Hybrid Fiber Engineered Cementitious Composites Research Articles

3D printing hybrid-fiber reinforced engineered cementitious composites (3DP-HECC): Feasibility in long-open-time applications

Hybridization of multi-scale and multi-functional fibers to generate Hybrid-fiber Engineered Cementitious Composites (HECC) offers a promising approach for enhancing ECC in 3D printing (3DP), addressing limitations such as restricted build-up height and operation time. This study strategically combined polyethylene (PE) fiber (1.0 %), steel fiber (0.5 %) and cellulose filaments (CF) at various dosages (0–0.25 %) to investigate the evolution of rheological behavior over different time intervals (0–60 min with 15 min intervals) and optimize the printability of 3DP-HECC with long-open-time. Incorporating of CF or steel fiber enhanced static yield stress, dynamic yield stress and plastic viscosity, particularly benefiting buildability with steel fiber inclusion. Moreover, CF integration effectively moderated the growth rates of static yield stress and dynamic yield stress while maintaining thixotropic index, mitigating extrusion defects and extending operation time to 60 min for structure-level printing. Conversely, steel fiber exhibited contrasting behavior. By integrating the evolution of time-dependent rheological parameters and practical printing observations, an optimum CF dosage of 0.20 % was identified for high-quality 3DP with superior build-up layers. Finally, a fiber hybridization strategy was suggested to optimize the printability of 3DP-HECC, providing theoretical guidance for implementing high-quality applications with extended operation time.

Mechanical performances and micro-level properties of basalt and PVA fiber reinforced engineered cementitious composite after high temperatures exposure

After high-temperature exposure, synthetic fibers with low melt temperature tend to exert negative influence on mechanical performance of engineered cementitious composite (ECC) and its elements. Basalt and PVA fiber reinforced hybrid-fiber ECC (basalt/PVA HF-ECC) is a promising way to address such drawback, due to the low cost, sustainability and high-temperature stability of basalt fiber. However, relevant researches only focus on fiber replacement and are still on primary stage, meanwhile their results show further performance improvements are required. In present study, basalt/PVA HF-ECC with superimposed basalt fiber content is proposed. Mechanical and micro-level related tests were conducted to investigate the effect of superimposed basalt fiber content after high-temperature exposure. Compressive test results showed basalt fiber could increase compressive strength at elevated temperatures. The optimal basalt fiber volume fraction was 0.8%, whereby compressive strength was higher than that of control PVA-ECC by 62.05%, 55.45% and 37.24% at 400 °C, 600 °C, and 800 °C. Tensile test results exhibited that stress-strain curves of basalt/PVA HF-ECC showed brittle behavior when PVA fiber melted at elevated temperatures, and first cracking strength also showed continuous increase as basalt fiber content increased. The optimal basalt fiber volume fraction was 1.2%, whereby first cracking strength was higher than that of control PVA-ECC by 48.43%, 42.38%, 36.30% and 50.41% at 23 °C, 400 °C, 600 °C, and 800 °C. Mercury intrusion porosimetry (MIP) tests showed basalt fiber reduced average pore diameter at elevated temperatures, while hardly exerted influence on porosity. At 600 °C and 800 °C, 0.8% and 1.2% content of basalt fiber decreased average pore diameter of control PVA-ECC by 13%–37%, and deduced peak heights of pore size distribution curves. SEM observation discussed and proved the basalt fiber contribution to strength improvement after high-temperature exposure. Rupture space related analysis was also used to discuss the tensile strain capacity deterioration at elevated temperatures. The present study investigates high-temperature mechanical performances and micro-level properties of basalt/PVA HF-ECC with superimposed basalt fiber content, thus promotes development of heat-resistant ECC with much reliable performances.

