Ultra High Performance Fiber Research Articles

Optimizing ultra-high performance cementitious functionally graded composite slab towards bullet impact resistance

This study develops functionally graded composite slab (FGCS) by a one-time grouting approach based on the design concepts of ultra-high performance fibre reinforced concrete (UHPFRC) and two-stage concrete (TSC). The anti-penetration performance of the FGCS targets is investigated against 7.62 mm in-service bullets with shooting velocity of 843 m/s. The results show that while the TSC target presents superior bullet penetration resistance, it concurrently poses a significant threat of widespread cracking damage. Upon weighing the factors of bullet penetration and risk of cracking, the FGCS emerges as a more viable candidate for protective structures. The FGCS target is cast through a one-time grouting method, and there is no interface delamination under the projectile impact. The optimized FGCS exhibits enhanced in-service bullet impact resistance and a reduced safety thickness of 80 mm compared to the normal UHPFRC.

Design oriented shear strength prediction model of UHPFRC beams

The application of Ultra-high performance fiber reinforced concrete (UHPFRC) to beams can effectively improve their strength and ductility properties. At present, there are more shear test studies on UHPFRC beams, but few theoretical studies on their strength calculation method. The fibers in UHPFRC can inhance the strength of the beams, and how to quantify the fibers’ contribution to the total strength is a research difficulty. Firstly, the shear strength database including 197 UHPFRC beam specimens is created. The key characteristics determining the shear strength, namely fiber volume fraction, stirrup configuration, and shear-span ratio, are determined by evaluating the test results. Then, considering the effects of the factors above, a truss-arch model is developed. The arch shear strength is determined by utilizing the shear deformation coordination of the arch compression structs and truss compression structs. Superimposing the shear strengths of the arch and truss models yields the shear strength of UHPFRC beams. Finally, the accuracy and reliability of the proposed method are assessed using the test database and compared to existing shear strength calculations. The study findings demonstrate that the mean value of the calculated to observed shear strength ratios produced by the suggested technique is 1.10, with a coefficient of variation of 0.28, indicating that the proposed method has superior calculation accuracy and reliability than existing methods.

In-situ nonlinear ultrasonic technique for monitoring damage in ultra-high performance fibre reinforced concrete (UHPFRC) during direct tensile test

This paper aims to employ the nonlinear ultrasonic technique for the in-situ monitoring of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) structures subject to tensile loads. The UHFPRC, characterized by specific mechanical properties of high compressive and tensile strength, provides the basis for this investigation. Particularly, the nonlinear parameter β of the nonlinear ultrasonic technique is extracted by formulating a theoretical model that accounts for the interaction of contacting rough surfaces under tensile loads. The experimental findings substantiate that β provides enhanced sensitivity and feasibility for evaluating crack conditions compared to the measurements obtained through conventional Linear Variable Differential Transformers (LVDT). Furthermore, this study explores the potential application of β to estimate tensile load condition by: i) establishing an estimation equation grounded in the relationship between tensile load and displacement (kN-mm); ii) incorporating β into this estimation equation to calculate the anticipated tensile load; and iii) comparing real and estimated tensile loads. The analysis outcomes reveal that estimated tensile loads are in good agreement with the actual loads. Although the estimation equation is based on the findings of this study, it underscores the potential applicability of β for estimating the load conditions in various structures.

Experimental evaluation of flexural behavior of UHPFRC slabs utilizing local constituents

New ultra-high performance fiber reinforced concretes (UHPFRCs) are being developed throughout the world using locally-sourced materials to reduce financial and logistical burdens. Understanding force protection capabilities of these new materials requires experimental data that are useful for validating constitutive models or fast-running computational tools. Flexural performance of two UHPFRCs from different regions of the world are compared via one-way slabs subjected to uniform quasi-static loads. Results are also compared to a normal-strength concrete and two high-strength concretes from different regions. Results showed increased unconfined compressive strength of concrete leads to increased flexural resistance and stiffness. Furthermore, fiber reinforcement greatly increases flexural capacity in slabs but can cause brittle failure when combined with high reinforcement ratios of conventional reinforcement. While the UHPFRCs had different mechanical properties, both increased the maximum flexural capacity and showed potential for significantly improved performance for force protection applications.

