Corrosion-induced deterioration and fracture mechanisms in ultra-high-performance fiber-reinforced concretet

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is an excellent material for harsh environments, but corrosion will change its internal microstructure and complicate the fracture evolution, bringing great difficulties in evaluating the long-term service life. Limited attention has been paid to the fracture mechanism of the UHPFRC upon corrosion. In the present study, integrating acoustic emission (AE) and digital image correlation (DIC) techniques are used to assess the micro/macrocracking characteristics of the specimens upon various corrosion degrees. Results show that the 56-day corroded UHPFRC with 2 vol% presents a remarkable decrease rate of 32%, 29% and 30% in the flexural stiffness, flexural strength and compressive strength. During the loading process, compaction of the original defects induced by fiber corrosion is concentrated in the elastic stage, the newborn cracks triggered by loading mainly occur in the strain-hardening stage, and the expansion of cracks mainly lies in the strain-softening stage. Corroded UHPFRC specimens with higher corrosion damage have a greater maximum strain value at the crack. In addition, the failure mode changes from shear crack failure to a brittle failure of tensile crack as corrosion damage increases. The macroscopic destruction of the corroded UHPFRC is a manifestation of internal microdamage evolution in fiber corrosion and matrix deterioration.</p

Performance of Isolated Footing with Several Corrosion Levels under Axial Loading

This research aims to illustrate the corrosion process and its effect on the deterioration of reinforced concrete (RC) isolated footings using a small-scale model (1/8) and present the results of a prototype-scale study using a numerical model with different concrete depths and corrosion levels under axial load. The experimental program consisted of testing five small-scale (1/8) model RC isolated footings under axial loading after subjecting them to accelerated corrosion tests with a constant current. The main variable in the small-scale sample test was the corrosion level. This study presents an experimental approach, using the constant current method and the finite element method (FEM) with the ABAQUS package, to examine its effect on the axial load behavior under different corrosion ratios, which were 0%, 4.21%, 9.11%, 24.56%, and 30.67%. On the prototype scale, the variables were the corrosion level and the RC depths of 300 mm, 400 mm, and 500 mm. The results indicated that the average deviation in ultimate load between the experimental and FEM outcomes for the small-scale was below 5.6%, while the average deflection deviation was 6.8%. Also, the study found that an increase in the depth of the RC footing and corrosion ratio led to a more pronounced impact of the cracking pattern in the concrete and corroded bars, as well as a greater difference in the failure load. The experimental results suggest that the proposed numerical model is accurate and effective. These findings have important implications for the evaluation of isolated footings affected by corrosion damage using FEM, and can help inform decisions related to their design and maintenance. The failure loads of non-corroded footings with different depths were compared with the ECP-203 provisions of the 2018 Egyptian Code, and how corrosion ratios can be simulated by numerical models. The percentage variation between the design loads by code and the numerical loads by ABAQUS for controlled footings with thicknesses of 300, 400, and 500 mm was found to be 73%, 80%, and 78%, respectively. Using the derived relationship, the equivalent corrosion ratio percentages were 23.8%, 20.2%, and 32%, respectively. Doi: 10.28991/CEJ-2023-09-06-011 Full Text: PD

Numerical simulation of acoustic emission activity in reinforced concrete structures by means of finite element modelling at the macroscale

Acoustic emissions have been widely used as a means to investigate the damage state of concrete structures. While successful applications have regarded the localisation of cracks, quantification of the damage and safety margin estimation have been elusive because the main approaches are mostly based on empirical observations. In this work, a methodology for the numerical simulation of acoustic emission events in reinforced concrete structures is proposed with the aim of filling this gap. It relies on a numerical model for reinforced concrete structures at the macro-scale which simulates the mechanical cyclic behaviour of the structure. Analysis of the stress and strain states in the numerical model provides the basis for the simulation of the occurrence and quantification of the events. A simple attenuation law is then used to estimate the acoustic event intensity recorded by the sensors. Application to a four-point bending test on a reinforced concrete beam confirms the capability of the model to reproduce the data recorded during the test, including the Felicity effect and the cumulative intensity curve. This could potentially open the path to a more quantitative use of acoustic emission data for structural assessment of reinforced concrete structures, directly linking mechanical models and acoustic observations

Condition Assessment of Existing Concrete Building Using Non-Destructive Testing Methods for Effective Repair and Restoration-A Case Study

