Behavior Of Concrete Research Articles

Structural Behavior of Reinforced Fibrous Concrete Beams Incorporating Nano Silicon Dioxide Powder

ABSTRACTThis research investigated the combined effect of nano‐silicon dioxide (NSD) and steel fibers (SF) on the structural behavior of reinforced concrete beams. Eight specimens were tested: four without SF and four with SF, with varying NSD percentages (1%, 2%, and 3%) replacing cement. The study examined the mechanical properties of concrete and structural behavior outputs, including load‐deflection, ductility, and damage patterns. Results indicate that NSD significantly enhances compressive strength, with increases of 8.7%, 25.2%, and 32.5% for 1%, 2%, and 3% NSD, respectively. Combined with SF, there are additional improvements in tensile and flexural strengths, leading to higher load capacity and reduced deflection. Beams with 1% steel fibers showed a 30% higher load capacity compared with those without fibers. The ACI code was found to underestimate the load capacity of beams with NSD and SF, indicating the need for updated equations. While NSD increased concrete brittleness, SF enhanced ductility and energy absorption. Future research should focus on optimizing NSD and SF dosages, studying long‐term durability, and validating findings through large‐scale tests.

On the use of self-compacting concrete based on desert sand and granite powder

This article is dedicated to the valorization of local materials as substitutes in self-compacting concrete. We were interested in studying the effect of adding granite powder as a substitute for cement in a self-compacting concrete made of 100% desert sand, and also as a substitute for river and/or quarry sands. First, the dosage of the superplasticizer on the cementitious paste is optimized and then confirmed this percentage in the case of concrete. Subsequently, several concrete formulations were produced. Then, the rheological, mechanical, and durability behavior of these self-compacting concretes with different percentages of granite powder and superplasticizer were studied by carrying out characterization tests in the fresh state [slump-flow, L box, sieve stability test, density] and the hardened state [Compressive strength, verification of static segregation, etc.]. From the results obtained, the concrete composition with 1.7 % superplasticizer and 10 % granite was found optimal, following the recommendations of the AFGC 2008 standard. The durability tests results of this concrete and the analysis of its behavior at high temperatures have confirmed that the formulation adopted can be used in severe working conditions.

Numerical Study For The Behavior of Novel Concrete Filled Built-up Cold Formed Steel Columns Under Compression Load

Numerical Study For The Behavior of Novel Concrete Filled Built-up Cold Formed Steel Columns Under Compression Load

High temperature performance of recycled fine concrete

The objective of this study is to explore the physical and mechanical behaviour of concretes comprising four different ratios of recycled fine (RF), namely (5%, 10%, 15% and 20%) along with that of a reference concrete (Cref-0%), under three different heating–cooling cycles (200 °C, 400 °C and 600 °C). The thermal properties of concrete during heating and cooling (20 °C – 600 °C – 20 °C) were also investigated. It was determined that the physical properties (mass loss and ethanol porosity) of recycled concrete (RC) with 5% of recycled fine (RC-5%) were similar to those of Cref-0%. At ambient temperatures, the higher the ratio of recycled fines, the lower the residual compressive strength and residual elastic modulus of the recycled concrete. After thermal loading at 600 °C, the residual mechanical properties of all types of concrete were equivalent, regardless of the content recycled fine.

Effect of cementitious capillary crystalline waterproof material on the mechanical behavior of concrete

Cementitious capillary crystalline waterproof material (CCCW) is a material that can react with substances inside the concrete, generating crystals that fill the pores and cracks in the concrete. This chemical reaction is expected to improve the mechanical properties of the concrete. This study investigated the effects of CCCW content and water-cement ratio (W/C) on the compressive behavior of cementitious capillary crystalline waterproof concrete (CCCWC). The results indicated that as the CCCW content increased from 0% to 1.5% for W/C of 0.4, the compressive and tensile strength values of concrete slightly decreased. This is because excessive CCCW generates too many crystals within the concrete, leading to internal matrix expansion and crack formations. However, in the cases of W/C of 0.45 and 0.5, the compressive and tensile strength values of the CCCWC increased wit increasing CCCW content from 0% to 0.5%, but declined with 1.5% CCCWC addition. The reaction between CCCW and concrete generates numerous crystals, which densify the concrete matrix and enhance its strength. Moreover, with increasing W/C, the CCCWC's compressive strength and tensile strength decreased due to the increased porosity of the concrete matrix and the reduced availability of the concrete constituents that react with CCCW. Furthermore, the appropriate choice of CCCW content and W/C can significantly enhance the slope and peak stress of the stress-strain curve. Based on this, a compressive constitutive model of CCCWC was established. The findings showed that the optimal CCCW content varied with W/C. For instance, for a W/C of 0.4, the maximun compressive strength of 54.82 MPa was achieved without any CCCW addition. In contrast, the addition of 0.5% CCCW to concrete produced with W/C of 0.45 and 0.5 resulted in the highest compressive strengths of 50.98 MPa and 44.90 MPa, respectively.

