Concrete Structural Components Research Articles

Effect of carbonation, chloride and external sulphates on the leaching behaviour of major and trace elements from concrete

Abstract The effect of the exposure of concrete structural components to CO2, chloride and external sulphates on the leaching of major and trace elements (Al, Ca, K, Na, S, Si, Ba, Sr, Cr and V) was investigated for concrete made with OPC and fly ash using a tank leach test and the Dutch availability test NEN 7341. Concrete specimens were carbonated under natural and accelerated conditions (2 vol.% CO2) before testing. Exposure to chloride or external sulphates was simulated by adding NaCl (30 g/L) or Na2SO4 ( 3 or 30 g SO 4 2 - / L ) to the tank leach test eluent. The results show that concrete leaching depends significantly on the abovementioned environmental factors. In particular, the cumulative release of Cr during the tank leach test increased proportionally to carbonation depth. More V was released from carbonated concrete. Replacement of the cement by a fly ash with more Cr and V had no discernible effect on Cr release, but resulted in additional V release in proportion to the level of cement replacement. Exposure of concrete to NaCl solution enhanced the release of Cr, but not V. Exposure to Na2SO4 solution increased the release of Cr and V considerably. It is suggested that the dissolution of CrO 4 2 - and VO 4 3 - substituted AFt/AFm governs the leaching of Cr and V.

Residual strength evaluation of concrete structural components under fatigue loading

This paper presents methodologies for residual strength evaluation of concrete structural components using linear elastic and nonlinear fracture mechanics principles. The effect of cohesive forces due to aggregate bridging has been represented mathematically by employing tension softening models. Various tension softening models such as linear, bilinear, trilinear, exponential and power curve have been described with appropriate expressions. These models have been validated by predicting the remaining life of concrete structural components and comparing with the corresponding experimental values available in the literature. It is observed that the predicted remaining life by using power model and modified bi-linear model is in good agreement with the corresponding experimental values. Residual strength has also been predicted using these tension softening models and observed that the predicted residual strength is in good agreement with the corresponding analytical values in the literature. In general, it is observed that the variation of predicted residual moment with the chosen tension softening model follows the similar trend as in the case of remaining life. Linear model predicts large residual moments followed by trilinear, bilinear and power models.

Automated Color Model–Based Concrete Detection in Construction-Site Images by Using Machine Learning Algorithms

AbstractConcrete structural component detection in color images is a key pre-process in various applications such as construction progress measurement, structural health monitoring, and three-dimensional as-built modeling. The goal of this research was to identify an automated color model–based concrete detection method that (by using a machine learning algorithm) can detect concrete structural components in color images with a high level of accuracy. A data set consisting of more than 87 million pixels was generated from 108 images of concrete surfaces with a variety of surfaces. Transformations from the RGB color space to non-RGB color spaces were performed to increase separability between concrete and background classes and to achieve robustness to changes in illumination. To find the optimal combination of color space and machine learning algorithm, the performance of three machine learning algorithms (e.g., a Gaussian mixture model, an artificial neural network model, and a support vector machine mod...

A general 3D approach for the analysis of multi-axial fracture behavior of reinforced concrete elements

The behavior of cracked reinforced concrete structural components is here analyzed through a three-dimensional model, which includes all the interface phenomena generated along cracks, such as aggregate bridging and interlock, tension stiffening and dowel action, as well as the non-linear response of concrete in compression and in tension. The model is able to effectively describe the progressive development of multi-axial cracking, by considering the crack re-orientation and the change of the crack spacing as loading increases. The proposed formulation, which is expressed in terms of secant stiffness matrix, is obtained by taking into account the flexibility contributions of cracks and of the concrete between adjacent cracks, in both the singly and the multi-cracked stage. Finally, this model is implemented into a finite element code and is validated through comparisons with significant experimental data available in the literature.

