Effects Of Concrete Cracking Research Articles

Coupling effect of concrete cracks and stray current on chloride-induced corrosion of rebar

Either concrete cracking or stray current promotes the corrosion of rebars; however, the coupling effects of concrete cracking and stray current on the rebar corrosion are still unknown. In this work, the effect of concrete cracking patterns coupled with stray current on rebar corrosion is presented by both experimental and finite element simulation. Specifically, there is a strong coupling effect when crack width is less than 100 μm, which manifests that ion concentration and electric field intensity increase pronouncedly with decreasing crack width. Simulation shows that the coupling effect leads to an asymmetric distribution of ions and electric fields at the crack tip, which in turn causes the asymmetric corrosion of rebars. Under the coupling effect, the highest corrosion rate reaches 3 μA/cm2 and is more than three times higher than that in a natural environment. Our findings contribute to understanding and evaluating accurately rebar corrosion in practical application.

Monitoring of crack repair in concrete using spherical smart aggregates based on electromechanical impedance (EMI) technique

Cracks will inevitably occur in concrete structures or members during the construction process and service life due to aging, environmental factors, external loads, etc. To improve the strength and stability of the cracked concrete structures, many methods have been proposed to repair the cracks. However, the monitoring of the repairing process and repair quality has not been fully studied. The previous studies have proved that the spherical smart aggregates (SSAs) based on the electromechanical impedance (EMI) technique have outperformed the traditional smart aggregates (SAs) based on the EMI technique in structural health monitoring of civil structures, however, SSAs have not been applied to the monitoring of the concrete crack repair. In this work, the monitoring of the concrete crack repair using the SSAs based on the EMI technique was explored. A total of eight concrete specimens were prepared, and cracks in the concrete specimens were simulated by manually cutting under laboratory conditions. According to the principle of grouting method, two repair agents including cement paste and cement mortar were used to repair the cracks. The impedance signals of 28 d were measured, and three quantitative indicators, namely root mean square deviation, mean absolute percentage deviation, and correlation coefficient deviation were used to evaluate the quality of the concrete repair effect. The results indicate that the SSAs show excellent sensitivity and stability over the traditional SAs. In addition, the normalized values of the quantitative indicators were analyzed to distinguish the types of repair agents. A mathematical expression of exponential function was also proposed by fitting the experimental data to quantitatively evaluate and predict the repair effect of concrete cracks. Further, the influences of temperature, humidity, crack depth and width on the experimental results were analyzed and discussed. The numerical simulation was also presented to validate the reasonability of the experimental results.

Experimental Study On Acoustic Emission Characteristics of SAP Mortar Self-Healing Process

Self-healing properties of super absorbent polymer (SAP) concrete can reduce the harmful effects of concrete cracking in structures. This study examines the self-healing process of mortars with different SAP content under dry and wet conditions through acoustic emission testing (AE) and elastic wave velocity testing. Findings indicate that the SAP mortar healing process has three stages: rapid water absorption, smooth water absorption, and drying. In a dry environment, increasing SAP content enhances AE activity, indicating internal crack self-healing via further hydration of unhydrated cement particles. In a wet environment, AE activity increases with increasing SAP content during the second healing cycle, indicating self-healing of the mortar matrix. These results suggest the use of SAP concrete could potentially mitigate future structural damage.

Optimization of spore production and activation conditions of concrete crack healing bacteria and research on crack repair effect

Currently, research on the spore production rate and spore activation rate of microorganisms is mostly used in the pharmaceutical and food industries, with little research on their application in repairing concrete cracks. The spore production ability of mineralized microorganisms and the spore activation ability in the concrete environment are key influencing factors in ensuring the repair effect of concrete cracks. The effects of various factors on the spore production rate and spore activation rate of Bacillus alcalophilus (Bacillus cohnii) were studied using a single factor controlled variable method in this paper, and the optimal spore production culture conditions and activation conditions were determined. Furthermore, the mineralization reaction after microbial spore activation and the repair effect of concrete cracks were investigated. The results showed that under optimal spore production culture conditions, the spore production rate reached 93.9 %. The spore activation rate of microorganisms was as high as 94.5 % under optimal spore activation conditions. The rate of microbial spore activation was 78.6 % at room temperature (20 ℃) without heat shock treatment. Calcite calcium carbonate produced by the mineralization reaction after microbial spore activation could be used to repair subsequent concrete cracks. The optimal concentration of calcium acetate required for microbially induced carbonate deposition was 100 g/L. The concrete crack with a width of 1.12 mm could be repaired after 28 days of repair age, and the concrete strength recovery rate was 70.81 % when the microbial self-healing agent prepared by Bacillus alkalophilus (Bacillus cohnii) was incorporated into concrete.

