Concrete Structural Components Research Articles

Behavior of zero cement reinforced concrete slabs under monotonic and impact loads: Experimental and numerical investigations

Currently, there is a shift toward the use of low-carbon construction materials to reduce global carbon dioxide emissions. Zero-cement concrete (ZCC) synthesized from alkaline activated fly ash (FA) is a promising alternative for Portland cement in the construction industry to reduce global CO2 emissions, increase the consumption of waste materials, and save energy. A substantial amount of research on the impact load behavior of ordinary reinforced concrete (RC) structural components has been conducted. However, investigations on the behavior of zero cement concrete (ZCC) slabs under impact loads have not been reported. In this work, twenty simply supported two-way flat reinforced fly ash ZCC slabs (including two normal concrete (NC) slabs as reference samples) were tested under monotonic and impact loads. The test samples were categorized into eight groups on the basis of various parameters. Twelve RC slabs (1 NC and 11 ZCCs) were prepared for repeated impact tests, and eight slabs (1 NC and 7 ZCCs) were prepared for monotonic loading tests. Various parameters were investigated herein, including slab thickness, bar spacing, molarity concentration of alkali activators, hammer height, and hammer mass. Nonlinear finite element models were also developed and validated by using ABAQUS software for additional parametric study purposes. The results revealed that the behavior of ZCC slabs is approximately similar to that of NC slabs. The results also revealed that an increase in the ZCC slab thickness, reinforcement ratio, hammer height, and hammer mass has a noticeable effect on the dynamic response of the slab. However, increasing the molarity concentration of alkali activators has clearly a slight influence on the impact loadtime history. When the slab thickness was increased or the bar spacing was reduced, the static and impact energy absorption capacities were increased by 1.5 and 2.0 times, respectively. For impact load tests, the damage degree, penetration, and cracking pattern at failure were approximately typical for all test samples at the first hit except when the hammer mass and impact height were changed. For the samples subjected to monotonic loading, a flexural response was observed for almost all the slab samples at the first loading stage, and cracking started from the midpoint of the slab and propagated toward the slab edges; ultimately, punching shear failure was observed.

Research Progress on Recycled Aggregate Concrete Structural Components (I):Short-Term Mechanical Performance

Research Progress on Recycled Aggregate Concrete Structural Components (I):Short-Term Mechanical Performance

Research Progress on Recycled Aggregate Concrete Structural Components (II):Long-Term Service Performance

Research Progress on Recycled Aggregate Concrete Structural Components (II):Long-Term Service Performance

Preparing Design Aids for Fe550 Steel for M20 Grade of Concrete Using SP-16

Abstract: The main purpose of this paper presentation is to develop design aids for Fe 550 grade of steel from sp 16 handbook. The design aids prepared will be in the form of tables which will benefit in the calculations of various components of concrete structures. To prepare design aids for FE550, you would need to focus on creating resources that cover various aspects related to structural design, specifically for materials like Fe550. Design aids typically include information on material strength, stressstrain relationships, flexural members, compression members, shear and torsion, development length, anchorage, deflection calculation, and general tables, explanations of the basis of preparation, and worked examples illustrating the use of the design aids.

Preparing Design Aids for Fe550 Steel for M25 Grade of using Concrete from SP-16

Abstract: The main purpose of this paper presentation is to develop design aids for Fe 550 grade of steel from sp 16 handbook. The design aids prepared will be in the form of tables which will benefit in the calculations of various components of concrete structures. To prepare design aids for FE550, you would need to focus on creating resources that cover various aspects related to structural design, specifically for materials like Fe550. Design aids typically include information on material strength, stressstrain relationships, flexural members, compression members, shear and torsion, development length, anchorage, deflection calculation, and general tables, explanations of the basis of preparation, and worked examples illustrating the use of the design aids.