Fracture Analysis and Fatigue Remaining Life Prediction of Concrete Structural Components Accounting for Tension Softening and Size Effects

This paper presents methodologies for fracture analysis and fatigue remaining life prediction of concrete structural components with and without accounting for tension softening and size effects. Stress intensity factor (SIF) is computed by conducting finite element analysis (FEA) and compared with that obtained by using analytical approach. The domain integral method has been used to calculate the strain energy release rate (SERR) and SIF by post-processing the FEA results. Nonlinear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Details of size effect in the computation of SIF and remaining life prediction have been presented. Size effect has been accounted for by modifying the Paris law, leading to size adjusted Paris law. Numerical studies have been conducted for fracture analysis, crack growth studies and remaining life prediction. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature.

Fracture Analysis of Concrete Structural Components Accounting for Tension Softening Effect

This paper presents methodologies for fracture analysis of concrete structural components with and without considering tension softening effect. Stress intensity factor (SIF) is computed by using analytical approach and finite element analysis. In the analytical approach, SW accounting for tension softening effect has been obtained as the difference of SIP obtained using linear elastic fracture mechanics (LEFM) principles and SIP due to closing pressure. Superposition principle has been used by accounting for non-linearity in incremental form. SW due to crack closing force applied on the effective crack face inside the process zone has been computed using Green's function approach. In finite element analysis, the domain integral method has been used for computation of SIR The domain integral method is used to calculate the strain energy release rate and SIF when a crack grows. Numerical studies have been conducted on notched 3-point bending concrete specimen with and without considering the cohesive stresses. It is observed from the studies that SW obtained from the finite element analysis with and without considering the cohesive stresses is in good agreement with the corresponding analytical value. The effect of cohesive stress on SW decreases with increase of crack length. Further, studies have been conducted on geometrically similar structures and observed that (i) the effect of cohesive stress on SW is significant with increase of load for a particular crack length and (iii) SW values decreases with increase of tensile strength for a particular crack length and load.

Procedure for nonexplosive demolition of concrete during reconstruction of hydroelectric generating sets

Working experience with nonexplosive demolition of reinforced concrete is presented. New methods for demolition of the components of concrete and reinforced-concrete structures are coming into ever-increasing use for the reconstruction of water-development works. Thus, systems with blast generators (BG) have been successfully used at the Volga HPPs to break-up tamped and base concrete in the impeller chambers of hydraulic-generating sets and in the cones of the draft tubes. The operating principle of the BG is based on the molding and detonation of charges of a liquid explosive mixture (LEM) formed from components, which taken individually are not dangerously explosive: oxidizing agent and combustible. In addition to the blast generators, an effective portable shelf, which is suspended on cables and can be displaced along the vertical by traveling winches, a protective rack, which is mounted on the support ring of the turbine and protects the entire machine room from falling fragments and dust, and equipment for the removal of material and a forced-ventilation system are component parts of the layout [1]. The high cost of the equipment, however, restricts the economic expediency of their use at hydroelectric power plants during reconstruction involving small volumes of concrete demolition. When the blasting operations are conducted, moreover, the structural components, and in a number of cases, working mechanisms are negatively affected, even when mercy blasting is employed. Due to the effect of the shock wave and seismic load, disturbances of the perimeter concrete, which are precisely of explosive origin, and which are characterized by cracks with different degrees of opening, may develop in the impeller chamber, and particularly in those with a small diameter. In construction, and also at some of quarries, nonexplosive rupturing compositions (NRC) have come into widespread use for the production of dimension stone. They can be used under restricted conditions: in a dense urban setting, during reconstruction of active establishments, and when the entity being demolished is situated in a zone of operating mechanisms for which complete safety should be ensured. This applies, for example, to the reconstruction of concrete components in the bases of power-generating equipment [2]. Nonexplosive rupturing compositions are a product of the crushing of carbonate rocks, which is pulverized, and combined with special additives. This powdery material is light gay, dusty, incombustible, and explosion-proof, and exhibits alkaline properties. When mixed in a certain proportion with water, the effective mixture hardens with an expanding volume. In a compressed medium, the increase in volume causes the pressure to rise to 40 – 50 MPa; this will contribute to cracking and failure of reinforced-concrete structures. A modified nonexplosive limestone mixture SIGB (formerly known as NEM-1 — nonexplosive expansive mixture), which also makes it possible to demolish materials of various strengths, has recently been developed for mining and drilling operations. The fact that work production is not accompanied by emission of gaseous and solid substances, sound and seismic vibrations, i.e., complete safety and environmental conservation are ensured, and does not require use of expensive and complex equipment, is a basic advantage of this method of demolition. SIGB is a gay, dusty, incombustible, explosion-proof material, and exhibits the following basic properties:

