Spalling Of Cover Research Articles

Spalling of concrete cover of cyclically loaded columns and fire behaviour of columns with concrete spalling

Fire following an earthquake is a threat to seismically damaged structural members with spalling of concrete cover. To evaluate the fire behaviour of the damaged members, it is important to determine the spalling length and thickness reasonably. In this paper, 16 columns were cyclically loaded to check their concrete cover spalling features. Based on the test results and PEER’s database, formulas are proposed for flexure-critical rectangular columns to approximately evaluate the spalling length and thickness of the columns’ concrete cover. Then, thermal and mechanical performance of the damaged columns in fire is numerically studied. It is found that: (a) the maximum spalling length generally increases with the increasing column’s drift ratio and axial load ratio, but it does not exhibit monotonic trend with the change in the shear span ratio and volumetric transverse reinforcement ratio; (b) the ratio of the equivalent spalling length to the maximum spalling length generally increases with the increasing column’s drift ratio and axial load ratio; and (c) fire endurance of the damaged column calculated using the equivalent model is 7–18% higher than that using the realistic model, and a discounted factor of .8 is recommended for the former.

Potential Effects of Corrosion Damage on the Performance of Reinforced Concrete Member

Corrosion of steel in reinforced concrete is one of the most serious issues for the owners. The main consequences of this phenomenon include loss of cross section of steel area, induced the expansive pressure which caused cracking of concrete, spalling and delaminating of the concrete cover. Thus, it reduces the bond strength between steel reinforcing bar and concrete, and deteriorates the strength of whole structure. In this study, a non-linear finite element analysis was conducted to investigate the potential effects of corrosion damage. A series of corroded reinforced concrete cylinder is used in the parametric study to assess the influence of different level of corrosion to the structural performance. As a result, a clear picture of corrosive expansion was investigated and the relationship between the expansive pressure and the degree of corrosion was identified to be the important factors of the structural deterioration.

Probability of Failure of Corroding Reinforced Concrete Columns under Eccentric Loading

The load-carrying capacity of an eccentrically loaded reinforced concrete column affected by corrosion of reinforcement will progressively decrease with time due to the buildup of corrosion-induced damage in the form of loss of reinforcement area, cracking and spalling of concrete cover. Due to the complexity of corrosion problems, a probability-based assessment of failure, instead of a deterministic approach to ascertain safety, is prudently more appealing. An attempt has been made to propose a method for computing probability of failure of corroded eccentrically loaded columns using Monte Carlo simulation (MCS) of a proposed limit state safety function based on a time-dependent strength prediction model for the residual strength. The MCS covers a large number of possible combinations of all governing parameters related to strength within their prescribed distributional characteristics. The results show that MCS can be used to estimate probabilities of failure, and that the corrosion current density and the ratio of eccentricity of the applied axial load to the depth of the section, e/h, are the two significant factors that affect the probability of failure at a prescribed corrosion period the most.

Flexural Behavior of Ferrocement Plates Incorporating Steel and PET Fibers

Ferrocement plate with steel meshes incorporating fibers in an identical matrix were tested under bending. The main objective of the study was to investigate the effects of combining reinforcing steel meshes with discontinuous fibers as reinforcement in thin mortar matrix. The variable parameters were chosen as (a) number of mesh layers, single and double (b) the types of fiber i.e steel and polyethylene terephthalate (PET). Everything else being equal, the test results shows that addition of steel fibers to the matrix of ferrocement can effectively increase its flexural strength and energy absorption to failure. Cracking and spalling of mortar cover also significantly reduced. On the other hand, the contributions of same volume fraction of PET fibers are not significant compared to steel. However, addition of PET fibers control the early cracking of thin mortar and showed slight improvement in flexural strength and energy absorption to failure compared to control specimens. Reinforcing ferrocement plates incorporating steel or PET fibers is recommended for providing technical and economical advantages as no negative effect was observed.

Modeling corrosion‐induced damage of reinforced concrete elements with multiple‐arranged reinforcement bars

Aggressive environmental conditions, such as exposure to the sea climate or use of de‐icing salts, have considerable influence on durability of reinforced concrete structures due to the reinforcement corrosion‐induced damage. Recently a coupled 3D chemo‐hygro‐thermo‐mechanical (CHTM) model for modeling of processes related to the chloride induced corrosion of steel reinforcement in concrete was developed. The model is briefly discussed and subsequently employed in the 3D finite element analysis of reinforced concrete (RC) beams exposed to aggressive environmental conditions, which were recently tested by Dong et al. . In the analysis, the corrosion‐induced damage is simulated by accounting for the interaction between several rebars. Moreover, the influence of the stirrups is also investigated. The numerical results are compared with experimental results and it is demonstrated that the numerical model realistically replicates corrosion‐induced damage of concrete. The same as in experimental tests, the beams without stirrups exhibits severe damage due to spalling of concrete cover and the presence of stirrups reduces the corrosion‐induced damage.

