Fiber-reinforced Cement-based Composites Research Articles

Self-healing performance of engineered geopolymer composites subjected to sodium sulphate

Engineered geopolymer composites (EGCs) have self-healing potential due to their multiple fine-cracking features. However, water immersion, as a self-healing condition for fibre-reinforced cement-based composites, may limit the self-healing ability of EGCs due to water would not directly participate in the precipitation reaction. By contrast, sodium sulphate is proved as an effective activator to promote the geopolymerisation process, while the self-healing performance of EGCs exposed to sodium sulphate has not been comprehensively demonstrated in the literature. Therefore, this paper investigates the self-healing performance of the EGCs subjected to sodium sulphate (Na2SO4) under wet-dry cycles. The results show that the EGCs preloaded at 3 days attain a higher increment of C-(A)-S-H gels at the cracks than those preloaded at 28 days, indicating the EGCs cracked at the early age have better self-healing performance under sulphate exposure. Besides, ettringite and calcium carbonate are detected as the self-healing products in the EGCs preloaded at 3 days, while the ettringite cannot be found in the EGCs preloaded at 28 days. The EGCs exposed to 5 % Na2SO4 solution and wet-dry cycles can achieve self-healing by forming more CaCO3. Increasing the Na2SO4 concentration to 10 % can accomplish self-healing by facilitating the C-(A)-S-H and CaCO3 formation, enhancing the tensile stiffness recovery and crack width reduction ratios for the EGCs with tensile strains of 2 % and 4 % at 3 days. Decreasing the preloading level also improves the tensile stiffness recovery and crack width reduction ratios regardless of the Na2SO4 concentration and preloading age, since the self-healing products are easier to fill the small cracks. Through a combination of Na2SO4 solution and wet-dry cycles, this study develops a new strategy for the accomplishment of self-healing of EGCs.

Effect of High Temperature on Micro-Structure and Mechanical Properties of Fiber-Reinforced Cement-Based Composites

Synthetic fibers can effectively inhibit the formation and propagation of micro-cracks in concrete, significantly reducing the number and scale of cracks within the concrete matrix, thereby enhancing the concrete’s crack resistance and seepage prevention capabilities. In this study, two types of synthetic fibers, polyvinyl alcohol (PVA) and polypropylene (PP), were incorporated into cement mortar to investigate their microstructural evolution at elevated temperatures and their influence on the mechanical properties of the mortar. Both fibers were added at a volume content of 0.5%. The mortar samples were subjected to the following temperature conditions: 20 °C (ambient), 200 °C, 400 °C, and 500 °C. The results indicate that the synthetic fibers employed in this study improved the tensile properties of the mortar at room temperature (20 °C). This enhancement persisted up to 400 °C, beyond which, at 500 °C, the mechanical properties of the fiber-reinforced mortar deteriorated significantly. At 400 °C, the tensile strength of the PVA group increased by approximately 16% compared to the unblended fiber group (JZ) and by about 45% compared to the PP group. After treatment at 500 °C, the tensile strength of mortar specimens in the PVA group and the PP group decreased by 36.47% and 24.14%, respectively, compared with that at 20 °C. The porous structure formed due to the high-temperature ablation of the synthetic fibers contributed to relieving the internal pressure within the mortar.

Mechanical Properties of Chopped Basalt Fiber-Reinforced Cement-Based Composites

Mechanical Properties of Chopped Basalt Fiber-Reinforced Cement-Based Composites

Effect of expansive agent on the mechanical properties of carbon-fibre-reinforced cement-based composites

Improving the flexural strength of a cement-based composite (CBC) reinforced with chopped carbon fibre (CF) while maintaining good workability is highly attractive for building high-rise large-span structures. A sulfoaluminate-based expansive agent (EA) was used to optimise the mechanical properties of CBCs reinforced with chopped CF by improving the fibre–matrix interfacial properties. The results of single-fibre pull-out tests showed that the interfacial frictional bond strength was improved by up to 51% owing to the addition of the EA, whereas the chemical debonding energy remained nearly unchanged. The effects of various concentrations of EA on the strength of cement pastes containing various lengths and volume fractions of CF were then investigated. The results indicated that, benefitting from the EA-induced high interfacial bond strength, the flexural strength and fluidity of the CF-reinforced cement paste could be further optimised. For example, utilising the EA, the flexural strength could be improved by 28% for a cement paste containing 0.5% CF of length 15 mm.

