Search Results (30)

This study investigated the mechanical responses and self-healing capability of incorporating superabsorbent polymer (SAP) particles in Fibre-Reinforced Ultra-High-Performance Concrete (UHPC) mixes under repetitive flexural and sustained tensile loadings. UHPC with SAP addition of 0.3% and 0.4% of the binder ratio were studied along with a control UHPC mix. The methodology included investigating the mechanical properties of these mixes under ambient, water, and 100% of relative humidity (RH) curing conditions. In addition, the mechanical performance of ambient-, water-, and 100% RH-cured prismatic specimens (100 mm × 100 mm × 500 mm) under repeated load was studied under the same curing conditions. Prismatic specimens (75 mm × 75 mm × 500 mm) were kept under cure conditions of wet and dry cycles with applied tensile load for 28 days for the sustained tensile load. The results showed that incorporating SAP into UHPC enhances the elastic modulus, flexural strength, and tensile strength. Also, mixes with SAP have exhibited compressive strength above 120 MPa after 90 days. Furthermore, the load recovery of the prisms under repetitive flexural load and prisms under sustained tensile loading demonstrated the self-healing efficiency of SAP incorporated into the UHPC mixes higher than the control mix specimens. Full article

Recent material science advances have resulted in the use of High-Performance Concrete (HPC) and Ultra-High-Performance Concrete (UHPC) in superstructures, which were chosen for their superior strength. However, under cyclic loads, these materials frequently show fatigue. Carbon-Fibre-Reinforced Polymer (CFRP) rods are replacing steel rebars due to their corrosion resistance and excellent strength-to-weight ratio and are thus gaining popularity in both infrastructural and superstructural design. However, due to a lack of understanding of their bond mechanics, modelling the interaction between CFRP rods and these advanced concretes in finite element simulations remains complex, particularly under cyclic loading. The bond behaviour of CFRP rods and both standard Grade 40 concrete and Ultra High-Performance Fibre-Reinforced Concrete (UHPFRC) under cyclic stresses is investigated in this work. A finite element model of connected concrete cube samples was built and analysed under cyclic stress, combining these concretes with CFRP rods. Furthermore, these samples were subjected to dynamic actuation testing to develop a traction-based constitutive model for the CFRP–concrete interface. In finite element models, an interface element devised for this study effectively approximated the binding, matching experimental data. The new analytical interface element improved simulation precision by 19% in displacement and 49% in pull-out force, resulting in a significant improvement in predicting the performance of the CFRP–UHPFRC bond under cyclic loading. The improved performance of the CFRP–UHPFRC bond under cyclic loading is attributed to the optimised interface model that enhances the bond integrity between CFRP rods and concrete. Full article

To investigate the toughening effect and stress–strain relationship of steel fibre-reinforced steel slag micropowder ultra-high-performance concrete (UHPC), nine sets of specimens with coarse aggregate and steel fibre contents were prepared for axial compression and elastic modulus tests. This study examines the variations in compressive strength and peak strain of the steel slag micropowder UHPC specimens to determine the corresponding characteristics of the stress–strain relationship. The results indicate that the experimental groups mixed with 1%, 1.5%, and 2% steel fibre increased the peak strain by about 20.3%, 25.3%, and 26.2%, respectively, compared to the non-steel fibre specimens. It can be seen that the toughening effect of UHPC with steel fibre and slag micro powder is good. With a fixed steel fibre content, the compressive strength and peak strain of steel slag micropowder UHPC initially increase and then decrease as the coarse aggregate content increases. The maximum compressive strength is achieved when the steel fibre content is 1.5% and the coarse aggregate content is 20%. A constitutive equation suitable for steel fibre-reinforced steel slag micropowder UHPC was derived through curve fitting based on the experimentally obtained stress–strain curves. The calculated values from the equation show deviations within 10% of the measured values, indicating a good fit. Nonlinear analysis of the entire compression process of prismatic specimens using the finite element method confirms the rationality of the constitutive equation, as the simulated curve closely aligns with the experimental curve. This research findings provide a reference for the engineering application of steel slag micropowder UHPC. Full article

