Properties Of Ultra-high-performance Fiber-reinforced Concrete Research Articles

Influence of Type and Volume Content of Steel Fiber on the Compressive Strength of Ultra-High Performance Fiber Reinforced Concrete

The paper presents the results of determining the compressive strength of various compositions of Ultra-High Performance Fiber Reinforced concrete (UHPFRC) with fiber volume content from 1 to 3%. Four types of fibers were used: corrugated fiber of 15/0.3 mm and 22/0.3 mm, straight fiber of 13/0.3 mm and hooked-end fiber of 30/0.5 mm. It was found that corrugated and hooked-end fiber leads to an increase in compressive strength by 10–30 MPa when its content is increased from 1 to 3%. Straight fiber has no noticeable effect on the mechanical properties of UHPFRC. Empirical equations for predicting the compressive strength of UHPFRC depending on the strength of concrete matrix, geometric dimensions and content of dispersed reinforcement for compositions with corrugated and hooked-end fibers have been obtained. It is found that increasing the volume content of aggregate in the concrete matrix composition from 0.2 to 0.4 m3/m3 leads to an increase in the strength of UHPFRC. The strength of specimens with corrugated fiber increased by 5.3–13.3 MPa, with hooked-end fiber – by 14–19.3 MPa, with straight fiber – 5–7 MPa. It is also noted that the most intensive growth of mechanical characteristics due to the increase in the aggregate volume content in the composition is observed at a higher percentage of fiber volume fraction.

Fabrication and Characterization of Partial Bio-nano-silica Inclusion in Fibre-Reinforced Concrete for High-performance Applications

Ultra-high-performance fibre-reinforced concrete (UHPFRC) is a specialized type of concrete (to create a very dense matrix) that is used for both new construction and renovation projects in order to improve the lifespan of structures. Researchers analyse and evaluate only the microstructure, porosity, and fresh and hardened concrete properties of UHPFRC but limited their exploration on the reduction of the mechanical properties of UHPFRC due to the presence of metallic particles and micro-fractures that occur during the generation of hydrogen. Hence, the present study aims to eliminate the existing problem by hybridization approach (mixing of bio-nano-silica (nS) and polypropylene) with different percentages to further improve the strength properties of UHPFRC. The result showed that the compressive strength is increased by 15.5% compared to traditional concrete due to the filling ratio of nS in the pores of the concrete; in addition, the fibre’s surface and roughness also contributed to the strength enhancement.

Curing–dependent structural behavior of ultra-high-performance hybrid fiber-reinforced concrete beams

The application of ultra-high-performance fiber-reinforced concrete (UHP-FRC) is exceptionally versatile. However, a comprehensive understanding of UHP-FRC beam structural performance characteristics is lacking. The majority of research has concentrated on the behavior of structural members following standard water curing. This study investigated the impact of the curing regime on the structural performance of UHPC beams. The four different curing regimes used were standard, simulated hot arid weather, steam curing at various ages, and 5% sodium sulfate curing. Experimentally measured mechanical properties of UHP-FRC have been determined following ASTM guidelines, and the investigated beams have been tested under displacement-controlled four-point loading. Additionally, ACI 318 and FHWA-HIF codified formulas were employed in this study to predict the moment capacity of the tested beams. As a result of the various steam systems of varying ages, the load-carrying capacities of the beams were improved. By accelerating cement hydration, steam curing produces a stronger bond between fibers and the cementitious matrix, improving flexural strength. The control beam (under standard curing) showed a smaller maximum deflection, while all other beams showed similar deflection capacity. By accelerating the drying shrinkage, the beams under the 28-day standard with hot air curing were negatively impacted, with an average deflection value around 5% lower than control beams. The cured beams under simulated hot, arid conditions had the lowest flexural rigidity. A steam-cured beam had the highest moment-curvature performance, while a beam cured under simulated arid conditions had the lowest. Additionally, the ACI 318 design equation significantly underestimated beam maximum moments, while the FHWA approach marginally overestimated beam maximum moments with a predicted-to-tested average of 0.82.

