High-performance Fiber-reinforced Cementitious Composites Research Articles

Seismic performance of repaired severely damaged precast columns with high-fiber reinforced cementitious composites

Post-tensioned precast concrete columns have advantage of re-centering capability for lateral movement by earthquakes. In this paper, cyclic tests were conducted for repaired and strengthened precast columns with severe damage by large lateral movement. Removing the damaged cover concrete and thickening by high performance fiber reinforced cementitious composite (HFRCC) was adopted. The jacket section had additional details of chemical anchors into the foundation and additional transverse reinforcing bars in the thickened concrete. The repair and strengthening increased the flexural strength and stiffness of prestressed precast concrete columns. The flexural strength of the repaired columns with additional chemical anchors was improved by more than 30%. When the shear failure of the jackets was prevented by adding transverse reinforcement, the repaired column showed stable flexural behavior at maximum load and thus enhances displacement ductility. Thickened jacket sections remarkably increased energy dissipation capacity through cracking and interface failure.

Fiber pullout behavior of HPFRCC: Effects of matrix strength and fiber type

This study investigated the effects of fiber type and matrix strength on the fiber pullout behavior of high-performance fiber-reinforced cementitious composites (HPFRCC). The correlation between single fiber pullout behavior and flexural behavior of HPFRCC was also evaluated. Two different steel fibers, i.e., straight and hooked steel fibers, and three different matrix strengths were adopted. Test results indicate that the fiber pullout performance was improved with increasing matrix strength. The hooked fibers exhibited higher bond strengths and pullout work than the straight fibers, but at large slips, they showed smaller shear stress at the interface than their counterpart. In addition, the straight fibers were more effective in improving the pullout performance with the matrix strength than the hooked fibers. For the straight fibers, the shorter fibers provided higher bond strengths and maximum shear stress at the interface than the longer fibers. The flexural performance of HPFRCC beams was improved with increasing matrix strength. The beams with medium-length straight fibers (lf/df=19.5/0.2mm/mm) gave the best flexural performance, whereas those with hooked fibers exhibited the worst flexural performance. Due to several influential factors, the correlation between the single fiber pullout behavior and flexural behavior of HPFRCC beams was quite low.

Nonlinear FE modelling and parametric study on flexural performance of ECC beams

Engineered Cementitious Composite (ECC) is a special class of the new generation of high performance fiber reinforced cementitious composites (HPFRCC) featuring high ductility with relatively low fiber content. In this research, the mechanical performance of ECC beams will be investigated with respect to the effect of slag and aggregate size and amount, by employing nonlinear finite element method. The validity of the models was verified with the experimental results of the ECC beams under monotonic loading. Based on the numerical analysis method, nonlinear parametric study was then conducted to evaluate the influence of the ECC aggregate content (AC), ECC compressive strength (fECC), maximum aggregate size (Dmax) and slag amount (ϕ) parameters on the flexural stress, deflection, load and strain of ECC beams. The simulation results indicated that when increase the slag and aggregate size and content no definite trend in flexural strength is observed and the ductility of ECC is negatively influenced by the increase of slag and aggregate size and content. Also, the ECC beams revealed enhancement in terms of flexural stress, strain, and midspan deflection when compared with the reference beam (microsilica MSC), where, the average improvement percentage of the specimens were 61.55%, 725%, and 879%, respectively. These results are quite similar to that of the experimental results, which provides that the finite element model is in accordance with the desirable flexural behaviour of the ECC beams. Furthermore, the proposed models can be used to predict the flexural behaviour of ECC beams with great accuracy.

Biaxial behavior of high-performance fiber-reinforced cementitious composite plates

A total of 127 plate specimens were fabricated and tested, of various mixture proportions, fiber types, and casting methods, in order to investigate the behavior of both plain concrete and high-performance fiber-reinforced cementitious composite (HPFRCC) specimens under multi-axial loading. The majority of the test specimens were initially fabricated as larger loaf specimens, to achieve proper fiber directionality in the out-of-plane direction, and then cut and trimmed, with steel brush platens used for loading to minimize friction between the testing machine and the plate specimens. The test results indicate that HPFRCC materials can exhibit enhanced biaxial compression performance, compared to plain concrete specimens, due to passive confinement provided by fibers in the out-of-plane direction. The multi-axial behavior of HPFRCC materials obtained from the tests was further used to construct biaxial failure curves, and several modeling parameters have then been derived for nonlinear finite element analysis of HPFRCC planar members subjected to biaxial stresses.

