Mitsuhiro Shigeishi

Acoustic emission to assess and monitor the integrity of bridges

Abstract Increased axle loads and traffic density necessitate strengthening and widening of traditional masonry arch bridges. The question remains as to how to evaluate the condition of a bridge and assess the effect of modern traffic on its serviceability? The focus of this paper has been the evaluation of the potential for the acoustic emission technique to provide cost effective in-situ long term monitoring of bridge condition. The work was performed on a bridge chosen to be representative of both masonry and reinforced concrete construction methods. The results demonstrate that acoustic emission technique can be applied to condition assessment of bridges. These results confirm that strong acoustic emission signals are obtained from reinforced concrete structures and demonstrate that acoustic emissions can be detected in masonry structures but at lower energy levels. The experimental programme has shown that AE is useful in detecting crack growth and determining the position of the crack tips at a much earlier stage in their development, before they are noticed during visual inspection

Acoustic emission moment tensor analysis: Development for crack identification in concrete materials

Abstract The moment tensor analysis of acoustic emission (AE) provides quantitative information on kinematics of cracks. Simple AE moment tensor analysis has been developed and named SiGMA-AE analysis. In-plane unconfined compression tests of mortar and concrete plates with a slit are carried out. The inclination of slits are varied as 0, 30 and 45° to the loading axis. The sources are located from detected AE signals. Then, orientations of cracks, crack types and crack volumes are determined by the SiGMA-AE analysis. Furthermore, it is clarified that the damage parameters can be estimated from the moment tensor components. The results show close correlation between the calculated crack volumes and the damage parameters.

A Proposed Standard for Evaluating Structural Integrity of Reinforced Concrete Beams by Acoustic Emission

A series of studies has been performed to evaluate the structural integrity of reinforced concrete (RC) beams by acoustic emission (AE). Cyclic loadings were applied to RC beams with a single reinforcing bar, large repaired beams, beams deteriorated due to corrosion of reinforcement, and two beams with different damage levels in an aging dock. The test results demonstrated that the Kaiser effect starts to break down when shear cracking starts to play a primary role. It has been also shown that high AE activity is observed during unloadings after serious damage (slips between the concrete and the reinforcement or those between the original concrete and the repaired part) has occurred. A standard for evaluating structural integrity of RC beams by AE is proposed, based on these results.

AE energy analysis on concrete bridge beams

Concrete bridges were built originally to have a cost-effective maintenance free life of 120 years, however both in Europe and the USA this has proved to the totally optimistic. Concrete bridges require major maintenance after twenty to thirty years in order to extend their life The Acoustic Emission technique has been successfully applied to monitor and provide information on the safety of concrete bridges, but the processing of the AE data is often not trivial. This paper proposes a method of AE analysis to assess concrete bridges based on the fact that the AE energy is one of the effective parameters to evaluate the damage of a concrete structure. Results from experiments on concrete beams with different design and loading configurations are presented. It is argued that in some cases the state of damage of bridge beams can be estimated from the AE energy analysis when approximately 45% of the ultimate load has been applied.

Acoustic emission characteristics of concrete-piles

Abstract Acoustic Emission (AE) characteristics due to microcracking are studied in full-scale prestressed concrete-piles. By applying AE techniques, fundamental study on the fracture mechanism of the piles under both cyclic and monotonic loads is made. The prestressed concrete-piles are subjected to bending and shear loads. Crack growth is monitored, and three-dimensional (3-D) AE source locations are conducted along with crack classification and crack orientation by SiGMA analysis. The results obtained are compared with those of the pile integrity test (PIT) and visual observation. To investigate AE characteristics of damaged piles, uni-axial load is applied to the damaged RC piles installed in an experimental pit of sand. AE is monitored directly in the RC piles. In addition, indirect monitoring is carried out by using a wave-guide nearby the pile. In both the direct and indirect monitorings, AE sources are located, applying one-dimensional source location. Locations estimated are compared with the real damaged zone. Finally, conditions of AE generation of the damaged RC piles are discussed with respect to crack width and crack orientation.