Understanding the efficiency of autogenous and autonomous self-healing of conventional concrete mixtures through mechanical and microscopical analysis

Among the ways to counter the effects of concrete cracking, self-healing appears to be very promising. This research aims to appraise the effect of autogenous and autonomous self-healing on the condition recovery of mechanically loaded concrete specimens proportioned with distinct raw materials. A commercially available crystalline admixture (CA), different types of SCMs, and chemically modified versions of CA were combined with cement to proportion distinct mixtures. Ninety-six specimens from each mixture were manufactured and cured for 28 and 180 days at 20 °C and 100 % RH, after which they were pre-loaded using up to 90 % of their corresponding compressive strength and restored at the same curing conditions for 90 days. Non-destructive, microscopic, and mechanical test procedures were conducted on the samples after the secondary curing; results indicate that SCMs enhanced the natural healing. However, mixtures to which CA was added demonstrated the highest healing ratios, indicating promising recovery of mechanical properties.

Multi-span composite girders with composite dowels – Experimental investigations and design approach to account for the beneficial effect of shear force redistribution along the composite interface

The broad use of composite dowels as shear connectors in multi-span steel and concrete composite members is currently hindered by insufficient regulations for hogging moment regions, where the connectors are located in cracked concrete slabs and have reduced shear resistance. This paper reports on the results of three beam tests that illustrate the ability of continuous steel and concrete composite beams with composite dowels to redistribute shear forces from impaired connectors located in hogging bending regions to intact connectors in sagging bending regions. The effect of concrete cracking on the load-bearing behaviour of composite dowels is analysed with regard to their strength, stiffness and ductility by means of three full-scale member tests. This paper proofs the existence of a beneficial shear force redistribution process along the interface of multi-span composite members and quantifies the shear force transfer occurring between connectors in sagging and hogging bending regions. In addition, the paper provides an economical design method for continuous composite girders. Previously developed models regarding the shear resistance of single composite dowels in cracked concrete are refined aiming to provide both safety and ease of use. These models are subsequently extended into a comprehensive design strategy that allows us to consider the beneficial shear force redistribution processes along the interface when designing the shear connection of multi-span composite beams with composite dowels.

EIS based assessment of electrodeposition effect of concrete cracks: Experiment and equivalent model

In this study, the electrochemical impedance spectrum (EIS) is proposed to evaluate the effectiveness of concrete cracks repaired through electrodeposition. The EIS responses of the concrete cracking and electrodeposition repairing processes are investigated. The obtained results show that the impedance of concrete decreases with increasing crack width. The impedance of concrete increases gradually during the electrodeposition process. In order to characterize and forecast the EIS responses during the concrete cracking and electrodeposition repairing processes, a new equivalent circuit model is proposed. The crack repairing rates are defined in terms of the crack resistance and total impedance of concrete. After 14 days of electrodeposition repairing, the crack repairing rates can eventually reach 79.35% and 77.81% in terms of crack resistance and total impedance, respectively. In addition, the influences of the w/c ratio, crack width, and crack tortuosity of concrete on the EIS responses of concrete repaired by the electrodeposition process are calculated and discussed.

Study on influence of geometric characteristics of cracks on HAM coupling transfer and thermal performance of multi-layer cellular concrete wall

The effect of concrete cracks on the evaluation of the thermal performance of walls has not been effectively considered within the assessment of the thermal and hygroscopic performance of buildings. Based on the dual permeability model, a conjugate method is proposed to reconstruct the PDE equation of unsaturated porous materials with cracks. The reliability of the model is verified from three angles: the heat-moisture coupling benchmark of matrix material, the analytical solution of two-dimensional single fracture heat flow coupling problem and the moisture absorption problem of unsaturated cracks. The reliability of the model is verified from three perspectives: the benchmark of thermal and hygroscopic coupling of matrix materials, the analytical solution to the two-dimensional single-break thermal flow coupling problem, and the hygroscopic problem of unsaturated cracks. The effect of heat and moisture transfer in cracked concrete was quantified by detailed modeling of cracks in terms of the probability of over-penetration, crack roughness, crack density, length, and angle of a two-dimensional discrete crack network, showing that cracks contribute to moisture transfer. This is followed by a 10 day experimental simulation of the meteorological environment, comparing the quantities of moisture accumulation, thermal performance, internal surface temperature and humidity within the fractured and non-fractured wall structures, illustrating the potential adverse effects of cracks on thermal performance and moisture transfer in walls under characteristic conditions. Finally, the necessity of applying moisture-proof layer to the damaged wall is demonstrated by comparing the results before and after the application of the moisture-proof layer.

