Field and Laboratory Evaluation of the Portable Falling Weight Deflectometer

Modulus (stiffness) is one of the primary inputs to mechanistic pavement design procedures and provides insight into long teim pavement performance. Despite the importance of modulus, some aspects of pavement construction and management are still based on measurement of parameters that are not directly connected with long-term performance or on empirical based judgments. The goal of this research is to evaluate the effectiveness of the Portable Falling Weight Deflectometer (PFWD) in two critical areas that do not make use of modulus: evaluating the support capacity of pavements during the spring thaw, and evaluating the adequacy of subgrade and base compaction during construction. The performance of ten asphalt and gravel surfaced low volume roads were evaluated through spring thaw and recovery. Instrumentation was used to quantify the condition of the test sections on days when measurements were made. Comparisons were made to the traditional FWD as well as other portable measuring devices. .It was shown that the PFWD was able to follow seasonal stiffness variations and compared well with FWD derived moduli on both asphalt and gravel surfaces. Actual values varied with drop weight, loading plate diameter, drop height, and number of drops. Recommendations were made for using the Prima 100 PFWD to determine when to place and remove load restrictions. Field and laboratory tests were conducted in order to develop correlations between composite modulus, percent compaction, and water content for a range of soil types indicative of New England subbase material. It was shown that composite modulus is affected by the degree of compaction and the water content relative to optimum. Comparisons were made between multiple PFWDs. PFWD derived composite moduli were not highly susceptible to operator technique. Recommendations were made for field testing and future use