Strength Of Concrete Cylinders Research Articles

Behaviors of triaxial woven fabric composites reinforced concrete cylinders under eccentric compression

Concrete reinforced by textile composite materials has long been a focus of substantial interest in the engineering applications. In this paper, the compression performance of concrete cylinders confined by carbon fibers, glass fibers, and carbon–glass hybrid triaxial woven fabric composites under three different eccentricities were investigated. Moreover, the digital image correlation analysis method was introduced to observe the compression process and failure modes of reinforced concrete cylinders. Meanwhile, the strain process of yarns during the failure was also analyzed. The result showed that all of triaxial woven fabric composites can increase the strength of concrete cylinders, while the strength decreased with the increase of eccentricity and the mechanical performance converged gradually. In addition, using triaxial woven fabric composites made of glass fibers can promote the ductility of concrete cylinders. It also indicated that employing carbon–glass hybrid triaxial woven fabric composites can not only have the advantages of increasing the strength and ductility of concrete cylinders, and low cost, but also effectively reduces the eccentric sensitivity.

Predicting Confinement Effect of Carbon Fiber Reinforced Polymers on Strength of Concrete using Metaheuristics-based Artificial Neural Networks

This article deals with the study of predicting the confinement effect of carbon fiber reinforced polymers (CFRPs) on concrete cylinder strength using metaheuristics-based artificial neural networks. A detailed database of 708 CFRP confined concrete cylinders is developed from previously published research with information on eight parameters, including geometrical parameters like the diameter (d) and height (h) of a cylinder, unconfined compressive strength of concrete (f_co^'), thickness (nt), the elastic modulus of CFRP (Ef), unconfined concrete strain (?_co), confined concrete strain (?_cc) and the ultimate compressive strength of confined concrete (f_cc^'). Three metaheuristic models are implemented, including particle swarm optimization (PSO), grey wolf optimizer (GWO), and bat algorithm (BA). These algorithms are trained on the data using an objective function of mean square error, and their predicted results are validated against experimental studies and finite element analysis. The study shows that the hybrid PSO model predicted the strength of CFRP-confined concrete cylinders with a maximum accuracy of 99.13% and GWO predicted the results with an accuracy of 98.17%. The high accuracy of axial compressive strength predictions demonstrated that these prediction models are a reliable solution to the empirical methods. The prediction models are especially suitable for avoiding full-scale, time-consuming experimental tests that make the process quick and economical.

Static elastic modulus prediction at early ages using a modified resonant test for concrete cylinders using mems microphones

Concrete Young’s modulus is seldom verified on-site due to the time-consuming and costly nature of current testing standards. This article proposes a new, quick and affordable testing methodology to estimate the ultimate static elastic modulus of normal strength concrete cylinders on-site at early ages using a smartphone. Impact-resonance tests were performed on several concrete cylinders from different mixtures at different ages, using an accelerometer and a smartphone microphone to measure the cylinders' flexural and longitudinal resonant frequencies. Measurements from both sensors were compared to show the validity of estimating the dynamic elastic modulus using acoustic signals from the cylinders recorded with a smartphone's built-in microphone. The cylinders' static and dynamic elastic moduli were determined, and the change in elastic modulus over time as the cylinders aged was also examined. This study shows the advantages of microphones over accelerometers, being less susceptible to measurement errors and proposes a filter algorithm to extract the resonant frequencies from environmental noise. A forecasting methodology to estimate static elastic modulus based on early dynamic impact-resonant tests can help engineers make early decisions on their supplied concrete on-site.

The Effect of Petung Bamboo Reinforcement Threads on Reinforced Concrete (RC) Beams

The bamboo reinforced concrete (RC) beam is used as an alternative to steel reinforcement (a non-renewable material), due to the high tensile stress value, readily available, and relatively cheap. Therefore, this study aims to evaluate the effect of petung bamboo reinforcement threads on reinforced concrete beams. This provided several treatments for various analyses, namely (1) Petung reinforcement without apus bamboo skin thread (P). (2) Petung reinforcement thread using apus bamboo skin at distances of 5 and 10 mm (U5 and U10). Based on the compressive strength of concrete cylinders, a quality of 21.212 MPa was produced. The average flexural strength also provided the P, U5, and U10 variants of 12.606, 17.916, and 14.383 MPa, respectively. This indicated that the addition of apus bamboo skin threads in petung reinforcement increased the flexural strength of the reinforced concrete beams. These conditions were subsequently capable of increasing the cross-sectional area of the petung bamboo’s main reinforcement.

