Engineered Cementitious Composites Matrix Research Articles

Fracture mechanical properties and interfacial characteristics of engineered cementitious composites containing coarse aggregate

Engineered cementitious composites (ECC) have significantly high deformability, but their application in the field of engineered crack prevention is severely limited by their high shrinkage and high cost. To address this issue, a safer and more economical ECC was designed in this paper by adding coarse aggregate (CA) into the ECC matrix (i.e., ECC-CA). Then, experimental studies on the fracture properties of ECC-CA were carried out from both macroscopic and microscopic perspectives, by considering four CA mass contents and three CA particle sizes. The results show that ECC-CA maintains good mechanical properties and deformation capacity as ECC. Its crack mouth opening displacement corresponding to the largest particle size (13–17 mm) and the largest mass content (30 %) is equivalent to 47.8 % of that of ECC, which is about 40 times higher than that of conventional concrete. Further, the interfacial transition zone characteristics between each phase medium and matrix were analyzed in ECC-CA for the purpose of clarifying the crack initiation and evolution trends, elucidating the influence of CA on the fracture mechanism of ECC-CA (i.e., fiber cage effect) based on both macroscopic performance and microscopic characteristics.

Axial behavior of concrete cylinders retrofitted with a hybrid system of CFRP textile grid and engineered geopolymer composite

Fiber-reinforced polymer (FRP) textile grid-reinforced engineered cementitious composites (ECCs) are effective in strengthening concrete structures. Considering environmental interest, engineered geopolymer composites (EGCs) have been employed as an alternative to ECC. In this study, we present a retrofit scheme for CFRP textile grid-reinforced EGC matrix composites for concrete cylinders and compare the axial behavior of strengthened concrete cylinders with a conventional FRP-reinforced ECC strengthening system. Axial compressive specimens were tested for various parameters, including the number of FRP textiles, original concrete strength, and damage level of the original concrete cylinder. The results indicated that the strengthened concrete cylinders failed in a ductile manner owing to the progressive rupture of the CFRP textile grids. The CFRP-EGC strengthening layers improved the axial bearing capacity, stiffness, and ductility of the concrete cylinders. The axial bearing capacity increased by 89.4%–170.4 %; therefore, the contribution of enhanced confinement effect was 36.7–113.6 %. The confinement effect provided by the grids ranged from 0.805 to 1.958 MPa and played a major role in the CFRP-EGC strengthening layers. Comparatively, the CFRP grid utilization is more efficient in the EGC matrix than in the traditional ECC matrix. Moreover, the influence of the pre-damage on the behavior of the concrete cylinders was compensated for by the strengthening layers.

Elasticity and Load-Displacement Behavior of Engineered Cementitious Composites produced with Different Polymeric Fibers

Engineered Cementitious Composites (ECC) are ultra-ductile materials, and the fibers used provide superior flexibility and strain capacity. This study investigates the use of two different types of polymeric fibers, Polypropylene (PP) and Polyvinyl Alcohol (PVA), with volume fractions of 1 and 2%, and studies their effect on stress-strain relationships, load-displacement behavior, toughness, and elasticity of ECC mixes produced with two strength levels, 30 and 60 MPa. The results showed that mixtures with PVA fiber ionic coating had a better performance than those with PP fibers due to the chemical reaction between the PVA fibers and the ECC matrix. This performance was confirmed by Scanning Electronic Microscopy (SEM). For normal-strength concrete (30 MPa), the modulus of elasticity increased by 7.8 and 9.6% for mixes with PP and PVA fibers, respectively, while in high-strength mixes (60 MPa), it increased by 9.4 and 10.85%, respectively. Toughness increases with increasing matrix strength, which is associated with an increase in cement content and fiber fraction. This study also investigates the effect of incorporating a PVA solution in ECC mixes, which leads to an increase in yield stress. This behavior was observed in the stress-strain behavior of 60 MPa mixes with 2% fibers which were compared to 30 MPa mixes with 1% fibers.