Ductility in concentrically loaded reinforced concrete columns

In recent years, the use of high-strength concrete materials has been regulated into Australian design standards. The use of high-strength concrete is desirable in many cases. For instance, in reinforced concrete columns of high rise buildings, the columns can carry more load with a smaller cross section compared to reinforced concrete columns built of normal strength material. However, there are some disadvantages, one being the reduction of ductility. The Australian Concrete Standard AS3600 deals with this issue by changing the tie arrangement in reinforced columns for different concrete strength grades. This study reviews the ductility index used to measure the ductility of reinforced concrete columns and uses an analytical model to predict the ductility index of several practical example columns. These columns are designed and detailed using the requirements of the Australian Concrete Standard. The outcome of a parametric study shows that the columns designed and detailed using the rules in the Australian Concrete Standard may not necessarily have the ductility index which the code assumes. Another well-known deficiency observed in the behaviour of reinforced high-strength concrete columns is premature spalling of the cover concrete. The Australian Concrete Standard addresses premature cover spalling by modifying a reduction factor which is applied to the strength of the concrete when the squash load of a reinforced concrete column is calculated. This reduction factor accounts for many issues not only premature cover spalling. Using an analytical model, it is shown that the code formula for estimating the squash load is too conservative and needs adjustment for very large columns with small cover to core ratio.

Experimental Analysis of Reinforcement Corrosion on Bond Behaviour

The corrosion of reinforcement is the major cause of damage of reinforced concrete structures. This has an impact on safety, serviceability and durability of the structure. The corrosion of steel in concrete reduces the cross sectional area of the reinforcement and decreases the bond between reinforcement and concrete. Corrosion products have a higher volume than steel, which produces internal stresses that lead to the cracking and spalling of the concrete cover. The paper analyses the effect of the chloride-initiated corrosion of reinforcements on bond behaviour.

Experimental and analytical evaluation of concrete cover spalling behavior due to local corrosion

Experimental and analytical evaluation of concrete cover spalling behavior due to local corrosion

A simple model for the calculation of the axial load-carrying capacity of corroded RC columns

In the present paper, a simplified model is used to determine the axial load-carrying capacity of compressed short reinforced concrete columns subjected to corrosion processes. The model considers members with circular and square cross-sections and accounts for—cover spalling, —concrete core confinement induced by transverse steel reinforcement, —buckling of longitudinal reinforcing bars. Strength reduction in concrete cover and core due to cracking induced by rust formation, reduction of steel area in longitudinal bars and transverse stirrups due to general and pitting corrosion and loss of confinement pressure are considered. The load-carrying capacity and load-axial strain curves here generated analytically fit well the existing experimental data.

Modeling of concrete cracking due to corrosion process of reinforcement bars

The reinforcement corrosion in Reinforced Concrete (RC) is a major reason of degradation for structures and infrastructures throughout the world leading to their premature deterioration before design life was attained. The effects of corrosion of reinforcement are: (i) the reduction of the cross section of the bars, and (ii) the development of corrosion products leading to the appearance of cracks in the concrete cover and subsequent cover spalling. Due to their intrinsic complex nature, these issues require an interdisciplinary approach involving both material science and structural design knowledge also in terms on International and National codes that implemented the concept of durability and service life of structures.In this paper preliminary FEM analyses were performed in order to simulate pitting corrosion or general corrosion aimed to demonstrate the possibility to extend the results obtained for a cylindrical specimen, reinforced by a single bar, to more complex RC members in terms of geometry and reinforcement. Furthermore, a mechanical analytical model to evaluate the stresses in the concrete surrounding the reinforcement bars is proposed. In addition, a sophisticated model is presented to evaluate the non-linear development of stresses inside concrete and crack propagation when reinforcement bars start to corrode. The relationships between the cracking development (mechanical) and the reduction of the steel section (electrochemical) are provided. Finally, numerical findings reported in this paper were compared to experimental results available in the literature and satisfactory agreement was found.

