Concrete Beam Specimens Research Articles

Electromagnetic wave-driven deep learning for structural evaluation of reinforced concrete strength

Monitoring the performance of reinforced concrete structures, particularly in terms of strength reduction, presents significant challenges due to the practical limitations of traditional detection methods. This study introduces an innovative framework that incorporates a non-destructive technique using electromagnetic waves (EM-waves) transmitted via Radio Frequency Identification (RFID) technology, combined with two-dimensional (2-D) Fourier transform, fractal dimension analysis, and deep learning techniques to predict reductions in structural strength. Experiments were conducted on three reinforced concrete beam (RCB) specimens exhibiting various levels of reinforcement corrosion. From these, a dataset of 1,800 EMwave images was generated and classified into “normal” and “reduced strength” categories. These categories were used to train and validate a Convolutional Neural Network (CNN), which demonstrated robust performance, achieving a high accuracy of 0.91 and an F1-score of 0.93 in classifying instances of reduced structural strength. This approach offers a promising solution for detecting strength reduction in reinforced concrete infrastructures, enhancing both safety and maintenance efficiency.

Evaluation of Bond Strength of Concrete Repaired Using Polyurethane Grout Material under Static and Impact Loads Coupled with Statistical Analysis.

The effectiveness of repair work relies on whether the interface substrate can achieve sufficient bond strength when subjected to numerous stresses. This study investigated the bond properties of repaired normal concrete (NC-to-NC) elements, including cube, beam, and U-shaped specimens, after undergoing natural fracture due to flexural and tensile stresses. The specimens were repaired using a polyurethane (PU) matrix by gluing the two parts and applying compression, splitting, and drop-weight impact (DWI) tests to evaluate the bond strength properties. The results revealed that the PU matrix effectively repairs NC substrate with adequate bond strength, which exceeds the minimum allowable bond strength specified in the ASTM ACI 546-06 to rehabilitate damage concrete structures. The reference beams exhibit a peak applied load capacity of 15.6 kN with less deflection than the repaired samples. The compressive strength of the NC-to-NC repaired specimens loaded along and parallel to the interface plane revealed a decrease in compressive strength of 47.3% and 31.5% compared to the NC-R samples, respectively. The mean number of blows at the cracking stages appeared nearly equal for reference and repaired NC-to-NC specimens. The reference specimens exhibited an average number of 24 and 31 blows at the initial and failure stages, respectively, which were higher by 9.1% and 5.2% than the NC-to-NC repaired specimens. The PU binder showed promising results in achieving adequate interfacial bond strength under static and impact loads.

Strength Model for Prestressed Concrete Beams Subjected to Pure Torsion

A torsional strength model for prestressed concrete beams was proposed considering the initial crack angle, principal stress angle, and longitudinal strain, which are affected by the axial stress induced by the effective prestress. The use of the torsional effective thickness was also proposed to calculate the torsional strength of prestressed concrete beams by considering the effect of prestress. The shear element in the torsional member was simplified under the assumption that the principal tensile stress and principal compressive strain were negligible in the ultimate state. The torsional strength was determined when the principal compressive stress or shear stress at the crack surface in the shear element reached the failure criterion according to the multipotential capacity model, which considers concrete crushing and aggregate interlocking as the main resistances to the applied load. The proposed strength model was verified using test specimens collected from existing experimental studies. The proposed model accurately evaluated the torsional strength of prestressed concrete beam specimens, regardless of the key variables of the prestressed concrete specimens, where the mean value of the tested results to the calculated torsional strengths was 1.123, and the corresponding coefficient of variation was 17.7% for 104 prestressed concrete beam specimens, while the ACI 318-19 torsional design method gave the mean and coefficient of variation of 0.880 and 24.3%, respectively.