Sustainable construction material: Ultra-high performance fibre reinforced concrete (UHPFRC) for railway bridges in Malaysia

UHPFRC is a new concrete technology being used in many countries including Malaysia. UHPFRC favourable material properties open up new potential for precast options in bridge construction and have been widely used as beams for highway bridges in Malaysia. Nevertheless, PRC beams were preferred despite heavy in weight and large sections although these properties affect the design of the bridge substructure as well the cost of construction. This research is to review the applicability of Grade 140/155 UHPFRC beam for railway bridges in Malaysia. Laboratory tests for mechanical properties of UHPFRC were conducted and results were verified and complied with the French Standard, NF P18-470: 2016. The characteristic cylinder and cube compressive strengths were 151 and 155 MPa while the tensile limit of elasticity, post-cracking tensile strengths and modulus of rupture were 7.8, 8.4 and 24.3 MPa respectively. Structural analysis and design as per NF P18-710: 2016 requirement was then performed for a 15 meter UHPFRC IB650 beam to justify its applicability against a Grade 40/50 PRC U-beam of an existing railway bridge in which the ultimate shear and moment capacities of both beams were compared. The ultimate shear and moment capacities of the 4 numbers of U-beams/deck were 4,092 kN and 13,324 kNm respectively and when compared to UHPFRC IB650 beam, six numbers/deck were required with ultimate shear and moment capacities of 4,836 kN and 14,574 kNm respectively. For durability, the modulus of elasticity and depth of water penetration for UHPFRC were 50.8 GPa and 2mm respectively compared to 34 GPa and 11mm for Grade 40/50 concrete.

Bayesian calibration and reliability analysis of ultra high-performance fibre reinforced concrete beams exposed to fire

A study of uncertainty quantification and reliability of ultra-high-performance fibre reinforced concrete (UHPFRC) beams exposed to fire is presented. The study sets forth two methodologies, the first involving the stochastic calibration of temperature-dependent thermal properties of UHPFRC via Bayesian inversion, and the second concerning the computation of the reliability of UHPFRC beams in fire via Monte Carlo Simulation (MCS). Using the calibrated posterior probability distributions of temperature-dependent thermal properties of UHPFRC in stochastic heat transfer analyses results in predictive temperature distributions that reasonably track (within 95% confidence interval) the temperature response reported on UHPFRC beams specimen subjected to 80 and 60 minutes standard fire. Stochastic temperature distributions based on the calibrated thermal properties were sequentially transferred via a time series surrogate model, into a structural-fire reliability analysis of UHPFRC beams designed to the specifications of the ACI 544. Reliability analysis is conducted and the obtained reliability index generally reduced with increasing fire exposure for the UHPFRC beam considered and fire resistance is estimated based on a reliability target of 0.7.

Experimental and analytical study of ultra-high-performance fiber-reinforced concrete modified with egg shell powder and nano-silica

Presently, the rate for the development of ultra-high-performance concrete (UHPC) is increasing due to the requirement of long-span bridges, challenging architectural plans, and high-rise buildings. UHPC is still weak in tension and consumes a lot of cement, making it non-eco-friendly. This research is aimed at modifying the cement's matrix by incorporating two sustainable solid waste mineral admixtures, eggshell powder (ESP) and nano-silica (NS), to enhance the bonding between fibers and the binder's matrix and improve the strength characteristics of ultra-high-performance fiber-reinforced concrete (UHPFRC). The improving impacts of the ESP and NS on the double-hooked end (DHE) steel fibers were studied and analyzed by evaluating various strength parameters, i.e., compressive, splitting tensile and flexural strength and the load-deflection performance. To characterize the durability properties of UHPFRC, chloride ion coefficient, ultra-sonic pulse velocity (UPV), and water absorption tests were also carried out. Optimization of added materials was also done using a statistical tool called a design of experiments. Multi-variable statistical analysis was performed using response surface methodology (RSM) and analysis of variance (ANOVA). Both the experimental and statistical test outcomes depicted that introducing 5% ESP and 5% NS significantly improved the effectiveness of DHE steel fibers when the concrete was subjected to splitting tensile and flexural strength. UHPFRC with the 5% ESP and NS depicted 81% and 94% higher flexural strength than the reference mixture. While UHPFRC had almost 35 times higher flexural toughness than its counterparts. The inclusion of 5% and 10% eggshell powder depicted a favorable impact on the resistance of UHPFRC against the infiltration of water and chloride ions. The test outcomes of the present research confirmed the suitability and effectiveness of using ESP and NS as a partial substitute for OPC and significantly improved the engineering properties of UHPFRC, which was verified by the analytical results.