Experimental study on bond durability of GFRP bar/engineered cementitious composite exposed to freeze-thaw environments

Glass fiber reinforced polymer (GFRP) bars and engineered cementitious composites (ECC) present better structural performance as compared to conventional concrete with reinforcing steel bars. However, the bond behavior of the GFRP bar to ECC matrix under freeze-thaw (FT) cycles in cold climates remains underexplored. Therefore, this study aims to investigate the bond durability of GFRP bars and ECC under FT conditions. An experiment was conducted with 33 pullout specimens, categorized according to concrete types (normal concrete and ECC), compressive strengths (30 MPa and 50 MPa) and the number of FT cycles (0, 100, 150, and 200 cycles). Assessment parameters included surface degradation, failure modes, mean bond strength, weight loss, and the relative dynamic modulus of elasticity. Results indicated ECC specimens exhibited greater durability compared to normal concrete specimens, with no significant improvement in durability observed with increased compressive strength. Specifically, the mean bond strengths of N30 (30 MPa normal concrete) specimens, E30 (30 MPa ECC) specimens, and E50 (50 MPa ECC) specimens decreased by 88.41 %, 38.86 %, and 58.21 % after 150 FT cycles, respectively. Failure modes correlated strongly with concrete type and the number of FT cycles. SEM and composition analyses revealed the effects of FT cycles on the concrete matrix, the bond interface, and the GFRP bars. The ascending branches in the bond stress-slip curves of specimens subjected to FT cycles were effectively modeled using Malvar's model. Based on the declining relative dynamic modulus of elasticity and the correlation between laboratory and natural FT cycles, the estimated fatigue lives for GFRP bar/E30 specimens subjected to 250 FT cycles are 35.7, 71.4, and 46.2 years in Beijing, Detroit, and Vancouver, respectively. This research provides insights on GFRP bar/ECC's longevity in practical engineering contexts.

Optimisation of the Mechanical Properties and Mix Proportion of Multiscale-Fibre-Reinforced Engineered Cementitious Composites.

Engineered cementitious composites (ECCs) are cement-based composite materials with strain-hardening and multiple-cracking characteristics. ECCs have multiscale defects, including nanoscale hydrated silicate gels, micron-scale capillary pores, and millimetre-scale cracks. By using millimetre-scale polyethylene (PE) fibres, microscale calcium carbonate whiskers (CWs), and nanoscale carbon nanotubes (CNTs) as exo-doped fibres, a multiscale enhancement system was formed, and the effects of multiscale fibres on the mechanical properties of ECCs were tested. The Box-Behnken experimental design method, which is a response surface methodology, was used to construct a quadratic polynomial regression equation to optimise ECC design and provide an optimisation of ECC mix proportions. The results of this study showed that a multiscale reinforcement system consisting of PE fibres, CWs, and CNTs enhanced the mechanical properties of ECCs. CWs had the greatest effect on the compressive strengths of highly ductile-fibre-reinforced cementitious composites, followed by CNTs and PE fibres. PE fibres had the greatest effect on the flexural and tensile strengths of high-ductility fibre-reinforced cementitious composites, followed by CWs and CNTs. The final optimisation results showed that when the ECC matrix was doped with 1.55% PE fibres, 2.17% CWs, and 0.154% CNTs, the compressive strength, flexural strength, and tensile strength of the matrix were optimal.

The Effect of Fiber End on the Bonding Mechanical Properties between SMA Fibers and ECC Matrix

In order to investigate the effect of fiber end on the bonding mechanical properties between shape memory alloy (SMA) fibers and Engineered Cementitious Composites (ECC), this study designed and fabricated five groups of specimens with variations in SMA fiber end shape, diameter and depth-to-diameter ratio. Direct tensile tests were conducted on these specimens under displacement control. The failure modes, stress–strain curves and various performance indicators were analyzed to evaluate the bonding mechanical properties and the effects of different factors. The results revealed that for straight-end SMA fibers, increasing the diameter and depth-to-diameter ratio both led to a decrease in bonding strength. On the other hand, the N-shaped end provided sufficient anchorage force for SMA fibers, resulting in a maximum pull-out stress of 926.3 MPa and a fiber strength utilization of over 78%. Increasing the fiber diameter enhanced the maximum pull-out stress and maximum anchorage stress for N-shaped-end SMA fibers but reduced the fiber strength utilization. These research findings provide a solid theoretical basis and data support for achieving a synergistic effect between SMA fibers and the ECC matrix.