Effect of PVA fibers on durability of nano-SiO2-reinforced cement-based composites subjected to wet-thermal and chloride salt-coupled environment

Abstract 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.

Effect of clinoptilolite on properties and fractal characteristic of pore structure of polypropylene fiber-reinforced cement-based composite

To further analyze the effect mechanism of clinoptilolite on the macro-mechanics and microstructure of polypropylene fiber-reinforced cement-based composite, the samples with 0, 5%, 10%, 15%, 20% and 25% clinoptilolite contents were investigated by compression test, flexural test, X-ray diffraction (XRD), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP), and the pore structure characteristics were quantitatively analyzed by fractal theory. Results showed that: With the increase of clinoptilolite content, the compressive strength, flexural strength and porosity of samples first increased and then decreased. The addition of clinoptilolite reduced the 7-day strength but increased the 28-day compressive strength, 60-day compressive strength, 28-day flexural strength and 60-day flexural strength of the samples by about 6%, 14.3%, 13.9% and 19.1%. It was recommended that the clinoptilolite content should not exceed 15%. Due to the filling effect and pozzolanic effect of clinoptilolite, adding clinoptilolite into the matrix could promote a hydration reaction to produce more C-S-H gels and reduce the proportion of more harmful pores and harmful pores, effectively improving the internal pore structure of the matrix. Meantime, it was found that the evolution law of pore structure based on fractal dimension calculated by the thermodynamic fractal model was consistent with the variation law of the pore size distribution curves and pore volume measured by MIP. Furthermore, a polynomial relationship model between clinoptilolite content, the quantitative fractal characteristic of pore structure and the macroscopic mechanical behaviors was established, which indicated that the pore fractal dimension could quantitatively describe the effect of clinoptilolite content on the pore microstructure.

New damage evolution law in plastic damage models for fiber‐reinforced cementitious composites

AbstractNowadays, fiber‐reinforced cement‐based composites (FRCC) can develop ductile behavior with high toughness when the matrix, fibers, and interface are optimally designed. These materials are promising solutions for constructing more resilient structures. In this context, the widespread use in large‐scale applications requires reliable models to predict the performance of FRCC structures. Usually, the studies on numerical modeling of FRCC apply the damage laws developed for quasi‐brittle concrete, making damage increase faster than really occurs in the presence of fibers. Therefore, the present paper proposes a new damage evolution model for FRCC based on energy dissipation concepts. It is assumed that the dissipated energy contributes fully to the evolution of the scalar damage and plastic strain variables, which is a technical advance from the previous works. The damage evolution is obtained with experimental envelopes of uniaxial stress–strain tests and the focal point from loading–unloading cycles. The results showed that the model accurately predicted experimental results using the damage‐plasticity framework. Furthermore, there are no empirical constants in the proposal, which means that it can be applied to any class of FRCC. An application regarding damage evaluation near a load transfer device in jointed plain cementitious pavements is presented. The damage distribution reveals that using FRCC materials has induced smaller damage values when compared with using conventional concrete. Consequently, cracking is reduced in such zones, increasing the structural life of the pavement.

Recent Advances in Properties and Applications of Carbon Fiber-Reinforced Smart Cement-Based Composites.