Synergy effect of hybrid steel-polyvinyl alcohol fibers in engineered cementitious composites: Fiber distribution and mechanical performance

The fiber distribution is a crucial factor governing the superb strain-hardening and multiple cracking behavior of engineered cementitious composites (ECC). However, the desired uniform distribution of fibers is challenging in ECC with large amounts of binders and fibers, especially for hybrid fiber system. In the present study, we employed image analysis to investigate the fiber distribution characteristics in hybrid steel-polyvinyl alcohol (PVA) fiber ECC and its influence on the mechanical performance. Special attention was paid to the impact of additional steel fiber content and its size. The results show that the dispersion coefficient of PVA fibers in hybrid fiber system was at most 50% higher than that of mono fiber system. Fiber hybridization rendered more fibers distributed in smaller angles of 0°–40°, which helped to enhance the fiber bridging capacity. The addition of steel fibers significantly improved the flexural properties of ECC, with maximized strength at steel fiber content of 1.0% and maximized deformability at 0.6% dosage. The incorporation of steel fibers greatly enhanced the crack control ability of hybrid fiber ECC. The average crack width was reduced to 36.1 μm when the volume fraction of steel fiber gone to 1.0%. Furthermore, larger sized steel fibers played a more pronounced role in improving the fiber dispersion, fiber orientation and mechanical properties than that with smaller size. Synergy effect of hybrid steel-PVA fiber on fiber distribution and mechanical properties was revealed. The findings are expected to contribute to the blending ratio design of hybrid fibers and the selection of fiber size in preparing ECC. And the obtained robust ECC can provide strong support for performance enhancement and maintenance of building engineering.

Crack morphology tailoring and permeability prediction of polyvinyl alcohol -steel hybrid fiber engineered cementitious composites

The intrinsic tensile strain-hardening properties of engineered cementitious composites (ECC) determines its multiple cracking and crack control characteristics. The relatively low permeability of cracked ECC is of special significance for more efficient use of cementitious materials, which contributes to the mitigation of carbon emissions. The crack morphology of ECC plays an important role in tailoring the permeability of cracked ECC, as well as the durability of structures made or strengthened by ECC. In the present study, the characterization of crack morphology is conducted by digital image processing (DIP) method, which mainly involves the grey processing, background elimination, binarization and pixel column labeling of digital image. Crack morphologies of ECC are modified by blending PVA fibers with a volume content of 2.0% and steel fibers with volume contents of 0.0%, 0.3%, and 0.6%. A permeability model for cracked hybrid fiber ECC (HyECC) has been proposed based on the Weibull distribution of crack width and crack number. The results indicate that the addition of steel fibers in ECC optimizes the crack morphology, yielding more tortuous and finer cracks. The average crack width decreases from 67.3-115.8 μm in mono fiber system to 46.0-67.6 μm in hybrid system with steel fiber content of 0.6%. The average crack width and crack number increase with the tensile strain, while the average crack spacing behaves in an opposite manner. The evolution of crack morphology could be described by Weibull distribution as a function of tensile strain. The permeability model derived from the crack morphology and the modified Hagen-Poiseuille law well predicts the permeability of cracked HyECC. It reveals that the addition of steel fiber enhances the impermeability of cracked HyECC, especially at large strains. The flow rate at tensile strain of 1.5% is reduced from 7.75 × 10−7 m3/s to 4.82 × 10−9 m3/s as the steel fiber content increases from 0.0% to 0.6%. The findings are expected to support the material-efficient design, crack control and durability improvement of ECC in structural applications.

Mechanical performance of basalt and PVA fiber reinforced hybrid-fiber engineered cementitious composite with superimposed basalt fiber content

• PVA/basalt HF-ECC with multiple cracking behavior was achieved by superimposition of basalt fiber. • Increasing basalt fiber superimposing content improved overall strength of PVA/basalt HF-ECC. • The advised optimal superimposing volume fraction of basalt fiber is 0.8%. • The effect of basalt fiber on tensile strain capacity was analyzed by micro-mechanical analysis. The large-scale application and popularity of engineered cementitious composites (ECC) is hindered by the relatively high price and increased CO 2 footprint of PVA fiber. PVA and basalt fiber reinforced hybrid-fiber ECC (PVA/basalt HF-ECC) is a promising way to deal with such drawbacks. Hence, this study focused on the influence of basalt fiber superimposing content on the properties of PVA/basalt HF-ECC. Compressive tests indicated basalt fiber could elevate compressive strength and its corresponding strain, the obtained maximum values were 46.37 MPa and 0.47 % as basalt fiber content increased up to 1.2 %. Tensile tests showed that first cracking strength and ultimate tensile strength increased up to 6.62 MPa and 7.85 MPa as basalt fiber content increased up to 1.2 %. Although tensile strain capacity continuously decreased to 0.62 %, all specimens showed multiple cracking behavior due to the superimposed performances derived from PVA and Basalt fibers. Mercury intrusion porosimetry test showed volume fraction of large capillary pore that influences strength decreased up to 31.65 % when basalt fiber content increased to 1.2 %. Based on test results, predicting equations of mechanical properties were proposed by curve fitting and showed good agreement with test results. Micro-mechanical analysis was conducted based on modified crack bridging model, and its results further interpreted change mechanism of tensile strain capacity. This study explores the feasibility of developing PVA/basalt HF-ECC by basalt fiber superimposition and facilitates the popularity of ECC.

