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35 (a) PQI Non-Nuclear Density Gauge (b) PaveTracker Non-Nuclear Density Gauge Figure 15. Non-nuclear, non-roller-mounted devices used to measure the density of HMA layers. 1.7 Intelligent Compactors/Rollers modulus. There is also a temperature sensor in the system, with Mounted Response which feeds data into the computer for use in modulus calcu- Measuring Devices lations. In addition, the system takes this reading and alters the compaction effort of the roller to avoid the damaging effects These systems offer real-time pavement quality measure- of over-compaction. Stiffness readings are taken continuously ment with no negative impact to the contractor's progress. and presented as a modulus value developed by Bomag and They use accelerometers to measure parameters of the com- called Evib, in the form of MN/m2. pactor's vibratory signature. Other sensors are also used to The Evib value should be related to the dynamic modulus of gain information about the pavement. Information from the the material being compacted. However, this computed value sensors is then used to make decisions about pavement quality. is expected to be affected by the underlying support conditions. Although these roller-mounted systems have been shown To date, the Evib value has not been evaluated or checked against to be beneficial to a contractor from a control standpoint, dynamic modulus values measured in the laboratory or esti- they have not been used for acceptance and confirmation mated through other NDT devices. of the design-modulus values. Two of these systems were The system is fully integrated into a vibratory roller that is used in the demonstrations sponsored by FHWA at the part of an operational paving train (see Figure 16). The true test NCAT and MnROAD facilities and included in the NCHRP of this "intelligent compaction" system is whether it actually Project 10-65 field evaluations. They are described in the saves time (fewer passes), improves uniformity of the mat, following paragraphs. and renders accurate, consistent readings. As for this part of the analysis (impact on the contractor's progress), assuming that the system does what it claims, it can only help the contractor's 1.7.1 Asphalt Manager and progress. Varicontrol System This system, developed by Bomag, contains an onboard 1.7.2 Ammann Compaction Expert pavement analysis system based on the electrical charge gen- erated by strategically mounted quartz-crystal accelerometers Ammann-America, the U.S. branch of the Swiss manufac- that measure the acceleration of the vibratory drums of the turer Ammann Compaction, Ltd., has introduced the Ammann compactor. An onboard computer transforms the data from Compaction Expert (ACE) to the U.S. market. The goal of the the sensors using an FFT into the frequency domain. This ACE is the same as for the Asphalt Manager. The major differ- transformation allows the computer to calculate the material's ence is that the ACE seems to take the paving environment