Acid attack on hydrated cement: effect of organic acids on the degradation process

Owing to their ability to form buffer solutions, the attack of organic acids on concrete structural components can be highly aggressive. This work considers the changes in microstructure, chemical and phase composition in hardened Portland cement paste (hcp) exposed to acetic acid/sodium acetate or citric acid/sodium citrate buffer solutions. The degradation products were investigated using 29Si and 27Al NMR spectroscopy with XRD and ICP-OES. Exposure to acetic acid/sodium acetate at pH 3.9 ≤ pH ≤ 5.5 decalcifies hcp to produce aluminosilica gels (0.1 ≤ Al/Si ≤ 0.3) with Si predominately in Q3/Q4 sites and NBO values (non-bridging oxygen per Si atom) 0.6 ≤ NBO ≤ 0.9. Cross-linking processes causing the formation of the gel from C–A–S–H dreierketten incorporate Al, originally in crystalline phases and C–A–S–H phases. Degradation by citric acid/sodium citrate is governed by the precipitation of expansive calcium citrate which continuously removes degraded surface material. Pore-blocking at the degradation front inhibits acid transport deeper into the material. A new mathematical expression is presented which enables the calculation of NBO for aluminosilica gels of known Al/Si ratio from 29Si NMR spectra despite overlapping signals. The expression was verified by a stochastic computer model based on a Si quartz lattice with substituted Al and vacancies. The model simulated the measured 29Si NMR spectra of aluminosilica gels.

Autonomous damage segmentation of post-fire reinforced concrete structural components

The existing methods for detecting fire damage in reinforced concrete (RC) structures rely heavily on manual visual inspection, which is time-consuming and challenging due to poor visibility and safety concerns. To address this, an automatic damage segmentation network at the pixel level is proposed. Using a dataset of 403 high-resolution images of fire-damaged RC components, the study employed MobileNetv3 as the encoder in a UNet model, enhanced with three average pooling layers. Among four submodules tested, SPPF demonstrated the best performance in the MB-SPPF-UNet network, achieving an MIoU of 82%, a 7% improvement over the Baseline-UNet. While OCRNet showed the best performance among ten state-of-the-art networks, its MIoU was still 8% lower than MB-SPPF-UNet. The generalization capabilities of the networks were evaluated using four crack datasets, with MB-SPPF-UNet showing a performance decrease of 5%-10%. However, this is acceptable given its primary application in segmenting post-fire concrete spalling and exposed reinforcement. The study aims to establish an efficient damage segmentation network using deep learning for quick assessment and reference in firefighting, rescue, and structural repair efforts.

A hybrid method for bond-slip behavior of reinforcement rebar in steel-polypropylene hybrid fiber reinforced concrete structures in marine environments

Fiber-reinforced concrete is an advanced class of construction materials that display higher mechanical and durability performance, but limited information is available on the bond behavior of reinforcement rebar in steel-polypropylene hybrid fiber reinforced concrete (SPHFRC) in marine environments, which produce crack states commonly seen in reinforced concrete structural components. In this study, a hybrid method for predicting the bond response behavior of SPHFRC under monotonic and cyclic loading was developed. The proposed method combining mechanical-driven model and generative adversarial networks (e.g., GAN) method. Experimental databases were constructed. Two empirical models were developed. The GAN method enhanced its prediction accuracy through adversarial training support by database and hyper-parametric analytics. Finally, to verify the accuracy and effectiveness of the developed model, a total of 65 SPHFRC specimens under cyclic loading were conducted. The comparison shows that this model can reproduce the corrosion-induced bond deterioration of SPHFRC. The model can also capture the cyclic bond degradation of SPHFRC and other types of ultra-high-performance concrete with an acceptable range.

