By: Glenn Wrobleski, Equipment Division Manager
One of the newest PAVE TECH tools is designed for fast and easy testing of the load bearing capacity of a pavement base – including open graded base – and conforms to ASTM E2835 Standard Test Method for Measuring Deflections using a Portable Impulse Plate Load Test Device (light weight deflectometer).
Falling weight deflectometers (FWD) have been used for a long time to measure the physical properties of soils, sub-grades, base, etc. HNA 2012 saw PAVE TECH introduce a light weight deflectometer (LWD) as an affordable option to the expensive and time consuming FWD. Measurement and documentation of compaction quality are the key reasons a LWD could be in your future – especially if you’re involved in commercial installation of permeable pavements (PICPs).
Measurement: A LWD is a precision instrument that measures the deflection of the base (in fractions of mm) and the time (in milliseconds) taken to create the deflection. The data is converted to a measure of the load bearing capacity of the material being tested. The measurements are stored for future use with a time stamp and GPS location of the tests. A series of tests over the entire base area can be accomplished in very little time and without any complicated procedures.
The test results not only indicate a measure of the load bearing capacity but also provide data and a graphical display showing if further compaction is possible. All data is available immediately so no time is lost waiting for test results or interpretation.
Documentation: Whether you install the base or not, once you lay pavers you have implied your acceptance of the base. When base in installed by other site contractors (common on commercial projects) you likely rely solely on the word of others that the base is “to spec.” But what does “to spec” even mean? Most permeable project specifications do not give much guidance regarding base compaction. Specifications are often vague at best; such as stating only a requirement to make x number of passes with a vibratory roller. The problem is that open-graded bases do not allow for traditional measurements of compaction density such as a nuclear density test. But a Light Weight Deflectometer (LWD) is a solution to this problem
The LWD accurately measures compaction density of all type of material – including open graded aggregates – up to a depth of 600mm (24”). By measuring and documenting the quality of the base, you have valuable information to contribute to the quality of the project. At the same time you also have valuable information to protect yourself from liability if the project proceeds and there is an issue with base quality. The fact that you made others aware of a problem does not mean the problem will be fixed. By properly documenting your measurements of poor base quality you can proceed with paver installation without delay and without fear of liability if and when a failure occurs.
A LWD is an important new tool and vital for measuring and documenting the quality of base – especially open graded base – and other materials. For more information on LWD’s as well as all the other tools and equipment used in commercial/mechanical paver installation please contact PAVE TECH.