Comparative analysis of flexural strength prediction in SFRC using frequentist, Bayesian, and Machine Learning approaches

Steel fiber reinforcement significantly enhances the flexural strength of concrete, which is vital for structural integrity. Annex L of the new Eurocode 2 classifies steel fiber-reinforced concrete by its flexural performance, aiding engineers in designing resilient structures. This study investigates the flexural behavior of steel fiber-reinforced concrete (SFRC) using three data-driven methodologies: Frequentist Inference (FI), Bayesian Inference (BI), and Machine Learning (ML). A comprehensive database was constructed from three-point bending tests on SFRC specimens, encompassing various compressive strengths, fiber quantities, and geometric parameters, to identify key factors influencing material properties.The findings indicate that all three methodologies yield comparable predictive capabilities for flexural responses in SFRC. Notably, FI models emphasize the importance of compressive strength and fiber volume fraction, along with fiber properties such as non-dimensional length and tensile strength. BI models enhance predictive stability by integrating prior knowledge and quantifying uncertainty, demonstrating their advantage, particularly in data-scarce situations. Additionally, ML analysis reveals that linear regression (LR) models can achieve accuracy similar to or greater than that of more complex models. This research provides novel insights into the application of BI and ML in concrete technology, emphasizing their potential to enhance predictive modeling. Additionally, it offers practical guidelines for optimizing SFRC design through a case study that compares residual flexural strengths obtained via Bayesian analysis, classifying the material in accordance with Annex L of the new Eurocode 2.

Flexural tensile behaviour of alkali-activated slag-based concrete and Portland cement-based concrete incorporating single and multiple hooked-end steel fibres

In this study, three-point bending tests on notched beams according to EN 14651 have been performed to evaluate the flexural post-cracking behaviour of alkali-activated slag-based concrete (AASC) and Portland cement-based concrete (PCC) incorporating single (3D) and multiple (4D, 5D) hooked-end steel fibres in different volume fractions up to 0.75%. According to the experimental results, the post-cracking residual flexural strength increases with the increase in the fibre volume fraction for each fibre and concrete matrix type. AASC mixes incorporating 3D and 4D fibres show higher values of residual flexural strength for the same crack opening than PCC mixes with the same fibre type and dosage. Only for the mixes incorporating 5D fibres, steel fibre-reinforced PCC (SFRPCC) mixes outperform steel fibre-reinforced AASC (SFRAASC) mixes in terms of post-cracking behaviour. According to EN 14651, the values of the residual strengths and , corresponding to a crack mouth opening displacement (CMOD) of 0.5 mm and 2.5 mm, respectively, and their corresponding characteristic values and , respectively, can be derived from the experimental load-CMOD curves. Following the fib Model Code 2020, each mix can then be classified according to the values of and the ratio. As a result, empirical models have been developed for SFRPCC to predict the values of and and the applicability of such models to SFRAASC is evaluated in this study. Once the values of and are known, tensile constitutive models can be derived according to the fib Model Code 2020 and used as input parameters for finite element modelling. In this study, the accuracy of the code-based constitutive model to predict the flexural behaviour of SFRAASC and SFRPCC is evaluated using the concrete damage plasticity (CDP) model available in ABAQUS. The numerical model based on the tensile stress-strain curve in the fib Model Code 2020 can qualitatively capture the post-cracking behaviour of SFRAASC and SFRPCC incorporating 3D, 4D and 5D at 0.25% fibre volume fraction, despite overestimating their tensile strength. For higher fibre volume fractions, the CDP model, in conjunction with the mode I parameters derived from the fib Model Code 2020, is unable to adequately describe the post-hardening behaviour exhibited by the composites.

