Evaluating the Methodology of Light Weight Deflectometer (LWD) To Be Used For Construction Quality Control and Assurance of Reclaimed Asphalt Pavement (RAP) Aggregates

Abstract

Reclaimed Asphalt Pavement is being produced from asphalt concrete, is mostly aggregate material and is itself granular and can be used in a variety of applications for which freshly produced natural aggregates have traditionally been used and does not behave like aggregate (Hoppe, Lane, Fitch, & Shetty, 2015). According to recent VCTIR study (2015), there is approximately 4.7 million tons of excess RAP stockpiled in VA. RAP has a binder content over the top of aggregate and due to the complex nature of the RAP. The quality control of compacted unbound aggregate pavements is performed by the traditional method of the nuclear density gauge (NDG) (Smith & Diefenderfer, 2008). However, the nuclear density gauge does not provide accurate results for density and moisture content measurements on reclaimed asphalt pavement (RAP) (Viyanant et al., 2004). For this reason, the light weight deflectometer (LWD) is another preferable tool for compaction quality control of soil pavements in highway construction to determine the elastic modulus (Fleming et al., 2000; Fleming et al., 2007; Nazzal et al. 2007; Mooney & Miller, 2009; Vennapusa & White, 2009; Ebrahimi & Edil, 2013; Khosravifar, 2015). The LWD works with dropping weight from a given height on a circular plate over the soil ground and measures applied force and deflection using geophone which is underneath center of the plate (Fleming et al. 2000; Ebrahimi & Edil, 2013). Some studies stated the depth of influence for the LWD is 0.9-1.1 times the plate diameter which means between 27 and 33 cm (Kavussi et al. 2010; Kudla et al. 1991; Mooney & Miller, 2009; Nazzal et al. 2007; Ryden & Mooney, 2009; Senseney & Mooney, 2010). Therefore, if the thickness of the layer under observation is less than the plate diameter then the determine modulus is affected by the layer underneath the test layer. In that case the determined modulus is the result of the combined response of test layer and the layer underneath it. For this situation, multilayer system method has to be used to back-calculate the tested layer’s elastic modulus (Nazzal et al. 2007). There is a lack of research on the confirmation of validity of the LWD. The multilayer system and depth of influence effects has not been implemented with RAP and RAP-VA blends materials. Therefore, the purpose of this research is to focus on how to use the LWD tool to analyze the reclaimed asphalt pavement in order to develop methodology to implement quality control during construction of roadways. To achieve this scope, first phase of the research covers laboratory testing program using the Large Scale Model Experiment (LSME) and proctor mold tests to obtain the target elastic modulus values of VA, RAP, and RAP-VA blends materials with LWD. Additionally, the nuclear density gauge is not useful for bituminous materials and LWD device does not provide moisture content control therefore speedy moisture tool was calibrated and performed for each material in the laboratory. The second phase of the research validates laboratory findings in the field implementation. The study will be geared towards the evaluation of suitable quality assurance (QA) /quality control (QC) methods for RAP-Virgin Aggregate blends in the field. Also, this test method can be implemented for VA materials.