Optimal design of a low-cost high-performance hybrid fiber engineered cementitious composites

Engineered cementitious composites (ECC) is a fiber reinforced high-performance cementitious material with an ultra-high tensile strain capacity (above 3%) and excellent durability. However, such excellent strain capacity far exceeds some engineering requirements and is usually not fully utilized. Meanwhile, its high cost limits it application only in local engineering. In this study, a low-cost high-performance hybrid fiber ECC (HF-ECC) with both polypropylene (PP) fiber and polyethylene (PE) fiber was manufactured. Both macroscopic and microscopic mechanism analyses were conducted to investigate the effect of fiber characteristics and proportions on the performance of HF-ECC. The results show that the ultimate tensile strain of HF-ECC can reach 5% even the volume fraction of PP and PE fibers account for 1%, respectively. Its fiber cost is 43.8% lower than that of pure PE-ECC, which reduces the corresponding total cost by 27.5%. This paper presents an in-depth investigation of the characteristics of HF-ECC, direct tension, compression, fiber-bridging, pore structure, fiber distribution, and fiber dispersion. Finally, the optimal design of the HF-ECC is conducted through pseudo-strain-hardening indices and multi-criteria evaluation.

Bond behavior and anchorage length of deformed bars in steel-polyethylene hybrid fiber engineered cementitious composites

Steel-polyethylene hybrid fiber engineered cementitious composites (HECC) featuring relatively high tensile strength and ductility, high elastic modulus, and high temperature resistance, making it an ideal alternative material under severe loading conditions. To understand the bond behavior between the HECC and rebar, direct pullout tests were conducted to systematically investigate the effects of rebar diameter d, anchorage length la, and cover thickness c on the bond performance. The experimental results indicate that the variation of bond strength with d is not apparent; la affects negatively while c influences positively on the average bond strength; and the critical c for HECC is about 4d. Additionally, the bond strength of HECC specimen is obviously higher than that of ECC and stirrups-confined concrete due to the crack-bridging effect of hybrid fibers at different scales. As noted, the ductility of HECC specimens is comparable with that of stirrups-confined concrete specimens, indicating that stirrup can be partially replaced when HECC is used which can simplify construction. Then, a calculation equation for the average bond strength of HECC is proposed, and the critical anchorage length of the rebar embedded in HECC is about 40% less than that embedded in ECC. Lastly, the design anchorage length of the rebar embedded in HECC is suggested based on a reliability analysis which is much smaller compared with the minimum embedment length of rebar in concrete predicted by the existing standards, providing a useful reference for reinforced HECC structural design.

Damage assessment of functionally graded reinforced concrete beams using hybrid fiber engineered cementitious composites

This paper describes an experimental investigation on functionally graded reinforced concrete (FGRC) beams using hybrid fiber engineered cementitious composites (HYFECC) and the main aim of this present paper is to examine the dynamic characteristics and damage evaluation of undamaged and damaged FGRC beams under free-free constraints. In this experimental work, reinforced concrete beams have been cast with HYFECC functionally graded materials in three different layers of 25 mm thickness each in the tension zone. Damage of FGRC beams was obtained by cracking of concrete for one of the beams in each set under four-point bending tests with different percentage variation of damage levels as 50%, 70% and 90% of maximum ultimate load. And the main dynamic characteristics such as damping, fundamental natural frequencies and mode shapes at each and every damage level have been assessed by means of non-destructive technique (NDT) with hammer excitation. The natural frequency and damping values obtained through dynamic tests for FGRC beams were compared with control RC beam at each level of damage acquired through static tests. The experimental results emphasize that the static load increases with an increase of HYFECC layers in FGRC beams as compared with reference one. Eventually, a comparison between experimental and numerical natural frequency values obtained by finite element analysis which has been developed to verify the RC and FGRC beams under undamaged condition.