Experimental and theoretical investigation on axial tensile behavior of ultra-high performance concrete (UHPC) with recycled steel fibers from waste tires

Experimental and theoretical investigation on axial tensile behavior of ultra-high performance concrete (UHPC) with recycled steel fibers from waste tires

Effect of loading area on triaxial compression behavior of microcapsule-based self-healing concrete

Concrete is customarily subjected to a complex triaxial stress state in structures under service. True triaxial experiments using cubic specimens in laboratory settings often utilize shims marginally smaller than the specimen surface for loading purposes. However, the influence of shim dimensions on the triaxial mechanical characteristics of concrete remains obscure. Therefore, in this study, for urea-formaldehyde (UF)/epoxy microcapsule-based self-healing concrete, shims of varying sizes were designed to conduct true triaxial compression experiments, examining the effects of loading area size and microcapsule content on triaxial mechanical behavior. The crack damage morphology was observed using a scanning electron microscope (SEM), the rupture of microcapsules was analyzed through energy-dispersive X-ray spectroscopy (EDS), and the micropore structure was determined via nuclear magnetic resonance (NMR). The research findings reveal that reducing the loading area induces stress concentration near the shim edge, significantly decreasing the first peak strength with a maximum reduction of 37%; while also increasing the second peak strength, with a maximum increase of 52%. Notably, a “sleeve-like” delamination occurs when the loading area is below 95% of the specimen surface area. Incorporating microcapsules into concrete enhances ductility and porosity, achieving a maximum 1.9% increase in first peak strain and 1.98% in porosity. This study may offer valuable insights and data for the optimization of concrete materials and structural design, thereby contributing to the safety and durability of engineering structures.

Effect of steel fibers on the stress–strain behaviour of aligned steel fiber ultra-high performance concrete under uniaxial compression

The mechanical properties of ultra-high performance concrete (UHPC) can be significantly enhanced by aligning the fibers. Aligned steel fiber UHPC (ASF-UHPC) was fabricated using a uniform magnetic field, yet the corresponding stress-strain relationship has not been extensively studied, hindering accurate calculations. To address this gap, ASF-UHPC was prepared and subsequently subjected to CT scans and uniaxial compression tests to investigate its stress-strain behavior. The analysis of failure mode and stress-strain curves revealed distinct anisotropic characteristics in compressive stresses and fiber distributions. Various steel fiber parameters, including the alignment orientation, volume fraction, and length, were systematically analysed to assess their impact on the material properties. A unit-cell model was developed to elucidate the influence of the fiber alignment orientation on UHPC performance. The results demonstrate that a parallel fiber alignment significantly enhances the elastic modulus, albeit with a Poisson ratio similar to that of the matrix, owing to the limited lateral confinement. Conversely, perpendicular fiber alignment restrains lateral deformation, enhancing the material strength and toughness. Randomly distributed fibers offered a degree of horizontal confinement, whereas inclined fibers induced horizontal thrust, leading to excessive lateral deformation and consequent elevation of the Poisson ratio. Finally, predictive equations for UHPC elastic modulus and compressive strength, along with an analysis model for stress-strain characteristics, were refined taking into account the direction of fiber arrangement.

Effects of air content on rheological behavior and segregation of self-compacting concrete

Self-compacting concrete (SCC) offers significant advantages due to its low yield stress and plastic viscosity, yet challenges such as bleeding and segregation can compromise its stability. Maintaining a uniform aggregate distribution is essential to prevent these issues. Air-entraining admixtures (AEA) are often used to introduce air bubbles that enhance SCC's resilience in freeze-thaw conditions and potentially improve stability. This study addresses contradictions in prior research regarding the impact of entrained air on SCC's rheological behavior, experimentally evaluates the effects of varying air content on SCC's workability and segregation resistance, and establishes correlations between rheological characteristics and segregation stability. A comprehensive series of rheological tests, including slump flow diameter, flow time, blocking rate, segregation stability, plastic viscosity, yield stress, and segregation index, was conducted on SCC mixes with different AEA dosages. Regression models revealed significant correlations between air content and both the stability and workability of SCC, with results indicating that optimal AEA levels improve flowability and reduce segregation risks. These findings provide valuable insights into designing stable, high-performance SCC formulations tailored for challenging structural applications.