Postfire Residual Strength and Morphology of Concrete Incorporating Natural Rubber Latex Exposed to Elevated Temperatures

The exposure of concrete to elevated temperatures is known to cause diverse severe damages in concrete composites. Hence, measures to improve the performance of concrete during exposure to fire are continually proposed. The present study investigated the postfire residual strength and morphology of concrete incorporating natural rubber latex exposed to elevated temperature. Four different concrete mixes were considered for the investigation, namely, a control sample made without natural rubber latex, the second sample containing 1% natural rubber latex, the third sample containing 1.5% natural rubber latex, and the fourth sample containing 3% of natural rubber latex. The concrete samples (150 mm cubes and 100 × 200 mm cylinders) were exposed to varying temperatures 300°C, 800°C, and 1000°C, after the curing process. Nondestructive tests using Schmidt rebound hammer and ultrasonic pulse tester were carried out on samples. The compressive strength and split-tensile strength of concrete cubes and cylinders, respectively, were determined. Micrographs and elemental distribution in the sample were studied using the scanning electron microscopy (SEM-EDX) apparatus. It could be seen from the results that the concrete strength properties reduced as the exposure temperature increased. The results also showed that NRL could be sparingly utilized as a concrete admixture, at 1% content. The performance of concrete was not stable at over 300°C when NRL addition was above 1%.

Experimental and statistical investigation on synergistic effect of nano based epoxy hybrid FRP on strength and durability of circular concrete columns

Strengthening and retrofitting of concrete structures using fiber reinforced polymer (FRP) wrapping is a promising technique in construction sector. Epoxy is the commonly used matrix which possess a higher rate of degradation under exposure to harsh environment. The evaluation of strength and durability of concrete cylinders confined by multi walled carbon nanotube (MWCNT) incorporated epoxy with hybrid sisal and basalt fiber composite systems exposed to various environmental conditions forms focus of this paper. Specimens are subjected to various environmental exposure such as elevated temperature, acidic, alkaline and sea water conditions. Two varieties of epoxy viz. neat epoxy and MWCNT modified epoxy systems are considered. Mechanical and durability properties are analyzed based on axial compressive behavior, stress strain response, visual inspection and modes of failure. The MWCNT incorporated epoxy based hybrid FRP confined specimens exhibited a strength reduction less than 10% when compared with unexposed confined specimens under aggressive environmental conditions, while unconfined specimens showed strength reduction by 40% when compared to unexposed unconfined specimens. The MWCNT modified epoxy based hybrid confinement showed an energy absorption of 6.24 times that of unconfined specimens upon chemical exposure. Ultrasonic Pulse Velocity test revealed efficacy of confinement system in protecting concrete core from a sudden failure, which in turn increases the compressive strength of system. A statistical analysis using ANOVA was employed to find significance of these factors and confirmed with experimental results. The effect of MWCNT incorporation is significant in FRP confinement and shows the possibility of the FRP system to be adopted as a major retrofitting material in alkaline and sea water environments.