Corrosion-induced cover spalling and anchorage capacity

The aim of this study is to enhance our understanding of anchorage capacity in reinforced concrete structures with corrosion-induced cover spalling. Our objectives were to study the influence of corrosion-induced cover spalling on bond strength, and to validate an existing one-dimensional (1D) analysis for anchorage capacity in such cases. Thus, earlier developed bond and corrosion models suited for detailed three-dimensional (3D) finite element (FE) analysis were first combined with a new computation scheme to simulate corrosion-induced cover spalling. The 1D and 3D FE analyses were validated through two types of experiments, i.e. eccentric pull-out tests and beam tests, as well as a comparison with an existing empirical model. The application of 3D FE analysis showed that the corrosion of stirrups advances the emergence of cracking and spalling, while bond strength is only slightly influenced by the corrosion of stirrups after cover spalling if yielding of stirrups has not taken place. Moreover, it was shown that stresses in the stirrups due to corrosion in adjacent bars rapidly diminished within a short distance from the main bar, and that the corrosion of stirrups influenced the shear capacity more prominently than the induced stresses in stirrups due to the corrosion of main bars.

Influence of corrosion on the bond strength of steel rebars in concrete

The problem of the durability of reinforced concrete structures is arisen, dramatically, in the last decades, showing that one of the most dangerous degradation phenomena is connected to the rebars corrosion. When active corrosion grows the oxides occupy a volume of about 2–4 times, with respect to the sound bar, causing a loss of bond, cracking and cover spalling. In this paper the corrosion effects at the steel–concrete interface are analysed. At this aim, pull-out tests are carried out, with different corrosion levels, for the definition of the bond-slip constitutive relationships of the damaged rebars. Furthermore, an analytical model is developed for evaluating the internal pressure due to corrosion products, for concrete specimens without stirrups, in order to provide a procedure for the definition of the maximum bond as a function of the corrosion percentage. Finally the analytical results are validated through a comparison with the experimental outcomes.

Chloride Ion Penetration in RC and SFRC Precast Tunnel Lining Segments

Steel corrosion induces distress in concrete structures, resulting in the cracking and spalling of the concrete cover, which accelerates further damage. Chloride ions (Cl–) and carbonation are the primary causes of steel corrosion in concrete. This study investigates the effects of Cl– in precast concrete tunnel lining (PCTL) segments through conducting various tests on cylindrical cores extracted from conventional reinforced concrete (RC) and steel fiber-reinforced concrete (SFRC) segments. The full-scale PCTL segments were fabricated and cured at an industrial precast plant. Experimental results show that the external specimens (extrados and intrados faces) of both the RC and SFRC PCTL segments exhibited lower Cl– penetration due to surface treatment using a cement slurry. The Cl– diffusion coefficient was a function of the exposure period and concentration of the salt solution for both the RC and SFRC segments. SFRC PCTL segments better resisted the ingress of Cl– than control RC segments due to a barrier effect induced by steel fibers (SF), which helped inhibiting the penetration of Cl– into the hardened concrete. This study demonstrates the potential of SFRC as a more durable alternative for precast segmental tunnel linings compared to conventional RC.

Experimental and numerical studies on seismic performance of hollow RC bridge columns

To investigate the seismic performance and to obtain quantitative parameters for the requirement of performance-based bridge seismic design approach, 12 reinforced concrete (RC) hollow rectangular bridge column specimens were tested under constant axial load and cyclic bending. Parametric study is carried out on axial load ratio, aspect ratio, longitudinal reinforcement ratio and transverse reinforcement ratio. The damage states of these column specimens were related to engineering limit states to determine the quantitative criteria of performance-based bridge seismic design. The hysteretic behavior of bridge column specimens was simulated based on the fiber model in OpenSees program and the results of the force-displacement hysteretic curves were well agreed with the experimental results. The damage states of residual cracking, cover spalling, and core crushing could be well related to engineering limit states, such as longitudinal tensile strains of reinforcement or compressive strains of concrete, etc. using cumulative probability curves. The ductility coefficient varying from 3.71 to 8.29, and the equivalent viscous damping ratio varying from 0.19 to 0.31 could meet the requirements of seismic design.

Deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion

A three-dimensional reinforced concrete (RC) deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion is presented in this study. The finite element formulation accounts for both material and geometrical nonlinearity. Damage modelling considers uniform and pitting corrosion and includes the reduction of cross-sectional area of corroded bars, the reduction of ductility of reinforcing steel and the deterioration of concrete strength due to splitting cracks, delamination and spalling of the concrete cover. The beam finite element is validated with reference to the results of experimental tests carried out on RC beams with corroded reinforcement. The application potentialities of the proposed formulation are shown through the finite element analysis of a statically indeterminate RC beam and a three-dimensional RC arch bridge under different damage scenarios and corrosion penetration levels. The results indicate that the design for durability of concrete structures exposed to corrosion needs to rely on structural analysis methods capable to account for the global effects of local damage phenomena on the overall system performance.