Stress⁻Strain Properties and Gas Permeability Evolution of Hybrid Fiber Engineered Cementitious Composites in the Process of Compression.

Polyvinyl alcohol (PVA)-steel hybrid fiber reinforced engineered cementitious composites (ECC) characterized by optimal combination of high strength and high ductility were developed recently. These composites exhibit even tighter crack width than normal ECC, showing great potential for lower permeability in cracked state, and consequently improving the durability of ECC structures. In addition, the wide variety of promising applications in underground or hydraulic structures calls for knowledge on the mechanical behavior and corresponding permeability properties of strained ECC under multiaxial stress, as they are essential for structural analysis and durability design. Experimental investigations into the compressive properties and the in-situ gas permeability of PVA-steel hybrid fiber ECC were performed in this study, with special focus on the impact of additional steel fiber content and confining pressure. The test results show that the presence of a low confinement level allows ECC to attain a substantial improvement on compressive behavior but impairs the enhancement efficiency of additional steel fiber. The permeability evolution of strained ECC corresponds to the variation of radial strains, both of which experience little change below the threshold stress but a rapid increase beyond the peak axial strain. Apart from exhibiting low permeability at relatively small strains in the pre-peak stage, ECC can also exhibit low permeability at higher levels of compressive strain up to 2.0%. However, unlike the case in tensile loading, impermeability of cracked ECC in compression would be weakened by additional steel fibers, especially in the post-peak stage. The present research is expected to provide insight into performance-based durability design of structures made of or strengthened with ECC.

Flexural Performance of Hybrid Engineered Cementitious Composite Layered Reinforced Concrete Beams

This paper presents the experimental investigation to evaluate the flexural performance of newly developed hybrid Engineered Cementitious Composite (ECC) layer at tension zone around the main reinforcement of beam. Four different ECC mixes are used in the beam to evaluate the flexural performance, hybrid ECC based on the low modulus poly vinyl alcohol (PVA) and high modulus steel short random fibre reinforcement. The aim of hybridation is to improve the flexural, energy absorption and ductility performance of reinforced concrete beams. In addition to the compressive strength, young’s modulus, uniaxial tensile strength and bond strength of ECC mixes are determined. ECC with PVA fibre with 2.0% volume fraction mix is kept as reference mix, hybridation is made with PVA (1.35%) and steel (0.65%), PVA (1.00%) and steel (1.00%) and finally with PVA (0.65%) and steel (1.35%). This hybridization has a remarkable achievement in mechanical properties and in the flexural behavior in ECC layered RC beam. From the results, it has been observed that mono fiber ECC reinforced with PVA of 2.0% and hybrid fiber ECC reinforced with 1.35 % of PVA fiber and 0.65% of steel fiber has reasonable flexural characteristics than the conventional beam.

Shear Strength of Beams Made Using Hybrid Fiber–Engineered Cementitious Composites

This paper reports the results of an experimental investigation of the shear behavior of beams made using hybrid fiber–engineered cementitious composites (HFECC). The paper specifically deals with the shear behavior of beams made using strain hardening engineered cementitious composites that incorporate relatively low volume ratios (Vf≤2%) of discontinuous, randomly distributed hybrid fibers (steel and polyethylene) and how the strain hardening characteristics of the fiber composite impact the shear behavior of the beam. A total of 21 beams reinforced with longitudinal steel bars and with various combinations of polyethylene (PE) and steel (ST) fibers were tested in a three-point loading setup at a shear span to depth ratio of 3. The total volume fraction of the fibers in the composites ranged from 0 to 2%, and the matrix was either cementitious paste or cementitious mortar. The beams were tested in controlled deformations to enable capturing the postpeak behavior. It is shown that HFECC made using cementitious paste was effective in increasing the shear strength by up to 8 times relative to the nonfibrous matrix. In addition, the ductility, multiple cracking behavior, and shear strain capacity of the beams were considerably improved. Improvements were also observed in the HFECC beams made with cementitious mortar but to a lesser extent, in which the shear strength increased up to 3 times relative to the nonfibrous matrix. The results also showed that when used in HFECC, the PE fibers were nearly as effective as steel fibers in increasing the shear strength. The addition of fibers allowed the beams to reach or exceed their calculated flexural capacity in spite of the relatively large longitudinal reinforcement ratio used. A fiber volume of 1% is shown to be an adequate minimum shear reinforcement for beams with compressive strengths ranging from 40 to 65 MPa, irrespective of the hybridization ratio and the binding matrix.