Flexural performance of reinforced concrete beams repaired with BFRP grid-TSUHDC

Due to the influence of time, load, and external environmental factors, many reinforced concrete beams have been damaged and require repair. Tailings are waste generated during mineral production, resulting in substantial environmental pollution and economic losses due to the excessive generation of tailings and low comprehensive utilization. In the UHDC, tailings replaced quartz sand, while BFRP grids itself is an environmentally friendly material. Two repair methods were evaluated in this study, Tailings Sand Ultra-High Ductile Concrete (TSUHDC) and Basalt Fiber Reinforced Polymer (BFRP) grid-TSUHDC, grounded in the principles of green and sustainable development. Five reinforced concrete beam specimens were designed and fabricated for bending performance tests and finite element simulations. The effects of different repair methods and levels of damage on the flexural performance of reinforced concrete beams were investigated. The results reveal that, compared to untreated reinforced concrete beams, both TSUHDC and BFRP grid-TSUHDC repair methods enhanced bending load-bearing capacity. However, the stiffness of specimens repaired with TSUHDC decreased when subjected to 80 % of the pre-applied failure load. When the pre-applied failure load is less than 80 %, the recommended repair approach is the use of TSUHDC for repair. For cases where the pre-applied failure load exceeds 80 %, BFRP grid-TSUHDC is the preferable option. The flexural bearing capacity formula for this type of repair method was derived by improving existing formulas, yielding prediction results in close alignment with the experimental results.

Deterioration of Prestressed Concrete Beam Specimens Exposed under Chloride (20 years) and Carbonation (15 years) Environments

Deterioration of Prestressed Concrete Beam Specimens Exposed under Chloride (20 years) and Carbonation (15 years) Environments

Flexural Strength of Reinforced Concrete Structures Exposed to Corrosive Media

This study investigated the effect of corrosion on the flexural behavior and midspan deflection of reinforced concrete beam members. Control, corroded, and resin-coated concrete beam specimens were tested to determine their failure load, midspan deflection, rebar diameter measurements, and mechanical properties. The results showed that corrosion significantly reduced the flexural strength and increased the midspan deflection of beams due to weakening of the reinforcing steel. The average failure load of corroded beams decreased by 25.73% compared to the control beams. Similarly, the average midspan deflection of corroded beams increased by 103.8% over the control beams. Measurements of rebar diameters before and after corrosion revealed reductions of up to 0.87% in corroded samples, substantiating corrosion-induced thinning. Additionally, mechanical properties testing showed decreases in ultimate tensile strength, yield strength, and strain ratio while increasing ductility for corroded rebars. Resin coating prevented much of the strength loss and provided protective benefits near that of the control specimens. The relationship between failure load, midspan deflection, diameter measurements, mechanical properties and corrosion damage was investigated through analytical comparisons. Corroded samples consistently demonstrated lower failure loads, higher deflections, reduced diameters and strengths versus controls. Conversely, coated samples performed similarly to controls, validating the coating's effectiveness. This research quantitatively confirms literature reports that corrosion degrades reinforced concrete through weakening of rebar-concrete bond and steel deterioration over time if left unprotected. The findings emphasize the importance of mitigating corrosion to ensure structural integrity, safety and durability of reinforced concrete infrastructure.

Mixed mode fracture properties of interface for composite MPC and cement concrete specimen with asymmetric semicircular bending beam

This paper investigates the interface fracture behavior of composite magnesium phosphate cement (MPC) and concrete asymmetric semicircular bending beam (ASCB) specimens under various loading conditions including pure mode I, mixed mode I&II, and pure mode II. Initially, finite element simulations are employed to compute and analyze the basic geometric characteristics of the ASCB specimens.. Subsequently, experimental tests are performed to determine the flexural strengths for different pre-crack lengths, and the critical stress intensity factors of ASCB specimens are obtained through testing. Then, parameters for the interface cohesive model are derived. Finally, the interface cohesive model for the composite MPC and concrete ASCB specimen is validated through numerical simulation. The present work show that a pure mode I opening crack represents the weakest form of the structure, and the flexural strength decreases with an increase in precrack length. The crack resistance at the repair interface is approximately 60% lower than the bearing capacity of pure mode II fractures. Intensity factor envelope analysis reveals that mixed mode I&II fractures should be avoided in composite structures experiencing complex stress states. The cohesive model effectively captures the interfacial bonding performance. When combined with the extended finite element method (XFEM), the cohesive model facilitates accurate simulation of the specimen’s interface fracture, demonstrating consistency with experimental results.

