Performance Fiber Reinforced Cement Composites Research Articles

Seismic retrofit of severely damaged beam-column RC joints using HPFRCC

The purpose of this paper is to use high performance fiber reinforced cement composites materials (HPFRCC) in seismic repair and retrofit of the concrete exterior beams-column joints without special seismic details with severe damage, considering the effect of slab and transverse beam. For this purpose, four external beam-column joints with scale ½ have been subjected to cyclic loading. Initially, two original joints without special seismic details suffered severe damage, which led to shear failure due to unconfinement and slip of beam rebars in the core. Then the damaged joints were repaired using HPFRCC materials and a similar load history was applied to the repaired specimens. The cyclic behavior of repaired joints was evaluated with the behavior of original specimens and the results were presented in the form of load bearing capacity, stiffness degradation, ductility, and dissipated energy. The results show that the use of HPFRCC materials in the joint core area of the repaired specimens has resulted in better confinement and integrity of the longitudinal rebars of the beam and column and in addition, has caused the flexural plastic hinge in the beam. This mechanism has improved the cyclic behavior and significantly increased the bearing capacity, energy dissipation and ductility in the repaired specimens.

Experimental evaluation of flexural behavior of HPFRCC beams reinforced with hybrid steel and GFRP bars

In this paper, seven beams were reinforced with the steel and Glass Fiber Reinforced Polymer (GFRP) bars in a hybrid system and the experimental behavior of beams was investigated. Three groups of beams were reinforced, including only-GFRP, only-steel, and hybrid steel-GFRP rebar subjected to four-point bending tests, respectively. To enhance the ductility of beams, conventional concrete was substituted with the High Performance Fiber Reinforced Cementitious Composites (HPFRCC). The beams of the first and second group were separately constructed by conventional concrete and HPFRCC; however, the third group was only consisted of HPFRCC. Moreover, the beams were reinforced in proportion to the percentages of the balanced ratio of longitudinal rebar. The results indicated that HPFRCC concrete positively influenced on the strength, ductility, and energy absorption of reinforced beams using composite and hybrid bars. The flexural capacity of hybrid reinforced concrete beams was between 86 and 115% of only-GFRPs and between 47 and 63% of only-steel beams and their ductility was between 88 and 235% compared to only-steel fiber reinforced concrete beams. Energy absorption in only-GFRP and only-steel samples were 50 and 34% compared to the hybrid beams. In hybrid beams, the higher ratios of effective (ρsf,f) was, the greater energy absorption was observed.

Mechanical and Environmental Proprieties of UHP-FRCC Panels Bonded to Existing Concrete Beams

Among the techniques used to retrofit existing reinforced concrete structures, methods involving Ultra High Performance Fiber Reinforced Cementitious Composites (UHP-FRCC) are widely regarded. However, current practices make the use of this material for in-situ application expensive and complicated to perform. Accordingly, a new method to strengthen existing concrete beams by applying a precast UHP-FRCC layer on the bottom side are introduced and described herein. Two test campaigns are performed with the aim of defining the best conditions at the interface between the reinforcing layer and the existing beam and to reducing the environmental impact of UHP-FRCC mixtures. As a result, the eco-mechanical analysis reveals that the best performances are attained when the adhesion at interface is enhanced by means of steel nails on the upper surface of the UHP-FRCC layer, in which 20% of the cement is replaced by fly ash.

Tensile behaviour identification in Ultra-High Performance Fibre Reinforced Cementitious Composites: indirect tension tests and back analysis of flexural test results

Within the framework of the European Programme Horizon 2020, the Research Project ReSHEALience is currently running with the objective of developing a new approach for the design of structures exposed to extremely aggressive environments, based on Durability Assessment based Design and Life Cycle Analysis. To this aim, new advanced Ultra-High Performance Fibre Reinforced Cementitious Composites with improved durability, called Ultra-High Durability Concretes, are under investigation to characterize their tensile response in both ordinary and very aggressive conditions. In this context, the first step is to develop an effective approach for identifying the main parameters describing the overall behaviour in tension. In the present study, indirect tension tests have been performed via two techniques, based on Double Edge Wedge Splitting and 4-Point Bending Tests. Starting from the test results, a combined experimental-numerical identification procedure has been implemented in order to evaluate the effective material behaviour in direct tension in terms of stress–strain law. In the paper, the mechanical characterization for the reference mix is reported so to describe the identification procedure adopted.