English

This paper presents an overview on the concrete structural components subjected to impact loading. The review includes empirical formulae, analytical models, and numerical simulations. Various empirical formulae on penetration depth, perforation, and scabbing limits as well as their ranges of application have been provided. It has been observed that the information available on the validation of these models is limited. There is wider scope to study the performance of well known empirical formulae. Penetration resistance function play an important role in any analytical model. It has been observed that the major limitation is rigid projectile assumption. There is scope to develop new/improved analytical models to represent projectile characteristics. The numerical simulation of concrete structural components subjected to impact loads is a complex phenomenon. From the review, it is observed that employing appropriate material model for concrete, equation-of-state, contact algorithm and definition of yield surface plays significant role in the accurate simulation of concrete structural components. There is ample scope to develop improved methodologies in terms of development of material models and contact algorithms, which can be employed in nonlinear explicit finite element analysis of concrete structural components subjected to impact loading. Defence Science Journal, 2010, 60(3), pp.307-319 , DOI:http://dx.doi.org/10.14429/dsj.60.358

Remaining life prediction of concrete structural components accounting for tension softening and size effects under fatigue loading

This paper presents analytical methodologies for remaining life prediction of plain concrete structural components considering tension softening and size effects. Non-linear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Various tension softening models such as linear, bi-linear, tri-linear, exponential and power curve have been presented with appropriate expressions. Size effect has been accounted for by modifying the Paris law, leading to a size adjusted Paris law, which gives crack length increment per cycle as a power function of the amplitude of a size adjusted stress intensity factor (SIF). Details of tension softening effects and size effect in the computation of SIF and remaining life prediction have been presented. Numerical studies have been conducted on three point bending concrete beams under constant amplitude loading. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature for all the tension softening models.

External Prestressing Technique for Strengthening of Prestressed Concrete Structural Components

This paper presents the details of an innovative external prestressing technique for strengthening of prestressed concrete girders. The technique has been developed for anchoring the external prestressing to the sides of the end block. In the proposed technique, transfer of external force is in shear mode on the end block and the required transverse prestressing force is smaller compared to conventional techniques. In order to validate the technique, an experimental investigation has been carried out on two posttensioned end blocks (EB-1 and EB-4). Steel brackets are provided on either side of the end block for transferring external prestressing force and these are connected to the anchor blocks by expansion-type anchor bolts. Performance of the end blocks has been studied for design, cracking, and ultimate loads. A ductile failure is observed in EB-1 whereas a sudden failure is observed in EB-4. The slip and slope of the steel bracket have been recorded at various stages during the experiment. These values are found to be smaller in EB-1 than in EB-4 due to a higher anchorage depth of bolts. Finite-element analysis has been carried out by simulating the geometry, loading, material nonlinearity, and test conditions. Linear and nonlinear static analysis has been conducted for the specified loadings and the responses have been compared. From the analysis, it has been observed that the computed slope and slip of the steel bracket are in good agreement with the corresponding experimental observations.

State-of-the-art review on fracture analysis of concrete structural components

This paper presents a critical review of literature on fracture analysis of concrete structural components. Review includes various fracture models, tension softening models, methodologies for crack growth analysis and remaining life prediction. The widely used fracture models which are based on fictitious crack approach and effective elastic crack approach have been explained. Various tension softening models such as linear, bi-linear, tri-linear, etc. have been presented with appropriate expressions. From the critical review of models, it has been observed that some of the models have complex expressions involving many parameters. There is a need to develop some more generalised models. Studies have been conducted on crack growth analysis and remaining life prediction using linear elastic fracture mechanics (LEFM) principles. From the studies, it has been observed that there is significant difference between predicted and experimental observations. The difference in the values is attributed to not considering the tension softening effect in the analysis.

