High-performance Fiber-reinforced Cement-based Composites Research Articles

Interaction between high performance fiber reinforced cement-based composites and steel reinforcement

This paper presents results on the interaction between a mild steel reinforcing bar and two High Performance Fiber Reinforced Cement-based Composite (HPFRCC) matrices, a Hybrid Fiber Reinforced Concrete (HyFRC) composite with and without high cement replacement by fly ash and an Engineered Cementitious Composite (ECC). The experimental program consists of rebar pull-out tests conducted under both monotonic and cyclic loading with and without transverse steel spiral reinforcement. In addition, fiber pull-out tests to investigate the synergy between micro- and macrofibers in HyFRC on rebar pull-out resistance were also conducted. The multiscale crack control in HyFRC avoids matrix splitting and instead guarantees the more ductile frictional rebar pull-out behavior. The HyFRC matrix without fly ash exhibits the best rebar bond performance among all HPFRCCs under investigation.

Evaluation of deformation-based seismic performance of RECC frames based on IDA method

Engineered Cementitious Composites (ECC) is a typical High Performance Fiber Reinforced Cement-based Composite (HPFRCC), which possesses the characteristics of ultra-high tensile ductility and energy dissipation capacity. One of the potential applications of ECC is to replace conventional concrete in the seismic resistant structures. However, to date, the investigation on seismic performance of ECC at the structural level is still limited. This paper aims at evaluating the seismic performance of RECC frame on the basis of Performance-based Seismic Design (PBSD) concept and discussing the feasibility and practicability of applying ECC in structures for improving the seismic performance. The non-linear behavior of ECC material was simulated especially considering the strain hardening behavior in tension. By using the Incremental Dynamic Analysis (IDA) method, three types of frames, consisting of a normal RC frame, a RECC frame and an RECC/RC composite frame, were analyzed to evaluate the structural dynamic behavior of the frames. Comparative studies on the deformation limit states at five levels of seismic performance for these three different types of frames validated that RECC frames have superior deformation capacity comparing to traditional RC frames under high intensity earthquake. Comparison results also indicated that rationally applying ECC in key region of the structures can not only improve the seismic performance and deformation capacity of structures but also control the construction cost.

Influence of the Amount of Steel Fibers on Fracture Energy and Drying Shrinkage of HPFRCC

The fracture energy of the high‐performance fiber‐reinforced cement‐based composite (HPFRCC) can be modified within wide limits by the variation of the amount of steel fibers added to the fresh mix. First of all, considering the actual engineering conditions in Qingdao, the materials commonly used in Qingdao were selected. The optimal reference mix proportion of the HPFRCC cementing material was proposed through determination of fluidity and flexural strength. Based on the optimal mix proportion, the uniaxial tensile, fracture, and dry shrinkage properties of HPFRCC with different steel fibers are systematically studied. Stress‐strain diagrams of the different samples were measured under the uniaxial tensile test, wedge splitting test, and three‐point bending test. The steel fiber content was varied between 0 and 200 kg/m3. The load bearing capacity and the fracture energy were determined experimentally. In addition, moisture loss as a function of time and shrinkage was determined in an environment of 20°C and 50% RH (relative humidity). The results indicate that the maximum load increases significantly in the HPFRCC series reinforced by 150 and 200 kg/m3 of steel fibers. Both have a hardening branch developed after the first crack deflection due to the high percentage of fibers bridging the crack surfaces. The load bearing capacity and fracture energy increased almost linearly with the steel fiber content. It was found that the three‐point bending test is more applicable in measuring the fracture energy of HPFRCC than the wedge splitting test. The addition of steel fibers decreased the moisture diffusion and consequently the drying shrinkage of HPFRCC, and there was minimum weight loss and deformation when the steel fiber content was 150 kg/m3. The results obtained will be presented and discussed.

Utilization of Local Ingredients for the Production of High‐Early‐Strength Engineered Cementitious Composites

The rapid repair and retrofitting of existing transportation infrastructure requires dimensional stability and ductile repair material that can obtain sufficiently high strength in a few hours to accommodate the large loading and deformation at an early age. Engineering cementitious composites (ECCs) is a class representative of the new generation of high‐performance fiber‐reinforced cement‐based composites (HPFRCC) with medium fiber content. The unique properties of tremendous ductility and tight multiple crack behavior indicate that ECC can be used as an effective retrofit material. The wide application of this material in China will require the use of all local ingredients. In this study, based on Chinese domestic ingredients, including matrix materials and all fibers, high‐early‐strength ECC (HES‐ECC) was designed under the guidance of strain‐hardening criterion of ECC. The matrix properties and fiber/matrix interfacial micromechanics properties were obtained from three‐point‐bending test and single‐fiber pullout test. The mechanical properties of HES‐ECC were achieved by direct tensile test. The experimental results show that HES‐ECC was successfully developed by using all Chinese materials. When using the domestic PVA fiber at 2%, the strength requirement can be achieved but only a low ductility. When using the domestic PE fiber at 0.8%, the strength and deformation requirement both can be obtained. The HES‐ECC developed in this study exhibited compressive strength of more than 25 MPa within 6 hours, and an ultimate tensile strength of 5‐6 MPa and tensile strain capacity of 3‐4% after 60 days. Moreover, the cost of using domestic fiber can be largely reduced compared with using imported fiber, up to 70%; it is beneficial to the promotion of these high‐early‐strength ECCs in the Chinese market.