Development of an Ultra-High-Performance Fibre-Reinforced Concrete (UHPFRC) Manufacturable at Ambient Temperature

Ultra-high-performance fibre-reinforced concrete (UHPFRC) manufacturing typically requires heat curing. UHPFRC production at a ready-mixed concrete (RMC) plant is often difficult because specific equipment is required for heat curing. Concerns associated with ultra-high-performance concrete (UHPC) construction include the energy costs and environmental impacts of the heat curing and transportation from the factory to the construction site. Few studies have been conducted on the manufacturing of UHPFRC under standard curing conditions. The strength properties of UHPFRC manufactured under standard curing are typically poorer than those of UHPFRC manufactured under heat curing. The materials and mixture proportions required for the UHPFRC manufacturable under ambient temperature conditions were investigated. Five types of cement and four types of powder materials were tested, as well as the fine aggregate needed to achieve proper fluidity. This paper reports that the cement having low C3A and high C3S is suitable for the UHPFRC manufacturable at ambient temperatures; the allowable volume of fine aggregate was 600 kg/m3 for the UHPFRC having a proper dispersion of steel fibres; the highest water-binder ratio (W/B) of 21% was found for the UHPFRC cured under ambient temperature.

Revealing the effect of silica fume on the flexural behavior of ultra-high-performance fiber-reinforced concrete by acoustic emission technique

Silica fume (SF), a commonly used supplementary cementitious material for preparing ultra-high-performance fiber-reinforced concrete (UHPFRC), is known to greatly influence the microstructure of cementitious materials and the interfacial properties of fibers in cement matrix. These effects can be crucial to the mechanical properties of UHPFRC. This paper studied the effect of SF on the four-point flexural behaviors of UHPFRC. It was found that the load (strength)-deflection curve showed a more pronounced hardening branch and a steeper softening branch by SF addition, indicating potentially both increased toughness and brittleness properties at the respective stages. To reveal the implicit mechanism inducing these changes, the microstructural alteration during the flexural deformation of UHPFRC was analyzed by acoustic emission (AE) technique. Two types of acoustic events, i.e., matrix cracking and steel fiber vibration, were clearly distinguished, and the results suggest a two-fold effect brought by SF addition: The fiber-matrix interface was toughened but the cement matrix became more brittle. The flexural behaviors of UHPFRC were predominantly impacted by the latter effect with 10% SF addition, whilst the former effect played a dominant role at higher SF dosage rates (≥20%).

Nonlinear Inverse Analysis for Predicting the Tensile Properties of Strain-Softening and Strain-Hardening UHPFRC.

The tensile stress–strain response is considered to be the most important and fundamental mechanical property of ultra-high-performance fiber-reinforced concrete (UHPFRC). Nevertheless, it is still a challenging matter for researchers to determine the tensile properties of UHPFRC. As a simpler alternative to the direct tensile test, bending tests are widely performed to characterize the tensile behavior of UHPFRC, but require further consideration and a sophisticated inverse analysis procedure. In order to efficiently predict the tensile properties of UHPFRC, a nonlinear inverse method based on notched three-point bending tests (3PBT) was proposed in this paper. A total of fifteen UHPFRC beams were fabricated and tested to evaluate the sensitivity of the predicted tensile behavior to variations in fiber volume fraction. A segmented stress–strain model was used, which is capable of describing the various tensile properties of UHPFRC, including strain softening and strain hardening. A more approximate formulation was adopted to simulate the load–deflection response of UHPFRC beam specimens. The closed-form analytical solutions were validated by tensile test results and existing methods in literature. Finally, parametric studies were also conducted to investigate the robustness of the proposed method. The load–deflection responses obtained from notched 3PBT could be easily converted into tensile properties with this inverse method.