Durability Behaviours of Engineered Cementitious Composites Blended with Carbon Nanotubes against Sulphate and Acid Attacks by Applying RSM Modelling and Optimization

Chemical deterioration, including sulphate and acid attacks, is a major issue affecting the long-term durability of engineered cementitious composite (ECC) constructions that contact water from various sources, including groundwater, seawater, sewer water, and drinking water. This research enhances ECCs’ strength and resilience against chemical attack by combining cementitious composites with multiwalled carbon nanotubes (CNTs) and polyvinyl alcohol (PVA) fibre volume fractions using multiobjective optimization. The central composite design (CCD) of RSM was applied to generate thirteen mixes of different potential combinations of factors (multiwalled CNTs: 0.05% to 0.08%, PVA: 1–2%) and eight outcome responses were studied, although eight response models—six quadratic and two linear—were successfully designed and assessed using analysis of variance. The coefficients associated with R2 for all the models were exceptionally high, with values varying from 84 to 99 percent. The multiobjective optimization predicted the best outcomes and developed optimal values for both variables (CNTs: 0.05% and PVA: 1%). The results showed that, at 0.05% of CNTs in ECCs, an ultimate improvement of 23% in compressive strength was seen. Additionally, when CNTs are used to grow in the ECC matrix, the expansion owing to sulphate resistance and length change due to acid attack are both reduced. In addition, when the percentage of CNTs increases in ECCs, the weight loss and pH value owing to acid attack, as well as the rate of chloride permeability test results, are reduced. Furthermore, CNTs and PVA fibres with 0.05% and 1–1.5% concentrations offer optimal construction sector outcomes.

Influence of Fiber Orientation on the Water and Ions Transportation of Engineered Cementitious Composite (ECC).

An engineered cementitious composite (ECC) belongs to a type of high-performance fiber-reinforced materials. Fiber alignment causes the anisotropy of such materials. Herein, the influence of the fiber orientation on water and ion penetration into an ECC was studied. Fiber alignment was achieved using an extrusion approach. Water absorption, sorptivity, chloride penetration resistance, sulfate attack resistance, and freezing-thawing resistance of specimens with fiber aligned horizontally (AH), vertically (AV), and randomly (R), corresponding to the direction of the exposure surface that was studied. The results showed that fibers oriented perpendicular to the water path delayed water migration into the ECC matrix. The sorptivity was significantly affected by the fiber direction. The sorptivity of the AH specimens was 35% and 13% lower than that of the AV and R specimens, respectively. After 180 days of exposure, the chloride penetration depth of the AH specimens was 5.7 mm, which is 13.6% and 20.8% lower than that of the AV and R specimens, respectively. The sulfate ingress profile indicates that the fiber-matrix interface oriented perpendicular to the penetration path can effectively delay sulfate migration. The fiber orientation also influences the compressive strength gain under immersion conditions (Na2SO4 solution, Na2SO4 + NaCl solution, and water). Compared with the AH and R specimens, the AV specimens are more sensitive to the immersion condition. In contrast, the fiber orientation has no significant effect on ECC specimens under freeze-thaw cycles. These findings indicate that controlling the fiber alignment and orientation in an ECC can improve its durability under certain exposure conditions.