Under the strategies of low-carbon and environmental protection, promoting green technology innovation to achieve carbon neutrality in the construction field has become a universal goal. As the building material with the highest consumption, concrete has gradually begun to transform into a multi-functional and intelligent product. Therefore, the research on carbon fiber-reinforced cement-based composites (CFRCs) is of relative interest. It mainly uses carbon fibers (CFs) with high elasticity, strength, and conductivity to disperse evenly into the concrete as a functional filler, to achieve the intelligent integration of concrete structures and function innovatively. Furthermore, the electrical conductivity of CFRC is not only related to the content of CFs and environmental factors but also largely depends on the uniform dispersion and the interfacial bonding strength of CFs in cement paste. This work systematically presents a review of the current research status of the enhancement and modification mechanism of CFRC and the evaluation methods of CF dispersion. Moreover, it further discusses the improvement effects of different strengthening mechanisms on the mechanical properties, durability, and smart properties (thermoelectric effect, electrothermal effect, strain-sensitive effect) of CFRC, as well as the application feasibility of CFRC in structural real-time health monitoring, thermal energy harvesting, intelligent deformation adjustment, and other fields. Furthermore, this paper summarizes the problems and challenges faced in the efficient and large-scale applications of CFRCs in civil engineering structures, and accordingly promotes some proposals for future research.

Effects of Strain Rate and Fiber Content on the Dynamic Mechanical Properties of Sisal Fiber Cement-Based Composites

In this paper, a split Hopkinson pressure bar (SHPB) was used to investigate the dynamic impact mechanical behavior of sisal fiber-reinforced cement-based composites (SFRCCs), and the microscopic damage evolution of the composites was analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS). The results show that the addition of sisal fibers improves the impact resistance of cement-based composite materials. Compared with ordinary cement-based composites (OCCs), the SFRCCs demonstrate higher post-peak strength, ductility, and energy absorption capacity with higher fiber content. Moreover, the SFRCCs are strain rate sensitive materials, and their peak stress, ultimate strain, and energy integrals all increase with increasing strain rate. From the perspective of fracture failure characteristics, the failure of OCCs is dominated by the brittle failure of crystal cleavage. In contrast, the failure mode of the SFRCCs changes to microscale matrix cracks, multi-scale pull-out interface debonding of fibers (fine filaments and bundles), and mechanical interlock. This research provides an experimental basis for the engineering application of high-performance and green cement-based composites.

Experimental Investigation on the Compressive Stress-Sensing Ability of Steel Fiber-Reinforced Cement-Based Composites under Varying Temperature Conditions

This study investigates the piezoresistive (self-sensing) properties of short stainless-steel fiber-reinforced mortar under varying temperature conditions. Different reinforced mortars were produced by varying fiber and aggregate content. First, Electrical Impedance Spectroscopy (EIS) measurements were used to characterize the electrical properties of the mortar specimens. EIS measurements were performed at temperatures of 24 °C, 35 °C, and 50 °C. Second, to investigate the self-sensing capacity of the different composites, the fractional changes of electrical impedance at 1 kHz were monitored under two conditions: temperature variation alone (cooling down from 35 °C or 50 °C to room temperature), and temperature variation combined with cyclic compressive loading (up to 5 MPa). The results of the former were used to compensate for the effect of temperature variations in the latter. Both temperature and mechanical loading produced meaningful variations in the electrical impedance and piezoresistivity of the investigated composites. Conclusions are drawn with respect to the stress and temperature sensitivity of the composites. The real and imaginary parts of the electrical impedance of the mortar produced with the highest fiber volume fraction (0.01%) and higher aggregate content (volume fraction of 60%) were distinctly sensitive to temperature and stress, which suggests the possibility of using the same composite as a stress and temperature sensor.

