Age and remaining lifetime of concrete determined by monitoring

Structures are load bearing objects which become fatigue over period of continuous load application leading to strength reduction. The strength loss associated with reduced internal energy of the structural system consumed during work for sustaining the applied force in the static equilibrium position Deformation monitoring is a major component of accumulating measured values and data, that may be used for further computation, deformation analysis, preventive maintenance and alarming of impending structural danger. Structural Health Monitoring is engineering process of observation and determination of damages and flaws, including characterization of strategy for rehabilitation of structures, which enables assurance of continuity of functionality and structural loading purposes. The process involves observation of structural system over time period, using periodically sampled and dynamic response measurement and equipments. Collection of damage-sensitive features from the measurements, and statistical analysis are used to determine the current state and condition of structural systems. For long term observations, output of the process are periodically updated, which can provide information regarding the ability of structure to perform functionally and adequately, in the midst of prevailing information of degradation resulting from operational environments.

Bulletin of the Polish Academy of Sciences Technical Sciences, 2015

This paper proposes a comprehensive classification of test methods for the diagnosis of concrete structures. The main focus is on the ranges of suitability of the particular methods and techniques for assessing the durability of structures, depending on the principal degradation mechanisms and their effects on this durability. The survey covers non-destructive testing (NDT) methods, which do not in any way breach the integrity of the tested structures, and semi-destructive testing (SDT) methods requiring material samples to be taken or any other minor breach of structural integrity. An original taxonomy of physical, chemical and biological diagnostic methods, useful in assessment of concrete structures durability, is proposed. Equipment specific for selected advanced testing methods is presented as well as exemplary test results.

This paper deals with the use of non destructive testing methods (NDT) to assess indicators of concrete durability and mechanical properties of reinforced concrete structures. On site, NDT methods based on electromagnetic or ultrasonic wave propagation (such as radar, impact echo, ultrasonic transmission device…) are used because they are more or less sensitive to water content and mechanical properties depending on the method. It has been shown, in a former project [1, 2], that the NDT results called "observables" are linked to mechanical and durability indicators (Young's modulus, compressive strength, porosity and saturation degree). Meanwhile, the relationship between observables and indicators depends on the concrete mix design. A calibration protocol is then proposed to get this relationship for the right mix of the reinforced structure studied by using a minimal number of cores. The cores are non-destructively characterised in laboratory or used to determined reference indicators by standardised destructive methods. The aims of this paper are first to present the ND calibration protocol on cores and then to validate this proposed calibration protocol. To achieve this goal, some NDT results obtained on site and on the corresponding core are compared and durability indicators deduced from NDT calibration are compared with reference durability indicators.

2016

This paper presents a series of laboratory experiments on a scaled reinforced concrete bridge deck as well as results of a pilot project on an existing bridge. The ultimate goal is to develop a structural health monitoring system based on evaluation of the dynamic bending stiffness which would be derived from easy to use measurement devices. The experiments are aimed at measuring the deflection for static load, and the dynamic response due to a moving mass, representing a traffic load. The two types of applied sensors are accelerometers and linear variable differential transducer (LVDT). Lab results include dynamic response from uncracked, partial cracked and fully cracked conditions, which influenced the dynamic stiffness. Changes of stiffness therefor is to be believed to be a parameter for crack conditions. The concept has been applied to an existing bridge to prove its value.

High losses due to recent catastrophic natural events have raised the interest of the research community in the field of structural maintenance and protection against environmental actions such as seismic ones. Structural monitoring, has become a very important tool for public safety and safeguard of critical and historical constructions. The paper focuses on monitoring system state of art in order to take advantage of the most critical issues of existing monitoring systems. An integrated monitoring system is briefly described; it combines structural issues with geotechnical and seismological ones, for ordinary and emergency situations.