Development of a Reliable Machine Learning Model to Predict Compressive Strength of FRP-Confined Concrete Cylinders

The degradation of reinforced concrete (RC) structures has raised major concerns in the concrete industry. The demolition of existing structures has shown to be an unsustainable solution and leads to many financial concerns. Alternatively, the strengthening sector has put forward many sustainable solutions, such as the retrofitting and rehabilitation of existing structural elements with fiber-reinforced polymer (FRP) composites. Over the past four decades, FRP retrofits have attracted major attention from the scientific community, thanks to their numerous advantages such as having less weight, being non-corrodible, etc., that help enhance the axial, flexural, and shear capacities of RC members. This study focuses on predicting the compressive strength (CS) of FRP-confined concrete cylinders using analytical models and machine learning (ML) models. To achieve this, a total of 1151 specimens of cylinders have been amassed from comprehensive literature studies. The ML models utilized in the study are Gaussian process regression (GPR), support vector machine (SVM), artificial neural network (ANN), optimized SVM, and optimized GPR models. The input parameters that have been used for prediction include the geometrical characteristics of specimens, the mechanical properties of FRP composite, and the CS of concrete. The results of the five ML models are compared with nineteen analytical models. The results evaluated from the ML algorithms imply that the optimized GPR model has been found to be the best among all other models, demonstrating a higher correlation coefficient, root mean square error, mean absolute percentage error, mean absolute error, a-20 index, and Nash–Sutcliffe efficiency values of 0.9960, 3.88 MPa, 3.11%, 2.17 MPa, 0.9895, and 0.9921, respectively. The R-value of the optimized GPR model is 0.37%, 0.03%, 5.14%, and 2.31% higher than that of the ANN, GPR, SVM, and optimized SVM models, respectively, whereas the root mean square error value of the ANN, GPR, SVM, and optimized SVM models is, respectively, 81.04%, 12.5%, 471.77%, and 281.45% greater than that of the optimized GPR model.

Preliminary Investigation on Properties of Novel Sustainable Composite: Fish Scales Reinforced Cement Concrete

This study focused on analysing the effect of fish scales reinforcement on fresh and hardened-state properties of concrete. For this purpose, 24 cubes and 24 cylinders were casted at a design mix ratio of 1:2.3:4.3. The water-cement ratio of 0.57 was maintained. The fish scales reinforcement levels of 0%, 1%, 1.5% and 2% by weight of cement were maintained for casting of specimens. For fresh-state assessment, the workability of concrete mixes was observed by slump test and the results showed that, with the addition of fish scales, the slump value decreased due to increase in water demand. With the addition of 2% Fish Scales, the workability of concrete mixes reduced by 36.40%. The compressive strength and tensile strength of concrete cubes and cylinders were tested with Universal Testing Machine (UTM) at curing period of 7 and 28 days. Out of 48 specimens casted, a total of 24 specimens were subjected to compressive strength test while other 24 specimens were tested for tensile strength. The results reported that with addition of 2% fish scales in concrete, the tensile strength of concrete increased but the compressive strength initially decreased and later increased. It can thus be concluded that the fish scales can be incorporated in concrete with steel to enhance the tensile strength of concrete. Keeping the initial decrease in compressive strength of concrete in consideration, it can be recommended that the fish scale reinforced concrete can be safely used in light weight structures and non-structural elements like floor slabs and ribs.

Ponašanje valjkastih uzoraka betona ovijenih CFRP-om – laboratorijska studija

The research presented in this paper focuses on the application of innovative materials for the repair and strengthening of RC columns of buildings in seismically active regions. The analytical and laboratory research for defining the compressive strength and elastic modulus of concrete cylinders confined with CFRP (Fibre Reinforced Polymers) was carried out at the Skopje-based Institute of Earthquake Engineering and Engineering Seismology – IZIIS in order to present the possibilities and benefits of using these materials. Selected results from laboratory testing of built-in materials, and some analytical results from the designed CFRP-confined RC columns for quasi static tests, are presented in this paper.

Experimental Investigations on the Long Term Material Properties of Rubberized Portland Cement Concrete

The paper presents the results of a research work aimed at assessing the long-term strength and elastic properties of rubberized concrete. The parameters of the research were the rubber replacement of fine aggregates and the age of testing the specimens. Compressive and splitting tensile strength of concrete cylinders were obtained at the age of 5 years, coupled with the static and dynamic modulus of elasticity of all concrete specimens. Additionally, the material damping coefficient was assessed by means of non-destructive tests. The density of the rubberized concrete decreases with the percentage replacement of natural sand by rubber aggregates. A significant drop in the values of density after 5 years was observed for specimens made with rubberized concrete. The static and the dynamic moduli of elasticity decrease with the increase in rubber content. A similar trend is observed for the compressive and tensile splitting strength.