Effect of Hybrid Fibers on Flexural and Tensile Properties of Ultrahigh Performance Fiber-Reinforced Cementitious Composites: Experiments and Calculation

AbstractThis paper addresses effects of hybrid fibers on the flexural and tensile properties of ultrahigh performance fiber-reinforced cementitious composites (UHPFRCC). The workability, compressiv...

Influence of local fiber distribution on tensile behavior of strain hardening UHPFRC using NDT and DIC

This paper introduces the uniformity factor μ2 for considering the local fiber distribution within elements made with Ultra-High Performance Fiber Reinforced Cementitious Composites (UHPFRC). The influence of μ2 on the strain-hardening response of UHPFRC under uniaxial tension is investigated quantitatively by means of experimental campaign and mechanical analysis. The uniaxial direct tensile test (DTT) was carried out on dumbbell specimens, extracted from a slab, to characterize the tensile behavior of UHPFRC using digital image correlation (DIC) system. Before DTT, actual fiber distribution of each specimen was measured by non-destructive test (NDT) method. Based on the present results and available literature, it is concluded that μ2 plays a significant role in tensile strain-hardening response, especially hardening strain εUtu and matrix discontinuities energy gUf, of UHPFRC. The average μ2 value for a given UHPFRC structural element is proposed to be applied for scaling the representative tensile response to intended applications.

Tailoring Confining Jacket for Concrete Column Using Ultra High Performance-Fiber Reinforced Cementitious Composites (UHP-FRCC) with High Volume Fly Ash (HVFA)

Ultra-High Performance Fibre-Reinforced Cementitious Composites (UHP-FRCC) show excellent mechanical performances in terms of strength, ductility, and durability. Therefore, these cementitious materials have been successfully used for repairing, strengthening, and seismic retrofitting of old structures. However, UHP-FRCCs are not always environmental friendly products, especially in terms of the initial cost, due to the large quantity of cement that is contained in the mixture. Different rates of fly ash substitute herein part of the cement, and the new UHP-FRCCs are used to retrofit concrete columns to overcome this problem. To simulate the mechanical response of these columns, cylindrical specimens, which are made of normal concrete and reinforced with different UHP-FRCC jackets, are tested in uniaxial compression. Relationships between the size of the jacket, the percentage of cement replaced by fly ash, and the strength of the columns are measured and analyzed by means of the eco-mechanical approach. As a result, a replacement of approximately 50% of cement with fly ash, and a suitable thickness of the UHP-FRCC jacket, might ensure the lowest environmental impact without compromising the mechanical performances.

Experimental Strengthening of the Two-way Reinforced Concrete Slabs with High Performance Fiber Reinforced Cement Composites (HPFRCC) Prefabricated Sheets

Reinforced concrete structures are required to be strengthened and retrofitted for various reasons, including errors during design and/or construction, so in most cases, strengthening of structural elements is much more economical than rebuilding the structure. Employing HPFRCC with tensile stiffening behavior has been developed in order to strengthen the concrete structures over the recent few years. In this paper, applying HPFRCC for strengthening two-way reinforced concrete slabs has been investigated. A total of five two-way slabs were constructed and examined to reach their own collapse stage, one of the specimen was as non-strengthened control slab, and the others were strengthened in various forms. The strengthening was carried out in two ways; by installing precast plate in the tensile area and the other by installing precast plate in both tensile and compression area at two different percentages of the fiber. The bending behavior, cracking, yielding and rupture of the experimental specimens were evaluated. The results revealed that the installation of HPFRCC pre-fabricated laminates significantly ameliorated the bending performance of reinforced slabs, so that the ductility, energy absorption value, cracking strength, and initial hardness of the slabs was increased and the crack width was decreased. Therefore, the proposed precast HPFRCC sheets can be employed in order to strengthen the deficient slabs.

A meso-mechanical model to simulate the tensile behaviour of ultra-high performance fibre-reinforced cementitious composites

A simple model is proposed to predict the uniaxial tensile behaviour of ultra-high performance fibre-reinforced cementitious composites (UHPFRC) based on a meso-level description of the involved mechanics. The model relies on quantifiable material properties of the both matrix and fibres, on basic information concerning the fibre structure (such as fibre volumetric fraction, fibre orientation and geometry) and on three model parameters. Pullout tests on short fibres embedded in ultra-high performance cementitious matrix with different orientation angles and embedded lengths were developed for estimating the representative value of the average fibre-to-matrix bond-strength to be adopted, as well as for defining the fibre efficiency function describing the effects of fibre orientation on the pullout force. The model performance is validated against a series of uniaxial tensile tests on UHPFRC specimens covering a wide range of tensile behaviours. It is shown that the tensile response of UHPFRC can be well reproduced both in the hardening and softening stages with a single set of model parameters, and for a significant range of fibre contents and orientation profiles.