Methods of analysis of a reinforced concrete section under bending with axial force in the post-yield range

Predicting the behaviour of plastic hinges subjected to large inelastic deformations caused by extreme loads such as earthquakes plays an important role in assessing maximum stable deformation capacities of framed concrete structures. This paper presents the analytical procedure for analysing the behaviour of a reinforced concrete section under bending with axial force in the post-yield range. The following stages of section behaviour are defined: the uncracked, first cracked, yielding, cover crushing, cover spalling, buckling of bars and limit stages. The relationship between the moment and curvature in these stages, including the effects of concrete confinement, the spalling of the concrete cover, and the inelastic buckling of the reinforcing bars, is considered. The presented method makes it possible to estimate the ductility of reinforced concrete members with various longitudinal and transverse reinforcement.

Behavior of Rectangular Columns Constructed with SCC and Steel Fibers

Extensive research has shown that properly detailed and closely spaced transverse reinforcement in reinforced concrete columns can ensure ductile behavior during earthquakes. However, in regions of high seismicity, detailing requirements can result in heavily congested sections; the use of self-consolidating concrete (SCC) can facilitate construction in these situations. Although extensive research exists on the axial load behavior of traditional concrete columns, only limited research exists on the behavior of columns constructed with SCC. Research over the past two decades has also shown that use of steel fiber-reinforced concrete (SFRC) can improve the strength and ductility of columns by delaying cover spalling and improving core confinement. Recent research has also shown that the combined use of SCC and steel fibers can ease problems associated with the workability of traditional fiber-reinforced concrete. This paper presents the results from an experimental program that was conducted to study the axial behavior of reinforced concrete columns constructed with SCC and SFRC. Full-scale columns having rectangular cross sections were tested under pure axial compressive loading. The columns were detailed with varying amounts of transverse reinforcement in accordance with the requirements of the Canadian Standards Association. The results confirm that increasing confinement with closely spaced transverse reinforcement in rectangular SCC columns results in improvements in behavior and ductility. In addition, the results demonstrate that the use of SFRC in rectangular columns results in improvements in performance and ductility.

Seismic Fragility Assessment of RC Bridges under Marine Environments

The chloride-induced corrosion of steel bars is focused in this study which is one of the major causes of deterioration of RC bridges under marine environments. The steel corrosion usually causes cracking and spalling of the concrete cover due to the expansion of corrosion products. Structural distress due to loss of bond or reduction of the cross-sectional area can be caused with time. A girder bridge exposed to the marine environment is studied to present the fragility curves variance in time in this study. The damage states of the bridge are determined to five stages by using the maximum displacement ductility. The proposed method will be useful to evaluate the seismic performance of new or existing bridges considering steel rebar corrosion.

Behavior of Reactive Powder Concrete Columns Under Eccentric Compression Loading

The strength of concrete columns is controlled by the strength of the material and the geometry of the cross section. The use of Reactive Powder Concrete RPC technology has proven most popular with superior strength, stiffness and durability being the major advantages. An experimental investigation was carried into the behavior of RPC columns subjected to axial load with initial eccentricity. Twelve columns were prepared with 120mm square section at the midsection and were hunched at the ends to apply eccentric loading. The specimens were tested up to failure to evaluate the effects of the variation of the concrete type (normal or RPC), presence of steel fibers and longitudinal steel ratio. Experimental data on strength, lateral displacement and failure mode was obtained for each test. The comparative analysis of the experimental results showed that the use of RPC caused substantial variation in the ultimate strength and failure modes. Also, inclusion of steel fibers in RPC was an effective way to prevent spalling of the concrete cover and increase the ductility, as well as, high ratio of longitudinal reinforcement delays the buckling of the columns and increases strength.

Effect of Confinement on the Axial Load Response of Ultrahigh-Strength Concrete Columns

AbstractTwelve ultrahigh-strength concrete (UHSC) columns confined by rectangular hoops and crossties were constructed and tested under pure axial load. Primary variables of the investigation were the amount, spacing, and configuration of transverse reinforcement, and concrete compressive strength, ranging from 50 to 200 MPa. The amount of transverse reinforcement ranged from 53 to 151% of that required by the American Concrete Institute (ACI) seismic design provisions. Four different configurations of transverse reinforcement were investigated that included hoops as well as hoops and crossties. The behavior of UHSC columns are characterized by sudden spalling of the concrete cover and extremely brittle failure unless the columns are adequately confined with transverse reinforcement. Therefore, more confinement is required in a column with higher concrete strength than in a column with lower concrete strength to achieve a reasonable postpeak response and sufficient deformability. The amount of transverse ...