrups and surpassing the original beam's performance. Additionally, finite element analysis was conducted, and the results supported the accurateness of the developed model in simulating responses and crack patterns throughout all loading stages.

Effect of Hybridization of Carbon Fibers on Mechanical Properties of Cellulose Fiber–Cement Composites: A Response Surface Methodology Study

Fiber-reinforced cement composites, particularly those incorporating natural fibers like cellulose, have gained attention for their potential towards more sustainable construction. However, natural fibers present inherent deficiencies in mechanical properties and can benefit from hybridization with carbon fibers. This study focuses on the incorporation of cellulose and carbon fibers, in varying contents, into fibrocement composites, employing a Response Surface Methodology (RSM) to optimize the material characteristics. The methodology involves testing, encompassing flexural tensile, compression, and fracture toughness tests. The results indicate an increasing trend in flexural strength for higher carbon fiber content, peaking near 5%. A plateau in flexural strength is observed between 1.2% and 3.6% carbon fiber content, suggesting a range where mechanical properties stabilize. Compressive strength shows a plateau between 1.2 and 3.6% and reaches its highest value (≈33 MPa) at a carbon fiber content greater than 4.8%, and fracture toughness above 320 MPa·m1/2 is achieved with carbon fiber content above 3.6%. This study offers insights into optimizing the synergistic effects of cellulose and carbon fibers in fibrocement composites.

Physically simulating the dispersion of chopped carbon fibres in mortar

Carbon fibre dispersion exerts a critical influence on the characteristics of carbon fibre-reinforced cement mortars (CFRCMs). This study accordingly investigated the dispersion of chopped carbon fibres (CCFs) in mortar using physical experiments with a transparent simulated mortar system comprising colloidal silica and silica sand as replacements for cement and aggregate, respectively, and evaluated the microstructures and conductive performances of corresponding CFRCM specimens. In the simulated solutions, bundled CCFs in order were more prone to disperse into single fibres than clustered ones in disorder due to no physical fixation, colloidal silica prevented the formation of CCF clusters during stirring, and the shear force of moving sand dispersed but also broke CCFs. In the CFRCMs, sand aggregates reaggregated dispersed CCFs while larger sand particles increased CCF dispersion and improved specimen conductivity. Thus, decreasing the amount of CCFs clusters before dispersion, and a short stirring time in a single direction should be provided to prepare CFRCMs with well-dispersed CCFs. Meanwhile, a more dispersible aggregate and less formation of void should be also essential.

Simplified Procedure to Determine the Cohesive Material Law of Fiber-Reinforced Cementitious Matrix (FRCM)-Substrate Joints.

Fiber-reinforced cementitious matrix (FRCM) composites have been largely used to strengthen existing concrete and masonry structures in the last decade. To design FRCM-strengthened members, the provisions of the Italian CNR-DT 215 (2018) or the American ACI 549.4R and 6R (2020) guidelines can be adopted. According to the former, the FRCM effective strain, i.e., the composite strain associated with the loss of composite action, can be obtained by combining the results of direct shear tests on FRCM-substrate joints and of tensile tests on the bare reinforcing textile. According to the latter, the effective strain can be obtained by testing FRCM coupons in tension, using the so-called clevis-grip test set-up. However, the complex bond behavior of the FRCM cannot be fully captured by considering only the effective strain. Thus, a cohesive approach has been used to describe the stress transfer between the composite and the substrate and cohesive material laws (CMLs) with different shapes have been proposed. The determination of the CML associated with a specific FRCM-substrate joint is fundamental to capture the behavior of the FRCM-strengthened member and should be determined based on the results of experimental bond tests. In this paper, a procedure previously proposed by the authors to calibrate the CML from the load response obtained by direct shear tests of FRCM-substrate joints is applied to different FRCM composites. Namely, carbon, AR glass, and PBO FRCMs are considered. The results obtained prove that the procedure allows to estimate the CML and to associate the idealized load response of a specific type of FRCM to the corresponding CML. The estimated CML can be used to determine the onset of debonding in FRCM-substrate joints, the crack number and spacing in FRCM coupons, and the locations where debonding occurs in FRCM-strengthened members.

Rheology of Superabsorbent Polymer-Modified and Basalt Fiber-Reinforced Cement Paste with Silica Fume: Response Surface Methodology

A composite's rheology can be changed by adding superabsorbent polymer (SAP) and basalt fibers and using silica fume. This study aimed to investigate the effects of these components on the viscosity and shear stress parameters of the paste. The proportions of the components were varied, with SAP content ranging from 0.01% to 0.03%, basalt fiber from 0% to 0.50%, silica fume (micro silica) at 15%, and water content from 0.40 to 0.50. Response surface methodology was used to optimize the mixture proportions, and the rheological properties of the resulting pastes were characterized using a rheometer. Results showed that the addition of SAP and basalt fiber had a significant impact on the rheological properties of the paste, with increasing amounts of both resulting in increased viscosity and shear stress. Overall, this study highlights the potential of SAP and basalt fiber in advances of the rheology of cement paste and provides insight into the optimal proportions of these components for achieving desired rheological properties. The findings of this study could be useful in developing high-performance concrete with enhanced rheological properties, which could have a wide range of applications in the construction industry. In addition, 0.50% BF, 0.01% SAP, and 0.445 water-to-cement were found as optimum proportions regarding the rheology of the cement paste.

