Zhao, G., Yao, Y., Li, S., Jiang, Y. (2018). Maximum allowable deflection by light weight deflectometer and its calibration and verification (Joint Transportation Research Program Publication No. FHWA/IN/JTRP-2018/21). West Lafayette, IN: Purdue University. https://doi.org/10.5703/1288284316866
Implementing a quality assurance (QA) process for compaction of aggregates using light weight deflectometer (LWD) requires construction of a 100 ft. long, 24 ft. wide test section prior to other uses. However, there are numerous cases where aggregates are used in construction of subgrade, subbase course, and base course in small areas, such as bridge approach, lane widening, patching, and shoulders, and construction of a test section is not possible. In addition, there are over 70 LWDs currently used in construction projects by Indiana Department of Transportation (INDOT). Maintaining a quality control process requires timely and appropriate calibration and verification of the LWD devices.
This study performed intensive laboratory experiments on the aggregate materials commonly used by INDOT to determine the target deflection values for compaction QA and evaluate the effects of the moisture content and the interface condition of the inner wall of the Proctor mold on LWD test results. Intensive experiments were also performed in the test pits with LWD to determine the effect of the thickness of aggregate layer and close the gap between the LWD measurements made in-situ and in the Proctor mold. Extensive field LWD testing was conducted during construction of many projects in 2016 and 2017 to validate the compaction of various types of projects. Statistical tests were performed on historical compaction QA data from LWD testing and LWD verification data. It was concluded that moisture content has a significant effect on LWD deflection or modulus. Unbound aggregates compacted near the optimum moisture are capable of providing a stable modulus value when becoming wet and experiencing dramatic gains in modulus with decreasing the moisture content. Maximum allowable deflections were developed for QA of aggregate compaction, particularly in small areas. It was also found that annual verification is necessary to ensure repeatability of LWD deflection measurements.
Recommendations were made for immediate and future implementations, such as improvement of the current field practice of compaction QA with LWD in terms of test frequency, test position, and moisture content test. Finally, it was recognized that urgent effort is needed to determine the optimum interval for LWD calibration and necessary training is needed to further improve compaction quality and consistency of compaction QA with LWD.
small area compaction, aggregate, quality assurance, lightweight deflectometer (LWD), Proctor test, test pit, moisture content, deflection, modulus, target deflection, experimental-mechanistic (EM) procedure, maximum allowable deflection
Joint Transportation Research Program
Indiana Department of Transportation
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