Flexural Capacity of the Normal Sections of Concrete Beams Strengthened with Corrugated Steel Plates

To explore the law of load-carrying performance enhancement of concrete beams reinforced with corrugated steel plates (CSPs), three groups of controlled bending tests were conducted on five beam specimens. The load-bearing capacity of concrete members commensurately increased with the thickness of reinforcing flat and corrugated steel plates. Additionally, for the same amount of steel, the load-bearing capacity of concrete beams improved more with CSP reinforcement than with reinforcement with flat steel plates. Accordingly, a theoretical formula for the moment of inertia of the combined section of a CSP-reinforced concrete beam was derived. Comparison verification showed that the calculation results for the beams reinforced with CSPs of different thicknesses were highly accurate. Finally, based on the damage mode of the CSP-reinforced concrete beam specimens, a formula for calculating the flexural bearing capacity of the positive cross-section of the beam with corrugated steel reinforcement was established. The calculated values agreed with the experimental values, which validated the flexural load capacity theory pertaining to positive sections and the flexural capacity model for reinforced beams.

Influence of surface roughness and interfacial agent on the interface bonding characteristics of polyurethane concrete and cement concrete

As a new type of concrete material, polyurethane concrete has excellent physical and mechanical properties which is widely used in the maintenance and reinforcement of damaged areas of concrete pavement. Because of the difference in the performance between polymer concrete and ordinary concrete, it is of great significance to accurately evaluate the bond performance between polymer concrete and ordinary concrete in order to avoid interface damage in the subsequent use of the repaired pavement. In this study, the bonding specimens were made by changing the roughness and interfacial agent of the bonding interface between polymer concrete and cement concrete, and splitting tensile test and direct shear test were carried out to explore the bond properties between them. Polymer concrete-cement concrete composite beam specimens were made to simulate the maintenance and reinforcement of cement concrete pavements with polymer concrete in the actual projects, and the flexural performance test was carried out to explore the common mechanical characteristics of bonding specimens. The test results showed that the bond performance of polymer concrete and cement concrete was closely related to the interface roughness and the interfacial agents, and the addition of polymer concrete improves the common stress characteristic of composite beam specimens. The test results provide a basis for polymer concrete as a rapid repair material for concrete pavement repair.

Comprehensive analysis of bond stress transfer mechanisms in glass fiber-reinforced polymer-reinforced concrete beams using acoustic emission monitoring

The present study investigates the critical bond characteristics between glass fiber-reinforced polymer (GFRP) bars, which is essential for the application bars as corrosion-resistant components in structural concrete. The interfacial bond deterioration and stress transfer mechanisms have been investigated in the present study by employing acoustic emission (AE) monitoring in hinged-type GFRP-reinforced concrete (GFRP-RC) beam specimens. The bond strength of the test specimens, governed by chemical adhesion, mechanical interlocking, and frictional resistance, has been intricately examined. Various AE signal parameters as well as historic and severity indices derived from the AE signal parameters have been meticulously evaluated and correlated with bond stress and rebar slip variations. The present study has also introduced an innovative approach of using the sentry function for the assessment of bond deterioration and associated mechanisms. The results of the present study demonstrate the reliability of AE parameters in monitoring debonding and bond strength variation, the effectiveness of the sentry function in evaluating damage progression, and the utility of historic and severity indices in capturing micro-mechanism transformations. The accurate localization of debonding and the qualitative distribution of bond stress have also been demonstrated by through correlations between cumulative AE parameters and rebar slip, Additionally, the present study also highlights the significance of peak frequency variations in AE signals, serving as a crucial tool for quantifying the mechanical interlocking and interfacial friction. The results contribute significantly to precise assessments and development of effective strategies for mitigating bond deterioration in GFRP-RC elements.

