Time Domain Reflectometry for Void Detection in Grouted Posttensioned Bridges

2003 ◽  
Vol 1845 (1) ◽  
pp. 148-152 ◽  
Author(s):  
Michael Chajes ◽  
Robert Hunsperger ◽  
Wei Liu ◽  
Jian Li ◽  
Eric Kunz
Keyword(s):  
Electrical Properties ◽  
Damage Detection ◽  
Transmission Lines ◽  
Time Domain ◽  
Detection Method ◽  
Time Domain Reflectometry ◽  
Concrete Bridges ◽  
New Method ◽  
Electrical Transmission ◽  
Void Detection

The presence of voids is a serious problem in grouted posttensioned bridges because voids greatly reduce the corrosion-protective capabilities of the grout. Current methods for void detection suffer several significant drawbacks. A new method utilizing time domain reflectometry (TDR) is discussed. TDR is a well-developed method for detecting discontinuities in electrical transmission lines. A recent study has indicated that TDR can be used as an effective nondestructive damage detection method for concrete bridges. A void changes the electrical properties of transmission lines and therefore introduces electrical discontinuities. It can be detected and analyzed by TDR. Experiments on short specimens that are used to model grouted posttensioning ducts with built-in voids have been conducted and demonstrate the potential of TDR as a void detection method.

A NEW METHOD TO MEASURE BULK ELECTRICAL CONDUCTIVITY IN SOILS WITH TIME DOMAIN REFLECTOMETRY

1990 ◽  
Vol 70 (3) ◽  
pp. 403-410 ◽  
Author(s):  
W. K. P. VAN LOON ◽  
E. PERFECT ◽  
P. H. GROENEVELT ◽  
B. D. KAY
Keyword(s):  
Electrical Conductivity ◽  
Transmission Lines ◽  
Time Domain ◽  
Correlation Coefficients ◽  
Time Domain Reflectometry ◽  
New Method ◽  
Measuring System ◽  
Reflection Measurement ◽  
Bulk Electrical Conductivity ◽  
Water Saturated

The bulk electrical conductivity of a porous medium can be determined by measuring the reflection of an electromagnetic pulse in transmission lines which are installed in this medium (the method is known as Time Domain Reflectometry (TDR)). The reflection is not only influenced by the medium, but also by the measuring system. A new method is described which corrects for influences of the measuring system by comparing a reflection measurement with a reference measurement performed in air. Calibration measurements were made in water and in water-saturated sand and loam soils. Columns with different, well-determined solute concentrations were prepared. Linear regression analyses were performed between the electrical conductivity determined with TDR and the electrical conductivity of the solutions. All slopes were close to one and the correlation coefficients were high: 0.993, 0.993 and 0.968 for water, sand and loam, respectively. For the two soils significant intercepts were found. These might be related to the surface charge of the soil particles. Key words: Dielectric constant, soil water, electrical conductivity, solutes

Use of Time-Domain Reflectometry (TDR) to measure the water-content of sandy soils

Soil Research ◽  
1995 ◽  
Vol 33 (2) ◽  
pp. 265 ◽  
Author(s):  
PJ Gregory ◽  
R Poss ◽  
J Eastham ◽  
S Micin
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Transmission Lines ◽  
Time Domain ◽  
Water Storage ◽  
Sandy Soils ◽  
Time Domain Reflectometry ◽  
Soil Water Storage ◽  
Use Of Time ◽  
Daily Evaporation

We investigated the potential sources of error when using time domain reflectometry (TDR) to measure the water content of sandy soils and evaluated the technique as a means of measuring evaporation from columns of soil and changes in soil water storage beneath crops. Inaccurate depth location of the transmission lines or the development of a hole at the tip of the transmission lines introduced an error about 10 times larger than the errors associated with hardware and software. Calibration in two sandy soils gave a curve of similar shape to that found by others except for values of dielectric constant < 6 when measured values of water content were less than those expected. Daily evaporation from soil columns measured by weighing and with TDR showed large differences between the two techniques (up to 32%) but compensating errors over time allowed cumulative evaporation to be estimated with TDR to within 6.6% of that determined by weighing over a 162 h period. Under field conditions, the agreement between TDR and neutron probe measures of changes in soil water storage in the upper 0.3 m was good and generally within 10% over both 14 day and longer periods.

Quantitative, zerstörungsfreie Feuchtemessung in Baustoffen vor Ort mit der Time Domain Reflectometry / Quantitative, non-destructive moisture measurement in building materials on site by time-domain re ectometry

1999 ◽  
Vol 5 (6) ◽  
pp. 609-618
Author(s):  
M. Stacheder ◽  
G. Grassegger ◽  
F. Grüner
Keyword(s):  
Time Domain ◽  
Building Materials ◽  
Salt Content ◽  
Time Domain Reflectometry ◽  
New Method ◽  
Measuring Methods ◽  
Surface Moisture ◽  
Non Destructive ◽  
Floor Cover

Abstract A new commercially available dielectric technique for the non-destructive determination of moisture in building materials based on the principle of 'time-domain reflectometry' (TDR) is presented. TDR measurements on samples of sandstone, brick, concrete and floor cover matched very well with results of conventional moisture measuring methods such as oven-drying or calciumcarbide-technique. The new method showed only a low influence of salt content or surface moisture of the material on the results.

scholarly journals Locating the frozen–unfrozen interface in soils using time-domain reflectometry

1982 ◽  
Vol 19 (4) ◽  
pp. 511-517 ◽  
Author(s):  
T. H. W. Baker ◽  
J. L. Davis ◽  
H. N. Hayhoe ◽  
G. C. Topp
Keyword(s):  
Transmission Lines ◽  
Time Domain ◽  
Freezing Temperature ◽  
Time Domain Reflectometry ◽  
Temperature Measurements ◽  
Soil Freezing ◽  
Electromagnetic Pulses ◽  
The Time Domain ◽  
Time Domain Reflectometer ◽  
Liquid And Solid Phases

The time-domain reflectometry technique was compared with the temperature measurement method for locating the frozen–unfrozen interface in water and sandy soils. This technique depends on the high-frequency (1–1000 MHz) electrical properties of water that change significantly and abruptly between the liquid and solid phases. Parallel wire transmission lines were inserted into the soil to guide electromagnetic pulses produced by a time-domain reflectometer (TDR). The frozen–unfrozen interface produced reflections measured by the TDR which were in turn used to locate the interface as it moved along the transmission line. In the laboratory it was possible to locate the interface using the TDR to within ±0.5 cm and in the field to within ±2.4 cm. These errors were equal to those associated with the temperature measurements. Keywords: soil freezing, temperature measurements, dielectric constant, time-domain reflectometry.

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