Effects of fibre orientation on tensile properties of ultra high performance fibre reinforced concrete based on meso-scale Monte Carlo simulations

The damage and fracture of ultra high performance fibre reinforced concrete (UHPFRC) is inherently dependent on fibre orientation and distribution. The effects of fibre orientation on the tensile properties of UHPFRC are investigated by meso-scale finite element (FE) simulations. The nonlinear bond-slip behaviour of fibre-mortar interfaces is explicitly modelled by zero-thickness cohesive elements with softening constitutive laws. After validation against existing experiments, extensive Monte Carlo simulations of FE models are conducted with different fibre volume fractions (1.5%, 2.0%, 2.5% and 3.0%) and orientation in the ranges of 0–90° (random), 0–30°, 30–60° and 60–90°, respectively. The fibre orientation is found to significantly influence tensile stress-strain relationships of UHPFRC, fracture patterns in the mortar, stress evolution in the fibres and bond-slip behaviour of the interfaces. Using more fibres is useful only when the fibres are reasonably oriented with respect to the tension direction, and a transition from brittle to ductile failure with strain hardening can be achieved by optimising the fibre orientation even for relatively low fibre content. Empirical equations are curve-fitted between the orientation number and key properties such as the elastic modulus, first-cracking stress and peak stress, which can be used to optimise tensile properties of UHPFRC members.

Investigation of long-term tension stiffening mechanism for ultra-high-performance fiber reinforced concrete (UHPFRC)

Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC) is promptly emerging concrete that has ultra-high compressive strength, and its ductile properties are ensured in the addition of steel fibers. Steel fibers in UHPFRC feature strain-hardening characteristics and exert the damage pattern as intimately spaced narrow cracks. The tensile performances of reinforced concrete elements are closely interrelated with the bonding interactions between the reinforcing rebars and concrete. Since the UHPFRC exhibits different tensile behavior and cracking behavior from traditional strength concrete, it is crucial to analyze the tension stiffening mechanism and cracking propagation of UHPFRC elements in long-term serviceability limit. This study presents the time-dependent tensile behavior of reinforced UHPFRC, especially on the instantaneous and sustained tension stiffening mechanism and post-cracking behavior for the long term. A newly designed testing rig was adopted to introduce the novel testing method. The testing rig was designed in a way to overcome the limitations in applying the sustained tensile loads found in the critical literature review. This novel testing method includes the design of the testing frame for intensive sustained tensile loads application, specimen preparations, and installations. To investigate the long-term tension stiffening mechanism, different types of sustained tensile loads, i.e., 20 kN, 40 kN, 60 kN, and 80 kN, were considered. The applied sustained tensile loads were ascertained from different percentages of cracking load (40 kN) of reinforced UHPFRC derived from the 28-day instantaneous tension stiffening test. Crack width and crack spacing of reinforced UHPFRC specimens were determined for both instantaneous and sustained tensile loads. Notably, crack propagation was considerably affected by the long-term sustained tensile loads compared to instantaneous tensile loads. The autogenous and drying shrinkage strains were 392 micro-strains (µɛ), and 170 µɛ, respectively, at 180-day, where the total shrinkage strain of 562 µɛ significantly influenced the time-dependent tension stiffening behaviors of UHPFRC. A maximum total average concrete strain of 3500 µɛ was found for the sustained tensile load of 80 kN at 180-day. In addition, the material properties of UHPFRC, such as compressive strength, splitting tensile strength, and modulus of elasticity tests, were also conducted, and the maximum compressive strength of 160 MPa was reported at 120-day.

Experimental and Numerical Investigation on the Size Effect of Ultrahigh-Performance Fibre-Reinforced Concrete (UHFRC).

In the last few years, there has been increasing interest in the use of Ultrahigh-Performance Fibre-Reinforced Concrete (UHPFRC) layers or jackets, which have been proved to be quite effective in strengthening applications. However, to facilitate the extensive use of UHPFRC in strengthening applications, reliable numerical models need to be developed. In the case of UHPFRC, it is common practice to perform either direct tensile or flexural tests to determine the UHPFRC tensile stress–strain models. However, the geometry of the specimens used for the material characterization is, in most cases, significantly different to the geometry of the layers used in strengthening applications which are normally of quite small thickness. Therefore, and since the material properties of UHPFRC are highly dependent on the dimensions of the examined specimens, the so called “size effect” needs to be considered for the development of an improved modelling approach. In this study, direct tensile tests have been used and a constitutive model for the tensile behaviour of UHPFRC is proposed, taking into consideration the size of the finite elements. The efficiency and reliability of the proposed approach has been validated using experimental data on prisms with different geometries, tested in flexure and in direct tension.