Analysis of composite bridge deck considering the effects of concrete cracking

Abstract Cracking in composite steel-concrete bridge decks is a common problem in civil engineering. Before, or shortly after, the bridge is subjected to live loads; various levels of cracking can appear, mostly due to plastic shrinkage and temperature effects. This paper presents an investigation of the behavior of cracked concrete in a composite deck slab of a railway bridge supported by steel girders using the finite element method. Eurocode 4-2 proposes a few simplified methods for calculating shrinkage and cracking effects in concrete. Through the proposed methods of analysis, an analytical simulation of a continuous composite steel-concrete bridge deck is performed and some practical recommendations for analyzing beam girders of this type are given.

Effect of CTAB on the healing of concrete cracks repaired by electrodeposition and the durability of repaired concrete

In this study, the surfactant cetyltrimethylammonium bromide (CTAB) was doped in an electrolyte solution to improve the healing effect of concrete cracks repaired by electrodeposition. The effect of the CTAB dosage (0.25%, 0.50%, 1.00%, 1.50%, 2.00%) on the healing of concrete cracks was investigated, as well as the durability of repaired mortar specimens. Under the current dosage range, the experimental results demonstrated that the healing effect of concrete cracks peaks at 1.00% CTAB dosage. Nevertheless, the extra more addition of CTAB could weaken the healing effect. In terms of the specimens repaired in electrolyte solution containing 1.00% CTAB, the steel-mortar adhesive strength, chloride ion resistance and corrosion resistance of steel were significantly enhanced compared with those of specimens repaired by electrodeposits without CTAB. Additionally, instead of influencing the composition of electrodeposits ZnO (formed in ZnSO4 solution) and Mg(OH)2 (formed in MgSO4 solution)), the different CTAB dosages could lead to diverse morphology of electrodeposits and different porosity of specimens.

Damage and quantitative indexes for steel reinforced concrete column with T-shaped section

This paper presents an experimental investigation on damage performance of nine steel reinforced concrete (SRC) columns with T-shaped section under different loading paths. The monotonic loading, low cyclic reversed loading and mixed loading were applied to specimens along the flange of specimen. Furthermore, different axial compression ratios and steel ratios were used to study the damage of specimen. The failure modes were observed and the load-displacement curves were analyzed. The results indicate that the specimens mainly showed the feature of bending failure accompanied by bond failure characteristic at the end of loading. The load-displacement curve was plump and symmetrical without obvious pinch under the low cyclic reversed loading. The ductility coefficient lied within the range of 5.34–9.41, which indicates that these columns had better deformation capability. Based on the experimental results, a modified damage model considering deformation and energy dissipation was proposed, where the effects of concrete cracking, loading path and effective energy dissipation on damage were studied. Moreover, the damage index at each loading stage was calculated. Meanwhile, the level of seismic performance of SRC T-shaped column was divided into five levels, namely the normal use, the basic normal use, the temporary use, the post-repair use, and the near serious damage. Many SRC T-shaped columns were chosen as the analysis samples to obtain the displacement angles under different loading stages. Based on statistic results, the corresponding relationship between quantitative index of displacement angle and the damage index was established.

Hydrothermal Aging and Bonding Properties of a New Room Temperature Cured Structural Adhesive in Building Components

his paper firstly explores the hydrothermal aging performance of a new room temperature cured structural adhesive at four different levels of relative humidity through dynamic mechanical analysis (DMA). The results show that the strengthening effect of post-curing was stronger than weakening effect of humidity. Then, the Arrhenius equation was introduced to calculate the ratio of the apparent activation energy of this adhesive at the glass transition temperature before and after hydrothermal aging. The little change of the ratio suggests that the adhesive boasts a strong resistance to hydrothermal aging. In addition, the adhesive was tested on concrete structures at room temperature to observe its repairing effect of concrete cracks. The observations reveal that the compressive strength of the cracked concrete block repaired by the adhesive was as high as 90.5% of that of the intact concrete block. Furthermore, the adhesive was used to bond rebars to concrete under three different constant tensile speeds. The results demonstrate that the bonding effect was better under slow constant loading.

