Ultra-high Performance Fibre-reinforced Cementitious Composites Research Articles

Influence of fiber orientation on the high cycle tensile fatigue resistance of ultra-high performance fiber reinforced cementitious composites (UHPFRC)

This paper quantitatively studies the influence of fiber orientation on the high cycle tensile fatigue resistance of ultra-high performance fiber reinforced cementitious composites (UHPFRC) within and beyond elastic domain. Eight tensile fatigue tests and re-analysis of sixteen fatigue tests from a previous study are conducted, which have specimens statically preloaded to the strain from 0.19‰ to 0.5‰ and from 1.1‰ to 2‰, considered to be in the elastic and post-elastic domains in tension, respectively. For the eight fatigue tests, the local fiber orientation and dosage of each specimen are determined before testing using a magnetic probe. During testing, specimen behavior is characterized by displacement transducers, digital image correlation and acoustic emission. Based on the above, the fatigue endurance limit at 10 million cycles is determined to be about SUte,10%= 0.9 of the elastic limit tensile stress for UHPFRC within elastic domain. For UHPFRC preloaded beyond the elastic domain, the fatigue resistance decreases with increasing pre-applied strain and decreasing average fiber orientation (increasing average angle between fibers and principle tensile direction). With pre-applied strain from 1.1‰ to 2.0‰, the endurance limit may be taken as SUte,10%=0.60 to 0.65 for typical UHPFRC structures. Two original fatigue resistance models are proposed, which describe the relationship between average fiber orientation, number of cycles and maximum fatigue stress for UHPFRC within and beyond the elastic domain.

Multi-performance experimental assessment of autogenous and crystalline admixture-stimulated self-healing in UHPFRCCs: Validation and reliability analysis through an inter-laboratory study

The huge benefits brought by the use of Ultra High-Performance Fibre-Reinforced Cementitious Composites (UHPFRCCs) include their high “intrinsic” durability, which is guaranteed by (1) the compact microstructure and (2) the positive interaction between stable multiple-cracking response and autogenous self-healing capability. Hence, self-healing capability must be properly characterized addressing different performances, thus providing all the tools for completely exploiting such large potential. Within this context, the need is clear for a well-established protocol for self-healing characterization. To this end, in the framework of the Cost Action CA15202 SARCOS, six Round Robin Tests involving 30 partners all around Europe were launched addressing different materials, spanning from ordinary concrete to UHPFRCC, and employing different self-healing technologies. In this paper, the tailored experimental methodology is presented and discussed for the specific case of autogenous and crystalline-admixture stimulated healing of UHPFRCC, starting from the comparison of the results from seven different laboratories. The methodology is based on chloride penetration and water permeability tests in cracked disks together with flexural tests on small beams. The latter ones are specifically aimed at assessing the flexural performance recovery of UHPFRCCs, which stands as their signature design “parameter” according to the most recent internationally recognized design approaches. This multi-fold test approach allows to address both inherent durability properties, such as through-crack chloride penetration and apparent water permeability, and more structural/mechanical aspects, such as flexural strength and stiffness.

Elastic limit tensile stress of UHPFRC: Method of determination and effect of fiber orientation

This paper discusses the influence of fiber orientation on elastic limit tensile stress of ultra-high performance fiber reinforced cementitious composites (UHPFRC). An original model relating elastic limit tensile stress to fiber orientation is proposed, and three determination methods of the elastic limit are compared. Five specimens are tested under uniaxial tension and characterized with digital image correlation, acoustic emission and displacement transducers. Before testing, the fiber distribution (local dosage and orientation) of each specimen is determined using a magnetic probe. After testing, three methods (offset with 2 different threshold values, and deformation modulus drop) are applied to determine the elastic limit tensile stress. The test results show that the proposed model estimates well the elastic limit tensile stress on the basis of fiber orientation. The modulus-drop method yields the most representative value for the elastic limit considering the underlying physical phenomena. It may be taken as definition of elastic limit tensile stress of UHPFRC.

Shear behaviour of RC-UHPFRC composite beams without transverse reinforcement

Strengthening existing reinforced concrete (RC) beams and slabs using a thin layer of ultra-high performance fibre reinforced cementitious composites (UHPFRC), plain (U) or reinforced (RU) with ordinary steel bars, has been shown to be a very effective way of increasing the flexural capacity in hogging moment regions. However, as the increase in the flexural strength can be very significant, the shear strength of the composite RC-RU or RC-U elements may govern the capacity of the strengthened element and must be conveniently assessed to provide suitable design recommendations. In this regard, the available experimental evidence concerning the shear strength of beams (or one-way shear strength for slabs) is relatively limited. In this work, the results of an experimental campaign are presented where the influence of important parameters was systematically evaluated, namely the reinforcement ratios in the original RC beam and the new UHPFRC layer, the size effect, the thickness of the UHPFRC layer and the sign of the being moment - hogging or sagging - changing the state of stress in the UHPFRC layer from tensile to compressive.The structural behaviour is discussed, and an analytical approach for calculating the shear strength is evaluated.