Evaluation of concrete made from recycled coarse aggregates by pulsed power discharge

In Japan, the most of waste concrete scraps have been reused as roadbed materials and the recycling ratio of waste concrete scraps has been kept over 95 % from 2000. However, it is expected that the demands of waste concrete scraps as roadbed materials would decrease even though the waste concrete scraps increase with the pulling down buildings in next decade. These facts mean that the recycling of waste concrete scraps would be in the negative situation. Therefore, the development of new recycling technology of waste concrete scraps is paramount importance in Japan. In this work, the pulsed power discharges inside of waste concrete scraps immersed in water were used to reproduce the coarse aggregate. In the experiments, the Marx generator, which storages the energy of 6.4 kJ/Pulse, was used as pulsed power source and the point to hemisphere mesh electrode was immersed in water. The pulsed voltages with 400 kV of peak voltage were applied to the concrete scraps placed on hemisphere mesh and the reproduced coarse aggregates were evaluated after the repetitive discharge treatment. From the experimental results, it is found that the coarse aggregates reproduced by 40∼60 pulsed discharge treatments have the enough qualities of the bone-dry density and the water absorption rate to satisfy JIS (Japan Industrial Standard) regulation (A 5005). In addition, the concretes consisted of the reproduced coarse aggregate also have the enough compressed strength and Young’s module to utilize as the construction material.

Effect of fly ash on the strength of concrete made from recycled aggregate by pulsed power

The performance of concrete made from recycled aggregate that produced by pulsed power technology due to the use of fly ash has been studied. Pulsed power technology has been proven to reproduce high quality recycled aggregate. Concrete made from 100% recycled coarse aggregate by pulsed power discharge can reach similar compressive strength to natural coarse aggregate concrete. The use of JIS type II fly ash as cement replacement of 25% and 50% mass without adjustment of water to cement ratio can reduce the compressive strength of concrete. However, with the same fly ash percentage, in 28 day of age, concrete made from recycled aggregate by pulsed power technology results better strength by 10.0% and 15.8% compared to natural aggregate concrete for 25% and 50% of fly ash, respectively. In addition, mixing method using two-stage mixing approach (TSMA) has been applied to improve concrete strength. This method in making recycled aggregate concrete can improve the strength of fly ash concrete made from recycled aggregate concrete up to 4.7%. Replacing 25% of cement mass with fly ash for concrete made from recycled aggregate by pulsed power technology has shown preferable result in strength, and can be improved by using TSMA method in mixing process.

A study on factors affecting geopolymerization of low calcium fly ash

This paper presents some factors affecting geopolymerization of low calcium fly ash for geopolymeric matrices. Low calcium fly ash samples were collected from two different coal-powered facilities: an Indonesian fertilizer plant and a Japanese power plant. Several series of tests were conducted using various ratios of fly ash to activator as well as ratios of activators to sodium hydroxide molarity. Each matrix consisted of a set molar ratio of three variations of Si/Al (1.5, 2, 2.5), Na2O/SiO2 (0.3-0.38), H2O/SiO2 (2.8 to 3.5), H2O/Na2O (9 to 10.6), and mass ratio of water/solid (0.31 to 0.45). The setting time of Japanese ash-matrices were longer than Indonesian ash. The compressive strength revealed that the Japanese and Indonesian matrices with activator ratios of 1.5 achieved 47.7 and 57.5 MPa respectively, while activator ratios of 2.5 reached 50.9 and 50.5 MPa. In addition, microstructural characterizations–XRF, XRD, SEM, EPMA-were performed. This study concludes that even ashes categorized as the same class, their mineral composition is different. Furthermore, coal combustion techniques modify ash particles, which in turn causes differences in setting time, while strength is not significantly affected.

SEPARATION OF AGGREGATE FROM ASPHALT CONCRETE USING PULSED POWER TECHNOLOGY

In this paper, authors propose a pulsed power application to separate aggregate from asphalt concrete. This study aims at extracting asphalt binder from asphalt concrete specimens using pulsed power technology and evaluating the quality of the asphalt concrete recycled aggregate and residues. Pulsed power was discharged into 5% asphalt content straight and modified asphalt concrete specimens. The results demonstrate that the extraction of modified asphalt binder from asphalt concrete is more difficult than that of straight asphalt and also requires more energy to produce approximately 1% asphalt content recycled coarse aggregate. Furthermore, the results suggest that recycled aggregate quality increases with increasing pulsed power energy.

Acoustic Emission Hit Generation Behavior of Basalt Fiber High Strength Mortar under Compression

Acoustic emission (AE) has been applied to study the fracture mechanics of concrete and other cementitious materials. In this paper, the AE hit generation behaviour is employed to investigate the fracture of high strength mortar containing basalt fiber under compression. A variety of amount and length of basalt fiber were used in mortar mix. Result shows that there is no significant effect observed on behavior of AE hit generation due to the differences amount and length of basalt fiber in mortar. All indicates the similar behaviour that can be described into three stages. At the second stage when maximum load starts to occur, AE hits are generated significantly indicating nucleation of many cracks. Materials failure in ductile manner since AE activities still can be recorded at long after post peak behaviour.