Repair of fire-damaged RC square columns with CFRP textile-reinforced ECC matrix

Fiber-reinforced polymer (FRP) textile reinforced engineered cementitious composite (ECC) matrix (TRE for short) is a newly developed composite system with great potential for the strengthening and life extension of damaged reinforced concrete (RC) columns after fire exposure. It combines the advantages of the lightweight and high strength of FRP textile and the ultra-high ductility of ECC material. However, there is a lack of research on the use of the TRE system to strengthen fire-damaged RC columns. This paper presents an experimental study on the axial compressive behavior of fire-damaged square RC columns strengthened with the TRE system. A total of 13 specimens were prepared and tested under axial compression. The test variables included the fire-exposure time (2 h or 3 h) used to produce the initial pre-damage of RC columns, the type of cementitious matrix (ECC or mortar), the number of TRE layers (2 layers or 3 layers), and the thickness of the concrete cover (20 mm or 40 mm). The failure modes, load capacity, secant stiffness, ultimate displacement, load–displacement curves of the specimens and the hoop tensile strains in the outermost layer of the CFRP textiles were investigated and discussed. The typical failure mode of the strengthened specimens was characterized by tensile rupture of the fiber rovings bridging the main crack in the strengthening jacket. The results showed that the use of the TRE system could significantly increase the load capacity, secant stiffness and ultimate displacement of fire-damaged RC columns. Depending on the design parameters, the enhancement percentages in the load capacity varied between 18% and 126%.

Axial behavior of pre-damaged RC columns strengthened with CFRP textile grid-reinforced ECC matrix composites

In this study, a high-ductility engineered cementitious composite (ECC) augmented with a high-strength carbon fiber-reinforced polymer (CFRP) grid was newly fabricated to strengthen reinforced concrete (RC) columns with pre-damage. Twenty specimens, including 4 reference specimens and 16 strengthened columns, were prepared. After the pre-application of the predicted loads to produce the designated damage levels, the damaged columns were strengthened with FRP textile-reinforced ECC restraints. The main test parameters included the pre-damage level and the number of CFRP grid layers. The experimental results indicate that the reinforced specimens exhibited satisfactory strengthening, even when the pre-damage level was severe. The ultimate load capacity and ductility increased by 37.7%–72.0% and 21.2%–140.6%, respectively, compared with the corresponding unreinforced reference specimens. However, both the ultimate compressive strength and ductility of the reinforced columns decreased with increasing pre-damage level. Accordingly, a strength prediction model was developed to address the adverse effects of the pre-damage and restraint contributions of the FRP grid, ECC, and hoop reinforcement. The proposed model agrees well with the test results.

Bonding Mechanical Properties between SMA Fiber and ECC Matrix under Direct Pullout Loads.

SMAF-ECC material composed of shape memory alloy fiber (SMAF) and engineered cementitious composite (ECC) has good bending and tensile properties, as well as good crack self-healing ability, energy consumption, and self-centering ability. The bond behavior between fiber and matrix is crucial to the effective utilization of the superelasticity of SMAF. The experimental study considered three variables: SMA fiber diameter, fiber end shape, and bond length. The pullout stress-strain curve of SMAF was obtained, and the maximum pullout stress, maximum bond stress, and fiber utilization rate were analyzed. Compared with the straight end and the hook end, the maximum pullout stress of the specimen using the knotted end SMAF is above 900 MPa, the fiber undergoes martensitic transformation, and the fiber utilization rate is above 80%, indicating that the setting of the knotted end can give full play to the superelasticity of the SMAF. Within the effective bond length range, increasing the bond length can increase the maximum anchorage force of the knotted end SMAF. Increasing the fiber diameter can increase the maximum pullout stress and maximum anchoring force of the knotted end SMAF but reduce the utilization rate of SMA fiber. This study provides a reliable theoretical basis for the bonding properties between SMAF and ECC.

High-strength engineered cementitious composites with nanosilica incorporated: Mechanical performance and autogenous self-healing behavior

It is highly desirable to achieve better self-healing performance of high-strength engineered cementitious composite (ECC) incorporating hydrophobic polyethylene (PE) fibers. This work demonstrated that admixing nanosilica was able to make the ECC matrix denser and strengthen the interfacial bond between PE fiber and matrix. The nano-modified mixtures achieved enhanced mechanical performances, narrowed the crack width and facilitated autogenous self-healing of PE-ECC. For instance, at 28 days, admixing nanosilica at 1 wt% improved the tensile strength, first-cracking strength, and strain capacity of M1 series ECC by 24.5%, 23.4%, and 58.1%, which reached 9.97 MPa, 7.03 MPa and 5.17%, respectively. The incorporation of 1 wt% NS also reduced the average crack width of PE-ECC by 59.5% and 59.4%, which reached 58.1 μm and 23.3 μm, for the M1 and M2 series, respectively. The narrower crack widths facilitated autogenous self-healing of PE-ECC specimens subjected to 30 wet-dry cycles, where particle-shaped product (mainly calcite) and dense product (mainly C–S–H gel) formed on the M1 and M2 series PE-ECC, respectively. It is intriguing that the high-volume fly ash PE-ECC (M2-1%) achieved the compressive strength of 80.7 MPa and 97.9 MPa at 28 days and 90 days, respectively. This environmentally sustainable mixture also achieved the first-cracking strength, tensile strength and strain capacity of 3.98 MPa, 7.78 MPa, and 5.28%, respectively, at 28 days of age.