Inverse Analysis of R-UHPFRC Beams to Determine the Flexural Response under Service Loading and at Ultimate Resistance

Ultra high performance fiber reinforced cementitious composites (UHPFRCs) have demonstrated their outstanding efficiency as structural materials. Determination of the bending resistance of members combining UHPFRC with steel reinforcement bars (R-UHPFRC) using material properties obtained by material testing gives satisfactory results. However, the synergetic interaction between rebar and UHPFRC in the tensile action due to bending, especially under loading–unloading of the structure is not yet well understood. This paper compared methods of analytical inverse analyses, as well as finite-element modeling and nondestructive testing (NDT), for determining UHPFRC material properties based on plates and R-UHPFRC members’ test results. It was demonstrated that UHPFRC in the tensile zone of R-UHPFRC members can enter into compression during unloading, influencing the structural response under service loading.

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.

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...

Detection and Measurement of Matrix Discontinuities in UHPFRC by Means of Distributed Fiber Optics Sensing.

Following the significant improvement in their properties during the last decade, Distributed Fiber Optics sensing (DFOs) techniques are nowadays implemented for industrial use in the context of Structural Health Monitoring (SHM). While these techniques have formed an undeniable asset for the health monitoring of concrete structures, their performance should be validated for novel structural materials including Ultra High Performance Fiber Reinforced Cementitious composites (UHPFRC). In this study, a full scale UHPFRC beam was instrumented with DFOs, Digital Image Correlation (DIC) and extensometers. The performances of these three measurement techniques in terms of strain measurement as well as crack detection and localization are compared. A method for the measurement of opening and closing of localized fictitious cracks in UHPFRC using the Optical Backscattering Reflectometry (OBR) technique is verified. Moreover, the use of correct combination of DFO sensors allows precise detection of microcracks as well as monitoring of fictitious cracks’ opening. The recommendations regarding use of various SHM methods for UHPFRC structures are given.

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.

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.

Effects of geometry and hybrid ratio of steel and polyethylene fibers on the mechanical performance of ultra-high-performance fiber-reinforced cementitious composites

This study aims to examine the several factors influencing the efficiency of the hybridization of steel and polyethylene (PE) fibers in improving the compressive strength and tensile performance of ultra-high-performance fiber-reinforced cementitious composites (UHPFRCC). For the mechanical tests, three types of steel fibers (i.e., short straight steel (SS), medium-length straight steel (MS), and twisted steel (T) fibers) and four lengths of polyethylene (PE) fibers (i.e., 12mm (SPE), 18mm (MPE), 27mm (LPE), and 36mm (LLPE)) were hybridized. Each specimen included 2vol.% of single or hybrid fibers, and the hybrid ratio was controlled by replacing 0.5% of the steel fibers with the same amount of PE fibers from 0 to 2%. Thus, a total of 7 single and 36 hybrid UHPFRCC specimens were fabricated. From the test results, it was found that the compressive strength decreased proportionally to the PE fiber content, but the decrease was more severe in hybrid specimens, including 1.5% PE fibers, than single fiber specimens, including 2.0% PE fibers. The tensile strength also decreased with an increase of PE fiber content, whereas strain capacity and energy absorption capacity per unit volume substantially improved with the inclusion of PE fibers. The SPE fibers showed the best hybridizing efficiency among PE fibers in improving the tensile strain capacity and energy absorption capacity of UHPFRCC, and the use of T fibers was the most effective in terms of cracking behavior.

Effect of fly ash on tensile properties of ultra-high performance fiber reinforced cementitious composites (UHP-FRCC)

This article presents and compare the tensile strain hardening behavior, compressive strength, energy absorption, and CO2 emission of environmental friendly ultrahigh performance fiber reinforced cementitious composites (UHP-FRCC) containing various fly ash contents as partial replacement of premix cement (consisted of 82% low heat cement and 18% silica fume). Six series of UHP-FRCC are considered in this study. The first two series are control series while the rest four series contain 20, 30, 40, and 50% fly ash as partial replacement of premix cement. A small amount of nano silica (2 wt.%) is also added to compensate the low early age strength properties of the fly ash based UHP-FRCC. Results show that fly ash contents of 30–40% exhibited better compressive strength, tensile strain hardening behavior, and energy absorption than the other fly ash contents in the UHP-FRCC. The UHP-FRCC containing 40% fly ash shows about 12, 14, 10, and 22% reduction in compressive strength, ultimate tensile strength, ultimate tensile strain, and energy absorption capacities, respectively, than the control, while its CO2 emission is about 35% lower than the control. The reported properties of UHP-FRCC containing 40% fly ash are still higher than other reported UHP-FRCC containing other SCMs as well as many reported UHP-FRCC containing no SCMs except the silica fume.

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.