섬유 및 ERCO 혼입율 변화에 따른 HPFRCC의 기초적 특성 및 자기수축 저감

최근 전 세계적으로 폭탄테러 및 폭발사고가 빈발하여, 인명 및 재산피해가 증가하고 있다. 따라서 방호 방폭 성능을 갖는 고성능 시멘트 복합재료(HPFRCC)에 대한 관심이 증가하고 있다. 이에 본 연구에서는 최적의 HPFRCC를 군부대 시설에 실제적으로 적용하기에 앞서 유 무기 복합섬유 혼입율 및 ERCO 혼입율 변화에 따른 HPFRCC의 기초적 특성 및 자기수축 저감 성능을 분석하고자 하였다. 그 결과, 적절한 유동성, 강도, 자기수축저감 효과를 종합적으로 고려할 때 복합섬유(SS+OL) 혼입율 1.5%에 ERCO 0.5%의 혼입이 가장 효과적인 것으로 평가 되었다. Recently, because of the terrorisms or warfare, the damages of human life or facilities have been increased. Hence, the Korean government launched the research group for high performance fiber reinforced cementitious composite (HPFRCC) with increased demanding on protecting and anti-explosive structures. Therefore, in this research, to apply the HPFRCC on military facilities with optimum performance on workability and performance, the fundamental properties and reduction of autogenous shrinkage of HPFRCC with various combinations of steel and organic fiber and emulsified refined cooking oil (ERCO) were evaluated. As a result, based on the comprehensive analysis, for favorable workability, strength, and autogenous shrinkage, 1.5 % of combined fiber of short steel fiber and long organic fiber and 0.5 % of ERCO was suggested as an optimum conditions.

Cyclic behavior of damaged reinforced concrete columns repaired with high-performance fiber-reinforced cementitious composite

A high-performance fiber-reinforced cementitious composite (HPFRCC) prepared with high-volume fly ash is proposed to repair damaged reinforced concrete (RC) columns. This study aims at developing an effective and easy-to-apply repairing technique for RC columns damaged in earthquake. Four columns with 200mm×200mm cross section and 900mm height were prepared and tested to 85% of the load-carrying capacity under amplitude-increasing lateral loads and a constant axial load. The damaged columns were repaired using the HPFRCC: two repair heights (300 and 500mm) and two repairing processes (with and without axial loads). The effectiveness of the repairing schemes was evaluated by comparing load-carrying capacities, displacement ductility, stiffness, and energy dissipation of the columns. The results indicated that the load-carrying capacity and ductility of the repaired columns could be respectively 14% and 29% higher than those of the original columns. With axial loads during repairing, the repaired columns displayed better cyclic performance. Increasing the repair height beyond the plastic hinge zone slightly improved the load-carrying capacity and ductility. Considering the performance-to-cost ratio, it is recommended that the repair height of HPFRCC be 1.5 times the depth or width of the damaged column.

Macroscopic and microstructural properties of engineered cementitious composites incorporating recycled concrete fines

Recycled concrete fines (RCF) are fine aggregates and particles from the demolition waste of old concrete. Unlike recycled coarse aggregates, RCF is seldom used to replace sands in concrete due to its high surface area and attached old mortar on the surface of RCF. This study investigated potential use of RCF as microsilica sand substitute in the production of engineered cementitious composites (ECC), a unique high performance fiber-reinforced cementitious composites featuring extreme tensile strain capacity of several percent. The results showed that it is viable to use RCF as microsilica sand substitute in the production of ECC and the resulting RCF-ECCs possess decent compressive strength and strain capacity. Microstructure investigation on the component level revealed that RCF size and content modify matrix toughness and fiber/matrix interface properties. The influence of RCF size and content on ECC properties was clearly revealed and explained by the resulting fiber bridging σ(δ) curves of RCF-ECCs calculated from the micromechanical model. Micromechanics-based design principle can therefore be used for ingredients selection and component tailoring of RCF-ECCs.

