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80 CHAPTER 3 Construction Quality Determination The approach taken for this project was to use fundamental required specifications. Two of the more common methods properties needed for mixture and structural design for the that have been used and adopted by most agencies are percent control and acceptance of flexible pavements and HMA over- within limits (PWL) and average absolute deviation (AAD). lays. The NDT technologies included in the field evaluation PWL is the procedure used by over 75 percent of the agencies were evaluated for their ability to determine these properties that have adopted statistical-based acceptance specifications. accurately on a practical and effective QA program. The NDT AASHTO R9, Acceptance Sampling Plans for Highway Con- technology or QA tests are used to confirm the design assump- struction, was used for preparing practical but effective pro- tions for the materials placed. cedures that agencies can use in deciding whether the product Chapter 2 identified those devices that were able to identify meets their specifications (AASHTO 2003). or discriminate areas with different material properties or con- Statistical control charts are the primary method for ditions. Chapter 3 presents the evaluation of the NDT devices determining whether the construction is in-control or out- with the potential to determine the quality of the unbound and of-control, and PWL is the primary method for judging the HMA mixtures placed on some of the projects. These devices acceptability of construction. To demonstrate the use of the include the GeoGauge for unbound materials and the PSPA NDT technology for use in a QA program, specific projects for HMA mixtures. Other evaluated devices, such as the DCP, were selected to cover the range of conditions encountered were not as successful in identifying anomalies. In addition, during construction. The following table contains the steps the intent of this chapter is to show the use of NDT devices needed to set up a QA program that uses NDT devices to judge that estimate modulus for defining construction quality. the quality of construction of unbound materials and HMA mixtures using the material modulus. 3.1 Quality Control and Acceptance Application 3.2 Control Limits for Of the many process control procedures that can be used Statistical Control Charts in highway construction, process control charts, particularly The upper and lower control or action limits are calculated statistical control charts, are most commonly used by contrac- from the NDT modulus tests in accordance with the following tors and material producers for verifying that their process is equations. under control. Although there are different approaches that can be taken in implementing NDT technologies to verify that UCLX = X + ( A3 )( s ) (17a) the process is in control, statistical control charts were used within this project. As a result, the NDT test methods must LCLX = X - ( A3 )( s ) (17b) produce results that can be adapted to existing AASHTO pro- cedures in pavement construction. The ASTM Manual on Where: Presentation of Data and Control Chart Analysis was used for UCLX = Upper control limit for the sample means. preparing practical procedures that contractors can use in X = Lower control limit for the sample means. LCL deciding whether their process is in control (ASTM 1992). X = Target value for a project. Similarly, there are different acceptance procedures that s = Pooled standard deviation that represents the pro- are used to judge whether the pavement material meets the cess variance.