Fabrication of ultra-high-performance concrete (UHPC) is costly, especially when commercial materials are used. Additionally, in contrast to conventional concrete, numerical procedures to simulate the behaviour of ultra-high-performance fibre-reinforced concrete (UHPFRC) are very limited. To contribute to the foregoing issues in this field, local materials were used in the fabrication process, while accounting for environmental issues and costs. Micro steel fibres ($L$: 13 mm, $d$: 0.16 mm, and $f_t:$ 2600 MPa; $L:$ length, $d$: diameter, $f_t:$ tensile strength) were used in 2% volumetric ratios. Compression and indirect tests were carried out on cylindrical and prismatic beams according to international standards. To further enrich the research and contribute to the limited simulation data on UHPFRC, and better comprehension of the parameters, numerical analyses were performed using the ATENA software. Finally, nonlinear regression analyses were employed to capture the deflection-flexural response of the beams. The results were promising, indicating cost-effective fabrication using local materials that met the minimum requirements of UHFRC in terms of compressive strength. Furthermore, inverse analysis proved to be an easy and efficient method for capturing the flexural response of UHPFRC beams. Full article

Ultra-high-performance fibre-reinforced concrete (UHPFRC) is a cementitious composite which contains fibres. UHPFRC has emerged as an effective structural retrofitting material due to its superior mechanical properties. In addition, UHPFRC has outstanding durability, ductility and workability; a low permeability; and a high abrasion and fire resistance. These improved characteristics of UHPFRC are obtained by reducing the content of free water in the concrete matrix (leading to less air voids), introducing high strength ductile steel fibres, replacing coarse aggregates with well graded fine aggregates and introducing highly active pozzolanic materials. UHPFRC has excellent bonding with normal strength concrete and it eliminates the issue of debonding which is common in other retrofitting techniques employing fibre-reinforced polymers or externally bonded steel plates. Therefore, considering various aspects, UHPFRC-based structural retrofitting possesses a number of advantages. This paper presents a review of previous studies employing UHPFRC for structural retrofitting applications, highlighting its advantages, limitations and challenges. Aspects of flexural strengthening, combined axial and flexural strengthening, shear strengthening, impact resistance and torsional strengthening are considered for this review. Altogether, the paper aims to enhance the awareness of UHPFRC for structural retrofitting as a step forward towards effective field applications and to outline the potential future directions of research. Full article

The reliability of numerical simulations of the structural response of nonhomogeneous materials to high velocity loadings is highly dependent on the used material model and parameters. For nonhomogeneous materials, such as fibres, reinforced concrete is widely used for the Winfrith model, but the question of appropriate material parameters for Ultra-High Performance Fibre Reinforcement Concrete (UHPFRC) under high velocity loadings is still open. The article deals with possible method of inverse identification of material parameters of a UHPFRC slab under blast loading for a Winfrith material model. Possible application is in the field of numerical simulation of protective or critical infrastructure response to blast loading. Experimental measurement of the time–deflection curve through laser scanning using the triangulation method gave us input data for an inverse identification phase conducted in Optislang software. Obtained material parameters from a given range are optimized for blast loading and their Pearson’s correlation coefficient provides us information about their significance for simulation. Full article

This work investigates the effect of various sand fractions on the ballistic resistance of ultra-high-performance steel-fibre-reinforced concrete (UHP-SFRC) samples. We specifically investigated replacing expensive and generally inaccessible microsands with commonly available sands. The tests and the measured values show that replacing part of the microsand with the more commonly and economically acceptable 0/2 mm aggregate fraction minimises the resulting mechanical properties and ballistic resistance. The most common type of ammunition was used to test all sample bodies, which is a 7.62 × 39 mm calibre with an all-metal jacket and a mild steel core. The damage’s extent and mode were determined using a 3D scanner operating on photogrammetry. Full article