Resistance of high-performance fiber-reinforced cement composites against high-velocity projectile impact

This paper presents experimental and numerical studies on the performance of seven high-performance fiber-reinforced cement-based composites against high velocity projectile impact (HVPI). The materials investigated involved four fiber-reinforced high-strength concretes (FRHSCs) with 28-day compressive strengths ranging from about 60 to 140 MPa, two strain hardening cement-based composites (SHCCs), and a fiber-reinforced high-strength mortar (FRHSM). Of the two SHCCs, one was reinforced with 0.5% steel fibers plus 1.5% polyethylene (PE) fibers by volume of the composites, whereas the other was reinforced with 2% of polyvinyl alcohol (PVA) fibers. The other composites were reinforced with 0.5% of steel fibers. Ogive-nose shaped projectiles, with a diameter of 28 mm and weight of about 250 g, were used for the HVPI tests at projectile velocities of ~400 and ~600 m/s. The localized damage, particularly the penetration depth, was examined and discussed. Results indicate that the higher compressive strength and greater toughness of cement-based composites, as well as the presence of strong coarse aggregate and fibers, contribute positively to the impact resistance of composites. In addition, it was found that the penetration depth of the composites subjected to HVPI is reduced with an increase in the elastic modulus, as well as with the “effective hardness index” calculated based on the hardness and proportion of the coarse aggregate and mortar matrix. Numerical studies were conducted to simulate the localized damage of the FRHSCs and SHCCs due to the HVPI using the finite element software LS-DYNA. The numerical models adapted predict the penetration depth well. The numerical simulation results indicate that it takes a longer time to stop the projectile traveling at the same initial velocity in the SHCC specimen than in the FRHSC specimen due to the absence of hard and strong coarse aggregate in the former.

Capillary Absorption and Chloride Penetration into High-Performance Fiber-Reinforced Cement-Based Composites (HPFRCC) as Influenced by Tensile Stress and Self-Healing

AbstractHigh-performance fiber-reinforced cement-based composites (HPFRCC) can be characterized by low porosity and fine pores as compared to normal concrete and therefore this interesting material absorbs little water or aqueous salt solutions if exposed to aggressive environment. These properties are indications for excellent durability and long service life of structural members or structures made with this high-performance material. In practice, however, most structures and structural elements are designed to be load bearing. The influence of an applied tensile stress on capillary absorption was investigated and results are presented in this contribution. It was found that the coefficient of capillary absorption increases rapidly if a tensile stress exceeding half of the tensile strength is applied. This observation has to be taken into consideration if HPFRCC is to be applied in aggressive environment. The maximum admissible stress must be reduced accordingly.

Tension stiffening in reinforced high performance fiber reinforced cement-based composites

High Performance Fiber-Reinforced Cement-based Composite (HPFRCC) materials carry tension to strains greater than the yield strain of reinforcing steel and exhibit distributed compression damage with minimal spalling. Characterization of the interaction between the composite and steel reinforcement to large strains (i.e., >0.005) remains largely unknown. Three HPFRCC materials as well as concrete with a single reinforcing bar are tested in a prismatic specimen in uniaxial tension up to fracture of the reinforcement. Multiple cracking of the composite led to uniform bar yielding throughout the specimen and early hardening of the reinforcement at the location of dominant cracks. The reinforcement fractured within the HPFRCC at lower strain levels relative to the reinforced concrete. A modified approach based on planar analysis to estimate flexural strength of reinforced HPFRCC components using tension-stiffening data is proposed.

Three-dimensional model for analysis of high performance fiber reinforced cement-based composites

High performance fiber reinforced cement-based composites (HPFRCCs) are distinguished from regular cement materials by their strain hardening behavior under uniaxial tension as well as significantly enhanced durability, damage tolerance, and shear resistance. This paper presents a three-dimensional constitutive model for the nonlinear finite element analysis of HPFRCC structures. The proposed material model is an orthotropic hypoplastic model. Based on the smeared rotating crack approach, the directions of orthotropy are assumed to coincide with the principal strain directions. The constitutive model is capable of accounting for the general nonlinear behavior of HPFRCC, including the effects of multiple narrow cracking, crack localization, and compression crushing. The performance of the proposed model is demonstrated using data from experimental tests carried out on a punching shear slab and a two-span continuous beam. Comparisons between numerical solutions and experimental results suggest that the developed material model is able to represent the observed experimental behavior with reasonable accuracy.