Stress-strain relationship of airfoiled-shaped milled-cut steel fiber-reinforced concrete under uniaxial compression: Experiments and analytical model

The long-term service of concrete structures to severe environments has driven up performance requirements in terms of durability, crack resistance and toughness. Milled-cut steel fiber (MSF) holds great potential for corrosion resistance and reinforcement of concrete, benefiting from its optimized geometric and surface properties. The stress-strain relationship and damage characteristics of milled-cut steel fiber-reinforced concrete (MSFRC) under compression can serve as experimental and theoretical foundations for structural design. Thus, this study conducted compression tests on MSFRC at three different contents (Vf=0.6 %, 1 %, 1.4 %) and investigated the experimental analysis results of the full-range compressive response. Crimped steel fiber (CSF) and hooked-end steel fiber (HSF) were selected as comparison groups to confirm the effect of fiber geometry. Failure mode, toughness, and parameters characterizing the uniaxial compressive behavior of various steel fiber-reinforced concrete were experimentally assessed. The results indicate that the addition of MSF fibers increases the toughness of concrete by over 25 % compared to other types of fibers. MSF prevents the propagation of axial primary cracks and controls the maximum crack width to less than 1 mm. The negative effect of high fiber dosage on compressive strength is mitigated in MSFRC, and the optimal strength and toughness can be achieved when containing 1 % volume fraction fibers. Empirical formulas are developed to accurately predict the compressive strength and elastic modulus of MSFRC by incorporating a fiber reinforcing index (RI), with R2 value of 0.93. Furthermore, a constitutive model describing the complete stress-strain behavior under uniaxial compression has been developed for MSFRC.

Influence of ambient temperature and humidity on the evolution of the tension softening behavior in concrete

The tension softening relationship is a crucial input parameter for modeling the crack propagation in concrete. To examine the influence of curing conditions on this parameter, fracture tests were performed on specimens kept at different temperatures and humidity levels across various ages. A best-fit maturity method for identifying optimal maturity model parameters was proposed and validated using test data. The results indicated that the area beneath the first branch of the softening curve increases, whereas the area under the tail decreases with ongoing hydration and higher humidity. The tensile strength ft and centroid coordinate σcg (vertical coordinate of softening curve area center) increase with rising temperatures up to 14 days, after which the trend reverses, with higher later-age ft and σcg observed in specimens exposed to elevated temperatures. Under high temperatures, the critical crack width wc (ultimate width at zero cohesive stress) and centroid coordinate wcg decrease. At the early stage, humidity has minimal effect on concrete softening properties. However, as the hydration progresses, the impact of decreasing humidity becomes more significant. At 60 days, ft, σcg, and wc are reduced by 23.3 %, 22.8 %, and 19.6 %, respectively, as humidity drops from 98 % to 30 %. The developed best-fit maturity method can predict various concrete properties with a maximum relative error within 7 %. The optimal activation energy Ea and moisture diffusion coefficient γ vary across temperature and humidity ranges, making it unfeasible to use a single set (Ea, γ) to predict properties under varying curing conditions.

Compressive behavior of concrete jacketed in basalt TRM shell: Experiments and predictions

