Frank Georg Schulz | TERRATEST

How a Light Weight Deflectometer is Different from a Falling Weight Deflectometer

Dec 2nd 2015 at 12:41 AM

Light weight and falling weight deflectometers are closely related devices in that light weight deflectometers use the same principles as falling weight devices to evaluate the physical properties and capacities of a pavement. The main difference between the two instruments is that the first requires larger, bulkier equipment (such as a rolling vehicle wheel) to stimulate load pulse while the latter requires a lighter falling weight to produce enough load pulse for testing.

Both these devices are non-destructive and non-intrusive instruments and while falling weight deflectometers (FWDs) have been around and widely used in pavement engineering for a very long time now, light weight deflectometers (LWDs) are gaining much attention for their compact design, ease of use, and flexibility in testing and evaluating the structural condition of pavements and surfaces in various construction and project settings. FWDs and LWDs play crucial roles in evaluating sites and determining or selecting the optimum maintenance and/or rehabilitation strategies for a certain location. Deflectometers are highly efficient tools in performing rapid and repeatable tests for in-situ characterization of the stiffness and compactness of pavement layers.

Both falling weight and light weight deflectometers use the same basic guiding principles to measure compaction in pavement surfaces. The deflectometer applies a load to the pavement surface being tested, simulating the magnitude and duration of expected loads. This delivers a transient impulse load to the pavement so that deflection sensors can measure pavement response ad different distances from the loading plate.

A typical falling weight deflectometer unit includes five major components, including a control system, a loading weight, a loading plate, a hydraulic system, and geophones. Pavement deflection can be affected by several factors when using an FWD. These include the thickness of the pavement layer being tested, the material type and quality, environmental factors, subgrade support, variability within the structure, and pavement discontinuities.

A light weight deflectometer, on the other hand, features several important components and mechanisms, including a top fix and release mechanism, a guide rot, a falling weight, a damping system, a sensor, and a loading plate, among many others. Modern light weight deflectometers feature advanced controller electronics for even more efficient and easier load-plate testing while on the field. Newest models even have integrated printers for instant print outs and are equipped with powerful software for fast and accurate evaluation, analysis, and management of data. These devices follow international standards of testing and measurement so you can be sure of their data accuracy and reliability.

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!

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