Susceptibility to Expansive Reactions of a Greener UHPC: Micro to Macro-Scale Study

Nowadays, in Europe, several infrastructures, such as bridges, viaducts, and maritime structures, are in an advanced state of degradation. Therefore, novel repair/rehabilitation techniques are sought. Recent advances in ultra-high-performance fibre-reinforced cement-based composites (UHPFRC) represent a significant step towards resilient structures. In addition to their remarkable mechanical properties (compressive strength > 150 MPa), they present extremely low permeability and, as a premise, very high durability. Despite their relatively high cost, UHPFRC can be a competitive solution for rehabilitation/strengthening applications where smaller volumes are needed. UHPFRC applied in thin layers (with or without reinforcement) can replace carbonated and/or cracked concrete acting as a protective watertight and/or strengthening layer. The structural capacity increases (stiffness, ultimate strength), and the durability is expected to improve significantly while keeping cross-sectional dimensions. Additional advantages are expected, such as reduced intervention time, fewer maintenance routines, reduced life-cycle cost, and longer service life. Although much of the focus on UHPFRC has centred on mechanical and/or structural performance, durability is inevitably linked with mechanical properties. The current work evaluated the durability of non-property and greener UHPC concerning expansive reactions, alkali-silica reactions and expansion due to external sulphates, by macro and micro-scale integrative study. Linear expansion tests were performed in UHPC specimens according to ASTM C 1260 and LNEC E−364. At the macro level, no deleterious expansion due to ASR or external sulphate occured. Expansion due to ASR was 0.0018% after 14 days of immersion in an alkali-rich environment, and no expansion was recorded regarding sulphate attack. However, SEM analysis reveals reactive products of ASR and sulphate attack, namely, ASR gel and ettringite, respectively, in UHPC specimens.

Experiment and mesoscopic modelling on the dynamic compressive behaviors of a new carbon fiber-reinforced cement-based composite

This paper presents an experimental and numerical study on the compressive behaviors of a new carbon fiber-reinforced cement-based composite (CFRCC) that is composed of magnesium oxysulfate cement, carbon fiber and some chemical admixtures. Parametric studies on the effects of carbon fiber content and strain rate on the compressive behaviors of CFRCC, are conducted using a series of quasi-static and dynamic compressive tests. The research item includes the failure morphology, stress-strain curve, dynamic increase factor (DIF), etc. Besides, a three-dimensional (3D) mesoscale modelling approach is proposed to simulate and analyze the mechanical responses and the failure mechanisms of CFRCC subjected to dynamic compressive loading, where the random dispersion of chopped fibers are realistically considered. The results indicate that the cracking and failure modes of CFRCC are significantly affected by the bridging effect of carbon fibers randomly dispersed in cement matrix. With the increase of fiber content, the dynamic peak stress and peak strain of CFRCC at similar strain rates show an increasing and decreasing trend, respectively. An evident strain-rate hardening effect could be found on the initial elastic modulus and the peak stress of CFRCC as well. While the relationship between the DIF of CFRCC and the logarithm of strain rate could be described using a quadratic function. Moreover, the mesoscale modelling approach has been validated by a good agreement between the numerical and tested results, demonstrating the feasibility of the developed mesoscale model in simulating and investigating the dynamic behaviors of CFRCC. All in all, the CFRCC has proven to be of great significance in resisting to impact loads, and more insights should be provided into its dynamic properties.

Research Progress on Durability of Cellulose Fiber-Reinforced Cement-Based Composites

The performance of cellulose fiber-reinforced cement-based composites (CFCCs) depends not only on the characteristics of the cement matrix and fibers but also on the bonding property of the matrix and fibers. The durability of cement-based composites including various properties such as impermeability, frost resistance, and carbonization resistance has an important impact on the long-term service life of the matrix structure. The presence of a large number of hydroxyl groups on the molecular chain of cellulose can promote the formation of intra- and intermolecular hydrogen bonds of cellulose. This special structure imparts the cellulose high hydrophilicity, which leads the cement hydration C-S-H gel to adhere to the surface of cellulosic fibers (CFs) and induce its growth. The cavity of CFs has good water absorption and can be used as an internal curing fiber for the continuous hydration of cement-based composites. But CFs in the Portland cement matrix tend to deteriorate under strong alkali conditions. This paper presents a review of the research on the durability of CFCCs. The methods and paths to improve the durability of CFCCs are summarized and analyzed from the perspectives of the internal curing of CFs, the deterioration of the performance of CFs in the matrix, and the use of many types of supplementary cementitious materials. Finally, the development and engineering application of CFCCs have been prospected.