Numerous studies have investigated the behavior of textile reinforced mortar (TRM)-confined concrete, yielding various stress-strain models predominantly derived from fiber-reinforced polymer (FRP)-confined concrete. Yet, these models frequently overlook the intricate constitutive behavior of TRM materials and inadequately capture how TRM delivers its confinement effects. This often leads to inaccurate representation of the true characteristics of the confinement system, particularly the crucial role of mortar. This paper focuses on the impact of variations in textile layers and mortar matrix strength on the stress-strain behavior of basalt TRM (BTRM)-confined concrete, aiming to enhance our understanding of the confinement mechanism. Additionally, the study critically evaluates the key components of an existing analysis-oriented stress-strain model for FRP-confined concrete and introduces a refined version that more precisely depicts the behavior of confined concrete. This refined model integrates an identified confinement mechanism to provide accurate predictions of BTRM-confined concrete behavior. Our results reveal that low-grade mortar significantly decreases the actual confinement stiffness of BTRM jackets, inducing a steeper decline in the stress-strain curve, while high-strength mortar slightly diminishes the hoop rupture strain. To address the challenges of quantifying the complex confinement effect-compounded by the variable stress state and constitutive behavior of TRM-a novel coefficient, termed km, is introduced to gauge the influence of mortar strength on the confinement stiffness within the confining pressure equation. Predictive outcomes, including stress-strain and axial-to-lateral strain curves, show close alignment with experimental data, particularly in the slope at the plateau stage. This research significantly advances the quantitative understanding of TRM confinement effects and proposes the potential for designing more ductile structures using these materials, which could lead to enhanced resilience against seismic events and other structural challenges.

Experimental study on the shear behaviour of high-strength lightweight concrete beams incorporating graphene oxide

Graphene oxide (GO) has achieved significant progress in the material behaviour of cement-based materials. However, research on its structural behaviour in high-strength lightweight concrete (HSLWC) structures is limited, which restricts its engineering applications. This study focused on investigating the effects of low contents of GO on the shear behaviour of HSLWC beams. A total of four HSLWC beams with GO contents of 0, 0.01, 0.03 and 0.05% (by weight of cement) were designed to observe failure modes, load‒deformation curves, shear capacities, crack behaviour and load‒strain curves under four-point loading by a 300 kN servo loading device. The results revealed that all the beams exhibited shear compression failure. GO improved the shear capacity of the HSLWC beams, and this strengthening effect increased with increase in GO content. When the content of GO was 0.05%, the ultimate load of the beam reached a maximum, which was 39.2% greater than that of the control beam. GO can endow the HSLWC beams with a certain degree of ductility. In addition, a modified JGJ 12-2006 model was proposed to predict the shear capacity of HSLWC beams containing different GO contents on the basis of a comparison of typical models. This study can provide exploratory engineering practice for evaluating and designing GO-reinforced HSLWC structures.

Influence of Specimen Width on Crack Propagation Process in Lightly Reinforced Concrete Beams.

Models used to study the fracture process of concrete are often considered 2D, ignoring the influence of specimen width. However, during the fracture process in pre-cracked concrete beams, the crack length varies along the thickness direction, especially in reinforced concrete. To study the influence of specimen width on reinforced concrete fracture behavior, a 3D numerical method was used to simulate the crack propagation processes of lightly reinforced concrete beams based on Fracture Mechanics. Nonlinear spring elements with different stress-displacement constitutive laws were employed to characterize the softening behavior of concrete and the bond-slip behavior between the steel bars and concrete, respectively. It is assumed that the crack begins to propagate when the maximum stress intensity factor at the crack tip along the beam width reaches the initial fracture toughness of concrete. To verify the validity of the proposed method, the completed crack propagation processes of lightly reinforced concrete three-point bending notched beams were simulated, and the calculated load-crack mouth opening displacement curves showed a reasonable agreement with the experimental data. Moreover, the impact of the 2D reinforced concrete beam model on the crack propagation process was analyzed. The results indicate that at the initial loading stage, the external load P obtained from the 2D model is significantly larger than the result from the presented 3D model.

Development and validation of the chronic condition physician-patient relationship scale (CC-PPR): A patient-informed measurement tool

ObjectiveSeveral tools exist to measure the physician-patient relationship; however few are specific to those with chronic physical health conditions, and none to date have been derived from the patient’s perspective. This research aimed to develop and validate a patient-informed tool for measuring the physician-patient relationship with patients who have a chronic physical health condition. MethodsStudy 1: An Australian sample of participants with a diagnosed chronic physical health condition and a self-reported good physician-patient relationship completed a three round Delphi poll to determine items of the chronic condition physician-patient relationship scale (CC-PPR). Fifty-two participants completed round one, 33 completed round two, and 24 completed all three rounds. Study 2: Exploratory and confirmatory factor analysis were conducted on a separate sample (N = 226) to explore the factor structure of the CC-PPR. ResultsThe CC-PPR comprised 22 items within a single-factor structure which demonstrated high internal consistency (Cronbach’s α = 0.97) and sound convergent validity. DiscussionThe CC-PPR reliably measures observable, concrete, and specific physician behaviours that patients with chronic physical health conditions believe are critical in forming a good physician-patient relationship. The CC-PPR has potential application in research, educational, and self-assessment contexts, including for the evaluation and development of competence in post-graduate and professional settings.