Shear behaviour of reinforced concrete beams strengthened with ultra-high performance fiber reinforced concrete (UHPFRC)

Ultra-high performance fiber reinforced concrete (UHPFRC) is an advanced cementitious composite with high compressive strength and low permeability. Due to its excellent mechanical properties and superior durability, UHPFRC is considered promising for strengthening of the existing concrete bridges. In order to examine its strengthening efficiency for shear capacity, an experimental study is carried out on shear-deficient beams without stirrups. Strengthening method comprising precast UHPFRC laminates being glued with epoxy resin on two lateral sides of the reinforced concrete beams, is examined. To investigate the robustness of the system under severe exposure conditions, some beams are subjected to freeze-thaw (FT) cycles. Beams are tested to failure under three-point bending configuration. Test results show that for epoxy resin bonding, UHPFRC shear strengthening is a promising method to increase the load and deformational capacity, and to limit the crack openings. The load capacity is doubled, and the deformational capacity is increased by around 60%. After exposure to 30 FT cycles, the strengthening efficiency and fracture behaviour of UHPFRC composite beams seem not to be affected. It seems that the interfacial bond strength is sufficient to prevent premature debonding between UHPFRC and NC, which under combined action of environmental exposure (e.g. FT) and mechanical loading might become a challenge. Finally, a finite element model is developed to predict and understand the shear behaviour of the reference and strengthened beams. In general numerical results show good agreement with the experimental results in terms of failure pattern and peak load prediction once the perfect bond model is used for the interface between UHPFRC and NC. In order to better understand the role of governing parameters on the shear capacity of the composite member, parametric studies are conducted focusing on the role of varying UHPFRC softening behaviour and UHPFRC-concrete interface properties.

Proposed shear capacity equation for ultra-high performance fiber reinforced concrete beam containing coarse aggregate

This paper proposes a shear capacity equation for ultra-high performance fiber reinforced concrete beam containing coarse aggregate (UHPFRC-CA) and without coarse aggregate (UHPFRC) that captures all UHPFRC’s direct and indirect shear influencing factors. Six beam samples (each sample containing two beam specimens) were tested for shear strength under four point loading configuration using shear span-depth ratio (a/d), percentage volume of steel fiber (Vf), shape of steel fiber and stirrup spacing (s) as shear design parameters to obtain their ultimate shear strength (Vu). The obtained Vu was subjected to Analysis of Variance (ANOVA) to assess the significance of adding a coarse aggregate factor (dca) to the proposed equation. The proposed equation was validated by comparing its Vu with this study’s experimental Vu, other researchers’ Vu and Vu estimated using existing shear equations. ANOVA results showed that dca is significant in the Vu of UHPFRC-CA beams. Findings also revealed that the proposed equation does not only predict the Vu of UHPFRC-CA beams with a very high degree of accuracy but also gives better estimates of the Vu of UHPFRC-CA and UHPFRC beams when compared with the existing shear equations considered in this study. Further findings showed that the proposed equation reflects the effect of changes in Vf, a/d, s, ρ, shape of steel fiber and maximum size of coarse aggregate better than the existing shear equations for UHPFRC beams. Therefore, the proposed equation can be safely use for the shear design of UHPFRC-CA beam whose compressive strength ranges from 150 N/mm2 to 170 N/mm2.

Strengthening of Reinforced Concrete Columns Using Ultra-High Performance Fiber-Reinforced Concrete Jacket