Compressive, bending and shear properties of reinforced concrete beams containing sawdust ash as partial replacement of cement

150x600 mm for the bending test and 150x150x450 mm for the shear test) specimens were used for this investigation. The concrete cube and RC beam specimens had SDA as a partial cement replacement within the range of 0%–10% by weight of cement at 2.5% intervals. 120 RC beam specimens were cast, followed by curing and testing at 28, 60, 90, and 180 days. Using the 4-point loading method, the bending and shear responses of the beams and associated parameters, like the formation and growth of cracks, were determined during the testing. The impact of SDA replacement on the characteristics of fresh and hardened concrete was also assessed using 105 cube specimens cast, cured, and tested at 7, 14, 21, 28, 60, 90, and 180 days. A concrete mix ratio of 1:1.3:2.4 and a constant water/binder ratio of 0.50 at optimum 5% SDA replacement produced (25 N/mm2 ) the required compressive strength. The results show that workability decreases as the SDA percentage increases. Generally, the values of concrete’s densities containing SDA in the mix were in the range of standard weight applications. At 28 days, samples up to 5% recorded a higher compressive, bending, and shear strength development rate than the control mix. The results show that cement partially replaced with up to 5% SDA can produce RC that meets the requirements for concrete for structural application.

Experimental study on the mechanical properties and structural performance of the rapid hardening concrete

Rapid-hardening concrete (RHC) is becoming more popular as a cast-in-place jointing material in precast concrete bridges and buildings due to its high tensile strength and crack resistance. RHC’s technical properties are highly regarded due to the working conditions of mega projects. The study assessed the impact of modern modifiers on concrete in order to select a composition of rapid-hardening concrete (RHC) with superior mechanical properties. Following an analysis of previous studies by other authors, microsilica and a polycarboxylate ether-based chemical additive was chosen as basic modifiers in the manufacture of RHC. In addition, four reinforced rapid-hardening concrete beams were tested for operational reliability and durability after 3 days of casting. The structural performance of RHC beams was evaluated in comparison to normal concrete beam specimens, and it was determined that crack distribution, load deflection, reinforcement strains, ductility, and toughness were all important factors in the evaluation. RHC beams exhibit higher ductility, toughness, ultimate loads, and deformability than NC beams. The tensile strength analysis revealed a positive impact of RHC, but the shrinkage crack related to heat hydration was crucial.

Stress-strain modelling for a composite reinforced concrete beam

The study is aimed at the features of modeling the stress-strain state of a concrete beam, reinforced with two types of fibrous composites. The necessity of strengthening existing reinforced concrete structures can be caused by the reconstruction or technical re-equipment, which often entails an increase in the load on the load-bearing structures of buildings and facilities, as well as during the elimination of the consequences of factors that led to a decrease in the bearing capacity or a failure of loadbearing structures. In order to study the applicability of the model, we analysed the results, obtained during bending and axial compression tests of T-section reinforced concrete beam specimens with welded frame reinforcement that were in operation and the results of a numerical study in a LIRA software suite. The stress-strain state of specimens was modelled in a nonlinear formulation using the finite element method. The conducted analysis and theoretical studies have shown the applicability of models, developed based on a limited test database, unclear, especially with regard to a wide range of compression coefficients, while the results of modeling the behavior of reinforced concrete beams have demonstrated sufficient accuracy for applying in the strengthening design using external composite reinforcement.