Performance of SIFCON based HPFRCC under Field Blast Load

Abstract As the threat of global terrorism increases a demand for reinforced concrete structures as a physical protection also become important. The protective structures are to withstand sudden occurrence of dynamic loads like terrorist impact and blast attacks as well as vehicle and industrial accidents. In order to resist such an expected loading, the HPFRCC (High Performance Fiber Reinforced Cementitious Composite) materials may take an appropriate role by its increased fracture energy absorbing capacity. The slab member was 100mm thick and 2000mm squared SIFCON (Slurry Infiltrated Concrete) based HPFRCC and the outer surface was wrapped basalt fiber sheet. By wrapping the basalt, the specimen may attain more confining effect and the final HPFRCC is named as KNU HPFRCC. The SIFCON has about 80MPa compressive strength with steel fiber volume fraction of 5%. The used steel fibers were 60mm long with 80 aspect ratio and its tensile strength was 1100MPa. The slurry composed of ordinary Portland cement, water, fine sand and silica fume. A field blast test was performed with a HPFRCC slab against 100kgf TNT and stand-off distance of 5m. The study investigates the behavior of KNU HPFRCC. This study investigates the performance of KNU HPFRCC in terms of the field explosion blast load test. Figure 1 shows KNU HPFRCC slab specimen after the blast load test.

Evaluation of Mechanical Properties of Hybrid Engineered Cementitious Composite (HECC)

This paper is focused on the study of Hybrid Engineered Cementitious Composite (HECC), a unique member of High Performance Fiber Reinforced Cementitious Composite (HPFRCC) which is blended with steel and polypropylene fibers making it as a hybrid cementitious composite. The combination of the steel and polypropylene fibers benefits the properties of the individual fiber and exhibits the synergistic response. The mortar based HECC as well as conventional concrete were tested for mechanical properties to know the strength and to understand the stress-strain relationship. The results shows that based on the hybridization, incorporating steel and polypropylene fibers improved the mechanical properties (compressive strength, splitting tensile strength and flexural strength) of HECC by bridging and minimizing the crack width thereby increasing the ultimate load. The stress strain relationship of HECC resulted in the higher value of modulus of elasticity compared to conventional concrete.

Analysis and Design of Blast Resistant Structure

In the past few years, the increase in the number of terrorist attacks has shown that the effect of blast loads on buildings is a serious matter that should be taken into design consideration. These man-made disasters have created a challenge to structural engineers world over about the deficiency in the design process. Blast loads are extreme, instaneous, unpredictive impulses acting over milliseconds. Due to this nature of blast loads, it is complicated to analyse the dynamic responses of the structures. Usage of advanced engineering materials for construction can solve these structural problems to an extent. This paper presents the analysis and design of an underground blast resistant shelter made up of high performance fiber reinforced cementitious composites (HPFRCC). This research focuses on an alternative section of cylindrical module of the shelter. The dynamic behavior of module under blast load is studied in finite element software Abaqus CAE 6.12. It is observed that the material stress-strain behavior is greatly influenced by strain rates of loadings. Shelter manually designed using codes in working stress method is verified with the analytical analysis

Fundamental properties and mechanical characteristics of high performance cement composite with steel fibres under high temperature

High-performance fibre-reinforced cementitious composite (HPFRCC) is characterized by multiple functioning composite materials comprising fibre and cement matrix. HPFRCC is able to withstand tensile stress forming distributed micro-cracks since embedded fibres in concrete are to improve energy-absorption capacity and apparent ductility. This characteristic can be applied to protect structures under an extreme state of loading, such as blast or impact. In order to determine a mix proportion, this study considered various variables in the mix. Following experimental results, this study suggests an optimum mix proportion of HPFRCC and investigated fundamental properties of the considered mixes. Flexural performance is one of the representing characteristics of the high-fracture energy-absorbing materials. This study investigated the flexural performance of HPFRCC, which used high-strength steel fibres with volume fraction 8%. Under ASTM 1609, load–deflection curves were obtained. The major test variables include silica fume replacement ratio 0 and 15% and exposure temperature, ambient and 400 °C. The flexural strength was similar to the compressive strength and the absorbed fracture energy was relatively greater than other typical HPFRCC. This may be a composite reaction of the strong bonding between fibre and matrix and high-compressive strength of the matrix itself.

