Significance and Use
5.1 Real-time detection and assessment of cracks and other flaws in concrete structures is of great importance. A number of methods have been developed and standardized in recent decades for non-destructive evaluation of concrete structures as well as methods for in-place evaluation of concrete properties. Review of some of these methods can be found in ACI 228.2R-13, ACI 228.1R-03, and ACI 437R-03. They include visual inspection, stress-wave methods such as impact echo, pulse velocity, impulse response, nuclear methods, active and passive infrared thermography, ground-penetrating radar and others. These methods in most of the cases are not used for overall inspection of the concrete structure due to limited accessibility, significant thickness of concrete components, or other reasons and are not applied for continuous long-term monitoring. Further, these methods cannot be utilized for estimation of flaw propagation rate or evaluation of flaw sensitivity to operational level loads or environmental changes, or both.
5.2 In addition to the previously mentioned non-destructive tests methods, vibration, displacement, tilt, shock, strain monitoring, and other methods have been applied to monitor, periodically or continuously, various factors that can affect the integrity of concrete structures during operation. However, these methods monitor risk factors that are not necessarily associated with actual damage accumulation in the monitored structures.
5.3 Monitoring the horizontal (opening) or vertical displacement of existing cracks can be performed as well using different technologies. These may include moving scales ( ), vibrating wire, draw wire, or other crack opening displacement meters, optical and digital microscopes, strain gages, or visual assessment. However, this type of monitoring is only applicable to surface cracks and requires long monitoring periods.
FIG. 1 Moving Scale Crack Opening Monitor
5.4 This guide is meant to be used for development of acoustic emission applications related to examination and monitoring of concrete and reinforced concrete structures.
5.5 Acoustic emission technology can provide additional information regarding condition of concrete structures compared to the methods described in sections . For example, the acoustic emission method can be used to detect and monitor internal cracks growing in the concrete, assess crack growth rate as a function of different load or environmental conditions, or to detect concrete micro-cracking due to significant rebar corrosion.
5.6 Accuracy, robustness, and efficiency of AE procedures can be enhanced through the implementation of fundamental principles described in the guide.
1.1 This guide describes the application of acoustic emission (AE) technology for examination of concrete and reinforced concrete structures during or after construction, or in service.
1.2 Structures under consideration include but are not limited to buildings, bridges, hydraulic structures, tunnels, decks, pre/post-tensioned (PT) structures, piers, nuclear containment units, storage tanks, and associated structural elements.
1.3 AE examinations may be conducted periodically (short-term) or monitored continuously (long-term), under normal service conditions or under specially designed loading procedures. Examples of typical examinations are the detection of growing cracks in structures or their elements under normal service conditions or during controlled load testing, long term monitoring of pre-stressed cables, and establishing safe operational loads.
1.4 AE examination results are achieved through detection, location, and characterization of active AE sources within concrete and reinforced concrete. Such sources include micro- and macro-crack development in concrete due to loading scenarios such as fatigue, overload, settlement, impact, seismicity, fire and explosion, and also environmental effects such as temperature gradients and internal or external chemical attack (such as sulfate attack and alkali-silica reaction) or radiation. Other AE source mechanisms include corrosion of rebar or other metal parts, corrosion and rupture of cables in pre-stressed concrete, as well as friction due to structural movement or instability, or both.
1.5 This guide discusses selection of the AE apparatus, setup, system performance verification, detection and processing of concrete damage related AE activity. The guide also provides approaches that may be used in analysis and interpretation of acoustic emission data, assessment of examination results and establishing accept/reject criteria.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.