The use of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) increased in the field of civil engineering throughout the last few decades. UHPFRC is being used considerably on a large scale in megastructure applications. High compressive and tensile strength permits reconstruction and optimization of the structural members. At the same time, its improved durability properties make it easier to extend the life of the design and can be used as thin layers, cladding, repairs, and column coverings. Although UHPC has an extremely high compressive strength, it exhibits very brittle fracture behavior compared to normal strength concrete (NSC). Since the ductility and fracture toughness of UHPC can be enhanced by adding fibers, the addition of fibers to production adds innovative features to UHPFRC structures and opens up new application areas for UHPFRC. The aim of this study is to investigate the axial behavior of square reinforced concrete (RC) columns strengthened with UHPFRC jackets. Nineteen specimens were cast (1000 mm in height and a cross-sectional area of 150 × 150 mm, whose interface treatment methods were prepared through vertical grooving (VG), horizontal grooving (HG), and without grooving (NG), with the jacket thickness (20 mm and 40 mm) and the number of strengthened sides of the column (two, three, and four sides). The results show a brittle failure for all strengthened specimens. The UHPFRC-reinforced RC columns with vertical grooving (VG) showed a higher ultimate load capacity compared to the columns with horizontal grooving (HG) and the columns without grooving (NG). The horizontal grooving (HG) gives a better result than the jacket without grooving (NG) and increases the cohesion area between the jacket and the column for two and three of the RC columns’ strengthened sides. But, in the case of strengthening the columns on four sides, the effect of confining the jacket to the column appears, and the grooving causes weakness in the body of the original column so that the jacket without grooving (NG) gives a better result than the jacket with horizontal grooving (HG).

Strength and sensitivity analysis of shear-deficient ultrahigh performance fiber reinforced concrete beams using hybrid neuro-fuzzy approach

Strength and sensitivity analysis of shear-deficient ultrahigh performance fiber reinforced concrete beams using hybrid neuro-fuzzy approach

Ultra-high performance fiber concrete for architectural purposes

The aim of the research works is the development of ultra-high-performance fiber concrete (UHPFRC) for architectual purposes, such as facade panels and their accessories. Research is aimed at achieving high utility properties in the form of high flexural tensile strength, low absorption and very good durability of the developed UHPFRC. The research is also focused on the development of the production technology itself, by pouring and spraying fresh UHPFRC mixtures into molds. The development of cast UHPFRC is also focused on the design and optimization of the production technology, which will enable an automatic production process and reduce costs for the production of flat facade panels. The development of sprayed UHPFRC will make it possible to produce 3D elements with higher utility properties compared to currently produced products from ordinary fiberglass concrete (GFRC).

Flexural properties of ultra-high performance fiber reinforced concrete based on three-dimensional random distribution of steel fibers

The distribution of fibers and the fiber bridging affect the flexural strength and energy dissipation of ultra-high-performance fiber reinforced concrete (UHFRC) members. In this study, an analytical model to predict the flexural behavior of UHPFRC was developed based on the three-dimensional random distribution of fibers. The probability distribution model of the fiber orientation was developed as a sine function, which agreed to the measured probability data from the randomly distributed fiber specimens. The number of fibers at the fracture surface was determined addressing the effect of fiber orientation. Based on the proposed model, the method to predict the load–deflection curve of UHPFRC beam was suggested addressing the fiber bridging stress at fracture surface and tension softening effect. For verification, the four points flexural tests were conducted for six UHPFRC beam specimens. The test results showed that the peak flexural strength and energy dissipation can be predicted by the proposed model. Further, the proposed model was applicable to predict the strength and deformation capacity of existing test specimens. Based on the proposed model, the aspect ratio of fibers to prevent the brittle failure due to fiber rupture was suggested addressing the fiber tensile strength and bond strength.

Effect of retrofit type on the blast performance and failure mode of HSC beams retrofitted with UHPFRC

This paper presents a strategy to prevent shear failure and improve the structural performance of existing high-strength concrete (HSC) beams under blast loading. The strategy involves retrofitting with ultra-high performance fiber reinforced concrete (UHPFRC), a novel material which is well-adapted for the blast hardening of concrete structures. Shock-tube air-blast tests are conducted on seven HSC beams which are retrofitted with UHPFRC. The objective was to characterize the effectiveness of various retrofit types on the blast behaviour of both shear-deficient and flexural-dominant HSC members. Three retrofit types were considered: U-jacketing (UJ), full-jacketing (FJ) and a tension-sided (T) overlay. Other parameters included the effects of the concrete substrate roughening method, as well as the tension steel ratio (1.6% or 2.4%) and presence of stirrups in the beams. Both the UJ and FJ retrofits were found to be effective in preventing shear failure in shear-deficient HSC beams having varying shear demands. In addition, both retrofits increased member strength and stiffness, thereby reducing blast-induced displacements and increasing overall blast resistance. Comparing the two retrofits, optimal performance was obtained with full-jacketing due its ability to delay concrete crushing. In HSC beams with sufficient stirrups, both the T-sided and FJ retrofits reduced blast-induced displacements; however, the use of full-jacketing was better able to control damage and increase blast capacity. The roughening method had no substantial effect on the FJ retrofit performance or failure mode, with no debonding observed in the tests.