Monitoring of fracture processes in reinforced concrete beams with DFOS: feasibility study

In this paper, we present the application of distributed fibre optic sensors (DFOS) for the detection of bending and shear cracks in reinforced concrete beam specimens loaded in three- and four-point bending in lab conditions. The main goal of this study is to prove the feasibility for future application of DFOS for monitoring of existing concrete structures such as bridges or tunnels. Each specimen was equipped with more optical fibres: most of them were externally attached in the grooves at the outer surface of the specimens and some of them were inside the specimens. Specimen geometries, arrangement of reinforcement bars and loading schemes of the specimens were determined by non-linear FEM before the tests, so that either dominant bending or dominant shear cracks appear during the loading. Some specimens were loaded step-by-step and some of them by continuous loading and the results were compared afterwards. The results showed, that DFOS can ensure exact crack monitoring in all loading stages of the reinforced concrete specimens, which is a good basis for future applications for monitoring of structures in the engineering practice.

Influence of Geogrid on the Flexural Behavior of Cracked Concrete Pavements

This paper investigates the influence of geogrid reinforcement on the flexural behavior of concrete pavements after the initiation of cracks up to failure. Two groups of notched concrete beam specimens with the dimensions of 150 mm × 150 mm × 550 mm were tested. The concrete specimens of the first group were tested under static loads. The concrete specimens of the second group were tested under cyclic loads. The geogrid was placed at a depth of 55 mm from the bottom of the concrete specimens. Test results illustrate that, when cracks are visible in the concrete specimens, the geogrid could maintain the flexural behavior of the concrete pavements within the acceptable service level. The geogrid significantly prolonged the fatigue life of the cracked concrete pavements reinforced with the geogrid. The geogrid increased the maximum cyclic loads of the concrete specimens reinforced with geogrid before eventually failing. The number of geogrid layers used as a flexural resisting material under cyclic loads acts a significant role in improving the behavior of the concrete pavements compared with the specimens reinforced with one layer of geogrid.

Evaluation of flexural failure for concrete beams partially reinforced by geogrid sheets

ABSTRACT The behavior of reinforced concrete beams with biaxial and uniaxial geogrids as a partial reinforcement with traditional steel bars under flexural loads has been experimentally studied. The effect of geogrid layers with traditional steel reinforcement in concrete beam specimens in compression and tension zones has also been investigated. Geogrid is one of the geosynthetic materials that exhibits both tensile and flexural behavior similar to traditional steel. To examine the effect of geogrids on traditional steel as a composite reinforcement system, strain gauges were fixed to the concrete beams and bottom reinforcement (steel bars). The studied parameters in this investigation are the number of geogrid layers, types of geogrids, and their position in concrete beams. First cracking load, failure load, initial and post-cracking, deflection, and ductility of beam specimen were investigated. The experimental results indicated that using geogrid sheet layers as partial reinforcement greatly contributed to resisting flexural stresses of concrete beams. An increase in the ductility and the capacity load of the concrete beam specimen was also observed. Based on this experimental investigation, the geogrids can be applied as additional or alternative reinforcement with/without traditional steel bars in concrete beams.

Experimental and Numerical Study of Torsional Solid and Hollow Section of Polyolefin Fiber-Reinforced Concrete Beams

An experimental and theoretical program was undertaken to enhance comprehension regarding how variations in fiber ratio impact the structural performance of both solid and hollow reinforced concrete beams when subjected to pure torsion. Polyolefin fiber was utilized in this study. To achieve this objective, a total of sixteen specimens of fiber-reinforced concrete beams were manufactured. Among these, eight were solid beams, while the remaining eight were hollow beams, all featuring rectangular cross-sections. These specimens were constructed employing polyolefin fiber. The findings indicated that incorporating polyolefin fiber into the concrete mixture led to improved mechanical properties in the cured concrete. The most significant enhancements were observed in the splitting tensile strength and flexural strength tests conducted on the specimens. Both solid and hollow beams exhibited notable enhancements in their torsional performance. These enhancements occurred as the polyolefin fiber percentage increased from zero to 1.5%, while the transverse and longitudinal reinforcement ratios remained constant. Furthermore, the reduction ratio of torsional strength becomes more noticeable when comparing solid and hollow sections in high-strength beams, as opposed to normal-strength beams.