Experimental Study on Influence of Methylcellulose on Tensile and Flexural Strength of Normal Strength Ordinary Portland Cement Concrete

Current study explores the possibility of improvement in various categories of concrete’s strengths (including tensile strength, flexural strength etc.) by using methylcellulose as an additive. The effect of methylcellulose on concrete’s compressive strength has also been investigated experimentally. Concrete samples were casted with several methylcellulose to binder ratios varying from 0.002 to 0.01 by weight of cement. Several tests were performed on concrete specimens including concrete cylinder and cube compression tests, split cylinder tests and modulus of rupture tests. Results showed that addition of methylcellulose increased the tensile strength of concrete. Addition of 0.2% of methylcellulose increased the tensile strength of concrete by 16%. This increase in tensile strength reached up to 73% of the control sample on addition of 1% methylcellulose. It was observed that the effect of methylcellulose on compressive strength of concrete depends upon the type of samples being tested (cube or cylinder). The compressive strength of concrete cylinders showed a plateau behavior with peak at 0.4% methylcellulose content with an increase of 18.7%. Effect of methylcellulose on concrete cylinder strength becomes insignificant beyond 0.6%. It was observed that addition of methylcellulose reduces the modulus of rupture values. The reduction in MOR was only 3% at 0.2% methylcellulose content but it grew to 30% at 1% methylcellulose content. The research presents an effective way of increasing tensile strength of concrete but without significant effect on concrete’s compressive strength and modulus of rupture values. These findings can be used to determine optimum content of methylcellulose to achieve desired performance from concrete depending upon the intended use.

Strength and strain modeling of CFRP-confined concrete cylinders using ANNs

Carbon fiber reinforced polymer (CFRP) has extensive use in strengthening reinforced concrete structures due to its high strength and elastic modulus, low weight, fast and easy application, and excellent durability performance. Many studies have been carried out to determine the performance of the CFRP confined concrete cylinder. Although studies about the prediction of confined compressive strength using ANN are in the literature, the insufficiency of the studies to predict the strain of confined concrete cylinder using ANN, which is the most appropriate analysis method for nonlinear and complex problems, draws attention. Therefore, to predict both strengths and also strain values, two different ANNs were created using an extensive experimental database. The strength and strain networks were evaluated with the statistical parameters of correlation coefficients (R2), root mean square error (RMSE), and mean absolute error (MAE). The estimated values were found to be close to the experimental results. Mathematical equations to predict the strength and strain values were derived using networks prepared for convenience in engineering applications. The sensitivity analysis of mathematical models was performed by considering the inputs with the highest importance factors. Considering the limit values obtained from the sensitivity analysis of the parameters, the performances of the proposed models were evaluated by using the test data determined from the experimental database. Model performances were evaluated comparatively with other analytical models most commonly used in the literature, and it was found that the closest results to experimental data were obtained from the proposed strength and strain models.

Performance evaluation of hybrid fiber reinforced low strength concrete cylinders confined with CFRP wraps

The improvement in the compressive strength (CS) and ductility of plain concrete always remained an active area for advanced research. The present study aims to enhance the strength of low strength hybrid fiber reinforced concrete (HFRC) cylinders confined with different number of carbon fiber reinforced polymer (CFRP) sheets by examining the axial CS, axial compressive strain, and compressive stress–strain behavior of low strength HFRC cylinders confined with CFRP sheets. The HFRC consisted of steel fibers and polypropylene fibers. Two groups of low strength HFRC specimens (12.5 MPa and 16.5 MPa) were fabricated to investigate the effect of CFRP confinement on the different CS of HFRC. The experimental outcomes depicted that the lateral CFRP confinement of concrete significantly improved the CS, axial compressive strain, and axial stiffness of low strength HFRC specimens. The improvements of 115.7% and 130.7% occurred in the CS of 12.5 MPa group for single and double CFRP layers, respectively. Similarly, the improvements of 37.4% and 112.6% occurred in the CS of 16.5 MPa group for single and double CFRP layers, respectively. Therefore, the CFRP confinement is more effective for low strength HFRC as compared with high strength HFRC in terms of axial CS and axial compressive strain.