Rheological and Flexural Strength Characteristics of Cement Mixtures through the Synergistic Effects of Graphene Oxide and PVA Fibers.

This study investigates the synergistic effects of incorporating graphene oxide (GO) and polyvinyl alcohol (PVA) fibers into cement paste mixtures, aiming to modify their rheological properties and flexural behaviors with resistance to crack formation. The relationship between static yield stress and critical shear strain was examined in ten cement paste mixtures with varying concentrations of 6 mm and 12 mm PVA fibers and 0.05% GO. Additionally, viscosity analyses were performed. For the specimens fabricated from these mixtures, flexural strength tests were conducted using the Digital Image Correlation (DIC) technique for precise strain analysis under load history. The results indicated a significant increase in static yield stress, viscosity, and critical shear strain due to the combined addition of GO and PVA fibers, more so than when added individually. Notably, in PVA fiber-reinforced cement mixtures, the integration of GO increased the crack initiation load by up to 23% and enhanced pre-crack strain by 30 to 50%, demonstrating a notable delay in crack initiation and a reduction in crack propagation. Microstructural analyses using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) revealed a concentrated presence of GO around and on the PVA fibers. This promotes increased C-S-H gel formation, resulting in a denser microstructure. Additionally, GO effectively interacts with PVA fibers, enhancing the adherence of hydration products at their interface.

Upcycling low-grade coal fly ash for the production of fly ash fibers and their applications in fiber-reinforced cement composites

Fly ash (FA) fibers were produced from low-grade coal FA, which exhibited high SO3 content, in combination with dolomite and basalt. To identify the optimal combination of these raw materials, glass samples were cast with varying ratios of these materials. Subsequently, an alkaline resistance test was conducted by immersing the ground glass samples in a 1 M Ca(OH)2 solution for a duration of 75 days. The results of the alkaline resistance test revealed that the formulation consisting of 70 wt% FA, 20 wt% dolomite, and 10 wt% basalt, exhibited the highest alkaline resistance with a weight loss of less than 2 wt%. Based on this formulation, FA fibers were then produced and utilized as a reinforcing phase in fiber-reinforced cement composite (FRCC) samples, ranging from 0.1 to 0.8 wt%. Mechanical testing showed that, after 28 days of air curing, the FRCC samples containing 0.8 wt% FA fibers exhibited the highest modulus of elasticity (MOE) at 16,890 ± 434 MPa, along with a modulus of rupture (MOR) of 13.86 ± 0.98 MPa and an impact strength of 1792 ± 134 J/m2. These results meet industry requirements, with a MOR and MOE exceeding 5 MPa and 7000 MPa, respectively, as well as an impact strength exceeding 1000 J/m2. Using the Archimedes method, the density of the FRCC samples containing 0.8 wt% FA fibers, is 1.71 ± 0.03 g/cm3, falling within the industry standard range of 1.5 to 2.2 g/cm3. Furthermore, according to the cost analysis, the production cost for FA fibers is $324.40 per ton, compared to $5000 and $1000 per ton for commercially available fibers. Consequently, utilizing FA fibers would result in significant savings for the raw material costs for FRCC production.

Assessment of self-healing behavior of polypropylene fiber-reinforced cement mortar with crystalline admixture: the effects of crack widths, cracking ages, and external conditions

Crystalline admixture (CA) is an effective self-healing agent for mortar. However, the effects of crack parameters (i.e. crack width and cracking age) and the service environment on the self-healing behavior of CA-containing mortar are not well understood. Herein, the self-healing behavior of mortar containing a self-developed CA was assessed by testing strength recovery, impermeability recovery, and crack closure in pre-cracked specimens. Three initial crack widths (0.2, 0.3, and 0.4 mm), five cracking ages (3, 7, 14, 28, and 56 days), and four external exposure conditions (humidity chamber, air exposure, water immersion, and wet-dry cycles) are investigated. Furthermore, the influence of different external conditions on the healing products at the region of crack and the pore structure of hardened paste containing CA are studied. The results show that adding 4.54% CA into mortar allows rapid healing of 300 μm-wide cracks. Although wider cracks (400 μm) are more difficult to heal, the sorptivity coefficients of the mortars with 400 μm-wide cracks after healing decrease. When the cracks are produced at an earlier age, the pre-cracked specimens have higher recovery ratios of strength and impermeability after healing, and the specimens pe-cracked at a later age still have acceptable compressive strengths after healing. The analysis shows that the strengths and impermeabilities of pre-cracked mortars containing CA exposed to the four external conditions are all recovered. The best self-healing performance is observed for the specimens exposed to water immersion and wet-dry cycles conditions. Somewhat less good self-healing was observed in the specimens exposed to humid chamber condition, while the worst self-healing performance was in the specimens exposed to air exposure condition. This study provides a theoretical basis for the application of novel CAs in cement-based materials.