High performance fibre reinforced cementitious composites: Six memos for the XXI century societal and economical challenges of civil engineering

Worldwide increasing consciousness for sustainable use of natural resources has made “overcoming the apparent contradictory requirements of cost and performance effectiveness a challenging task” as well as a major concern. High Performance Fibre Reinforced Cementitious Composites, by providing tailored and multiple functionalized performance can represent an asset for the construction industry to face the challenges imposed by the needs of our continuously and fast evolving society. The paper, moving from a parallel with “Six memos from the next millennium” by Italo Calvino, the author will provide his own perspective on the current state on the topic, trying to highlight the benefits achievable through a reliable and consistent incorporation into a design and construction practice for both new and existing buildings and structures.

Cyclic Behaviour of HPFRCC Coupling Beams with Diagonal Reinforcement

Coupled shear walls are efficient in resisting lateral forces induced by winds and earthquakes. However, it is difficult to construct coupled shear walls particularly because current design codes require complex reinforcing details within coupling beams. The objective of this study was to investigate the cyclic behaviour of HPFRCC (high performance fiber reinforced cement composites) diagonally reinforced concrete (DRC) slender coupling beams. For this purpose, HPFRCC and conventional reinforce concrete DRC coupling beams were made and tested. This experimental study shows that HPFRRCC DRC coupling produced better seismic behaviour than corresponding conventional DRC beams.

Properties of high-performance cementitious composites containing recycled rubber crumb

Concrete containing rubber crumb from waste tyre has been investigated previously and enhancement of material performance, for example, energy absorbing, has been observed. However, at the same time, the degradation of compressive and flexural strength, as well as some other physical properties are also inevitable. In this study, physical, mechanical properties and durability of High Performance Cementitious Composites containing rubber crumb (HPCC-R) were assessed. Moreover, 2% volume fraction of micro steel fibres were added to form High Performance Fibre Reinforced Cementitious Composites (HPFRCC-R) to increase its integrity. Experimental results were then compared to those of the base material without rubber crumb. The impact of different mix design methodologies, grading of rubber particles, and different curing conditions were investigated.It was observed that the drying shrinkage is neglectable after hot water curing at either 90°C or 60°C for HPCC-R. Under normal curing condition, drying shrinkage development follows the similar trend as the base material but end up with approximately 20% higher shrinkage at 28days’ age. The compressive strength and flexural strength of both HPCC-R and HPFRCC-R decrease significantly with the increase of the amount of rubber crumb. Applying hot water curing at 90°C and pre-treatment of rubber crumb using Na(OH) were identified as effective approaches to compensate the compressive strength loss. However, it was observed that impacts of different curing conditions are insignificant on the flexural strength development. The rapid chloride permeability test (RCPT) results of HPFRCC-R material under different curing conditions were at the same level, and as good as that of the base material. Mixing scheme of using rubber crumb as filler material instead of replacement of fine sand lead to better material performance regarding its compressive strength versus density ratio at a relatively high replacement ratio of 40% by volume. It is recommended to use “Addition” mixing scheme when a large amount of rubber crumb being used in HPFRCC in the future.

Performance of Two-way RC Slabs Retrofitted by Different Configurations of High Performance Fibre Reinforced Cementitous Composite Strips

Introduction:Considering the promising results gained from several studies using cementitious composites with strain hardening behaviour (High Performance Fibre Reinforced Cementitious Composites, HPFRCC) for repair and retrofitting concrete flexural members, in this paper the possibility of using HPFRCC for retrofitting two-way RC slabs is investigated.Methods:A total of five two-way slabs were made and tested to failure. Three slabs were retrofitted with a variety of different types of retrofit configurations and two other slabs, having low and conventional reinforcement ratios, were used as control slabs. A novel technique of bonding, designated NSM-HPFRCC, is proposed. Flexural responses of all slabs are evaluated and the bonding behaviour and associated failure modes are investigated.Results and Conclusion:It is shown that the proposed retrofit configurations, especially when accompanied by the NSM-HPFRCC technique, can greatly improve the flexural performance of retrofitted slabs; hence, they can be used successfully to retrieve the flexural reinforcement deficiency of weak slabs.

