United States Department of Transportation
i
Developing statistical limits for using the light weight deflectometer (LWD) in construction quality assurance.
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2014-07-01
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Abstract:The traditional methods of evaluating the compaction quality of pavement subbase and subgrade construction require considerable time and
resources. Therefore, there is a need for a safe, reliable, rapid, and cost‐effective field measurement technique for compaction testing of
unbound pavement layers. The Light Weight Deflectometer (LWD) is one such mechanism that offers field measurement of deflections and
stiffness of unbound pavement layers under a given load. The LWD is gaining increased attention for quality control and quality assurance
(QC/QA) during pavement construction. The Indiana Department of Transportation (INDOT) is planning on implementing the LWD in field QA/QC
for unbound layers of pavements. As such, this research investigates the feasibility of developing statistical limits for the compaction of specified
combinations of subbase and subgrade materials in terms of their maximum allowable LWD deflections.
Statistical limits were developed for six of the most common subgrade, subbase, or subgrade‐subbase combinations that are used for highway
pavement construction in Indiana: lime modified, cement modified, natural subgrade and No. 53 crushed stone (53CS) subbase overlaying these
subgrades. For the subbase layers, these statistical limits are applicable only to six inches of subbase over subgrade and may not be applicable to
a different layer configuration in terms of the number of lifts or thickness of lifts. The ultimate goal is for the developed statistical limits to
replace the need for site‐specific LWD limits derived from the onsite test sections, ultimately saving time and money.
Due to variability in the data and data limitations, caution must be exercised when generalizing the findings published in this report. Compared to
the data from the acceptance test sections, the data collected from test sections saw less variability between projects, for any given material
type. The test section data yielded maximum allowable deflections that did not vary significantly between projects for cement‐ and lime‐modified
subgrade, non‐modified subgrade, and six inches of #53 crushed stone over lime‐modified subgrade. Generally, within any specific contract
location (project site), the data indicates adequate confidence that the test pads generate control measurements that can be used reliably to
check the adequacy of compaction at that contract location. However, across different contact locations, even for the same material type, so
much variability was observed that it is not possible to guarantee that the control measurements generated from a limited number of test
sections (pads) can be confidently transferred to another site of the same material type.
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