Impact resistance of hybrid-fiber engineered cementitious composite panels

This paper investigates experimentally the impact resistance of a new hybrid-fiber Engineered Cementitious Composite (ECC) material reinforced with 1.75% polyvinyl alcohol fiber and 0.58% steel fibers. The ECC panels were subjected to impact from a small ogive–nose steel projectile, which was fired from a gas gun, travelling with an initial impact velocity ranging from 300m/s to 657m/s. A computer controlled high speed camera was used to record the impact process, the track of the projectile during impact, and the residual velocity of the projectile after perforation. The magnitude of the impact damage to the panels was evaluated from the measured damage parameters such as crater diameter, penetration depth and scabbing diameter after the impact testing. To evaluate the impact resistance capability of the new ECC material, the impact response of plain concrete panels, high strength concrete panels and hybrid-fiber ECC panels made of an ECC mix, which was recommended to be the most promising impact resistance material, were also tested. In addition to single impact tests, double impacts were conducted. The present study showed that the new hybrid-fiber ECC material has an excellent impact resistance to projectile penetration, evidenced by a number of capacities such as the greater absorption of the impact energy from a projectile, the higher fiber bridging capability and the better durability under multiple impacts.

Material Properties of a New Hybrid-Fiber Engineered Cementitious Composite

A new hybrid-fiber Engineered Cementitious Composite (ECC) containing 1.25% steel (SE) fibers and 0.75% Polyvinyl Alcohol (PVA) fibers is proposed, and material properties of the new ECC mix are tested in this paper. The compressive strength, modulus of elasticity, modulus of rupture and tensile properties under various strain rates of the new hybrid-ECC mix are investigated experimentally. The tested results are compared with those for a normal concrete mix, as well as those for other mono-fiber and hybrid-fiber ECCs reported in other literatures.

Material Properties of a New Hybrid-Fiber Engineered Cementitious Composite

A new hybrid-fiber Engineered Cementitious Composite (ECC) containing 1.25% steel (SE) fibers and 0.75% Polyvinyl Alcohol (PVA) fibers is proposed, and material properties of the new ECC mix are tested in this paper. The compressive strength, modulus of elasticity, modulus of rupture and tensile properties under various strain rates of the new hybrid-ECC mix are investigated experimentally. The tested results are compared with those for a normal concrete mix, as well as those for other mono-fiber and hybrid-fiber ECCs reported in other literatures.

High Velocity Impact Behaviour of Hybrid-Fiber Engineered Cementitious Composite Panels

High-velocity impact behaviour of hybrid-fibre engineered cementitious composite (ECC) panels subjected to an impact from a hardened steel, ogive-nosed projectile at velocities between 300-700 m/s is investigated and reported in this paper. The new ECC mix contains a proportion of 0.75% volume high-modulus steel fibres and 1.25% volume low modulus polyvinyl-alcohol (PVA) fibres. The mix is designed to achieve a desired balance between the strain hardening behaviour and impact resistance of material required for impact and blast resistant structures. The new hybrid-fibre ECC demonstrates its excellent capability for impact resistance and strong potential as a protective material with reduced impact damage and distributed micro cracking.

Engineered cementitious composites for effective strengthening of unreinforced masonry walls

In this paper, a total of 18 masonry wall panels were tested under both quasi-static and dynamic loadings to assess the extent to which a cementitious-based material known as Engineered Cementitious Composite (ECC) can enhance the out-of-plane resistance of unreinforced masonry (URM) walls. The masonry wall panels, which were retrofitted with an ultra-ductile hybrid-fiber ECC, were subjected to three types of load patterns, namely, patch load, uniformly-distributed load and low-velocity projectile impact. The results obtained from the above tests showed that the proposed ECC-strengthening systems are effective in increasing the ultimate load-carrying capacity of URM walls, improving their ductility, enhancing their resistance against multiple low-velocity impacts and preventing sudden and therefore catastrophic failure.