Buildings constructed during early 70’s & late 80’s of the last century in India are found to be in distressed conditions due to inadequate specifications and poor construction practices. The continuous monitoring of concrete structures using suitable NDT (Non Destructive Testing) methods and use of possible restoration methods help in a considerable reduction of the rate of deterioration of concrete structures thereby increasing the life span of  structures. NDT methods have greater advantage in evaluating the uniformity, homogeneity, approximate compressive strength, durability, the extent of corrosion of rebars in concrete etc. of damaged structures. The objective of the present study is to enhance the life of 50 year old existing hospital building (Partly RC and Brick masonry) in Kurnool, Andhra Pradesh. Condition assessments are carried out through a visual, field and laboratory evaluation of samples collected from the structure and results are presented in this paper. The paper also highlights the assessment of strength and durability of concrete to evaluate the extent of distress and damage in the building. Besides visual inspection, the Non Destructive Evaluation covering UPV & Rebound Hammer values and Half Cell Potential with respect to the status of corrosion of reinforcing bars and chemical tests on selected un-distressed RC columns, beams, and slabs are also presented and discussed. The repair and strengthening techniques using the latest materials and possible restoration works such as column jacketing, shotcreting, anticorrosive coatings, etc. have been suggested to enhance the life of the structure

Fracture characterisation and performance evaluation of corroded RC members by AE-based data analysis

Steel reinforcement corrosion has been regarded as one of the major causes of reinforced concrete (RC) structures failing prematurely, posing a serious structural durability problem worldwide. Detailed assessment of corrosion-induced damage and its effects on RC structures is critical for sustaining structural reliability and safety. This study develops and examines the feasibility of acoustic emission (AE) monitoring and data analysis methodologies to characterise corrosion-induced damage in RC members, followed by an evaluation of the effect of corrosion on load behaviour. Experimental investigations were conducted on a series of specimens of different configurations, namely concrete cubes with steel bars for pull-out tests and RC beams of different dimensions to be subjected to static and cyclic loading regimes. Focusing on developing evaluation methods based on AE monitoring and data analysis, a summary of work completed, and the associated findings are given as follows. Characterisation of the concrete cracking using parametric and waveform analysis was conducted to investigate the effect of corrosion on steel-concrete bond behaviour in the pull-out tests of concrete cubes. It was found that a small amount of corrosion (approximately 6%) could slightly increase the bond strength as a result of the rust expansion and reactionary confinement of concrete. Corrosion was also found to be able to mitigate the damage caused by cyclic loading. AE signal analysis indicates that the concrete cracking mode during the steel-concrete de-bonding process has changed as a result of steel corrosion. Characterisation of load behaviour and failure mode of corroded RC beams was conducted by flexural load tests aided by AE monitoring and digital image correlation (DIC). The DIC strain mapping results and AE signal features revealed that corrosion has an influence on the concrete cracking mechanism of the beam specimens. Corrosion has also altered the failure mode of a shear-critical beam specimen series to flexure owing to the change of steel-concrete bond behaviour. Numerical simulation of AE wave front propagation in RC media and tomographic evaluation of internal damage was implemented on one group of RC beam specimens tested in this study. The numerical model of the specimens was discretised using finite-difference grid meshing, and the different acoustic properties of steel and concrete were defined. On this basis, simulation of AE wave front propagation considering concrete cover cracking and steel rust layer formation was carried out using the fast-marching method. The effect of corrosion-induced damage on the AE rays was studied by examining non-linear ray tracing in the simulation. A tomographic reconstruction approach that solved by the quasi-Newton method provided a potential way to quantitatively evaluate the internal damage of RC beams using AE monitoring data. A novel method was developed for assessing the corrosion level in RC beams using a data-driven approach. Normalization of AE data was applied using principal component analysis to minimise variations in AE signal features caused by differences in the geometrical and material properties of RC beams as well as in the AE monitoring instrumentation setup. The machine learning models, including k-nearest neighbours (KNN) and support vector machines (SVM), were trained using the normalised AE features. The trained KNN models were found effective at predicting the corrosion level in RC beams using the secondary AE signals as input, which could be acquired from the cyclic loading of beams. Key words: Steel Corrosion, Concrete cracking, Steel-Concrete Bond, Reinforced Concrete Beam, Load Behaviour, Acoustic Emission, Digital Image Correlation, Tomographic Reconstruction, Data-driven