Study of the fire and thermal behaviour of façade panels made of natural fibre-reinforced cement-based composites

The thermal and fire behaviour of calcium aluminate cement-based composites with a variable metakaolin content (from 0 to 40 wt% addition) reinforced with nonwoven flax fabrics has been examined. The fire behaviour was assessed using epiradiator and small-scale fire testing. The composites did not emit smoke or generate flames, nor did they produce spalling. Their integrity was maintained above 1000 °C. Samples having a higher metakaolin content revealed a delay in the temperature of the unexposed surface until reaching 760 °C. The effect of exposure to high temperatures (250 °C, 450 °C, and 950 °C) on bending behaviour was examined. The fibres were found to maintain their reinforcing capacity up to 250 °C, while the matrix maintained its performance up to 450 °C. The addition of metakaolin reduced conductivity and diffusivity. The results of the thermal and fire behaviour of the tested composites indicated that they may be suitable for façade panels for outdoor applications.

The propagation speed of multiple dynamic cracks in fiber-reinforced cement-based composites measured using DIC

The primary purpose of this work is to explore the propagation speed and spreading direction of multiple dynamic cracks in steel fiber-reinforced cement-based composites using Digital Image Correlation (DIC). Three-point bending beams with an off-centered notch were employed to facilitate the initiation of mixed-mode crack. Specifically, beams with different fiber contents, 0% , 0.4% and 0.8% in volume fraction, were manufactured. Tests were carried out at low loading-line displacement rates (2.2 μm/s and 22 mm/s) using a servo-hydraulic machine, under impact loading (1.77 m/s and 3.55 m/s) using a drop-weight impact device. A high-speed video camera was used to record the process of (multiple) crack propagation. Besides the shear crack started from the notch tip, the flexural cracks initiated from the central bottom surface were also formed in all beams except those with a fiber content of 60 kg/m3 (0.8% in volume ratio) impacted at 1.77 m/s. The flexural cracks propagated with a maximum speed of 1297 m/s, whereas the shear cracks reached up to 1149 m/s. Such high speeds of multiple-crack propagation, more than 50% of the Rayleigh wave speed, have been rarely measured in the lab. In addition, the evolution of simultaneous crack formation was recorded; the influence of both fiber content and loading rate is examined. Furthermore, all three types of material were previously characterized through independent tests, the flexural strength, the toughness indices as well as the residual strength factors are reported.

Strategic strengthening of the interfacial transition zone (ITZ) between microfiber and cement paste matrix with carbon nanofibers (CNFs)

The interfacial transition zone (ITZ) governs the mechanical properties and durability of fiber-reinforced cement-based composites. It has been reported that strategic strengthening of the ITZ by simple coating of carbon nanofibers (CNFs) on microfibers resulted in a 22% enhancement of the fiber/matrix bond. In the current study, ingenious methods were used to characterize such CNF-reinforced ITZ (CNF-ITZ). Results show that strategic application of CNFs greatly densified the ITZ with much reduced voids and defects. A distinctive hairy microstructure, resembling the setae on the toes of geckos, and less portlandite were found in the CNF-ITZ. The indentation hardness and indentation modulus were enhanced in both the radial and the tangential directions. The resulting CNF-reinforced ITZ is tougher and stronger with improved mechanical properties against deformation and cracking, which leads to enhanced fiber/matrix bond and elevated load transfer efficiency between fiber and matrix.

Experimental Investigation of Thin-Walled UHPFRCC Modular Barrier for Blast and Ballistic Protection

The static response of ballistic panels and also its resistance to blast and ballistic impact is investigated in the framework of this study. By connecting individual ballistic panels together, the protective barrier can be constructed. The protective barrier can be featured as a system with high mobility and versatility that is achieved by linking basic interlocking plate elements together. The resulting protective barrier can be shaped according to many possible scenarios in a wall with various possible opening angles and a small post with the tetragonal base or a larger post with the hexagonal ground plan. The material solution of the protective barrier benefits from the application of ultra-high-performance fibre-reinforced cement-based composites (UHPFRCC), which meets the requirements for enhanced resistance against extreme loads such as blast or impact. Besides, by using UHPFRCC, thin and slender design can be adopted, which is advantageous in many ways. Slender design results in a lower weight, allowing for easy manipulation and replacement. To verify the behavior of the panels, the proposed barrier was subjected to various loadings at different strain rates. The experimental campaign demonstrated that the protective barrier has a reasonable load-bearing capacity and also sufficient resistance against projectile impact and blast effects.