Autogenous healing on the recovery of mechanical performance of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs): Part 2 – Correlation between healing of mechanical performance and crack sealing

This paper is the second part of a companion paper study focused on the autogenous self-healing capacity of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). In part 1 investigation has focused on the capacity of the material to completely or partially re-seal the cracks, as a function of its composition, maximum crack width and exposure conditions. Different flow induced alignment of fibres, with respect to the applied bending stresses have been also considered. The outcomes of the self-healing phenomenon, have been analyzed in terms of recovery of stiffness, strength and ductility, as measured by means of 4-point bending tests, performed before (pre-cracking) and after the conditioning exposure. In a durability-based design framework, self-healing indices quantifying the recovery of mechanical properties were also defined and their significance cross-checked. In this paper the crack closure will be evaluated, both through visual image analysis of the healed cracks as well as through a tailored indirect method, proposed by the first authors in a previous study. This method is based on the comparative analysis of the damage evolution curves built for both the pre-cracked and the healed stages from the evaluation of the flexural stiffness. Recovery of mechanical properties will hence be correlated to the identified amount of crack closure. In the authors' opinion, this step represents a fundamental contribution in order to reliably and consistently incorporate the effects of self-healing into tailored durability-based design approaches, based, e.g., on a “healable” crack width threshold concept.

On the use of crystalline admixtures in cement based construction materials: from porosity reducers to promoters of self healing

The project detailed in this paper aims at a thorough characterization of the effects of crystalline admixtures, currently employed as porosity reducing admixtures, on the self-healing capacity of the cementitious composites, i.e. their capacity to completely or partially re-seal cracks and, in case, also exhibit recovery of mechanical properties. The problem has been investigated with reference to both a normal strength concrete (NSC) and a high performance fibre reinforced cementitious composite (HPFRCC). In the latter case, the influence of flow-induced fibre alignment has also been considered in the experimental investigation. With reference to either 3-point (for NSC) or 4-point (for HPFRCC) bending tests performed up to controlled crack opening and up to failure, respectively before and after exposure/conditioning recovery of stiffness and stress bearing capacity has been evaluated to assess the self-healing capacity. In a durability-based design framework, self-healing indices to quantify the recovery of mechanical properties will also be defined. In NSC, crystalline admixtures are able to promote up to 60% of crack sealing even under exposure to open air. In the case of HPFRCCs, which would already feature autogenous healing capacity because of their peculiar mix compositions, the synergy between the dispersed fibre reinforcement and the action of the crystalline admixture has resulted in a likely ‘chemical pre-stressing’ of the same reinforcement, from which the recovery of mechanical performance of the material has greatly benefited, up to levels even higher than the performance of the virgin un-cracked material.

Design and Analysis of HPFRCC Blast Resistant Structures

In the past few years, the increase in the number of terrorist attacks has shown that the effect of blast loads on buildings is a serious matter that should be taken into design consideration. These man-made disasters has created a challenge to structural engineers world over about the deficiency in the design process. Blast loads are extreme, instantaneous, unpredictive impulses acting over milliseconds. Due to this nature of blast loads, it is complicated to analyse the dynamic responses of the structures. Usage of advanced engineering materials for construction can solve these structural problems to an extent. This paper presents the design and analysis of an underground blast resistant shelter made up of high performance fiber reinforced cementitious composites (HPFRCC). This research focuses on an alternative section of cylindrical module of the shelter. The dynamic behavior of module under blast load is studied in finite element software Abaqus CAE 6.12. It is observed that the material stress-strain behavior is greatly influenced by strain rates of loadings. Shelter manually designed using codes in limit state method is verified with the analytical analysis.

Impact of Reinforcement Ratio and Loading Type on the Deformation Capacity of High-Performance Fiber-Reinforced Cementitious Composites Reinforced with Mild Steel

AbstractHigh-performance fiber-reinforced cement-based composites (HPFRCCs) reinforced with mild steel have been proposed for use in structural elements to enhance component strength and ductility, increase damage tolerance, and reduce reinforcement congestion. Recent research has shown that HPFRCCs have a high resistance to splitting cracks, which causes reinforcement strains to concentrate when a dominant tensile crack forms, leading to early reinforcement strain hardening and reinforcement fracture. This paper presents the impact of longitudinal reinforcement ratio, ranging from 0.54 to 2.0%, and the influence of monotonic and cyclic loading histories on the deformation capacity of reinforced HPFRCC flexural members subject to three-point and four-point bending. Experimental results show that load cycling can decrease deformation capacity of flexural members by up to 67% when compared to monotonic deformation capacity. The impact of load cycling on deformation capacity is shown to be strongly affected ...

