Hisafumi Asaue

Damage Evaluation on Steel Plate Reinforced RC Slabs with One-side Access AE Tomography via Anchor Bolts

Severe deterioration in aging infrastructures, especially in concrete structures, is currently becoming a critical issue world-wide. Since the preventive and proactive maintenance of infrastructures are necessary for repair before approaching to the final phase as the appearance of large-scale deterioration, efficient non-destructive testing (NDT) is imperative for the damage evaluation of infrastructures. In this concern, we have developed acoustic emission (AE) tomography technique as the promising NDT. AE tomography can estimate distributions of elastic-wave velocities and attenuationrates nondestructively inside reinforced concrete (RC) members. These distributions are to be readily associated with the degradation. In this study, AE sensors and accelerometers were employed to measure AE activities in steel-plate RC slabs. In order to examine monitoring areas in comparison with those of AE sensors, AE activities were detected by the accelerometers attached to heads of anchor-bolts, which were applied as temporary fixing tools to install reinforcing steel-plates at the bottom of RC slab. In the case of deteriorated structures, the secondary AE activity is generated from existing defects induced by traffic loads. Consequently, AE tomography analysis was carried out from the arrival times and the amplitudes of the secondary AE activities. It is found that damaged areas evaluated by one-side access AE tomography from the distributions of elastic-wave velocities and signal attenuations are in remarkable agreement with locations of internal cracks observed from on-site core-drilled samples.

Evaluation of Deterioration of Concrete Due to Alkali-Aggregate Reaction Based on Through-the-Thickness Elastic Waves

There are many reports related to concrete structures deteriorated by alkali-aggregate reaction (ASR). In order to evaluate the progress of deterioration, a visual inspection of the structure has been principally carried out. However, this visual inspection cannot detect internal defects of the concrete structure, so that sometimes the results of inspection mislead maintenance or asset management. Therefore, the evaluation method which can assess the internal damage should be established. Authors have studied wave velocity tomography as indices to evaluate inside concrete damage.

Innovative AE Measurement by Optical Fiber Sensing for FRP

Recently, composite materials are widely applied to the civil structures due to their high corrosion resistance, lightweight, and high mechanical strength. Along with these conditions, a long-term and periodic measurement for damage monitoring for civil structures is imperative by fiber-reinforced plastics (FRP). The advantages of optical fiber sensing technology have attracted the attention in FRP measurement such as its long life, ready embeddedness, large-scale measurements, lack of disturbance by electrical noise, and excellent harmonization with FRP. In this study, detection of AE activity was confirmed for evaluation of precursory damage as a break using the FBG of optical fiber sensing with high-speed data sampling.

Evaluation of Tensile Failure Progress in FRP Using AE Tomography and Digital Image Correlation

Recently some applications of Fiber Reinforced Plastics (FRP) in actual structures have been reported. However progresses of failures in FRP are still not well known. Additionally the evaluation/inspection methods against defects of FRP in actual structures are of high demand. In this study failure progresses in a FRP sampled from an actual bridge were evaluated using Acoustic Emission Tomography (AET) and Digital Image Correlation (DIC) during a tensile test considering the applicability of these methods as future inspection methods in actual structures.

Fatigue Failure Evaluation of RC Bridge Deck in Wheel Loading Test by AE Tomography

In Japan, remediation and replacement of reinforced-concrete (RC) bridge decks consumes a major part of the road structure maintenance budget, and numerous studies have explored ways to expand the service life of the deck. Traditionally, corrective maintenance procedures and repairs have been conducted when noteworthy deterioration becomes visible to the naked eye, for example, as crack patterns on the deck surface. However, from the perspective of life cycle cost, to reduce maintenance budgets, the deterioration and damage should be evaluated before the damage reaches the surface (J Struct Eng 123: 1390–1401, 1997). Accordingly, in this study, internal damage of an RC deck due to fatigue failure is reproduced by a wheel loading testing apparatus, and the damage progress is evaluated by AE measurements as well as by elastic wave/AE tomography analysis.

Assessing Deterioration of an In-field RC Bridge Deck by AE Tomography

Deterioration of aging infrastructures is an important issue in many developing and well-developed countries. For maintenance of the infrastructures in limited budgets, proactive inspections and countermeasures are important before severe structural damage occurs. To assess the deterioration of those structures in a reliable and preferably nondestructive manner is highly demanded. Responding to the demand, acoustic emission (AE) tomography can be regarded as a powerful method since it builds the elastic-wave velocity distribution of the medium that AE waves propagate through while simultaneously locating AE sources. Such a method has been widely tested in laboratories but not yet fully realized in fields. In the present study, the applicability of two-dimensional (2D) and three-dimensional (3D) AE tomography techniques to the evaluation of internal damages in existing RC bridge deck was examined using the data obtained by single-side AE measurement. The overlay of 2D elastic-wave velocity distribution with AE source locations reveals that AE was active in moderate-velocity areas and the boundaries of low-velocity areas, which were regarded as deteriorated areas with progressing defects. Moreover, in the AE measurement, a large number of AE with small amplitudes were observed in the severely deteriorated panel; amazingly, primary AEs were captured, which implied the propagation of an internal crack in the deck.