Evaluation of Temporal Damage Progression in Concrete Structures Affected by ASR Using Data-driven Methods

Alkali-silica reaction (ASR) is a chemical reaction, which causes damage in concrete structures such as bridges, dams, and nuclear containments and powerplant structures. The ASR-induced damage may endanger the integrity and serviceability of structures. Several methods such as visual inspection, petrographic analysis, demountable mechanical strain gauges, and cracking index have been utilized for study the effect of ASR on structures, which are not always efficient in early damage detection and some are destructive and prohibited in nuclear structures. Nondestructive methods and structural health monitoring techniques can be alternatives for the condition assessment of structures. Among the nondestructive methods, acoustic emission (AE) is preferable due to high sensitivity of AE sensors, source localization ability, and sensing capability in one-side-access structures. The goal is the condition assessment of structures affected by ASR using AE. Therefore, in the current research, data-driven methods in combination with signal processing techniques are employed to find a potential temporal trend in the AE data and relate the trend to the damage progression caused by ASR. In addition, the effect of stress boundary condition on the ASR-induced damage distribution and its reflection on the AE data is investigated. Damage contours based on AE data are developed and utilized to compare event distributions though the medium-scale specimens with different confinements and investigate the temporal evolution of the distributions. Furthermore, the efficacy of differing information entropy calculation approaches for concrete structures undergoing Alkali-Silica Reaction (ASR) induced damage is investigated. The results of the studies indicate that confinement affects the distribution of AE events. In the confined specimen, the distribution of AE events in the mid-width region of the specimen is concentrated and has a sharp peak. However, in the unconfined specimen, the distribution of AE events is more uniform, and cracks are randomly distributed. The entropy results show that the randomness of events increases at the earlier stage of ASR, which is expected due to the microcrack formation and decreases at the later stage due to the formation of macrocracks. The overall outcome in this dissertation demonstrates the potential of using AE for condition assessment of concrete structures affected by ASR degradation. However, more research is required to standardize the method for the field application

An overview of burst, buckling, durability and corrosion analysis of lightweight FRP composite pipes and their applicability

© 2019 Elsevier Ltd. All rights reserved.The main aim of this review article was to address the performance of filament wound fibre reinforced polymer (FRP) composite pipes and their critical properties, such as burst, buckling, durability and corrosion. The importance of process parameters concerning merits and demerits of the manufacturing methods was discussed for the better-quality performance. Burst analysis revealed that the winding angle of ±55° was observed to be optimum with minimum failure mechanisms, such as matrix cracking, whitening, leakage and fracture. The reduction of buckling effect was reported in case of lower hoop stress value in the hoop to axial stress ratio against axial, compression and torsion. A significant improvement in energy absorption was observed in the hybrid composite pipes with the effect of thermal treatment. However, the varying winding angle in FRP pipe fabrication was reported as an influencing factor affecting all the aforementioned properties. Almost 90% of the reviewed studies was done using E-glass/epoxy materials for the composite pipe production. By overcoming associated limitations, such as replacing synthetic materials, designing new material combinations and cost-benefit analysis, the production cost of the lightweight FRP composite pipes can be decreased for the real-time applications.Peer reviewe

