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Often, the most comprehensive approach to analyzing something is to take it apart, but that may not be feasible when it comes to assessing pavement constructions. Furthermore, a visual inspection of the pavement can only provide so much information. Fortunately, there are several non-destructive tests (NDTs) that can provide a lot of information on pavement constructions. Below is a shortlist of NDTs that are commonly used to test the quality of pavements.
Falling-Weight Deflectometer (FWD)
Probably the most popular NDT method for pavement quality testing and FWD test is often used for testing highway pavement and airport runways, as it can apply loads comparable to those from moving trucks and aircraft.
The test involves a weight being dropped from a predetermined height onto a load plate touching the pavement to be tested. An array of sensors on the pavement determines the pavement deflection brought on by the test load. Signals sent from the load plate and sensors are analyzed by the test system to provide information on the test pavement.
A standard test setup involves the mechanical apparatus being towed by a vehicle with an on-board computer system that monitors and manages the test cycle. A standard test involves a series of rapid tests down a street or runway, lasting about one minute.
The degree of deflection under the load plate and at distances from it suggests how rigidity or elasticity of the pavement. FWD tests may be used on a completed structure to confirm if it meets quality standards.
In addition to being non-destructive, FWD tests are considerably faster than destructive tests and don't require the removal of a pavement sample. Furthermore, FWD test equipment is very easily transported, whereas destructive tests must often be performed in a laboratory.
Ground Penetrating Radar (GPR)
GPR is an NDT approach that can provide a comprehensive description of road conditions. A GPR test involves sending brief impulses of electromagnetic energy into the pavement with an antenna connected to a vehicle. These electromagnetic pulses are reflected to the antenna based on the location and composition of discontinuities in the sample. The reflected electromagnetic energy is then detected by the GPR system and displayed as a series of pulses called a waveform. The waveform is a document of the qualities and thicknesses of the various strata found inside the pavement.
Using GPR, it is possible to identify gaps and various transformations in the density, consistency, and moisture of pavement. GPR is useful on both uneven surfaces and multi-layered constructions. However, test depth and quality are hindered by very conductive materials like wet clays and soils.
Nuclear and Electrical Gauges
Nuclear gauges can evaluate the density of pavement with very little impact on the sample surface. These gauges have a retractable rod emanates a small amount of gamma radiation from its tip. When the tip is touched to the pavement, the gamma rays strike electrons in the pavement and some of the radiation is reflected to the gauge where it is detected. The quantity of reflected rays identified is directly relative to pavement density and the gauge can be calibrated to recognize signals for known pavement densities.
Similar to nuclear gauges, electrical gauges deliver a small quantity of current into a pavement sample to produce an electrical field. An electrical gauge ascertains pavement density by gauging the reaction to this field. These gauges were created as a substitute for nuclear gauges, which have radiation-related safety risks.
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