Flexural post-cracking performance of macro synthetic fiber reinforced super workable concrete influenced by shrinkage-reducing admixture

Most literature has focused on the effect of shrinkage-reducing admixture (SRA) in shrinkage mitigation resistance of concrete. This study aims to examine the impact of SRA on the efficiency of macro synthetic fibers (MSF) in enhancing the flexural post-cracking behavior of fiber-reinforced super workable concrete (FR-SWC). A comparative analysis of the influence of fiber combinations on the flexural post-cracking behavior of beams is also included. Results showed that a higher dosage of SRA, particularly at 5 % by mass of binder, had a noticeable negative impact on flexural post-cracking performance of beams while exhibiting positive effect on workability and shrinkage reduction. However, incorporating low dosages of SRA (1.25 % by mass of binder) did not have a significant impact on the ability of MSF. This was attributed to the reduction of the MSF-matrix bond strength caused by a significant delay in cement hydration. The characteristics of selected MSF type, including length and surface roughness had a positive effect on the post-cracking performance of FR-SWC, regardless of SRA dosage. The notched beams made with 100 % MSFA outperformed those made with fiber combination of 25 % MSFA and 75 % MSFB. Beams made with 100 % MSFA showed 55 % higher residual flexural tensile strength, 49 % higher equivalent flexural tensile strength, 50 % higher fracture energy, and 35 % higher equivalent flexural strength ratio compared to beams made with fiber combination of 25 % MSFA and 75 % MSFB. Therefore, the negative effect of SRA on the flexural-post cracking behavior can be partial compensated by adjusting MSF content and combinations.

Spalling behavior in ultra-high performance concrete: multi-technique insights and multi-scale fiber-rubber mitigation strategies

Explosive spalling of ultra-high performance concrete (UHPC) at elevated temperatures is one of the main problems limiting its application. While the intrinsic mechanism governing the spalling is determined by the UHPC matrix. Therefore, in this paper, multi-technique characterization approaches, i.e., acoustic signal characteristics, fractal characteristics of spalling fragments, and thermal cracks are employed to quantitatively characterize the spalling of the UHPC matrix. The effects of moisture content, heating rate, geometric characteristics of specimens, mineral admixtures, crumb rubber content, and fibers on concrete spalling are investigated to reveal the explosive spalling mechanism, reduce the risk of explosive spalling, and develop a spalling-resistant material. The waveform, cumulative energy, and spectrum of the spalling acoustic signal are used to assess the intensity of concrete spalling. The results show that the UHPC matrix with high moisture content, high heating rate, and large specimen size undergoes violent spalling events characterized by larger amplitude and smaller frequencies of acoustic signals. Incorporating crumb rubber increases the spalling events in the frequency range of 8000–10000 Hz, which plays a positive role in alleviating spalling. Meanwhile, the fractal characteristics of spalling fragments and thermal cracks can also quantitatively reflect the intensity of concrete spalling (i.e., the larger the fractal dimension, the more severe spalling). By minimizing the moisture content and heating rate, as well as increasing rubber content, the spalling fragments can be larger and the fractal dimension can be reduced. It is also found that saturated specimens spall with significant cumulative energy. While the specimens with a large size and low moisture content spall with lower cumulative energy and an increase in the proportion of spalling fragments in the small particle size range. A higher heating rate and larger specimens can induce a higher thermal stress, which can be more likely to spall explosively. While a lower moisture content can result in explosive spalling at a higher heating rate. Hence, it is believed that thermal stress can be the dominant factor affecting explosive spalling and the moisture content can be an accelerator. The addition of multi-scale fibers completely prevents explosive spalling by releasing vapor pressure from the channels created by fiber melting and improving the tensile strength of concrete, which also effectively restricts the thermal cracking of UHPC due to their hybrid bridging effects.

Thermal behavior of pervious concrete in wet conditions

Thermal behavior of pervious concrete in wet conditions