Acoustic Emission - NDT

High-performance concrete (HPC) applies to cement-based material with a strong capacity above 50MPa, has great ductility, and shows excellent performance. This paper reviews the properties of HPC, raw material, and cracking propagation. Reduction in porosity and improvement in microstructure increases the toughness of HPC. Natural materials such as supplementary cementitious material, aggregates, superplasticizers, and micro steel fibers can enhance HPC's mechanical properties and workability. Also, the causes of cracking and relevant test for observing crack propagation are discussed in this paper. Thus, HPC manufacturing tends to improve over the years by using relevant raw materials, common technology such as conventional casting and room temperature curing, and related precautions to reduce cracking in concrete to prolong the service life of concrete structures.

Acoustic Emission Testing (AET) is a non-destructive testing that uses stress waves emitted from materials undergoing stress and loads to evaluate and test the damaged areas around structures, big areas, and volumes. This research explains the whole theory behind this non-destructive testing method theoretically and experimentally

The US transportation infrastructure has been receiving intensive public and private attention in recent years. The Federal Highway Administration estimates that 42 percent of the nearly 600,000 bridges in the Unites States are in need of structural or functional rehabilitation1. Corrosion of reinforcement steel is the main durability issue for reinforced and prestressed concrete structures, especially in coastal areas and in regions where de-icing salts are regularly used. Acoustic Emission (AE) has proved to be a promising method for detecting corrosion in steel reinforced and prestressed concrete members. This type of non-destructive test method primarily measures the magnitude of energy released within a material when physically strained. The expansive ferrous byproducts resulting from corrosion induce pressure at the steel-concrete interface, producing longitudinal and radial microcracks that can be detected by AE sensors. In the experimental study presented herein, concrete block specimens with embedded steel reinforcing bars and strands were tested under accelerated corrosion to relate the AE activity with the onset and propagation stages of corrosion. AE data along with half cell potential measurements and galvanic current were recorded to examine the deterioration process. Finally, the steel strands and bars were removed from the specimens, cleaned and weighed.  The results were compared vis-à-vis Faraday’s law to correlate AE measurements with degree of corrosion in each block.
Keywords: acoustic emission, corrosion, durability, prestressed concrete, reinforced concrete

This study assesses the reliability of a non-destructive method for determining the in situ distribution of tree coarse roots within a scaled distance 6-fold the DBH by comparing the results with the actual 3D root architecture revealed by invasive methods. The root architecture of 22-year-old olive trees was determined non-destructively with a Root Detector device (Fakopp Enterprise Bt) using sonic speed and directly by a 3D digitizer (Fastrak, Polhemus) after soil removal. The radial and vertical distributions of the coarse root biomass and diameter in the soil as determined by the 3D digitizer were correlated with the root map detected by sonic speed. A highly significant correlation was observed between the coarse root biomass distribution and the sonic speed within 30 cm of soil depth, but this correlation decreased with increasing distance from the trunk, up to 120 cm. No correlations were observed between sonic speed and root diameter. The Root Detector was able to map the co...

this study assesses the reliability of a non-destructive method for determining the in situ distribution of tree coarse roots within a scaled distance 6-fold the DBH by comparing the results with the actual 3D root architecture revealed by invasive methods. The root architecture of 22-year-old olive trees was determined non-destructively with a Root Detector device (Fakopp Enterprise Bt) using sonic speed and directly by a 3D digitizer (Fastrak, Polhemus) after soil removal. The radial and vertical distributions of the coarse root biomass and diameter in the soil as determined by the 3D digitizer were correlated with the root map detected by sonic speed. A highly significant correlation was observed between the coarse root biomass distribution and the sonic speed within 30 cm of soil depth, but this correlation decreased with increasing distance from the trunk, up to 120 cm. No correlations were observed between sonic speed and root diameter. The Root Detector was able to map the coarse roots of the olive tree in the soil environment, but only under certain conditions. First, root detection was more efficient within 30 cm of soil depth, provided that more than 35% of the total biomass of lateral roots occurs within this depth range. Second, the distance of 120 cm from the trunk, scaled as 6-fold the DBH, may be considered the threshold over which the sonic speed and the detection of roots markedly decreased. Third, Root Detector technology is unable to detect root size in terms of geometric parameters such as root diameter. Root architecture, i.e., the root radial and vertical distribution in the soil, is involved in different plant functional roles, such as nutrient and water acquisition 1,2 and mechanically active anchorage in the soil, which determines tree stability 3. The importance of the mechanical role of root architecture in tree stability has been extensively described in previous studies 4-7. The failure of urban and forest trees is often a consequence of the low performance of this root feature caused by root decay, injury, breaking or low biomechanical acclimation to, for example , wind loads 8,9. High frequencies of storms, windstorms and other similar extreme events are generally responsible for more than 50% of the damage by volume to European forests 13,14 and are expected to increase under the observed ongoing climate changes 10-12. Furthermore, tree instability threatens property and people in urban forests 15. Hence, evaluations of root health/decay/injury and the root radial and vertical distribution in the soil in particular are crucial for both tree stability and consequently for safety in urban environments 16. Because roots grow belowground, the radial and vertical root distributions of trees and crop fruits are mainly determined by destructive methods that involve excavating the root system from the soil and digitizing the system using different 3D digitizers, such as magnetic (Fastrak, Polhemus, Colchester, VT, USA) 17,18 or sonic (GTCO Freepoint 3D) 3D digitizers 19. Following digitization, the root architecture can be reconstructed with different specific softwares: Floradig (CSIRO, Australia) or AMAPmod (AMAP, France). Fastrak-AMAPmod technology has already been used to digitize and analyse the 3D root architecture mainly of forest species (Pinus: 19; Picea: 8; Quercus: 18 20 ,), shrubs (Jathropa curcas: 21 Spartium junceum: 22), herbs (Zea mays: 23) and fruit species (Olea: 24). Using Fastrak technology, it is possible to estimate several root biometric and geometric parameters at different soil depths and radial distributions, such as biomass, length, diameter, and angle. However, some limitations have been noted for these root techniques, such as high sensitivity to wind fluctuations in the field for the sonic digitizer 25 and the interference with the Fastrak magnetic field by surrounding iron frames 26. Above all, root excavation methods are extremely time consuming and labour intensive, and they are not always an option, especially in urban environments, because of the presence of pavement as well as underground service lines, pipes, rocks, and other buried materials.