Prediction model for heating rate of section steel during the induction heating demolition process of steel reinforced Concrete：Experimental and numerical analysis

Traditional demolition techniques face challenges in effectively separating steel and concrete components of steel-reinforced concrete (SRC) structures. To address this issue, our research group has developed induction heating demolition (IHD) technology, a method allowing for environmentally sustainable and recyclable separation of section steel and concrete. To clarify the underlying mechanisms of the induction heating (IH) process applied to section steel, we undertook experiments on 32 samples of section steel. Our investigations focused on delineating the roles of two key parameters: the heating power (P) and the size of the sections involved. We found the heating rate (V) of the section steel to be significantly influenced by P, in conjunction with the flange and web plate thicknesses. To further unravel the transformations occurring in the steel's internal physical properties throughout the IH process, we devised a numerical simulation approach capable of faithfully replicating the IH process as it applies to section steel. This analysis revealed a diminishing IH efficiency for the section steel, with values declining from 0.7 to roughly 0.4 as the temperature escalated. Utilizing both experimental and numerical data, we formulated a predictive model for the section steel's V, aiming to facilitate the planning stage of IHD implementations. The model exhibits a predictive deviation maintaining a margin within 10 %, demonstrating its substantial reliability. This investigation provides novel strategies to curtail construction waste emissions in building demolition endeavors, thereby presenting a promising avenue toward more sustainable practices in the industry.

Investigation of different parameters affecting the crack width and kb coefficient of GFRP-RC beams

Crack width control is one of the criteria affecting the design of glass fiber-reinforced polymer (GFRP)-reinforced concrete (RC) structural components. The provisions available in the CSA S806-12 standard and ACI 440.1R-15 guideline for controlling the crack width of GFRP RC elements account for the bond between the GFRP reinforcement and surrounding concrete through the bond-dependent coefficient (kb). In those design standards and guidelines, each GFRP bar surface profile is assigned a kb value obtained from four-point bending beam tests. This study aims to experimentally investigate the parameters that affect the crack width and kb coefficient of GFRP reinforcing bars, enrich the literature with more kb results for ribbed and sand-coated GFRP bars, determine whether kb is a fixed value that is solely dependent on the bar surface profile (as assumed by the above standard and guideline), recalibrate the kb coefficient considering the experimental results of this study and available experimental data in the literature, and provide the FRP engineering community with an equation that is capable of anticipating kb values based on different configurational and material parameters. To achieve the objectives of this study, 16 large-scale RC beams were tested under a four-point bending test setup. The studied parameters included the clear concrete cover, bar spacing, bar diameter, concrete compressive strength, bar surface profile, and confinement provided by transverse reinforcement. The experimental results of this study were combined with the available database to recalibrate the kb values and propose a kb equation. The results showed that the kb coefficient varies when changing the reinforcement configuration of the beam.

Damage-plasticity modeling of shear failure in reinforced concrete structures

Shear failure is an important design consideration for reinforced concrete structural components. Therefore much attention has been drawn to the development of theoretical and computational models for characterizing its complex and progressive nature. This paper establishes a damage-plasticity constitutive relationship for concrete through the introduction of a new stress decomposition procedure, referred to as shear-normal decomposition. The stress tensor is decomposed into a shear stress tensor representing the shear state and a normal stress tensor representing the tensile/compression state. The degradation of the mechanical performance of concrete is accounted for through shear, tension and compression damage variables. The shear stress-shear strain curve of concrete is calibrated by experiments and is rendered independent of the tensile and compressive stress–strain curves. The coupling between tension-shear and compression-shear are accounted for by the criterion for shear damage evolution. Several numerical examples are presented that illustrate the unique advantages of the proposed model.

Bond-slip behavior between reactive powder concrete and H-shaped steel

The mechanical performance of the steel reinforced reactive powder concrete (SRRPC) structural components significantly depends on the steel-concrete interfacial bond behavior. This paper presents an experimental and analytical investigation on the bond-slip behavior between the reactive power concrete and the H-shaped steel. A total of 11 specimens, considering the cover thickness, embedded length, stirrup ratio and bonding part (whole section, flange and web), were tested through the push-out configurations. Results showed that the cover thickness has the most significant impact on the interfacial properties. Moreover, the SRRPC exhibited the highest residual bond strength compared with the other steel reinforced concretes. The five-stage model and the modified tri-linear model were proposed to describe the average bond stress-slip relationship. It was found that the five-stage model had an excellent accuracy while the modified tri-linear model can reasonably predict the average bond stress-slip relationship. Finally, a comprehensive analytical model was developed to investigate the local longitudinal strain of the shape, bond stress and relative slip.