Cracking behaviour of coal ash concrete based on acoustic emission technique

The continual rise of the power sector has resulted in massive production of coal waste by-products known as coal bottom ash (CBA) and fly ash (FA), which are formed when raw coal is burned to generate electricity. The disposal of CBA and FA contributes significantly to major environmental hazards and thereby extensive efforts are required to utilize these wastes. Recently, CBA in concrete has been successfully investigated in terms of microstructure, durability, and other common properties. However, it is non-trivial to remark that a topic that received less exploration is serviceability of structural performance, and the main concern being whether CBA aggregate affects the cracking of structural concrete due to the cyclic load. The crack identification is critically important because it gives the first sign of serious trouble indicating the load-carrying capacity and deficiencies in strength of structural elements. Therefore, this research aims to investigate the mechanical properties of plain concrete and cracking behaviour of reinforced concrete (RC) beam with inclusion of CBA. Thus, specimens were designed into four distinct combination replacements between half (50%) and full (100%) of coarse aggregate and fine aggregate using CBA with addition of 20% FA to the cement amount. The fresh concrete was tested by workability test while plain concrete specimens were made for compressive test, splitting tensile test and flexural tests to investigate the mechanical properties of concrete. Then RC beam specimens were cast for a 4-point bending test subjected to a cyclic load method to evaluate cracking behaviour. The assessment of the RC beam also used the acoustic emission (AE) technique that worked purposely for non-destructive testing (NDT). The experimental result shows that compressive strength of concrete for all replacements achieves targeted strength of 30 MPa at 28 days. However, splitting tensile and flexural strength decreased slightly when increasing the volume of CBA in the design mixture. Furthermore, the cyclic load criteria with respect to deviation from linearity (DFL) is promising to correlate to RC beam failure according to deflection in each specific load cycle. Nonetheless, the cracking behaviour of RC beams was mainly influenced by porous and high crushing index of coarse CBA and all tested RC beams failed to the flexural and shear crack failure. In AE parameter-based analysis, the correlation between average frequency and RA (rise time/amplitude) value shows that nucleation of cracks in early cycles are always recorded as a tensile mode with a high average frequency. Then, the crack switches to shear mode containing a high RA value at a subsequent cycle until ultimate load. The AE findings are well matched and consistent with the real visual inspection of crack damage that appeared on the RC beam surface during the experimental work in a laboratory. Thus, the obtained finding in this study indicates that the crack identification from AE technique is effective for structural monitoring, so it could benefit understanding the properties of CBA on the performance of concrete structures. Finally, the excessive usage of CBA in concrete contribute to large numbers of crack while producing wide crack width, but the utilization of CBA as a 50% gravel replacement has good structural performance under cyclic load test as they are comparable to the control RC beam

Assessment of Damage in Concrete Structures Using Acoustic Emission

Evaluating the integrity of concrete structures is an essential procedure to ensure structural safety and durability. Non-destructive testing (NDT) is needed for localizing and characterizing the growing damage in existing structures and also for quality control of new structures. Visual inspection is a commonly used method; however it is not suitable for early detection of damage and very dependent on the experience of the inspector. More research is needed to establish advanced methods for structural health diagnosis such as acoustic emission (AE). Acoustic emission is notably sensitive to active damage in concrete structures. This thesis includes three studies that mainly investigate the effectiveness of AE for condition assessment. The first study aims to present a review of AE-based methods for evaluating the state of in-service structures during load testing. Discussion on the reliability of the proposed methods for different types of structures is provided. Acceptance criteria and quantification limits are summarized based on previous researches. AE has shown promising results in assessing the structural condition of concrete members and its ability to detect micro-cracking is well established. The extensive applications of AE accomplished in field are fairly discussed and some recommendations were given for effective diagnosis. This study attempts to pave the way for the standardization of AE as an inspection and evaluation method for in-service concrete structures. The second study discusses the feasibility of utilizing AE for corrosion detection and quantification. The high sensitivity of AE enables it of detecting the weak stresses emerged due to corrosion initiation and propagation. The ability of AE to monitor the corrosion process was proven by several studies on small and medium scale specimens. Locating the corrosion damage by AE was successfully achieved in laboratory. Quantifying the corrosion damage is examined by means of intensity grading charts for cracked and un-cracked prestressed concrete specimens. However, further research is needed to establish the quantification limits and to extrapolate the results to in-service structures. The third study investigated the ability of AE to detect damage in prestressed concrete specimens. The study included eight beams that were monitored during cyclic load tests. Five specimens were preconditioned to different levels to present possible practical circumstances. Index of damage based on AE-cumulative energy was investigated for damage assessment. The results were in well agreement with the observed damage. However, this method is not convenient for field application as it involves exceeding the maximum admissible damage during the test. Thus, a modification to the index is proposed to facilitate field implementations. The modified index of damage showed a clear trend with the growing damage and the detection of yielding point was enabled in both cracked and un-cracked specimens. The studies presented in this thesis provide an overview of different AE-based methods that can serve as guidance for future researchers as well as a case of study for a newly developed method. The outcomes of these studies verify the viability of using AE for structural health diagnosis. AE showed promising ability for corrosion damage assessment. However most of AE-methods require the aid of a benchmark for absolute conclusions. Further investigation is needed for the standardization of AE as an independent non-destructive evaluation method