Early age cracking of structures often leads to aesthetic problems and service life reduction. Among the parameters involved in the stress build-up that causes this cracking process, the stiffness evolution is of major importance for models and numerical computations. This paper reports the use of six different techniques aimed for stiffness evolution assessment, applied on the same concrete mix, in a round robin experimental test within three laboratories. The observations are compared after having expressed the results at the same maturity. Some of the reported techniques provide original means for Young's modulus monitoring of concrete at early age both for industrial and research applications. Two sets of results emerge. Ultrasonic measurements provide values of Young's modulus much higher than the values provided by the static or quasi static tests at the time of the concrete setting. This difference decreases as the concrete hardens.

Static, dynamic and low cycle fatigue testing of 20…30 years old concrete have been carried out. Samples were taken from residential buildings in Cyprus and bridges in Ukraine. Dynamic strengthening factors were 2…4 times lower than those of 28 day concrete. Dynamic strengthening in splitting has been approximately 4 times smaller than that in compression. The static tensile-to-compressive strength ratio of old concrete is more than two times lower than that of young concrete. Modulus of elasticity is increasing with age more significantly than the strength. Elasticity modulus increase has been observed even in cases when there was no increase of strength. Ultimate strains were drastically lower than those of a young concrete. A reduction of approximately 50% has been observed. Up to the stress of 75% of a peak value, old concrete behaves as an elastic material.

Journal of Construction and Building Materials, 2019

This study investigates the feasibility of tracking the structural/dynamic properties of reinforced concrete (RC) structures while subjected to damaging earthquake loads. The methodology proposed implements an unscented Kalman filter scheme that updates the properties of a simplified non-parametric model of the structure. Calibration and validation of the methodology is accomplished using experimental and simulated data from a full-scale RC column test performed at the NEES Large High Performance Outdoor Shake Table. The results obtained show that peak displacement, stiffness, frequency, shear force and damping ratio are well monitored by the proposed approach at all performance levels. However, residual displacements are not captured due to the non-hysteretic nature of the model. Despite its simplicity , the proposed approach seems suitable for identification and damage assessment of highly nonlin-ear structures exhibiting nonstationary responses, as is the case of RC structures subjected to severe earthquake loads.

2017

Characterisation of cover concrete is often the most viable means for assessing the durability and has become increasingly evident over the past 20 years. A variety of field methods and laboratory techniques exist, which provide a number of properties, such as air permeability index, water absorption rate, water permeability index, chloride diffusivity, electrical resistivity, moisture content and porosity gradient. Most techniques are economical and appropriate for assessing the durability of structures subjected to a single mechanism of deterioration. In reality, structures may face multiple deterioration mechanisms, stress/strains due to both environmental and structural loading and related acceleration of deterioration. Developing an understanding of such multimode deterioration may help in addressing the performance gap between laboratory and field. In this paper, a brief review of some of the ways by which a performance testing strategy could be developed is given so that serv...

2010

The growing number of demand for a widespread of health monitoring for strategic buildings in seismic areas has emphasized the need to realize in-depth scientific studies, in order to verify the feasibility of economic and fast methods to detect anomalous vibrations, to execute post earthquake warning and monitoring, damage assessment and first damage scenarios. Generally, an effective system for structural health monitoring requires an appropriate number of sensors, suitably located in the structures, and complex elaborations of big amounts of data. The simplified method presented in this paper is based on a statistical approach that uses the most significant data recorded on the top floor of the building, with the purpose of extracting information on the maximum inter-story drift, used as damage indicator. The parameters considered in the method are (i) maximum top acceleration, (ii) the first modal frequency variations and (iii) the equivalent structural viscous damping variation. A big amount of experimental data relevant to several tests carried out on scaled R/C models and numerical non linear dynamic analyses have been used to verify the feasibility of this approach.

