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29 CHAPTER EIGHT Applications of Falling Weight Deflectometer Data-- Case Studies This chapter discusses how FWD data has been applied to of subgrades. A presentation by VDOT describes its FWD various agency activities. The case studies cover the follow- testing on its entire Interstate highway network. To provide ing topics: a structural component to Virginia's pavement management system (PMS), FWD data were collected on Interstate 77 Data collection and analysis refinement every 0.3 km (0.2 mi) and at three load levels. Additionally, Pavement rehabilitation and overlay FWD data were used to determine project acceptance. On PCC joint sealing evaluation Interstate 64, FWD testing was done at early-age cracking Pavement management systems sites. The data showed "weak structure" and the contractor Load transfer efficiency was "asked to remove and replace unaccepted pavement sec- Void detection tions" (Habib 2006). Spring load restrictions Nonresilient pavement layer behavior TxDOT owned 15 FWDs in 2003 and used them to test Utility cuts 5%10% of network-level highways for their PMS. On the Experimental paving materials project level, TxDOT collected FWD data for "load zoning, Project acceptance and evaluation design, forensic studies, joint load transfer on Jointed Con- Conversion of data from other NDT devices crete Pavement (JCP), and many projects for determining International practices structural adequacy" (Beck 2003). The Pennsylvania DOT outlines its pavement design pro- CASE 1. Data Collection and Analysis cedures in its Pavement Policy Manual (2007 ), including Refinement new pavement designs. According to procedures outlined in chapter six, "Pavement Design Procedures," new pavement The Kansas DOT sponsored a study of LTE and tempera- design submissions must include a table of Mr values backed ture, during which FWD planning lessons were learned. up by either FWD data or lab tests. Additionally, federal-aid FWD data were collected at one site along Interstate 70 at pavement preservation projects require patching percentages various times through the year. Because temperature has generated by FWD and by visual inspection. Back-calcula- such significant effects on LTE and other pavement proper- tion of Mr values is permissible only under five scenarios: ties, the Kansas DOT drafted the following recommenda- tions (Corn 2005): Full depth bituminous pavement sections, Existing bituminous overlays on thin concrete pave- Plan FWD data collection operations with climatic ments (original concrete pavements less than 8 inches conditions in mind. in depth or any parabolic sections), Test during temperate climate months. Existing bituminous overlays on concrete pavements Test approach and leave slabs. which suffer from severe alkali silica reaction (ASR) Do not test while the ambient temperature is higher than degradation, [and] 27 C (80 F), per the AASHTO recommendation. Directly on subgrade and subbase (this situation is "Don't expect the expected." rare) (Pavement Policy Manual 2007). VDOT uses FWD pavement testing at the project level, at the network level, and for forensic investigation of pavement CASE 2. Pavement Rehabilitation and Overlay failures. AC, jointed concrete pavement (JCP), CRCP, and composite pavements are all subject to FWD testing. At the project level, VDOT derives PCC elastic moduli, composite When contractors perform pavement resurfacing projects in modulus of subgrade reaction (k-value), LTE, and presence the state of Alabama, an FWD test is required ("ALDOT of voids from FWD rigid pavement testing. On flexible pave- Procedure 390 . . ." 2004, p. 14). ments, they derive SNeff, layer moduli, and resilient moduli