In this paper, a prediction model for the tensile behaviour of ultra-high performance fibre-reinforced concrete is proposed. It is based on integrating force contributions of all fibres crossing the crack plane. Piecewise linear models for the force contributions depending on fibre orientation and embedded length are fitted to force–slip curves obtained in single-fibre pull-out tests. Fibre characteristics in the crack are analysed in a micro-computed tomography image of a concrete sample. For more general predictions, a stochastic fibre model with a one-parametric orientation distribution is introduced. Simple estimators for the orientation parameter are presented, which only require fibre orientations in the crack plane. Our prediction method is calibrated to fit experimental tensile curves. Full article

Nowadays, in Europe, several infrastructures, such as bridges, viaducts, and maritime structures, are in an advanced state of degradation. Therefore, novel repair/rehabilitation techniques are sought. Recent advances in ultra-high-performance fibre-reinforced cement-based composites (UHPFRC) represent a significant step towards resilient structures. In addition to their remarkable mechanical properties (compressive strength > 150 MPa), they present extremely low permeability and, as a premise, very high durability. Despite their relatively high cost, UHPFRC can be a competitive solution for rehabilitation/strengthening applications where smaller volumes are needed. UHPFRC applied in thin layers (with or without reinforcement) can replace carbonated and/or cracked concrete acting as a protective watertight and/or strengthening layer. The structural capacity increases (stiffness, ultimate strength), and the durability is expected to improve significantly while keeping cross-sectional dimensions. Additional advantages are expected, such as reduced intervention time, fewer maintenance routines, reduced life-cycle cost, and longer service life. Although much of the focus on UHPFRC has centred on mechanical and/or structural performance, durability is inevitably linked with mechanical properties. The current work evaluated the durability of non-property and greener UHPC concerning expansive reactions, alkali-silica reactions and expansion due to external sulphates, by macro and micro-scale integrative study. Linear expansion tests were performed in UHPC specimens according to ASTM C 1260 and LNEC E−364. At the macro level, no deleterious expansion due to ASR or external sulphate occured. Expansion due to ASR was 0.0018% after 14 days of immersion in an alkali-rich environment, and no expansion was recorded regarding sulphate attack. However, SEM analysis reveals reactive products of ASR and sulphate attack, namely, ASR gel and ettringite, respectively, in UHPC specimens. Full article

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. Full article

Materials such as high performance (HPC) or ultra-high performance concrete (UHPC), and fibre-reinforced polymer (FRP) reinforcement can be used to improve the resource efficiency in concrete construction by, for example, enabling the production of thin-walled structures. When building filigree concrete beams two essential factors must be considered: the low stiffness of the structure and the bond between the materials. By prestressing the structural stiffness is improved while an adequate concrete cover ensures sufficient bond strength. Based on this the bending behaviour of prestressed T-shaped beams reinforced with FRP, focussing on determining the influence of four parameters on the bearing capacity, bond behaviour and failure mode, is investigated in this paper. Comprehensive experimental investigations prove the potential of the approach and show that a reduction of the web thickness down to 40 mm, a lower concrete quality, and the use of glass FRP instead of carbon FRP allow a more resource-efficient structure while the applied prestressing leads to a higher utilisation of the high performance materials. Full article

The mechanical performance of fibre-reinforced ultra-high-performance concrete based on alkali-activated slag was investigated, concentrating on the use of steel fibres. The flexural strength is slightly higher compared to the UHPC based on Ordinary Portland Cement (OPC) as the binder. Correlating the flexural strength test with multiple fibre-pullout tests, an increase in the bonding behaviour at the interfacial-transition zone of the AAM-UHPC was found compared to the OPC-UHPC. Microstructural investigations on the fibres after storage in an artificial pore solution and a potassium waterglass indicated a dissolution of the metallic surface. This occurred more strongly with the potassium waterglass, which was used as an activator solution in the case of the AAM-UHPC. From this, it can be assumed that the stronger bond results from this initial etching for steel fibres in the AAM-UHPC compared to the OPC-UHPC. The difference in the bond strength of both fibre types, the brass-coated steel fibres and the stainless-steel fibres, was rather low for the AAM-UHPC compared to the OPC-UHPC. Full article