Theoretical model on interface failure mechanism of reinforced concrete continuous beam strengthened by FRP

Fiber reinforced polymer (FRP) composites are increasingly being used for the repair and strengthening of deteriorated concrete structural components through adhesive bonding of prefabricated strips/plates and the wet lay-up of fabric. Interfacial bond failure modes have attracted the attention of researchers because of the importance. The objective of the present study is to analyse the interface failure mechanism of reinforced concrete continuous beam strengthened by FRP. An analytical solution has been firstly presented to predict the entire debonding process of the model. The realistic bi-linear bond-slip interfacial law was adopted to study this problem. The crack propagation process of the loaded model was divided into four stages (elastic, elastic-softening, elastic-softening-debonded and softening-debonded stage). Among them, elastic-softening-debonded stage has four sub-stages. The equations are solved by adding suitable stress and displacement boundary conditions. Finally, critical value of bond length is determined to make the failure mechanism in the paper effective by solving the simultaneously linear algebraic equations. The interaction between the upper and lower FRP plates can be neglected if axial stiffness ratio of the concrete-to-plate prism is large enough.

Experimental, numerical and analytical studies on a novel external prestressing technique for concrete structural components

This paper presents the details of a novel external prestressing technique for strengthening of concrete members. In the proposed technique, transfer of external force is in shear mode on the end block thus creating a complex stress distribution and the required transverse prestressing force is lesser compared to conventional techniques. Steel brackets are provided on either side of the end block for transferring external prestressing force and these are connected to the anchor blocks by expansion type anchor bolts. In order to validate the technique, an experimental investigation has been carried out on post-tensioned end blocks. Performance of the end blocks have been studied for design, cracking and ultimate loads. Slip and slope of steel bracket have been recorded at various stages during the experiment. Finite element analysis has been carried out by simulating the test conditions and the responses have been compared. From the analysis, it has been observed that the computed slope and slip of the steel bracket are in good agreement with the corresponding experimental observations. A simplified analytical model has been proposed to compute load-deformation of the loaded steel bracket with respect to the end block. Yield and ultimate loads have been arrived at based on force/moment equilibrium equations at critical sections. Deformation analysis has been carried out based on the assumption that the ratio of axial deformation to vertical deformation of anchor bolt would follow the same ratio at the corresponding forces such as yield and ultimate. It is observed that the computed forces, slip and slopes are in good agreement with the corresponding experimental observations.

A methodology for remaining life prediction of concrete structural components accounting for tension softening effect

This paper presents methodologies for remaining life prediction of plain concrete structural components considering tension softening effect. Non-linear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Various tension softening models such as linear, bi-linear, tri-linear, exponential and power curve have been presented with appropriate expressions. A methodology to account for tension softening effects in the computation of SIF and remaining life prediction of concrete structural components has been presented. The tension softening effects has been represented by using any one of the models mentioned above. Numerical studies have been conducted on three point bending concrete structural component under constant amplitude loading. Remaining life has been predicted for different loading cases and for various tension softening models. The predicted values have been compared with the corresponding experimental observations. It is observed that the predicted life using bi-linear model and power curve model is in close agreement with the experimental values. Parametric studies on remaining life prediction have also been conducted by using modified bilinear model. A suitable value for constant of modified bilinear model is suggested based on parametric studies.

Study of the thermal behaviour of a production unit of concrete structural components

We propose an economic and technical optimisation of a small concrete structures workshop. The heat released by the chemical hydration reaction is modeled and validated with experimental data. A nodal model of the thermal response of the incubator internal air, using an electrical analogy approach, is realised. The equivalent time is calculated and a battery of air treatment units is sized to reach the mechanical resistance for handling in an acceptable deadline whatever the meteorological conditions are.The solution minimizing energy costs by studying the influence of inherent parameters of the system and step regimes of the workshop has been conducted.