Processing of high-performance fiber-reinforced cement-based composites

High-performance fiber-reinforced cement-based composites (HPFRCC) are characterized by their high elastic limit and strain hardening and a progressive multiple cracking type of response to mechanical loading. The parameters that influence the performance of such composites include: fiber type(s), matrix properties and processing. Processing can substantially influence fiber dispersion, quality of performance and cost of production. In spite of its importance, relatively little is known about the relationship between processing and composite performance. This paper summarizes the results of two studies in which the influence of processing on the performance of Hatschek- and extrusion-produced HPFRCC was investigated. The effect of applying external pressure to freshly-formed, Hatschek-produced fiber-reinforced cement board was systematically evaluated. The results indicate that pressure can be used to enhance freeze–thaw durability. In addition, a rheological study was successfully carried out on extruded composites to reduce cost by altering the matrix composition.

Experimental and numerical investigations of low velocity impact behavior of high-performance fiber-reinforced cement based composite

Fiber-reinforced concrete (FRC) has been used in structural applications in order to enhance the structural performance under dynamic loading and reduce cracking and spalling phenomena by increasing toughness, ductility, and tensile strength of the concrete. High-performance fiber-reinforced cement based composite (HPFRC) is a high-strength FRC with enhanced high-performance characteristics. Recent studies have shown that HPFRC has higher impact resistance than other types of concrete. Therefore, it has been widely considered as a promising material for the construction of important and strategic structures. HPFRC panels are tested by drop projectiles up to an impact at which failure occurs. Mechanical properties of HPFRC are obtained to define material parameters in the MAT_SOIL_CONCRETE model in LS-DYNA, which is used to simulate the behavior of HPFRC panel under impact loading and perform parametric studies. Predicted crack and failure patterns on both sides of the HPFRC panel based on finite element simulation are in good agreement with their corresponding experimental results.

Rheology of Extruded Cement-Based Materials

Current research efforts seek to develop extruded high-performance fiber-reinforced cement-based composites (HPFRCC) for use in residential housing applications. Part of this effort focuses on reducing the high material cost that is associated with extrusion processing by replacing costly cellulose ethers with less expensive clay binders. The minimum amount of two different types of cellulose ethers that was needed to achieve extrudability was determined and then the possibility of reducing the ethers with two clay binders was explored. The results show that cellulose ether content can be reduced by using alternate clay binders. In addition, two different extrusion-based rheological characterization methods were used to describe the fresh state properties of the extruded materials: the Benbow-Bridgwater model and capillary rheology. Capillary rheology was shown to be effective at describing extrudability, providing an indication of the fresh state parameters necessary for extrusion.

Properties of Hybrid Fiber Reinforced Cement - based Composites

Three-point bending tests and uniaxial tension tests on Hybrid Fiber Reinforced cement-based Composites (HFRCC) were carried out. HFRCC contains both specially-processed steel fiber (steel cord) and synthetic fiber. As the result of the bending tests, it was confirmed that coarse and wide cracks were observed near the notch of the specimens reinforced with only steel cord. On the other hand, HFRCC showed high strength and ductility. Furthermore HFRCC developed in this study showed multiple cracks and pseudostrain hardening under uniaxial tension. Therefore it could be confirmed that HFRCC has a sufficiently high performance to qualify as High Performance Fiber Reinforced Cement-based Composites (HPFRCC) as defined in previous studies.

Applications of High-Performance Fiber-Reinforced Cement-Based Composites

Advanced composites and the fundamental understanding of their behaviour is a rapidly expanding branch within the field of civil engineering materials. In particular, fiber-reinforced cement-based materials have had a great evolution in these years, so that they are more and more utilized in the building sector. Besides, large efforts have been made to develop high-performance cements and concretes showing further performance improvements. High-performance fiber-reinforced cement composites include, for example, materials such as SIFCON (Slurry Infiltrated Fiber CONcrete), fiber-reinforced DSP (Densified with Small Particles), and fiber-reinforced MDF (Macro-Defect-Free) cements. Developments of these materials were possible due to: (a) the introduction of new reinforcement systems; (b) the development of high-performance cement-based matrices, which present greatly improved microstructural properties in terms of strength and durability; (c) the development of adequate processing techniques (including controlling chemical reactions) which allow us to obtain composite materials with surprising toughness properties. After a brief description of high-performance cement-based matrices and relative composites, two different examples among the above-cited products will be deeply presented.