Effect of high temperature on morphologies of fibers and mechanical properties of multi-scale fiber reinforced cement-based composites

By experimental research on the steel- polyvinyl alcohol (PVA) fibers- calcium carbonate whisker (CW) multi scale fiber-reinforced cement-based composites (MSFRC) after exposure of temperatures up to 900 °C, the flexural, compressive strength, and microstructures of multi scale fibers were investigated in this paper. The incorporation of steel-PVA fibers-CW can effectively improve the flexural and compressive strength of mortar after elevated temperatures. Compared with normal concrete, hybrid fiber reactive powder concrete (RPC) and engineered cement-based composites (ECC), the MSFRC present better capacity of high temperature resistance. The flexural and compressive strength increase first and then decrease with the increasing temperature, and the critical temperatures are 200 °C and 400 °C respectively. Models for describing the relationship between strength, CW content and temperature are proposed. The good high temperature resistance of MSFRC relates to the hybrid effect of melt of PVA fiber, good heat conduction of steel, and the phase transformation from aragonite to calcite of CW. Comprehensive morphology observations by digital camera and optical microscope are simple and useful way to evaluate the changes of fibers and CW at high temperature. This research is very beneficial for the applications of MSFRC in construction project with fire risk.

High-throughput design of fiber reinforced cement-based composites using deep learning

As the combinatorial space of a composite is virtually infinite and cannot be explored completely, a deep-learning method was proposed for high-throughput fiber-reinforced cement-based composites (FRC) design. First, a deep hierarchy network was developed to measure the relationship between the experimental variables and the FRC properties. A gradient-based high-throughput method based on the deep hierarchy network was then proposed to design FRCs, which were expected to have one or more certain properties. At last, a fine-tuning method was employed to guarantee its transferability for all types of FRCs. The results showed that the proposed method was able to design cement-fiber-water-curing-aging systems for carbon fiber reinforced cement-based composites (CFRCs). The fine-tuning method could transfer the CFRC model to design other FRCs. Thus, the proposed method showed promise for releasing the composite material property optimization from labor-consuming and low-efficiency laboratory tests.

Effects of brass coating and nano-SiO2 coating on steel fiber–matrix interfacial properties of cement-based composite

This study focused on the effects of steel fiber coatings on the interfacial properties of a fiber-reinforced cement-based composite. The impact of a brass coating on the interface between the steel fibers and cement matrix was examined, and the improvement effects of a nano-SiO2 coating and nano-SiO2 powder on both the microstructure and interfacial bond properties were compared. A chemical simulation experiment was designed to analyze the brass coating state in a cement hydration environment. The backscattered electron image analysis (BSE-IA) method was used to conduct quantitative analyses of the calcium hydroxide (CH), porosity, and unhydrated cement (UHC) to investigate the microstructure of the fiber–matrix interfacial transition zone (ITZ). Pull-out tests were conducted to determine the interfacial bond performance, and scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for micro-observation and element analyses. The results indicated that because of the destruction of the coating structure and the aggregation of CH caused by the dezincification of the brass in a cement hydration environment, the brass coating did not improve (but weakened) the interfacial microstructure and bond performance. Adding the nano-SiO2 powder directly was a useful method for achieving microstructure densification and defect reduction in both the ITZ and bulk paste, while the nano-SiO2 coating provided a more targeted improvement in the fiber–matrix ITZ, particularly near the fibers, leading to a more effective enhancement of the bond performance.