Monitoring the Durability Issues of Asphalt Concrete Mixtures

The asphalt concrete mixture is prone to environmental issues such as moisture damage and ageing. This may exhibit a great significance in the service performance of asphalt concrete pavement mixtures which may be more susceptible to many types of early distresses throughout its fatigue life. In the present investigation, asphalt concrete mixtures were prepared and compacted with the aid of laboratory roller compaction into a slab samples. optimum binder content was implemented. Extra samples were prepared at higher and lower binder content of 0.5 % (above and below the optimum). Asphalt concrete beam specimens were obtained from the prepared slab samples with the aid of a diamond saw. Part of the Asphalt concrete beam specimens were tested under four point’s repeated flexural stresses after practicing moisture damage while another part was subjected to long term ageing. The rate of change in the flexural strength was monitored and compared among the various testing conditions at 20 ºC environment and under constant micro-strain level of 750. It was observed that the lower flexural strength was observed for moisture damaged specimens while higher flexural strength could be detected for aged specimens as compared with the control mixtures. The binder content exhibits a significant influence on flexural strength of the asphalt concrete specimens since it declines significantly at higher or lower binder content as compared with that of specimens prepared at the optimum.

Experimental Investigation on the Utilization of Marble and Scoria Powder as Partial Replacement of Cement in Concrete Production

This paper explores how marble and scoria powder can be used as partial substitutes for ordinary Portland cement in creating C-25 concrete. Both materials contain over 50% of the major oxides found in cement, with marble high in CaO and scoria high in SiO2. Experimental investigations were conducted to study the chemical, physical, mechanical, and fresh properties of concrete containing marble and scoria powder. For the investigation, 13 different mixes, including the control mix, were used with a constant water–cement ratio of 0.5 and a slump range of 25–50 mm for concrete with a compressive strength (CS) of 25 MPa. Marble-to-scoria ratio of 2 : 1, 1 : 1, and 1 : 2 was used, and then the combined fraction of both marble waste and scoria in concrete was increased from 0% to 20% in 5% range. Including the control test specimens, a total of 117 (150 × 150 × 150 mm) concrete cubes for CS test, 39 (100 × 100 × 500 mm) concrete beam specimens for flexural strength test, 39 (100 × 200 mm) cylinder specimens for splitting tensile strength (STS) test and, 39 (100 × 100 × 100 mm) cube specimens for water absorption test were cast and tested at 3, 7, 28, and 56 days. The test results indicate that marble and volcanic scoria powders with marble-to-scoria ratio of 1 : 1 could replace cement up to 15% without compromising the CS and up to 10% without compromising the flexural and STS; also, the water absorption decreases up to 10% replacement; however, the workability of the fresh mix decreases as the combined replacement level of marble and scoria increases. Generally, a 10% replacement with marble-to-scoria ratio of 1 : 1 produces concrete with higher compressive, flexural, tensile strength, and water absorption manifestations when compared to conventional concrete.

A theoretical model for the prediction of fracture process zone in concrete under fatigue loading: Energy based approach

Characterizing the fracture behaviour of concrete and accurately predicting its service life under fatigue loading poses a significant challenge due to its heterogeneous nature and complex fracture mechanisms. The proposed study focuses on developing an energy based theoretical formulation for predicting the evolution of the fracture process zone throughout repetitive loading cycles. A stiffness degradation approach has been adopted for developing the formulations for the critical energy dissipation and fully developed fracture process zone. Subsequently, the proposed analytical expressions have been calibrated and validated by performing experiments under centre point bending and using available experimental results in the literature. Experiments have been conducted on a centre-point bend beam with varying aggregate size in conjunction with the digital image correlation (DIC) technique to estimate the fracture characteristics. The influence of specimen size and heterogeneity has been discussed in the context of predicting the fracture behaviour, critical dissipated energy, and process zone length of plain concrete beam specimens under fatigue loading. The results indicate that the process zone length and critical energy release rate increase with an increase in specimen size, while the same decreases with an increase in aggregate size.