Performance of corroded RC beams strengthened in flexure using UHPC: Effect of configuration and thickness of the UHPC layers

In the present paper, an experimental investigation was carried out to examine the effect of configurations and thicknesses of ultra high performance fiber reinforced concrete (UHPC) layers on the flexural performance of reinforced concrete (RC) beams strengthened using UHPC layers after undergoing different degrees of accelerated reinforcement corrosion. The beams were tested under flexure to evaluate the effect of UHPC strengthening (with combinations of three UHPC layer thicknesses and two configurations) on failure modes, flexural strengths, and stiffnesses. Statistical analysis of the flexural test results using analysis of variance (ANOVA) showed the significant effects of both configuration and thickness of the UHPC layers on the performance of corrosion-damaged RC beams in flexure, irrespective of the degree of reinforcement corrosion. The RC beams strengthened with UHPC layers applied on three sides exhibited the most significant increase in the ultimate flexural strength in the range of 6 to 63% and an increase in the stiffness in the range of 28 to 112% as compared to that of the uncorroded control beam. Furthermore, analytical models were developed to predict the flexural strength of the corroded beams strengthened using different configurations of UHPC layers. The close agreement of the ultimate flexural strength between the experimentally obtained results and analytically predicted values for the strengthened RC beams indicates the accuracy of the developed analytical models, which can be used to select an optimum strategy for strengthening the corrosion-damaged RC beams.

Composition-strength relationship study of ultrahigh performance fiber reinforced concrete (UHPFRC) using an interpretable data-driven approach

To study the relationship between composition and compressive strength of ultrahigh performance fiber reinforced concrete (UHPFRC), an interpretable data-driven approach is proposed. This approach addresses the high cost, complexity, time consumption and difficulty in studying the multivariate dependence effects of design parameters with traditional experimental methods. To construct the prediction model, 400 experimental data points are leveraged to compose the dataset, and five GridSearchCV (GSCV)-tuned ensemble machine learning (ML) approaches are evaluated. The GSCV-CatBoost model, with its higher prediction accuracy and lower error, i.e., R2 = 0.945, RMSE = 8.567 and MAE = 5.084, is proposed as a robust tool for predicting the compressive strength. Furthermore, the results of the SHAP analysis reveal that concrete age and steel fiber content are the most important features for predicting the compressive strength and those of the multivariate dependence effects analysis show that an increase in FRC will reduce the positive effect of the L/B on the compressive strength when the L/B exceeds 1. The feature importance and size effect of the specimen are noteworthy for material designers in the selection of suitable raw materials to achieve the desired strength properties. Finally, a reverse design method based on the abovementioned approach is proposed for the development of new UHPFRC materials. To maximize the effect of the model, the application range of the model is limited to the target compressive strength of 50–232 MPa and includes basic material parameters such as cement strength and silica fume, sand, steel fiber, water, and superplasticizer content.

Strengthening of the Riddes Viaduct Through UHPFRC-Based Rehabilitation

Built in the mid-1970s, the Riddes viaduct is an important viaduct in the Canton of Valais in Switzerland. Thorough inspection of the viaduct revealed structural deterioration of concrete due to alkali–aggregate reaction, as well as corrosion of the prestressing tendons. In an effort to restore the structural integrity of the viaduct, a retrofit intervention that consists of adding a 50 mm layer of an Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) to the deck was proposed. The layer is characterized by its low permeability and excellent mechanical properties. The contribution of the overlay to the load-carrying capacity and stiffness of the viaduct was investigated through a continuum finite element model. Results of the model revealed that the UHPFRC layer significantly enhances the flexural and torsional strength and stiffness of the box girder and ameliorates tensile cracking. The retrofit intervention was deemed beneficial, and the rehabilitation process was carried out.