Optimization of matrix viscosity improves polypropylene fiber dispersion and properties of engineered cementitious composites

• PP fiber dispersion can be improved by tailoring ECC matrix viscosity using VMA. • At optimal state, PP-ECC attains 7 % tensile strain and 3.5 MPa tensile strength. • Adding VMA beyond optimal state lowers ECC’s tensile strength and ductility. Engineered cementitious composites (ECC) is a durable cementitious material with high tensile ductility and strain-hardening characteristics. Although considered as a cost-effective fiber for ECC, polypropylene (PP) fiber is reportedly difficult to disperse in mortar matrix due to its high aspect ratio and hydrophobicity. In this study, the matrix viscosity of a low-carbon ECC based on limestone calcined clay cement was tailored as a variable to improve PP fiber dispersion under a pre-determined mixing protocol. The effect of matrix viscosity on the composite fresh and hardened properties was investigated experimentally. Results suggested an optimal range of matrix viscosity (10.3–11.5 Pa‧s) favors the composite tensile strength and strain capacity at 28 days. At the optimal state with a 0.1 % viscosity modifying admixture (VMA)-to-binder mass ratio, PP-ECC achieved 7.0 % tensile strain capacity and 3.5 MPa ultimate tensile strength. When matrix viscosity falls outside the desired range, both ultimate tensile strength and strain capacity were diminished. By tailoring the VMA dosage, the matrix viscosity can be adjusted for desired fiber dispersion, workability, and mechanical properties. The findings of this study provide a technical reference for the practical design and application of PP-ECC.

Enhancing long-term tensile performance of Engineered Cementitious Composites (ECC) using sustainable artificial geopolymer aggregates

Artificial geopolymer aggregate is an emerging technology in the field of solid waste recycling, aiming to ease the exploitation of natural aggregates as well as reduce the environmental burden of industrial/urban/agricultural waste and by-product accumulations. In this study, geopolymer aggregates (GPA) were strategically utilized to enhance long-term tensile performance and sustainability of high-strength Engineered Cementitious Composites (ECC). Accelerated aging test was conducted to evaluate the long-term performance of GPA-ECC, with the conventional fine silica sand ECC (FSS-ECC) as the control group. It was found that after accelerated aging (i.e., to simulate long-term curing condition), the compressive and tensile strengths of both GPA-ECC and FSS-ECC increased. In addition, owing to the flaw effect of GPA, the long-term tensile ductility of GPA-ECC was maintained, while that of FSS-ECC decreased significantly. Compared with FSS-ECC, GPA-ECC showed better multiple cracking behavior, higher strain energy density, and finer crack width under both short- and long-term conditions. Finally, a cost analysis of ECC matrix was conducted to exhibit the cost-efficiency and sustainability of GPA-ECC. This study provides a sustainable approach for enhancing the long-term tensile performance of high-strength ECC based on artificial aggregates.

Mechanical Behavior of Shape Memory Alloy Fibers Embedded in Engineered Cementitious Composite Matrix under Cyclic Pullout Loads.