An economic evaluation of soil bioengineering as a method for slope stability on abandoned mine land in Eastern Kentucky

ABSTRACT Unstable slopes are a serious problem on abandoned mine land (AML) in Kentucky and a number of other states. Current practices used to manage unstable slopes rely on modern conventional techniques that incorporate rock, concrete, or steel structural components. Implementation of these techniques has proven expensive due to recurring maintenance requirements. This study examines soil bioengineering technology as a viable alternative. In this study, the cost effectiveness of two common slope stabilization systems— rock gabions and rock riprap—has been compared with the innovative soil bioengineering system. Baseline cost estimates applied to all three systems were consistent with commercial scales. Assuming a useful life of 20 years for both the gabion and riprap systems, sensitivity analysis using net present values (NPV) in response to changes in both installation costs (I) and useful life (N) was conducted on both systems. Data was calculated over a range of applicable interest rates. The resulting values were compared to installation costs for the soil bioengineering system. This analysis confirms that soil bioengineering technology can be economically competitive with its conventional counterparts. Further, it is hoped the results of this study can lead to wider acceptance of environmentally conscious slope stabilization systems in mining regions throughout the country.

Issues related to structural aging in probabilistic risk assessment of nuclear power plants

Abstract Structural components and systems have an important safety function in nuclear power plants. Although they are essentially passive under normal operating conditions, they play a key role in mitigating the impact of extreme environmental events such as earthquakes, winds, fire and floods on plant safety. Moreover, the importance of structural components and systems in accident mitigation is amplified by common-cause effects. Reinforced concrete structural components and systems in NPPs are subject to a phenomenon known as aging, leading to time-dependent changes in strength and stiffness that may impact their ability to withstand various challenges during their service lives from operation, the environment and accidents. Time-dependent changes in structural properties as well as challenges to the system are random in nature. Accordingly, condition assessment of existing structures should be performed within a probabilistic framework. The mathematical formalism of a probabilistic risk assessment (PRA) provides a means for identifying aging structural components that may play a significant role in mitigating plant risk. Structural condition assessments supporting a decision regarding continued service can be rendered more efficient if guided by the logic of a PRA.

Distributed fiber Bragg grating strain sensing in reinforced concrete structural components

Fiber Bragg grating sensors are of particular interest for distributed sensor applications, where gratings can be addressed using time- and wave-length-division techniques to provide the strain distribution along a structural component. This paper describes the use of a prototype Bragg grating instrumentation system for monitoring the strain at several locations through reinforced concrete beams and decks which are tested to failure. Strain readings are obtained from a number of multiplexed sensors which are bonded to the rebar reinforcement, free floating in the concrete, and embedded in composite materials attached to the concrete.

Service life prediction of concrete structures by reliability analysis

This paper describes the development and application of a reliability-based system for the service life prediction and management of maintenance and repair procedures of reinforced concrete structures. By using statistical databases and probability theory, this system is capable of establishing levels of reliability in satisfying various governing conditions (also known as limit states) as determined by performance requirements or financial considerations. By using the reliability as a measure of performance requirements, inspection, preventive maintenance, repair and major rehabilitation decisions can be made based on economic analysis over the life-cycle of a structure. Therefore, this system will assist in making rational management decisions on a scientific basis. The paper details the derivation of governing conditions of reinforced concrete structural slabs and demonstrates the possible applications of this method in managing these components. Following similar procedures, reliability-based life-cycle management systems can also be developed for other concrete structural components.

Probabilistic methods for condition assessment and life prediction of concrete structures in nuclear power plants

A probability-based methodology is being developed in support of the NRC Structural Aging Program to assist in evaluating the reliability of existing concrete structures in nuclear power plants under potential future operating loads and extreme environmental and accidental events. The methodology includes models to predict structural deterioration due to environmental stressors, a database to support the use of these models, and methods for analyzing time-dependent reliability of concrete structural components subjected to stochastic loads. The methodology can be used to support a plant license extension application by providing evidence that safety-related concrete structures in their current (service) condition are able to withstand future extreme events with a level of reliability sufficient for public health and safety.