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.

Numerical simulation and design method of the interface of UHPFRC-strengthened RC structures using post-installed rebars

The interface using post-installed rebar (PR) connections has been proven to possess robust mechanical properties for strengthening reinforced concrete (RC) structures with ultra-high performance fiber reinforced concrete (UHPFRC). However, current studies have not yet clarified the design method for this type of interface, which significantly hinders its widespread application. To this end, this study is devoted to developing a design method for the interface of UHPFRC-strengthened RC structures using PR connections. Detailed finite element (FE) models were established to capture the interfacial performance, and their accuracy was verified using the experimental data. An extensive parametric study was performed to identify the essential factors for interfacial performance. The FE results revealed that the concrete between the rebars failed before the rebars when the post-installed rebar spacing was three times the diameter of the rebar. Moreover, it was found that the thickness of the UHPFRC layer had a negligible influence on interfacial shear strength. The detailing requirements for the interfacial design using post-installed rebars were given. Combining the experimental and numerical findings, a design method was proposed for the interface of UHPFRC-strengthened RC structures using PR connections. An existing experimental study on RC beams strengthened by UHPFRC was chosen to examine the applicability of the proposed design method. It was found that the well-designed beam exhibited good ductility and energy dissipation capacity. The perfect bond was proved to be acceptable for analysis simplification when the UHPFRC-strengthened RC structures were well-designed by the proposed method.

Development of Ultra High-Performance Fiber reinforced concrete barge for 5 MW wind turbine

Floating wind turbines are gaining more popularity today as one of the effective green energy harvesting systems. In the effort to reduce the cost of construction for floating wind turbines, concrete support structures and concrete barge have been developed. However, due to the concrete low tensile strength and susceptibility to chemical action and freezing temperatures, the concrete barges are designed with very large sections resulting in high energy consumption, high volume of construction materials, weightier structure and more heavy equipment for fabrication and installation. Therefore, in order to overcome these challenges, in this study Ultra High-Performance Fiber Reinforced Concrete (UHPFRC) is proposed for use in casting a barge for a floating offshore wind turbine and compared to a reinforced cement concrete (RCC) barge. The experimental tests conducted on the UHPFRC and RCC barge small sized prototypes, showed less heel on the RCC barge compared to the UHPFRC barge. However, the RCC barge experienced severe green water load which could cause it to capsize. The hydrodynamic analysis results from the finite element analysis showed less pitch motions in the UHPFRC barge in 7 out of the 12 DLCs considered. The roll motions were less than 50 in both barges with insignificant difference between them, while in heave motions, the UHPFRC barge experienced 10% to 20% less motions than the RCC barge in all 12 DLCs. In the structural analysis, the maximum deformation of the UHPFRC barge was 14 mm, which is 129% higher than the deformation of the RCC barge. In overall, the UHPFRC barge proved to be more effective in achieving better hydrodynamic motions for the barge floater in comparison to the RCC barge and can be considered as alternative to the conventional reinforced cement concrete material.

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.

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.

Ultra-high Performance Concrete as a Sustainable Structural Composite

The phenomenal strides in the modifications and the use of supplementary cementitious materials in conjunction with superplasticizers and discrete fiber distributions in concrete made it possible to arrive at the structural material termed as “ultra-high performance concretes” (UHPC) or its extension “ultra-high performance fiber reinforced concretes” (UHPFRC). Its development heralded a new era, opening new vistas in structural configurations and forms that could be a serious contender to structural steel constructions. Primarily, the chemistry and physics of concrete constituents and mixture design philosophy have not changed much, though the intricacies that are often neglected were effectively corrected from time to time. The use of materials ranging from the conventional to nanoparticles that could exhibit superior pozzolanic activity along with microfibers resulted in strengths well beyond 200 MPa. This opens up several avenues in structural configurations that are of high strength and durability. However, this isn’t a stipulation of replacing the present-day concrete in all structures with UHPC, but the key is to modulate the structural configurations to suit the needs of the particular application for ensuring sustainability in consonance with the capabilities of UHPC. The paper attempts to look at the possible avenues for such options in materials and structural forms to effectively assure sustainable construction alternates.