Determination of NSC-UHPC interface properties for numerical modeling of UHPC-strengthened concrete beams and slabs

Normal-strength concrete (NSC) structural components strengthened with ultra-high-performance concrete (UHPC) overlays are widely studied and have demonstrated their efficiency in improving structural capacity and durability. The behavior of UHPC-strengthened beams or slabs is highly influenced by the properties of the NSC-UHPC interface. This project aimed to develop NSC-UHPC interface models by determining their detailed shear and tensile laws in UHPC-strengthened beams or slabs, which are missing presently in the literature. Determination of the interface models was realized through test data analysis of 700 interface characterization specimens found in the literature and inverse analysis with nonlinear finite element (FE) calculations of 14 UHPC-strengthened beams and slabs test results. Two interface models were proposed for two types of interfaces with good or poor surface preparations, respectively: a concrete fracture (CF) model and an interface sliding (IS) model. Results showed that FE calculations with CF and IS models provide accurate replication of the mechanical behavior of strengthened beams and slabs in terms of stiffness (K), ultimate shear capacity (P), and deflection at ultimate shear capacity (Δ), while the calculations with perfect bond model were not satisfactory. Parametric studies on the nine interface parameters indicated that peak cohesion stress, shear stiffness, and tensile stiffness greatly impact the shear behavior of strengthened beams in the CF model, while only shear stiffness had a significant effect on the shear behavior of strengthened slabs in the IS model. Suitable choices for interface model parameters, as in the proposed CF and IS models, provided accurate results for modeling the bending and shear behaviors of UHPC-strengthened concrete beams or slabs.

Simplified multi-scale simulation investigation of 3D composite floor substructures under different column-removal scenarios

The robustness of structures to withstand progressive collapse is a significant theme. However, owing to the restricted experimental conditions, some issues regarding 3D composite floor substructures under a column-removal scenario remain unclear, such as different column-removal scenarios, boundary constraints, loading schemes, floor numbers, reinforced concrete (RC) floors, and structural or nonstructural components. To understand these issues, a progressive collapse study on 3D composite floor substructures subjected to uniformly distributed load (UDL) is carried out based on simplified multi-scale simulation. A 2 × 1-bay concrete-filled steel tubular (CFST) column-steel beam-RC floor substructure is employed to investigate the structural robustness under the corner column-, penultimate-edge column-, and middle-edge column-removal scenarios. It is found that the vertical resistance for the corner column-removal scenario is reduced by approximately 10–20% compared to the other two scenarios. The 3D substructure resists progressive collapse via the flexural action (FA), the catenary action (CA), and the RC floor. Compared with the real boundary constraints, the fixed and hinged supports at the beam ends can overestimate the CA, and disregarding boundary constraints can overestimate deformation performance. Moreover, the concentrated vertical load (CVD) severely underestimates the robustness of 3D substructures. The floor number, RC floor, shear wall, and steel brace significantly influence the progressive collapse performance of 3D substructures.