Elevated temperature resistance of ultra-high-performance fibre-reinforced cementitious composites

Elevated temperatures, specifically in the event of fire, are likely to cause extreme deterioration in fibre-reinforced polymer (FRP) strengthened reinforced concrete (RC) structures. Various types of high-performance cementitious composites (HPCC) have been explored for the protection of RC structural members against elevated temperature, but there is inadequate information in this regard for ultra-high performance fibre-reinforced cementitious composites (UHPFRCC) containing high-alumina cement (HAC) and ground granulated blast furnace slag (GGBS) in conjunction with hybrid fibres – a prospective fire-resistant UHPFRCC for structural members. In this study, the change in mechanical strength of UHPFRCC was examined before and after heat treatment, followed by thermal and microstructural analysis. Besides the control sample, three other samples containing up to 1·5% of basalt fibres, and 1 kg/m3 of polypropylene fibres, were prepared and tested. Another mix was also prepared with only 1 kg/m3 of polypropylene fibres. Each sample was heated to 400, 700 and 1000°C. Results showed that the use of hybrid fibres significantly improved the room temperature mechanical strengths of UHPFRCC, which were found to be 80 MPa and 14·3 MPa, respectively. However, the optimum residual compressive and flexural strength was attained by UHPFRCC with only PP fibres and hybrid fibres, respectively.

Experimental field investigation of impact and blast load resistance of Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs)

Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs) represent a class of cement composites which have superior characteristics in terms of material properties. These materials have, however, a significant increase in cost compared to conventional and even High Performance Concrete and it is therefore appropriate to identify applications which will fully utilise their mechanical properties and performance characteristics. A new class of UHPFRCC material has been developed through the experimental work of a research project entitled “Mix Design, Mechanical Properties and Impact Resistance of UHPFRCCs”, designated UHP-CY. The material is characterised by high compressive strength, high tensile/flexural strength and high-energy absorption capacity. The research work presented in this paper focused on the experimental investigation of the quality and the behaviour of this material in a highly demanding application, such as the impact and blast resistance of structures. The impact resistance of UHP-CY slabs was experimentally verified in a range of real firing shots, using several weapons and projectile types. A purpose-built experimental setup was developed for this work. It was observed that relatively thin slabs made of this material can be an outstanding protective overlay of existing structures, since they can prevent the penetration of strong projectiles without shaped charges. Moreover, these panels can also minimise the damage of retrofitted Reinforced Concrete structures, hit by projectiles with shaped charges. The presence of a high volume fraction (i.e. 6%) of steel fibres in UHP-CY overlays contributes substantially to the control of the back face spalling and fragmentation of the RC walls.

Properties of ultra-high performance fiber reinforced cementitious composites made with gypsum-contaminated aggregates and cured at normal and elevated temperatures

Aggregates in many parts of the Middle East are contaminated with gypsum. Therefore, in this study the effects of using gypsum-contaminated natural sand on the compressive strength and expansion of ultra-high performance fiber reinforced cementitious composites (UHPFRCCs) were investigated over a period of one year. Two groups of UHPFRCCs were designed with binary and ternary cementitious blends of Portland cement, silica fume, and/or ground granulated blast furnace slag. Each group consisted of five mixes with different SO3 contents of between 0.11% and 4.5% by weight of natural sand. For each mix, the samples were either water cured or steam cured over a 48h period. The microstructure of the cementitious composites was also studied by the SEM–EDX. Besides, some findings of UHPFRCCs were compared to those of Portland cement mortars. Test results indicated that UHPFRCCs showed a strength gain, particularly under steam curing and an insignificant expansion even in the presence of excess sulfates, in contrast to the mortars.

Effect of fiber content on mechanical and fracture properties of ultra high performance fiber reinforced cementitious composites

This study investigated the mechanical properties of ultra high performance fiber reinforced cementitious composites (UHPFRCC) with four different fiber volume fractions (Vf=1%, 2%, 3%, and 4%) within an identical mortar matrix. The higher amount of fiber resulted in an improvement of load carrying capacity and elastic modulus in compression up to 3vol.% of fibers. A higher pullout strength was obtained from the inclusion of fibers in the matrix, and 2vol.% of fibers provided the best performance in all aspects of fiber pullout behavior including average and equivalent bond strengths and pullout energy. The flexural strength was pseudo-linearly increased with increase in fiber volume fraction, despite an insignificant difference in the first cracking load. Furthermore, a bi-linear softening curve for UHPFRCC was suggested based on the result of inverse analysis, and it was verified through comparison with the experimental data.

The variation of flow-dependent tensile behavior in radial flow dominant placing of Ultra High Performance Fiber Reinforced Cementitious Composites (UHPFRCC)

The present research is chiefly concerned with the flow-dependent tensile behavior of Ultra High Performance Fiber Reinforced Cementitious Composites (UHPFRCC). The situation of fabricating a thin square-sectioned UHPFRCC plate with radial flow was considered. Both experimental and analytical study was performed to verify the validity of the analytical approach for prediction of the tensile behavior. In analytical work, the variation of the fiber orientation distribution according to the flow was first explored, and the consequent variation of the tensile behavior was estimated. The combination of the resistance by the fibers and the matrix, considering a probability density distribution for the fiber orientation distribution across crack surface, was considered in the analysis. The rotational movement of fiber in the fluid cementitious matrix was also taken into account. The comparison between the experimental and analytical results demonstrated the effectiveness of the proposed analytical approach.