Assessment of SSI interaction effects for deep diaphragm walls and adjacent buildings considering spatial variability of parameters, post-peak behavior and concrete cracking

Recent research works into the design and response evaluation of deep diaphragm walls and induced settlements to adjacent buildings demonstrated that the nonlinear behavior of surrounding soil, cracking effects affecting the structural members’ flexural rigidity and spatial variability of soil parameters are a prerequisite for a rigorous analysis of serviceability performance. However, as a result of the complexity of the mechanisms developed in the case of deep multi-propped retaining structures, most of the proposed Soil Structure Interaction (SSI) design methodologies are biased towards geotechnical or structural behavior by adequately capturing the nonlinearities of the one field and considering a rather simplified behavior of the other. With the aim to bridge the gap between the above design methodologies, a fully coupled analysis of a multi-propped diaphragm wall of an underground station with a supporting grout slab at the excavation bottom has been carried out. Further to the nonlinear behavior of the soil, the spatial variability of the grout treated zone strength and stiffness together with the post-peak behavior have been considered. In addition, the concrete cracking effects, associated with substantial decrease of structural members’ stiffness, have been taken into account. Comparative simplified empirical approaches disregarding cracking effects by adopting constant diaphragm wall flexural rigidity instead, have been carried out as well. Interesting conclusions were drawn relating the results of the above simplified approaches and the Serviceability Limit State (SLS) analyses with regard to the response of the diaphragm wall, the bending moment distribution along the wall and the displacement field in the surrounding soil and adjacent buildings.

Direct observation of the local bond behavior between corroded reinforcing bars and concrete using digital image correlation

Corrosion induced rebar deterioration and concrete cracking alter the local bond interactions in reinforced concrete. An experimental methodology for investigating changes in the local deformation at the interface, caused by rib height reduction and corrosion layer is proposed. The effect of concrete cracking is eliminated by re-casting corroded rebars into new specimens. Local bond interaction is examined using uniaxial tensile tests and recorded through an observation window. The recorded interaction was analysed using Digital Image Correlation (DIC). Prior to visible crack formation, strain distribution maps revealed diagonal cracks indicating that the bond failure is associated with mechanical anchorage until a degree of corrosion of around 12%. Measurements of local opening and sliding behavior at the interface confirm that the slipping interactions become dominant with increase in corrosion. Differences in the shape of individual rib tips and flat lengths in specimens with higher corrosion cause significant variation in local bond interaction.

Effect of concrete cracks on the corrosion of headed studs in steel and concrete composite structures

Corrosion of headed studs leads to the degradation of mechanical properties of shear connectors and thus decreases the durability of steel and concrete composite structures. The effect of concrete cracks on stud corrosion was investigated in this study. Accelerated corrosion tests on headed stud shear connectors and numerical simulation on chloride migration were presented. 3D corrosion morphologies of headed studs in concrete slabs with different concrete cover thicknesses and crack widths and depths were precisely measured by using an optical surface measurement technique. The results show that there was highly localized corrosion in the stud head, and cracks had significant effect on the corrosion distribution. Then, after finite element models for chloride migration were verified by experimental results, a parametric study was carried out. It was found that in concrete slab with higher crack depth, chloride concentration around the headed stud increased more rapidly, while the crack width had slight effect on the distribution of chloride concentration. Moreover, the length of the chloride transport path was found to be a significant parameter that affect the stud corrosion.

Effect and Mechanism of Encapsulation-Based Spores on Self-Healing Concrete at Different Curing Ages.

It has become an intelligent and environmental protection method to repair concrete cracks based on microbial-induced calcium carbonate precipitation (MICP). However, due to the high-alkali environment in concrete, even the microbial spores with strong alkali resistance find it difficult to survive for a long time, which affects the long-term self-healing effect of concrete cracks. In this paper, low-alkali sulfo-aluminate cement (SC) was used as a carrier to encapsulate spores, and the effects of the spore group and microbial group on the basic performances of concrete were studied. Then, the area repair ratio, water permeability, the repair ratio of anti-chloride ion penetration, and ultrasonic velocity were used to evaluate the self-healing efficiency of cracks, and the self-healing effects of two kinds of microbial self-healing agents on concrete cracks with different curing ages were further studied. Moreover, the growth, enzyme activity, and microbial morphologies of spores with and without encapsulation immersed in the simulated pore solution of cement-based materials at different times were studied to discuss the protective effect of the carrier on spores. Compared with the reference group, the results showed that the addition of two microbial self-healing agents would slightly affect the basic performances of concrete, but both were within the control range of concrete materials. For the early-age cracks, the two kinds of microbial self-healing agents could achieve a good self-healing effect, but for the later-age cracks, the concrete cracks of the microbial group could still be repaired well, while the self-healing effect of the spore group was greatly reduced. Moreover, the white precipitates generated at the crack mouth were all calcite CaCO3. In addition, the self-healing mechanism of different microbial self-healing agents on concrete cracks was discussed carefully. This study provides a new idea and method for the engineering application of microbial self-healing concrete.