Cyclic behavior of shear walls with HPFRCCs in the inelastic deformation critical region

This study presents a structural application of high-performance fiber-reinforced cement composites in the inelastic deformation critical region of the shear wall to improve the performance and reduce the disadvantages of conventional reinforced concrete members. Six small-scale wall specimens with the same aspect ratio and various configurations were tested under reversed cyclic loading, and their cyclic behaviors were evaluated and compared. The fiber cementitious material examined in this study exhibited excellent pseudo strain-hardening behavior in tension and high tensile ductility. The results of the quasi-static cyclic tests revealed that the deformation compatibility between the steel reinforcements and high-performance fiber-reinforced cement composite (HPFRCC) matrix could maintain composite integrity. Accordingly, the damage tolerance of the wall specimens for high inelastic deformation could be improved. Furthermore, the ultimate deformation and energy dissipation capacities of the wall specimens were dominated by the ductility and stability of the longitudinal reinforcements. Consequently, the combination of highly ductile mixture material and buckling-restrained measures of steel reinforcement, such as the steel sleeve presented in this paper, was proposed for use in shear walls under moderate or even higher axial loads. Copyright © 2016 John Wiley & Sons, Ltd.

Development and characterization of self-sensing CNF HPFRCC

Cement based brittle matrix composites that show deflection hardening called high performance fiber reinforced cementitious composites (HPFRCC) have the potential of offering high resiliency and environmentally sustainable benefits in numerous applications. HPFRCCs have been used in numerous applications; however, more information is needed to fully understand, predict the behavior, and add functionality to HPFRCCs. This experimental research program aims to develop and characterize a new type of HPFRCC, composed of polyvinyl alcohol microfibers, carbon nanofibers (CNF), and a high volume of fly ash to form a self-sensing HPFRCC. Processing of the CNF and the HPFRCC composite matrix are studied to ensure adequate fresh mix properties and fiber dispersion. The multi-functionality of the CNFs allow for increased mechanical properties and enhanced strain and damage sensing capabilities. Digital image correlation was used extensively to capture the tensile strain and provide a visualization of the behavior of the composite under increasing displacements. CNF contents of 0.167, 0.333, 0.5, and 1.0 % were studied. Through laser diffraction analysis, sonication of CNF in a CNF/water/superplasticizer solution was found to improve particle dispersion. Mechanical testing showed that dosages of CNFs less than or equal to 0.333 % increased compressive strength, tensile strength, and stiffness. CNF had little effect on tensile ductility and toughness. Piezoresistive self-sensing strain measurement was achieved in all specimens. The addition of CNF improved the strain-sensing and allowed for stronger correlations between measured strains and correlated gauge factors. Ultimately, a CNF content of 0.333 % showed optimal results in terms of enhanced mechanical properties and self-sensing behavior for strain.

Ductile behavior of high performance fiber reinforced cementitious composite (HPFRCC) frames

High performance fiber-reinforced cementitious composite (HPFRCC) materials exhibit strain-hardening behavior under tensile loading. Therefore, experimental studies were conducted to assess their structural performance and to compare them with normal concrete in reinforced concrete frames. The experimental results for reinforced concrete, reinforced composite, and reinforced HPFRCC frames with fixed foundation are presented herein. They indicate that using HPFRCC materials, instead of normal concrete in RC frames, increased the ultimate load, ultimate deflection, ductility ratio, and plastic hinge characteristics of frames. A 3D nonlinear numerical model was developed also, using the finite element (FE) method, and analytical models calibrated with experimental results and new data were generated. A good agreement between experimental and numerical results was observed.

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.

RC BEAMS STRENGTHENED WITH HPFRCC: EXPERIMENTAL AND NUMERICAL RESULTS

The study analyses the behaviour of reinforced concrete beams strengthened with high-performance fibre-reinforced cementitious composite (HPFRCC). Six beams were divided into two equal groups and strengthened. In total, nine beams were tested, including three control beams that were not strengthened. Control beams were over-reinforced. The beams of the first group were strengthened in the compressed part while those of the second group were strength­ened in the compressed and tensioned parts of the section. The experimental results of all tested beams were compared with numerical results. The positive and negative effects of strengthening the resistance and serviceability of the beams were experimentally determined. The obtained results showed that the load-carrying capacity of all strengthened beams increased and their deflections decreased; however, crack width in the beams of the second group increased while that of the beams of the first group decreased. The width of cracks increased because the number of cracks decreased. The findings of this study show a comparison of strains, deflections, cracking and load-carrying capacity and indicate that strengthening changed the failure of the beams.