The incorporation of superelastic shape memory alloy (SMA) fibers into engineered cementitious composite (ECC) materials can provide high seismic energy dissipation and deformation self-centering capabilities for ECC materials. Whether the SMA fibers can be sufficiently bonded or anchored in the ECC matrix and whether the mechanical properties of the SMA fibers in the ECC matrix can be effectively utilized are the key scientific issues that urgently need to be studied. In order to study the mechanical behavior of SMA fiber embedded in ECC matrix, four groups of semi-dog-bone pullout specimens were fabricated, and the cyclic pullout tests were conducted in this paper. The pullout stress, displacement, and self-centering capability were analyzed, and different influencing factors were discussed. The results show that the knotted ends can provide sufficient anchorage force for SMA fibers, and the maximum pullout stress of SMA fiber can reach 1100 MPa, thus the superelasticity can be effectively stimulated. The SMA fibers show excellent self-centering capability in the test. The minimum residual deformation in the test is only 0.29 mm, and the maximum self-centering ratio can reach 0.93. Increasing bond length can increase the ultimate strain of SMA fibers with knotted ends, but reduce the maximum pullout stress. Increasing fiber diameter can increase both the ultimate strain and the maximum stress of knotted end SMA fibers. While neither bond length nor fiber diameter has significant effect on the self-centering ratio. This paper provides a theoretical basis for further study of the combination of SMA fibers and ECC materials.

Effect of low temperature and moisture on bond properties of PVA fibres and engineered cementitious composite matrix

The chemical debonding energy, initial interfacial frictional bond strength and slip-hardening coefficient between polyvinyl alcohol (PVA) fibres and an engineered cementitious composite (ECC) matrix were obtained by means of single PVA fibre pull-out tests. The effect of three moisture states (fully saturated, semi-saturated and fully dry) on the bonding properties between the PVA fibre and ECC matrix at three target temperatures (25°C, 0°C and −20°C) was investigated. It was found that, at 25°C, the bonding properties decreased with an increase in moisture content. At 0°C and −20°C, the bonding properties increased with an increase in moisture content. At −20°C in the fully saturated state, the bonding load was too large to cause fibre rupture. The bonding properties were found to increase with decreasing temperature in the fully saturated and semi-saturated states and decrease with decreasing temperature in the fully dry state. This study of the effect of low temperature and moisture state on the bonding properties between PVA fibres and ECCs provides theoretical support for how to ensure good ductility when ECCs are in service at low temperature.

Multiscale Investigation on the Performance of Engineered Cementitious Composites Incorporating PE Fiber and Limstone Calcined Clay Cement (LC3).

Limestone calcined clay cement (LC3) is successfully used to fabricate engineered cementitious composites (ECC) exhibiting tensile strength σtu of 9.55 ± 0.59 MPa or tensile strain capacity εtu of 8.53 ± 0.30%. The high tensile strength of the composites is closely related to the improvement of fiber/matrix interfacial bond strength, and the high ductility is attributed to the enhancement of fiber dispersion homogeneity. For the case of ECC incorporating 50% LC3, the reduction of initial cracking stress σtc that favors the growth of the crack in a controlled manner also contributes to the improvement of strain hardening behavior. The composition analysis indicates that carboaluminates and additional hydration products including C-(A)-S-H and ettringite are generated, which contributes to the densification of the microstructure of the ECC matrix. The pore structure is thus remarkably refined. Besides, when ordinary Portland cement (OPC) is partly replaced by LC3, the consumed energy and equivalent CO2 emission decrease, especially the equivalent CO2 emission with the reduction ratio attaining 40.31%. It is found that ECC using 35% LC3 exhibits the highest mechanical resistance and ECC incorporating 50% LC3 shows the highest ductility from the environmental point of view.

Fatigue performance of corrosion-damaged beams strengthened with FRP grid-reinforced ECC matrix composites

An investigation on the flexural fatigue behavior of corrosion-damaged reinforced concrete (RC) beams that were strengthened with a fiber-reinforced polymer (FRP) grid-reinforced engineered cementitious composite (ECC) matrix is presented in this paper. The concrete cover, which was damaged by the corrosion of the tensile steel bars, was chipped away and reinstated with an ECC layer that was embedded with an FRP grid. A total of 12 beams were constructed, and 11 of them were subjected to cyclic fatigue loading. The test results indicated that the final failure mode of the strengthened beams was still dominated by the brittle fracture of the tensile steel reinforcements. The fatigue life of the beams increased significantly with increasing strengthening amounts of the FRP grid but decreased with the corrosion ratio and the upper limit fatigue load level. At a sufficient strengthening amount, the fatigue life of strengthened beams could be restored to that of the original uncorroded beams. By regression analysis of the stress range–fatigue life (S–N) curve, a prediction formula for fatigue life was derived with a satisfactory correlation coefficient. In addition, the tested midspan deflections and the results that were calculated using available empirical models or theoretical calculation approaches were compared and evaluated.