Mechanical and durability properties of ultra-high performance steel FRC made with discarded materials

This study investigates the mechanical and durability properties of 12 ultra-high performance fiber reinforced concrete (UHPFRC) mixes manufactured using alternate aggregate sources. Natural gabbro aggregates (GA), steel slag aggregates (SSA), and recycled concrete aggregates (RCA) were employed as coarse aggregates. The volume of the coarse aggregates was limited to 12.5% of the total UHPC volume. Three types of steel fibers were employed: macro hooked-end fibers, micro straight fibers, and a hybrid combination of these two fibers. The fiber volume fractions tested were 0% and 1%. Properties investigated were compressive and flexural tensile strengths, electrical resistivity, porosity, and rapid chloride permeability. Test results revealed that the effect of aggregate type was more pronounced on the flexural strength than compressive strength. UHPFRC with steel micro-fibers or a hybrid combination of both steel macro and micro-fibers had a more noticeable effect on the compressive strength than that with steel macro-fibers, irrespective of aggregate type. Moreover, UHPFRC specimens with steel macro-fibers showed the highest flexural strength, regardless of the aggregate type. The SSA improved all durability properties of UHPFRC, whereas RCA noticeably deteriorated the resistivity and chloride permeability. The incorporation of steel micro-fibers improved the porosity and chloride permeability of all UHPFRC mixes.

The effect of silane surface treatment on the mechanical properties of UHPFRC

Ultra-high performance fiber reinforced concrete (UHPFRC) is a new kind of cement-based composite material with high mechanical properties and excellent durability. However, the poor bonding properties between fiber and matrix in UHPFRC give rise to a weak fiber reinforcement effect. Therein, the surface of steel fiber was treated with γ-aminopropyl triethoxy silane to improve the interfacial bonding property of steel fiber. Optimal treatment of steel fibers with a silane coupling agent was determined through an orthogonal experiment. The mechanical properties, bending toughness, and energy absorption capacity of UHPFRC are investigated. The study found that bending toughness and energy absorption capacity of UHPFRC are increased by 47.6% and 78.0% with 2 vol% of treated steel fibers. The interface microstructure of steel fibers and matrix was characterized using advanced techniques, such as Fourier transforms infrared spectroscopy (FT-IR), X-ray spectroscopy (EDS), and electron microscopy (SEM). The mechanism of fiber treatment improving the interface bonding performance was revealed. This work provides a feasible method for the combination of reinforced steel fibers and the UHPFRC matrix.

Flow distance induced variation analysis of digitally segmented steel fibers in UHPFRC

Ultra-high performance fiber-reinforced concrete (UHPFRC) is a construction material with outstanding mechanical properties and durability. The degrees of dispersion and orientation of included steel fibers are known to have a decisive effect on UHPFRC’s material properties. In this study, UHPFRC specimens with different volumes of fibers were prepared to investigate the variation of spatial information of steel fibers in UHPFRC. Each sample was scanned individually through micro-computed tomography (micro-CT) to analyze the three-dimensional fiber statistics. To enhance the accuracy of the analysis, bundled fibers were digitally segmented through reliability-based maximum likelihood estimation (MLE) and a watershed algorithm. It was quantitatively found that the number of contact areas of bundled fibers decreased and fibers tended to be aligned more horizontally as flow distance increased. However, at the casting position and the opposite region, there was irregular distribution, which has the potential to affect the designed material properties of UHPFRC.

Effects of Steel Fiber Percentage and Aspect Ratios on Fresh and Harden Properties of Ultra-High Performance Fiber Reinforced Concrete

Steel fibers and their aspect ratios are important parameters that have significant influence on the mechanical properties of ultrahigh-performance fiber-reinforced concrete (UHPFRC). Steel fiber dosage also significantly contributes to the initial manufacturing cost of UHPFRC. This study presents a comprehensive literature review of the effects of steel fiber percentages and aspect ratios on the setting time, workability, and mechanical properties of UHPFRC. It was evident that (1) an increase in steel fiber dosage and aspect ratio negatively impacted workability, owing to the interlocking between fibers; (2) compressive strength was positively influenced by the steel fiber dosage and aspect ratio; and (3) a faster loading rate significantly improved the mechanical properties. There were also some shortcomings in the measurement method for setting time. Lastly, this research highlights current issues for future research. The findings of the study are useful for practicing engineers to understand the distinctive characteristics of UHPFRC.

