Detection of Sizes and Locations Air Voids in Reinforced Concrete Slab using Ground Penetrating Radar and Impact-Echo Methods (original) (raw)
Related papers
Journal of Applied Geophysics, 2011
Ground-penetrating radar (GPR) and ultrasonic 'pulse echo' techniques are well-established methods for the imaging, investigation and analysis of steel reinforced concrete structures and are important civil engineering survey tools. GPR is, arguably, the more widely-used technique as it is suitable for a greater range of problem scenarios (i.e., from rebar mapping to moisture content determination). Ultrasonic techniques are traditionally associated with the engineering-based, non-destructive testing of concrete structures and their integrity analyses (e.g., flaw detection, shear/longitudinal velocity determination, etc). However, when used in an appropriate manner, both techniques can be considered complementary and provide a unique way of imaging the sub-surface that is suited to a range of geotechnical problems. In this paper, we present a comparative study between mid-to-high frequency GPR (450 MHz and 900 MHz) and array-based, shear wave, pulse-echo ultrasonic surveys using proprietary instruments and conventional GPR data processing and visualisation techniques. Our focus is the practical detection of sub-metre scale voids located under steel reinforced concrete sections in realistic survey conditions (e.g., a capped, relict mine shaft or vent). Representative two-dimensional (2D) sections are presented for both methods illustrating the similarities/ differences in signal response and the temporal-spatial target resolutions achieved with each technique. The use of three-dimensional data volumes and time slices (or 'C-scans') for advanced interpretation is also demonstrated, which although common in GPR applications is under-utilised as a technique in general ultrasonic surveys. The results show that ultrasonic methods can perform as well as GPR for this specific investigation scenario and that they have the potential of overcoming some of the inherent limitations of GPR investigations (i.e., the need for careful antenna frequency selection and survey design in order to image through the rebar meshes). More importantly, we show that standard GPR data collection, processing and visualisation techniques can be used with both types of data without users needing to change existing operational protocols or survey criteria.
A Simple and Low Cost Method for Rapid Assessment of Air Voids in Hardened Concrete
Presented herein is a new technique and a low cost method to estimate the ratio of air voids in hardened concrete within 30 minutes using available flatbed scanner, black inkjet, personal computer and image treatment software This test method includes contrast enhancement steps ensuring black ink (air voids) in gray concrete (aggregate and paste), image acquisition and computer analysis of scanned image. It is applied on specimens of normal concrete (NSC), high strength concrete (HSC) and high strength concrete with Polypropylene fibers. Results obtained are compared with the peer values of wet concrete ratios of air voids. As compared with other ASTM procedures, it is concluded that this method may have superiority over other methods due to its simplicity, low cost, less time and no need of skilled technicians. It is recommended to be used for hardened concrete as well as rock specimens.
Technology Evaluation on Characterization of the Air Void System in Concrete
2009
The objective of this project was to evaluate current technologies that have the capability of characterizing the air void system in concrete within the first several hours of placement. This objective was met by developing a comprehensive technology assessment and literature review, and conducting a laboratory evaluation of two selected technologies: ultrasound and thermography. The literature review presents a comprehensive assessment of research developments in the area of material characterization and structural health monitoring, focusing on technologies that are currently used to characterize air voids in concrete and those that have the capability of characterizing the air void system in concrete within the first 24 hours of placement. Special focus was placed on determining which technologies and equipment development may have a strong potential of being implemented in the field. The laboratory evaluation of the two selected technologies describes results obtained from experiments aimed at demonstrating the feasibility of ultrasound and thermography technologies in characterizing the air void system of fresh concrete, with an eye toward field implementation. Experimental results showed that both technologies can capture physical features that are significantly affected by the air void system in concrete.
Inspection of Insulated Concrete Form walls with Ground Penetrating Radar
Construction and Building Materials, 2012
Insulated Concrete Form (ICF) walls are widely used for a full range of building designs including residential, theaters, schools, and hospitals. ICF manufacturers cite several advantages compared to traditional building materials but builders are concerned by honeycombing that may occur during the pouring of the concrete, where gaps are left in the concrete. The development of gaps generally occurs between the foam and the surface of the concrete. Acoustic sounding, a traditional inspection technique to locate voids, would be unsuccessful due to the plastic foam. In this research study, Ground Penetrating Radar (GPR) was proved successful in detecting gaps that developed between the foam and the concrete, voids intentionally created in the concrete, and voids that developed during the pouring operation. Small voids (e.g., less than 3 = 4 in.) were difficult to detect but are not likely to cause any hazard to the structural integrity of buildings. The tests were performed at different stages of concrete curing using both the 1500 MHz and the 2600 MHz antennas. It is shown in this paper that the first void in the concrete was detected at day 7. However the best results were achieved at day 28 of curing. Data analysis has shown the success of the 1500 MHz antenna, but also the limits of the 2600 MHz antenna in the detection of buried voids in ICF structures.
Void Detection and Thickness Measurement in Concrete Elements
ACI Materials Journal
In this research, a methodology is proposed to detect voids and measure thicknesses in typical concrete specimens in buildings. To develop this methodology, beams and concrete walls with voids represented by expanded polystyrene elements and hollow plastic or cardboard elements were made. Ultrasonic and ultrasonic pulse-echo equipment were used to scan and locate these elements, as well as measure the thickness of the specimens made of concrete. The dimensions of the simulated voids are very close to the length of the ultrasound waves, so post-processing of the data obtained was performed to improve the results of this research.