Vision method based on deep learning for detecting concrete vibration quality

The vibration quality of concrete is crucial to ensure the long-term safe operation of concrete structural components. In recent years, computer vision technology based on deep learning has achieved excellent results in the field of concrete quality inspection. However, when used for assisting construction inspection, this technology relies heavily on large-scale, labeled, high-quality image data. To solve this drawback, this study proposes a vision-based method that integrates semi-supervised learning and data augmentation for detecting the concrete vibration quality. Initially, StyleGAN2 was adopted as the data augmentation strategy to improve the diversity of the dataset. Then, SE-ResNet50, a model that couples an attention mechanism module and residual network, was employed as a classifier for accurately extracting information contained in images. Subsequently, in order to reduce the workload of data annotation, a novel semi-supervised learning method (Co-MixMatch) was proposed to train the model by coupling MixMatch with co-training. Finally, the trained model was deployed on mobile devices to assist onsite construction workers in detecting the quality of concrete vibration. A real-world concrete dam dataset was employed to verify the proposed method. Based on the experimental results, the proposed method improves the accuracy of the baseline method by 3.62% on average. Additionally, the proposed method achieves an accuracy of 0.9600, which is only 0.67% lower than that of supervised learning, while only requiring 20% of the labeled data. Therefore, the proposed method has great application prospects and can further promote the intelligent development of concrete vibration inspection.

Performance of 3D printed columns using self-sensing cementitious composites

Self-sensing cementitious composites can be used as an economical method of structural health monitoring. This is achieved by using the piezoresistivity effect to assist in the detection of defects and enabling repairs to be conducted early which can therefore avoid structural failures. This study uses an established self-sensing cementitious composite mix to 3D print column to examine its structural performance and sensing capabilities in components of large-scale concrete structures. An extrusion-based 3D printer was used to print hollow square column segments. These segments were then joined and filled with steel rebar reinforcement and cast concrete. Another column was created using mould cast concrete for comparison. The specimens were tested under static axial compression to determine their compressive properties, electrical resistivity and piezoresistivity response. The results showed that the 3D printed column performance can be monitored using the self-sensing composite until the printed shell cracks. The 3D printed column did show superior electrical properties with a lower electrical resistance of 274.2 Ω.cm. These results indicate that a different manufacturing approach to creating a 3D printed column should utilise the advantages of 3D printing for use in self-sensing concrete structures.

Shape memory alloy reinforcement for strengthening of RCC structures—A critical review

Significant performance and safety issues can arise from the deterioration of reinforced concrete (RC) structural components brought on by ageing processes and high stress occurrences. Shape memory alloys (SMAs), one of the options for restoring such components, have special qualities including recovering inelastic strain when unloaded (super elasticity) or heated (shape memory effect, SME). To lessen permanent deformations into RC constructions, super elasticity and SME of SMA bars can be used. The stiffness and strength of RC structures can also be improved by the addition of SMAs, allowing them to withstand loads of high intensities with minimal damage. Despite the wide range of studies done on the applications of SMAs in structures, a comprehensive analysis of the present state, key results, potential drawbacks, and future contemplation of SMA bars for the reinforcement of RC structures lacking in the literature. Additionally, detailed instructions for choosing the types and traits of SMAs best suited for a certain strengthening application are lacking. We conducted an extensive examination of the applications of SMA bars in RC beams, in order to fill the basic and practical gaps that were observed. The implementations were investigated from the viewpoints of crack recovery, strength augmentation, confinement, and shear strengthening of new and existing RC structures. The benefits and drawbacks of strengthening with SMAs are then discussed critically, particularly in light of other strengthening techniques and materials. The end of this review highlights the challenges of using SMAs as well as potential future opportunities that might arise from their effective use of RCC.

Approach for sustainability assessment for footbridge construction technologies: Application to the first world D-shape 3D-Printed fiber-reinforced mortar footbridge in Madrid