GBT Analysis of Steel-Concrete Composite Beams: Recent Developments

This paper reports the most recent developments concerning Generalized Beam Theory (GBT) formulations, and corresponding finite element implementations, for steel-concrete composite beams. These formulations are able to perform the following types of analysis: (i) materially nonlinear analysis, to calculate the beam load-displacement response, up to collapse, including steel plasticity, concrete cracking/crushing and shear lag effects, (ii) bifurcation (linear stability) analysis, to obtain local/distortional bifurcation loads and buckling mode shapes of beams subjected to negative (hogging) bending, accounting for shear lag and concrete cracking effects and (iii) long-term service analysis including creep, cracking and arbitrary cross-section deformation (which includes shear lag) effects. The potential (computational efficiency and accuracy) of the proposed GBT-based finite elements is illustrated through several numerical examples. For comparison purposes, results obtained with standard finite strip and shell/brick finite element models are provided.

Numerical modeling of continuous steel concrete composite girders considering cracking of concrete

In continuous steel concrete composite (SCC) girders, the concrete deck is susceptible to cracking because of the negative bending moment, which leads to the redistribution of forces and increases in deformations. The general practice adopted while designing the continuous SCC girder is to ignore the concrete deck in negative moment region and assume the steel girder to resist the entire negative bending moment, which may lead to an uneconomical design. In this regard, a simplified numerical procedure has been proposed, considering concrete cracking effects by aptly modifying the cross-sectional properties of the concrete deck. For this purpose, two different cross-sectional modifiers have been presented. The proposed procedure also incorporates partial shear connection. The proposed simplified numerical procedure is advantageous in terms of flexibility, generality, and the easiness with which it can be adopted in design offices for routine designs of SCC girders. The experimental results available in the literature used to validate the results of the proposed procedure show good agreement. Further, the effectiveness of the proposed procedure is demonstrated with the help of a parametric study. It is observed that a considerable reduction in the negative moment on the steel girder and reduction in deformations of the SCC girder can be achieved by adopting the proposed procedure. An example is solved to illustrate the proposed procedure in the appendix.

An Analytical Method to Predict the Structural Behavior of Timber-Concrete Structures With Brittle-to-Ductile Shear Connector Laws

Timber-Concrete Composite (TCC) structures allow taking synergistic advantage of the properties of both materials to optimize the overall performances in terms of lightness, slenderness, acoustic insulation, vibrational behaviour and environmental footprint. In the last years, ductile shear connectors have been developed to allow the structural ductility of TCC structures. Considering the limitations of current design methods, this work aims at developing a closed-form solution for accurately predicting the nonlinear structural response of a TCC structure directly from the materials' property and the shear law of ductile connectors. In particular, we have assumed a generalized shear law based on 3 parameters which allow considering shear law from a pure elasto-plastic to pure brittle behaviour.After a short introduction, Section 2 briefly presents the basics of the well-estabilished elastic theory for a 2-layer composite beam with a linear shear law in terms of horizontal shear vs. slip (Vh-s) law; Section 2.3 extends the semi-analytical method proposed by Bažant and Vitek for composite structures with a generalized shear law; Sections 3 extends the previous method by developing a new closed-form analytical solution for predicting the TCC structural response for a generalized elasto-plastic Vh-s shear law described by an initial linear response up to Vmax followed by a plastic plateau at a constant load, which can range from 0 to Vmax; Section 4 compares the model results with the ones of existing methods and FEM analysis. Furthermore, a parametric analysis is carried out to investigate the model sensitivity to the connector parameters; Finally, Section 5 presents a simple point-by-point design procedure of which prediction accuracy of the ultimate moment, deflection and slip was statistically assessed for a large range of possible TCC structures against FEM analysis. Eventually, the effect of concrete cracking is also considered and a correction factor is proposed for engineering purpose.

GBT-based time-dependent analysis of steel-concrete composite beams including shear lag and concrete cracking effects

Abstract In this paper, a GBT-based finite element previously developed by the authors for steel-concrete composite beams, which incorporates cross-section deformation (including shear lag effects) and concrete creep, is enhanced by including concrete cracking effects. In particular, a fixed smeared crack model with two orthogonal cracks is consistently combined with creep using a strain decomposition approach. As in the previous finite element, creep is modelled using a linear visco-elastic law and a Dirichlet series expansion of the creep function. A set of illustrative numerical examples is presented, to show the capabilities of the proposed element. For comparison purposes, shell finite element model results are provided. It is demonstrated that the proposed element makes it possible to obtain very accurate results with a relatively small number of cross-section deformation modes (cross-section DOFs) and finite elements, thus leading to significant computational savings with respect to shell element models.