Concrete is the most commonly used construction material. The physical properties of concrete vary with the type of concrete, such as high and ultra-high-strength concrete, fibre-reinforced concrete, polymer-modified concrete, and lightweight concrete. The precise prediction of the properties of concrete is a problem due to the design code, which typically requires specific characteristics. The emergence of a new category of technology has motivated researchers to develop mechanical strength prediction models using Artificial Intelligence (AI). Empirical and statistical models have been extensively used. These models require a huge amount of laboratory data and still provide inaccurate results. Sometimes, these models cannot predict the properties of concrete due to complexity in the concrete mix design and curing conditions. To conquer such issues, AI models have been introduced as another approach for predicting the compressive strength and other properties of concrete. This article discusses machine learning algorithms, such as Gaussian Progress Regression (GPR), Support Vector Machine Regression (SVMR), Ensemble Learning (EL), and optimized GPR, SVMR, and EL, to predict the compressive strength of Lightweight Concrete (LWC). The simulation approaches of these trained models indicate that AI can provide accurate prediction models without undertaking extensive laboratory trials. Each model’s applicability and performance were rigorously reviewed and assessed. The findings revealed that the optimized GPR model (R = 0.9803) used in this study had the greatest accuracy. In addition, the optimized SVMR and GPR model showed good performance, with R-values 0.9777 and 0.9740, respectively. The proposed model is economic and efficient, and can be adopted by researchers and engineers to predict the compressive strength of LWC. Full article

The objective of the contribution is to understand the fatigue bond behaviour of brass-coated high-strength micro steel fibres embedded in ultra-high performance concrete (UHPC). The study contains experimental pullout tests with variating parameters like load amplitude, fibre orientation, and fibre-embedded length. The test results show that fibres are generally pulled out of the concrete under monotonic loading and rupture partly under cyclic tensile loading. The maximum tensile stress per fibre is approximately 1176 N/mm², which is approximately one third of the fibre tensile strength (3576 N/mm²). The load-displacement curves under monotonic loading were transformed into a bond stress-slip relationship, which includes the effect of fibre orientation. The highest bond stress occurs for an orientation of 30° by approximately 10 N/mm². Under cyclic loading, no rupture occurs for fibres with an orientation of 90° within 100,000 load changes. Established S/N-curves of 30°- and 45°-inclined fibres do not show fatigue resistance of more than 1,000,000 load cycles for each tested load amplitude. For the simulation of fibre pullout tests with three-dimensional FEM, a model was developed that describes the local debonding between micro steel fibre and the UHPC-matrix and captures the elastic and inelastic stress-deformation behaviour of the interface using plasticity theory and a damage formulation. The model for the bond zone includes transverse pressure-independent composite mechanisms, such as adhesion and micro-interlocking and transverse pressure-induced static and sliding friction. This allows one to represent the interaction of the coupled structures with the bond zone. The progressive cracking in the contact zone and associated effects on the fibre load-bearing capacity are the decisive factors concerning the failure of the bond zone. With the developed model, it is possible to make detailed statements regarding the stress-deformation state along the fibre length. The fatigue process of the fibre-matrix bond with respect to cyclic loading is presented and analysed in the paper. Full article

Ultra-high-performance steel-fibre-reinforced concrete (UHP-SFRC) is a technologically advanced composite with a high ability to absorb and dissipate mechanical energy. This work investigates the possibility of increasing ballistic resistance by adding different percentages of corundum and basalt aggregate into this type of concrete. The most common type of ammunition, a 7.62 mm × 39 mm calibre with a full-metal jacket and a mild-steel core (FMJ-MSC), was used to test all samples. The size of the damage and the mode of failure were determined using a 3D scanner operating on the principle of photogrammetry. The experimental campaign showed that the addition of basalt and, especially, corundum aggregate has a positive effect on ballistic resistance. In particular, the increase in compressive strength and the slight decrease in depth of penetration (DOP) was observed in the case of the usage of the corundum aggregate. Full article