Research on the interface bonding performance between FRCM and masonry under salt erosion environment

Fabric reinforced cementitious matrix (FRCM) has a good application prospect in the field of masonry structure reinforcement. The interface bonding performance between FRCM and masonry is one of the important indicators to evaluate the reinforcement effect of FRCM. There are many studies on the interface bonding performance between FRCM and masonry under normal environment, but few on the interface bonding performance in salt erosion environment, which need to carry out further research. In this paper, based on the single shear test and digital image correlation technology (DIC), the influence of the interface bonding length on the interface bonding performance between FRCM and masonry in a conventional environment was studied and the effective bonding length was determined; the interface bonding performance between FRCM and masonry in the salt erosion environment was studied; the main research factors are the number of dry-wet cycles, the concentration of the salt solution and the types of matrix. Especially, in terms of matrix type, the effects of engineered cementitious composite (ECC) and mortar as FRCM matrix on interface bonding performance are considered. The results show that FRCM, ECC and mortar matrix do not hinder the transportation of salt and cause accumulation at the interface between composite materials and masonry; the slip failure of the textile in the matrix occurs mainly, and the fiber bundles in the matrix are corroded to a certain extent; the interface bonding performance of specimens in the salt corrosion environment using FRCM matrix will reduce, while the specimens using ECC and mortar matrix will improve.

Experimental Investigation on Dynamic Tensile Behaviors of Engineered Cementitious Composites Reinforced with Steel Grid and Fibers

Engineered cementitious composites (ECC) used as runway pavement material may suffer different strain rate loads such as aircraft taxiing, earthquakes, crash impacts, or blasts. In this paper, the dynamic tensile behaviors of the steel grid-polyvinyl alcohol (PVA) fiber and KEVLAR fiber-reinforced ECC were investigated by dynamic tensile tests at medium strain rates. The mixture was designed with different volume fractions of fibers and layer numbers of steel grids to explore the reinforcement effectiveness on the dynamic performance of the ECC. The volume fractions of these two types of fibers were 0%, 0.5%, 1%, 1.5%, and 2% of the ECC matrix, respectively. The layer numbers of the steel grid were 0, 1, and 2. The dynamic tensile behaviors of the PVA fiber and the KEVLAR fiber-reinforced ECC were also compared. The experimental results indicate that under dynamic tensile loads, the PVA-ECC reveals a ductile and multi-cracking failure behavior, and the KEVLAR-ECC displays a brittle failure behavior. The addition of the PVA fiber and the KEVLAR fiber can improve the tensile peak stress of the ECC matrix. For the specimens A0.5, A1, A1.5, and A2.0, the peak stress increases by 84.3%, 149.4%, 209.6%, and 237.3%, respectively, compared to the matrix specimen. For the specimens K0.5, K1, K1.5, and K2, the peak stress increases by about 72.3%, 147.0%, 195.2%, and 263.9%, respectively, compared to the matrix specimen. The optimum fiber volume content is 1.5% for the PVA-ECC and the KEVLAR-ECC. The KEVLAR-ECC can supply a higher tensile strength than the PVA-ECC, but the PVA-ECC reveals more prominent deformation capacity and energy dissipation performance than the KEVLAR-ECC. Embedding steel grid can improve the tensile peak stress and the energy dissipation of the ECC matrix. For the strain rate of 10−3 s−1, the peak stress of the A0.5S1 and A0.5S2 specimens increases by about 49.1% and 105.7% compared to the A0.5 specimen, and the peak stress of the K0.5S1 and K0.5S2 specimens increases by about 61.5% and 95.8%, respectively, compared to the K0.5 specimen.