Influence of steel fiber on compressive properties of ultra-high performance fiber-reinforced concrete

The compressive properties (include compressive strength and modulus of elasticity) of Ultra-high performance fiber-reinforced concrete (UHPFRC) are the most important performance index in structural design. This paper presents experimental results from tests conducted on 36 UHPFRCs with different volume fractions and aspect ratios of steel fiber to investigate the effect of steel fiber on the compressive properties of UHPFRC. The test results indicated that the compressive strength and modulus of elasticity of the hardened UHPFRC increase as the fiber volume fraction or aspect ratio increases. However, the increase trend of compressive strength and modulus of elasticity slowed down when the volume fraction exceeded 2%. It was observed that the steel fiber can restrain the occurrence and development of cracks when UHPFRC specimens are compressed, provided a positive effect for reinforcing UHPFRC, but it also reduced the flowability of fresh UHPFRC, which is negative for reinforcing effect. X-ray CT scanning revealed that the porosity and pore size of hardened UHPFRC increased with the increase of the fiber volume fraction due to its weakened flowability. A prediction model was established based on the analysis of the positive and negative effects of the steel fiber. Semi-empirical prediction formulas for the compressive strength and modulus of elasticity were proposed by regression analysis of the test data in this paper, which were verified and revised by the experimental database of 155 tests from literature. In addition, a relationship formula between modulus of elasticity and compressive strength of UHPFRC was presented, and was verified and revised by the experimental database of 320 tests conducted around the world.

Quantifying the Fatigue Material Properties of UHPFRC with Steel Microfibers at Cracks

AbstractThe addition of steel fibers to concrete in ultrahigh-performance concrete (UHPC) to form ultrahigh-performance fiber-reinforced concrete (UHPFRC) has been shown to have a great benefit by ...

Benefits of TiO2 photocatalyst on mechanical properties and nitrogen oxide removal of ultra-high-performance concrete

This study aims to develop a novel type of ultra-high-performance fiber-reinforced concrete (UHPFRC) with excellent mechanical properties and nitrogen oxide (NOx) removal capability. To achieve this, an inert filler, silica flour, was replaced with titanium dioxide (TiO2), which is known as a photocatalyst. The test results indicated that the average bond strength of a straight steel fiber embedded in ultra-high-performance concrete (UHPC) increased by replacing the silica flour with TiO2 powder up to 75% in general. Approximately 53% and 63% higher bond strengths and pullout energies, respectively, were thus achieved at 50% replacement rate. The tensile properties of UHPFRC were improved by TiO2, and its tensile strength slightly increased, while the strain capacity and g-value substantially increased. The energy absorbing capacity increased by as much as 78% due to the addition of TiO2 powder. Furthermore, the plain sample exhibited almost zero NOx removal efficiency, but increased with the replacement ratio of TiO2 powder up to 75%. The best NOx removal capability in the UHPC sample containing 75% TiO2 powder was thus 7.7 times higher than that of the plain sample.

The influence of normal curing temperature on the compressive strength development and flexural tensile behaviour of UHPFRC with vipulanandan model quantification

Ultra-high performance fibre reinforced concrete (UHPFRC) specimens were cast and cured at temperatures of 10, 20, 30, and 90 °C for periods of up to 360 days to investigate the long-term strength development. The influence of the three lower curing temperatures on the compressive and flexural tensile strengths and behaviour of UHPFRC was studied and compared to the results of 90 °C cured specimens. The results indicated compressive and flexural tensile strengths development at an early age were highly dependent on the curing temperature. The 90 °C cured specimens reached maximum compressive and flexural strengths within 7 days of casting. Specimens from the lower curing temperatures reached feasible striking compressive strengths (greater than 45 MPa) within 3 days of casting and achieved similar strengths to the 90 °C specimens after 90 days. Furthermore, various models such as the Vipulanandan model are developed to predict and correlate various mechanical properties of UHPFRC for any curing temperature, age and steel fibre content.