Determination of Properties of Air Voids in Concrete
Highway Research Board bulletin, 1953
A METHOD WAS DEVELOPED WHICH MAKES IT POSSIBLE TO DETERMINE THE CHARACTERISTICS OF THE ENTRAINED AIR VOIDS IN CONCRETE. BRIEFLY, THE PROCEDURE CONSISTED OF CUTTING AND POLISHING A SECTION OF CONCRETE TO EXPOSE THE DISTRIBUTED VOIDS. THE VOIDS THUS EXPOSED WERE THEN FILLED WITH A FLUORESCENT MATERIAL AND PHOTOGRAPHED UNDER ULTRAVIOLET LIGHT. AFTER DETERMINING THE SIZE DISTRIBUTION AND NUMBER OF VOIDS APPEARING ON A PHOTOGRAPH, EQUATIONS DERIVED BY USING THE METHODS OF MATHEMATICAL STATISTICS WERE APPLIED TO DETERMINE THE TRUE PROPERTIES OF THE DISTRIBUTED VOIDS. APPLICATION OF THE METHOD MADE IT POSSIBLE TO COMPARE THE VOID PROPERTIES IN DIFFERENT TYPES OF CONCRETE CONTAINING VARIOUS PERCENTAGES OF ENTRAINED AIR. THE EFFECTS OF THE TWO MOST WIDELY USED AIR-ENTRAINING AGENTS, DAREX AND VINSOL RESIN, WERE ALSO COMPARED. INFORMATION OBTAINED FROM THE TESTS INDICATES THAT THE AVERAGE DIAMETER OF THE VOIDS IN CONCRETE MAY VARY FROM ABOUT 0.1 MM. IN NORMAL CONCRETE TO LESS THAN HALF THAT S...
Detection of Defects in Concrete with Ground Penetrating Radar
Ground Penetrating Radar (GPR) is a nondestructive technique particularly well adapted to the inspection of concrete structures and can help to determine the structure inner geometry or to detect damaged areas. When the GPR is used on structures containing thin layers, for example the sealing layer of a bridge or the void into a masonry wall, it is important for the radar user to know the minimum thickness required to detect and estimate the thickness of those layers.
Ground-Penetrating Radar Signal Modeling to Assess Concrete Structures
To better understand reflected ground-penetrating radar (GPR) signals from sound concrete and delaminated concrete structures, five bare concrete slabs and nine slabs with simulated delaminations were constructed. Five concrete mixtures were used; all slabs were cast at 1.5 x 1.5 x 0.127 m. Delamination was simulated by placing polystyrene plastic pieces inside the slabs during casting. A method was developed to determine the complex dielectric constant of the five concrete mixtures. The effect of delamination was studied by comparing signals obtained from the bare concrete slabs with those obtained from the slabs with embedded polystyrene pieces. It was found that modeling the reflected signals using an average complex dielectric constant over the entire radar frequency range results in waveforms comparable to the measured ones. It was also found that reflections from air voids located at 50 mm from the surface overlap with the surface reflection. The distorted shape of the reflected signal, however, serves as an indication of the void presence.
Automated air void analysis on hardened concrete
Cement and Concrete Research, 2001
This paper presents the results of a European round robin test on air void analysis on hardened concrete (SMT-EC-research project -Contract No. SMT4-CT95-2006). Thirteen laboratories in Europe from seven countries participated in the intercomparison test of which seven used a manual method and six an automated measurement system. The results indicate that the results obtained with measuring methods using image analysis (IA) techniques all statistically lie in the group of all measurement results. The automated methods can be problematic when a high amount of porous sand grains is present in the concrete. A second disadvantage of these automated methods is that it is not possible with the current methods being used to measure the paste content of the sample. D
Image analysis of air voids in air-entrained concrete
1991
The application of image analysis techniques to characterize the air-void system in hardened concrete is demonstrated. Both lineal and areal feature analyses are investigated. Feature size distributions and total air contents are obtained using s both types of analysis. The areal analyses also include the measurement of individual feature perimeters for use in comparing void shapes. A two phase standard specimen ip developed to insure the consistency of measurements and repeatability of results. Correction methods, based on geometric probability, are developed to remove the distortions in the image analysis data resulting from frame edge effects. Separate r:nethods are presented for lineal and areal analyses. Using discrete class sizes, both correction procedures are expressed in a matrix format. The corrected areal feature distributions are used to obtain volume distributions of spherical air voids using standard stereological procedures. The procedures are applied to ten concrete specimens, at magnifications of 12x and 30x. The specimens represent concretes made using three different airentraining admixtures, as well as non-air entrained concrete. Air-void parameters calculated from corrected image analysis results for the ten specimens are compared to results obtained using the modified point count method and to freeze-thaw results obtained from surface scaling tests of companion specimens. The differences in the air-void systems created by the various air-entraining agents are studied by comparing different characteristics including: the Powers spacing factor, the Philleo factor, profile shape, average feature size, numerical density of features, and the cumulative percent of total air versus feature size.