Universal Use and Standardization of LWDs
Posted by Frank Georg Schulz on July 23rd, 2015
The standard test method for measuring deflections using a light weight deflectometer or LWD determines surface deflection as a result of impulse load application. This is quantified by assessing the deflection right at the center of the applied load as well as its values at varying distances away from the load. Deflections can either be directly correlated to the pavement's performance or indirectly as it is used to determine on-site (in-situ) material characteristics of various pavement layers. Data collected can also be used for quality control and assurance of the compacted layers, determination of the thickness requirements of highway and airfield pavement projects, as well as ensuring the structural evaluation of load carrying capacities.
Several considerations should also be noted when using LWDs for deflection measurements. First is how to handle data when the test is performed on unbound materials. Because subgrade and pavement materials are often stress dependent, utmost care should be taken when analyzing raw LWD test data on them so that they closely match the stress value applied by the wheel load right at the pavement surface. This ensures the accuracy and dependency of the data gathered. Second is how to analyze results when data is obtained from a smaller volume of unbound materials rather than under the influence of a traditional heavy moving wheel load. Remember that the volume of subgrade and pavement materials affected by the load is a function of the magnitude of the load.
The LWD test covers the determination and analysis of deflections of both paved and unpaved surfaces using a portable falling weight deflectometer. Unlike other falling weight deflectometer devices, the LWD is a portable device that is lightweight (significantly lighter than other falling weight devices) and can be used even for unbound pavement layers. Deflections measured by the device are useful in determining the stiffness as well as the suitability of bound and unbound pavement surfaces in various projects. Values are determined with the help of the appropriate forward or back calculation analysis techniques.
The values expressed in SI units are to be regarded as standard according to the ASTM. While the standard does not purport to cater to all safety concerns, it is the responsibility of the user to establish the appropriate safety practices and set the applicability of its regulatory limitations prior to use. ASTM standards allow for quality control over measurements, helping determine the structural integrity of pavements for various types of projects.
About The Author:
TERRATEST GmbH is world leader in development and manufacturing of Light Weight Deflectometers for dynamic load plate test. They offer the world’s first light weight deflectometer “TERRATEST 5000 BLU” with Bluetooth and voice navigation. For more information about their products visit their website!