Comparison of the design of prestressed concrete hollow-core floor units with Eurocode 2 and ACI 318

A typical 1200 mm (48 in.) wide × 200 mm (8 in.) deep prestressed concrete hollow-core unit is analyzed and designed in order to make a comparison between Eurocode 2 and ACI 318-08. This includes calculations for serviceability limit state of stress and moment of resistance, ultimate moment of resistance, ultimate shear capacities, flexural stiffness (that is, for deflection), and cover to pretensioning tendons for conditions of environmental exposure and fire resistance. Concrete cylinder strength is 40 MPa (5.8 ksi), and concrete cube strength is 50 MPa (7.3 ksi). The hollow-core unit is pretensioned using seven-wire helical strands. Worked examples are presented in parallel formation according to Eurocode 2 and ACI 318. For uniformly distributed loads, the design criterion between the service moment to service moment of resistance (Ms/Msr for EC2 and Ms/Msn for ACI 318) and the ultimate design bending moment to ultimate moment of resistance (MEd/MRd for EC2 and Mu/φMn for ACI 318) is well balanced for this example. Usually the service moment is critical unless the amount of prestress is small. For EC2-1-1, flexurally uncracked shear capacity VRd,c is only limiting when the span-to-depth ratio in this example is less than about 35. For ACI 318, flexurally cracked shear capacity φVci is limiting when span-to-depth ratio is 42, showing that shear cracked in flexure will often be the governing criterion.

Restorability of strength and stiffness of fire damaged concrete using various composite confinement techniques

In this paper, an experimental study was carried out to investigate the effectiveness of various composite confinement repairing techniques for the restoration of strength and stiffness of concrete cylinders. A total of 42 plain concrete cylinders were heated to a range of temperatures from 400 to 800 °C. They were tested under uniaxial compression. The test specimens were placed into six groups: undamaged non-repaired, fire damaged non-repaired, undamaged repaired with exclusively carbon fibre reinforced polymer (CFRP) composite jacket, fire damaged repaired with exclusively CFRP composite jacket, fire damaged repaired with cement slurry injection along with CFRP composite jacket and fire damaged repaired with epoxy resin mortar injected steel wire mesh jointly confined with CFRP composite wrapping system. The results indicated that the exclusively CFRP and epoxy resin mortar injected steel wire mesh jointly confined with CFRP composite wrapping systems were ineffectual to restore the stiffness, although it was noted that they were extremely useful to increase the strength, ductility, deformation capacity and energy dissipation capacity of fire damaged concrete specimens. However, it was found that the cement slurry injection along with CFRP composite wrapping system was functional in the restorability of stiffness, strength, ductility, energy dissipation capacity, and serviceability of fire damaged concrete equivalent to the undamaged concrete or even beyond that without increasing the cross-sectional size of specimens.

Performance and analysis of unidirectional GFRP actively confined high-strength concrete under monotonic and cyclic axial compression

For better understanding the response of unidirectional GFRP actively confined high-strength concrete under dynamic load, this paper mainly investigated the influences of active confinement on the cyclic axial compression performance of high-strength concrete cylinders. The active confinement was produced by the innovative combined action from core concrete expansion and external confinement of unidirectional GFRP at different confinement stiffness. A total of 24 unidirectional GFRP confined high-strength concrete cylinders were tested under monotonic and cyclic axial compression. The results show that the strength enhancement ratio of actively confined high strength concrete cylinders is higher than that of ordinary confined counterparts regardless of the loading modes. In addition, owing to the lateral prestress, the brittle macro cracking of the high strength concrete was reduced. The hoop rupture strain of the actively confined concrete cylinder increases with the increase of the active confinement. The results also show that the stress degradation rate of unidirectional GFRP actively confined high-strength concrete is improved remarkably due to the compactness of core concrete. Guided by the experiments, the high-precision models for the compressive strength and stress–strain relationship of unidirectional GFRP confined high-strength concrete under cyclic axial compression were developed.