As a means to improve sustainability in the construction sector, the 3D-printed concrete technologies (3DPCTs) are emerging as potential alternatives to traditional construction for reinforced concrete structural components. Traditional technologies are still used in most architecture and civil engineering applications, although D-shape technology for 3DPCTs (DS-3DPCT) has proven technically feasible for producing pilot structural elements such as footbridges. These pilots have been contextualized within research and industrial frameworks, in which relevant technical information is confidential and cost and environmental performance related conclusions are still to be validated and reported. Moreover, scarce research has been conducted on sustainability performance by DS-3DPCT, and that carried out is primarily incipient and focused on identifying governing indicators and some specific non-generalizable quantifications. Former studies ack dealing with sustainability by DS-3DPCT from a holistic and integrated perspective, which requires quantifying and coupling the three main economic, environmental and social pillars. This research project comprehensively develops a sustainability-oriented decision-making approach for assessing construction technologies for footbridges based on MIVES and Delphi method. The Castilla-La Mancha park DS-3DPCT footbridge constructed by ACCIONA S.A. in 2016 in Madrid was the representative case study to validate this approach applicability. The results quantify the case study as sustainable, with excellent values for greenhouse gas emissions reduction, generation of qualified jobs, benefits to brand, occupational risk prevention, and design flexibility. However, this DS-3DPCT requires more maturity in the technology to improve its economic values. This approach range of application might be extended to other structural typologies by introducing -when necessary-other relevant indicators and weights’ distributions.

Experimental studies on confined compressive strength of Stainless Steel Wire Mesh (SSWM) wrapped concrete columns

The findings of an experimental evaluation of the axial compressive strength of an M25 grade Plain Cement Concrete (PCC) column confined with locally available Stainless Steel Wire Mesh (SSWM) are presented in this paper. Various types of Fiber Reinforced Polymer (FRP) are usually employed to strengthen the load-bearing components of concrete structures. However, these FRP materials exhibits brittle failure and debonding of FRP strip or wrap. Stainless Steel Wire Mesh (SSWM), on the other hand, is a cost-effective substitute for FRP materials when it comes to strengthening of structural elements. In this study, effectiveness of SSWM for confinement of concrete columns is demonstrated through experimental study. For the research, column specimens with a diameter of 150 mm and a height of 300 mm are used. Test specimens are strengthened with one-layer circumferential wrap of SSWM. Three variants of SSWM i.e. SSWM 30 × 32, SSWM 40 × 32 and SSWM 50 × 34 are considered for the study. After 28 days of moist curing, SSWM is applied to the column surface using epoxy SIKADUR 30LP. Axial compressive load-carrying capacities of strengthened specimen are compared with that of control specimens. From the comparative study it is found that SSWM 40 × 32 performs better compared to other variants of SSWM considered for this study. Compared to the control specimen, the load-carrying capacity of the column strengthened with SSWM 40 × 32 is increased by 29.35%. For all the specimen, failure patterns are observed in addition to the load–displacement and stress–strain behaviour. Results of present experimental investigation establishes the suitability of SSWM for confinement or strengthening of concrete elements subjected to compression.

Numerical Performance Analysis of Concrete-Filled Hollow GFRP Beams including Inner Surface Bearing Stresses at the Interface

GFRP sections with filler concrete material form promising structural components for structures; therefore, the structural performance of them has been investigated with increasing popularity. However, the performance of these composites degrades when fully composite action cannot be developed at the interface in where the literature hosts limited knowledge. Different techniques, such as abraded and sand-bonded surface treatments, were investigated experimentally to improve the bond-slip behavior between GFRP and concrete; however, there is a need to define shear mechanism at the interface of the numerical models. In this study, first, the average frictional bearing strengths were extracted for the treated and untreated inner surfaces using experimental results; then, the coulomb friction model was utilized to transfer the shear stresses between two dissimilar materials. Numerical models were verified by the experimental results, and different parametric studies were investigated by varying the amount and shape of GFRP in the cross section, compressive strength of concrete including the non-linear material behavior and interface frictional contact models. The findings showed that the interface strength can improve the flexural capacity of the concrete-filled GFRP beams by about 15.4%. Square GFRP box sections can be suggested for the construction of hybrid beams instead of rectangular sections, whereas the 10% areal ratio in a square cross section reached 103% load capacity improvement. The increased nominal compressive strength of concrete in hybrid beams can increase the hollow GFRP beams’ nominal load capacities and elastic stiffness of the hybrid beams in between; however, the relative gain is reduced due to increased compressive strength of concrete.