Strengthening of Masonry Walls Using Hybrid-fiber Engineered Cementitious Composite

In this article, the experimental results of hybrid-fiber engineered cementitious composite (HFECC)-strengthened masonry walls subjected to quasi-static out-of-plane loadings are reported. The aim is to assess the extent to which HFECC-strengthening systems can improve the out-of-plane resistance of unreinforced masonry walls. A total of 12 masonry panels were fabricated and tested in the laboratory under both patch load and uniformly distributed load. Test results showed significant improvement of HFECC-strengthened masonry wall’s performance against out-of-plane loadings. To provide design aid for such HFECC-strengthened masonry walls, simplified theoretical models were also developed to predict its out-of-plane ultimate load-carrying capacities based on the observed failure mechanisms. The theoretically predicted values compared favorably with experimental data.

Performance of Hybrid-Fiber ECC Blast/Shelter Panels Subjected to Drop Weight Impact

This paper presents the results of an experimental study to evaluate the damage and failure mode of hybrid-fiber engineered cementitious composite (ECC) panels caused by large projectiles or fragments. The aim is to quantify the extent to which hybrid-fiber ECC improves the resistance of blast panels against impact loading. Drop weight tests were conducted on full-scale hybrid-fiber ECC blast/shelter panels (2 m×1 m×0.05–0.1 m) to study their response and performance under impact loading. Conventional steel reinforced concrete (RC) and steel fiber-reinforced concrete (FRC) blast panels were also tested to identify the advantages of using ECC in this application. Both the drop weight projectile with a hemispherical head and the panel specimen were instrumented to facilitate evaluation of the global and local response. The impact resistance of blast panels of different materials is evaluated in terms of the extent of damage, energy absorption capacity and residual resistance against multiple impacts. The dr...

Analytical Model for Tensile Strain Hardening and Multiple Cracking Behavior of Hybrid Fiber-Engineered Cementitious Composites

An analytical model for the design of strain-hardening and multiple-cracking behavior of engineered cementitious composites (ECC) containing hybrid fibers is proposed. The model predicts first crack strength and ultimate bridging strength of hybrid fiber ECC. The model also predicts the minimum (critical) volume fraction of fibers required to exhibit strain-hardening and multiple-cracking behavior in uniaxial tension. The model is verified with the experimental results of hybrid fiber ECC specimens. A parametric study is also performed, using this model, to evaluate the effects of fiber length, diameter, and interfacial bond strength on the first crack strength, the ultimate bridging strength and the critical volume fraction of fibers. It is shown that the critical volume fraction of fibers in hybrid fiber composites can be optimized by proper selection of fiber length, diameter, and interfacial bond strength. Low modulus fibers are found to have a more pronounced effect on the strain-hardening and multiple-cracking behaviors of hybrid fiber composites compared to high modulus fibers. The hybrid fiber concept is found to offer additional freedom in the design variables compared to composite containing one type of fiber.

Behavior of Hybrid-Fiber Engineered Cementitious Composites Subjected to Dynamic Tensile Loading and Projectile Impact

The characteristics of engineered cementitious composites (ECCs) subjected to dynamic tensile loading and high-velocity projectile impact have been investigated and are reported in this paper. Hybrid-fiber ECC containing a combination of high-modulus steel fibers and relatively low modulus polyethylene fibers was adopted to achieve a desired balance between the ultimate strength and the strain capacity of the material required for impact- and blast-resistant structures. Dynamic uniaxial tensile tests at varying strain rates of 2× 10−6 to 0.2 s−1 were carried out, and ECC was found to be able to provide much higher enhancement in tensile strength than plain concrete and still be able to maintain pronounced tensile strain-hardening behavior. At higher rates of strain, ECC showed multiple-cracking behavior, similar to that observed from quasi-static tests, with tight crack width of about 0.1 mm . The results from high-velocity (300–750 m∕s) impact tests demonstrated the potential of ECC in providing improved...