Effects of autogenous healing on the recovery of mechanical performance of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs): Part 1

This paper presents the results are shown of a thorough characterization of the self-healing capacity of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs). The capacity of the material will be investigated to completely or partially re-seal the cracks, as a function of its composition, maximum crack width and exposure conditions. The analysis will also consider different flow-induced alignments of fibres, which can result into either strain-hardening or softening behaviour, whether the material is stressed parallel or perpendicularly to the fibres, respectively. Beam specimens, initially pre-cracked in 4-point bending up to different values of crack opening, were submitted to different exposure conditions, including water immersion, exposure to humid or dry air, and wet-and-dry cycles. After scheduled exposure times, ranging from one month to two years, specimens were tested up to failure according to the same test set-up employed for pre-cracking. Outcomes of the self-healing phenomenon, if any, were analysed in terms of recovery of stiffness, strength and ductility. In a durability-based design framework, self-healing indices quantifying the recovery of mechanical properties were also defined and their significance cross-checked.

Influence of fibre orientation on the tensile behaviour of ultra-high performance fibre reinforced cementitious composites

The main objective of this study is to quantify the effect of fibre orientation on the tensile behaviour of Ultra-High Performance Fibre-Reinforced Cementitious Composites (UHPFRC). A strategy to align the steel fibres within the matrix based on the activation of an external magnetic field while casting is adopted to achieve a wide range of fibre orientation profiles. The uniaxial tensile test is used for determining the tensile stress-elongation curves of 22 specimens and the quantitative evaluation of the fibre density and orientation characteristics is performed resorting to an image analysis technique. Based on the obtained results it was possible to validate an analytical formulation for determining the tensile strength of UHPFRC and to quantify the involved parameters. It is also shown that length of the hardening branch of the tensile stress-elongation curve is also very well correlated with the same parameters used in the determination of the tensile strength.

Strength-enhanced ecological ultra-high performance fibre-reinforced cementitious composites with nano-silica

An economical and ecological (ECO) ultra-high performance fibre reinforced cementitious composite (UHPFRCC) with a high volume of mineral admixture as part of the binding materials and river sand as the aggregate was designed. The flowability and strength development of ECO-UHPFRCC with various dosages of nano-silica were studied. The effects of nano-silica on the morphology of hardened matrix microstructure and the hydrates characteristics were investigated by SEM, XRD, TG and nano-indentation. The results demonstrated that the mechanical properties of the ECO-UHPFRCC were significantly improved with the increased dosage of nano-silica; its compressive strength exceeded 200 MPa after 3 days of steam curing when mixed with 4% by weight of nano-silica. The static mechanical properties of ECO-UHPFRCC were enhanced as a result of the optimized micro-properties. The mechanism of the effects of nano-silica on the performance of ECO-UHPFRCC microstructure were investigated and discussed as well.

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.

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.

Numerical study of shear wall behavior coupled with HPFRCC beam and diagonal reinforcements

Article history: Received 6 September, 2015 Accepted 20 December 2015 Available online 21 December 2015 High performance fiber-reinforced cementitious composites (HPFRCC) are aggregates like cement grout with fine grains and fibers which can be used in many cases like seismic improvement of building components. One of these building components is connecting beam in coupled shear wall which can increase plasticity and energy absorption. In this paper nonlinear finite element model of coupled beam containing HPFRCC is analyzed and the influence diagonal reinforcement is investigated on cracking patterns, stress contours and hysteresis diagrams of shear wall. It was observed that diagonal reinforcements play significant role in shear load bearing capacity of shear wall coupled with HPFRCC beam. © 2016 Growing Science Ltd. All rights reserved.

Tailoring Engineered Cementitious Composites with local ingredients

Engineered Cementitious Composites (ECC) is a kind of High Performance Fiber Reinforced Cementitious Composites (HPFRCC) with a low fiber volume content of 2%. The unique properties of tensile strain hardening behavior and tight multiple cracks ensure that ECC can meet the stringent requirements of resiliency and durability of concrete infrastructures. While there are strong initiatives for the adoption of ECC in China, wider applications will require localization of material ingredients. In this paper, ECCs with local ingredients, including domestic PVA fibers, fly ash and crumb rubber, were developed under the guidance of micromechanics model for ECC. The fiber/matrix interface parameters and matrix parameters from single fiber pullout test and fracture toughness test respectively, were obtained for the tailoring of domestic ECC. The experimental results indicated that cost-effective ductile ECCs can be designed successfully using local material ingredients. These composites show an ultimate tensile strength of 4–5MPa and tensile strain capacity of 3–6%.