Design of square and rectangular CFST cross-sectional capacities in compression

Eurocode EN 1994-1-1 currently covers design of concrete-filled steel tubular (CFST) columns using normal strength materials with nominal steel yield strength (fy) not more than 460 MPa and concrete characteristic cylinder strength less than 50 MPa. As high strength materials have been increasingly used in construction, this paper aims to extend current design equation for square and rectangular CFSTs in EN 1994-1-1 to incorporate high strength materials. A comprehensive experimental database consisting of 443 square and rectangular CFST stub column test results was developed. Statistical evaluations were undertaken and the results indicate that the current cross-section slenderness limit for square and rectangular CFSTs is too conservative and can be safely relaxed from 52235/fy to 68235/fy. The design equation could be extended to incorporate high strength materials). Then, a reliability analysis in accordance with EN 1990 was performed to evaluate the applicability of the proposed design method. It was found that the current partial factors are safe for the design of square and rectangular CFSTs with normal strength materials even after relaxation of the cross-section slenderness limit. However, modification should be applied to the existing design equation for the design of high strength materials to yield an acceptable safety level. Finally, an experimental investigation on 10 stub column tests was carried out to further verify the applicability of the proposed design recommendation. It was found that the proposed design recommendation yields satisfactory predictions when compared to test results.

Strength and Durability of Concrete Cubes and Cylinders Wrapped with FRP

Experimental were conduct on the distressed reinforced cement concrete compressive element and on the same after they have been retrofitted for rehabitation. Presently, FRP materials are also been started use in construction field in the form of wrapping to enhance the load carrying capacity, shear and flexural strength as well as ductility. This is an experiment based project which deals with strengthening and load deformation relationship of reinforced cement concrete. Mix design is done M 30 grade of concrete as per IS: 10262-2009 for preparation of structural elements. In this research, increases in strength, stiffness and durability due to external wrapping of Carbon Fiber Reinforced Polymer (CFRP) sheets on concrete cylinders were studied. The research focused on behavior of plain and wrapped concrete cylinders with respect to parameters such as concrete compressive strength, fiber orientation of CFRP wrap. The experimental results were correlated to analytical models consisting of terms representing lateral pressure generated by the wrap in hoop direction. Keywords: Strength , Durability, Cylinder Wrapped, compressive elements

A Proposed Soft Computing Model for Ultimate Strength Estimation of FRP-Confined Concrete Cylinders

In this paper, the feed-forward backpropagation neural network (FFBPNN) is used to propose a new formulation for predicting the compressive strength of fiber-reinforced polymer (FRP)-confined concrete cylinders. A set of experimental data has been considered in the analysis. The data include information about the dimensions of the concrete cylinders (diameter, length) and the total thickness of FRP layers, unconfined ultimate concrete strength, ultimate confinement pressure, ultimate tensile strength of the FRP laminates and the ultimate concrete strength of the concrete cylinders. The confined ultimate concrete strength is considered as the output data, while other parameters are considered as the input data. These parameters are mostly used in existing FRP-confined concrete models. Soft computing techniques are used to estimate the compressive strength of FRP-confined concrete cylinders. Finally, a new formulation is proposed. The results of the proposed formula are compared to the existing methods. To verify the proposed method, results are compared with other methods. The results show that the described method can forecast the compressive strength of FRP-confined concrete cylinders with high precision in comparison with the existing formulas. Moreover, the mean percentage of error for the proposed method is very low (3.49%). Furthermore, the proposed formula can estimate the ultimate compressive capacity of FRP-confined concrete cylinders with a different type of FRP and arbitrary thickness in the initial design of practical projects.

전단파 속도 측정을 통한 콘크리트 강도 및 탄성계수 평가: 재령 3일에서 28일 실험결과

전단파 속도 측정을 통한 콘크리트 강도 및 탄성계수 평가: 재령 3일에서 28일 실험결과