Structural Survey, 2014

Purpose-Condition assessment on reinforced concrete (RC) structures is one of the critical issues as a result of structure degradation due to aging in many developed countries. The purpose of this paper is to examine the sensitivity and reliability of the conventional dynamic response approaches, which are currently applied in the RC structures. The key indicators include: natural frequency and damping ratio. To deal with the non-linear characteristics of RC, the concept of random decrement is applied to analyze time domain data and a non-linear damping curve could be constructed to reflect the condition of RC structure. Design/methodology/approach-A full-scale RC structure was tested under ambient vibration and the impact from a rubber hammer. Time history data were collected to analyze dynamics parameters such as natural frequency and damping ratio. Findings-The research demonstrated that the measured natural frequency is not a good indicator for integrity assessment. Similarly, it was revealed that the traditional theory of viscous damping performed poorly for the RC with non-linear characteristics. To address this problem, a non-linear curve is constructed using random decrement and it can be used to retrieve the condition of the RC structure in a scientific manner. Originality/value-The time domain analysis using random decrement can be used to construct a non-linear damping curve. The results from this study revealed that the damage of structure can be reflected from the changes in the damping curves. The non-linear damping curve is a powerful tool for assessing the health condition of RC structures in terms of sensitivity and reliability.

Sensors, 2024

Concrete structures have emerged as some of the most extensively utilized materials in the construction industry due to their inherent plasticity and high-strength characteristics. However, due to the temperature fluctuations, humidity, and damage caused by human activities, challenges such as crack propagation and structural failures pose threats to the safety of people's lives and property. Meanwhile, conventional non-destructive testing methods are limited to defect detection and lack the capability to provide real-time monitoring and evaluating of concrete structural stability. Consequently, there is a growing emphasis on the development of effective techniques for monitoring the health of concrete structures, facilitating prompt repairs and mitigation of potential instabilities. This paper comprehensively presents traditional and novel methods for concrete structural properties and damage evolution monitoring, including emission techniques, electrical resistivity monitoring, electromagnetic radiation method, piezoelectric transducers, ultrasonic techniques, and the infrared thermography approach. Moreover, the fundamental principles, advantages, limitations, similarities and differences of each monitoring technique are extensively discussed, along with future research directions. Each method has its suitable monitoring scenarios, and in practical applications, several methods are often combined to achieve better monitoring results. The outcomes of this research provide valuable technical insights for future studies and advancements in the field of concrete structural health monitoring.

Revista ingeniería de construcción, 2021

A Structures Assessment Methodology is presented, complementary to the Visual Inspection, which allows, through on-site non-destructive testing (NDT), to deliver as a result a comprehensive quantitative evaluation of the "Structural Health" of the different elements. This allows essential information to adjust maintenance cycles or make timely based decisions in critical situations, in order to guarantee future performance. The proposed methodology considers the execution of NDT to determine the state of the reinforcement, the characteristics of the concrete cover, and the presence of cracks. By means of the extraction of cores of smaller size (1") the ingress of carbonation or chlorides is determined. The results measured on-site are weighted to determine a Deterioration Index DI. The aggressiveness of the environment is included through an Environmental Exposure Index EEI. The incorporation of the results to the CTK-ConDiagÒ Model allows the combination of both indices, obtaining a Structure Global Deterioration Level SGDL, which measures the degree of damage determined at 6 levels. The proposed methodology is presented with the results of the study carried out on two specific bridges in Chile under different climatic conditions.

STRUCTURAL HEALTH MONITORING OF A CONCRETE STRUCTURESIN GAUTAM BUDDHA UNIVERSITY

Materials and Structures, 2017

Strength assessment of concrete in existing structures is a key issue. Many non destructive techniques (NDT) are available which can provide information about the material condition and several approaches can be used to derive strength estimates from NDT test results. However, common practice suffers from many drawbacks: (a) it is difficult to ascertain the level of accuracy/confidence of concrete strength estimates, (b) one lacks established guidelines for estimating the concrete strength variability, (c) the best way to combine NDT methods and coring remains an open issue. The RILEM TC 249 ''Non destructive in situ strength assessment of concrete'' is addressing these problems. A benchmark was carried out in order to compare (a) how experts define and can carry out an NDT investigation program and (b) how experts derive strength values from the NDT measurements. The benchmark was based on synthetic