Better Roads Digital Magazine
Issue link: http://read.dmtmag.com/i/325401
RoadScience 8 June 2014 Better Roads red area indicated a potential problem. Butler had seen green most of the time, but when he made two passes over an area and still saw red, he knew an adjustment had to be made. Butler had been working in a soil with heavy clay content, and an accelerometer-based instrument would have had dif- ficulty finding the trouble, Cat says. Butler realized the red probably resulted from too much moisture. He switched from the compactor to a tractor and disk and spent about 15 minutes turning the soil so it would dry more quickly. Then it was time to take another pass with the CS74B. The screen turned green, and Troxler density samples later con- firmed the target had been achieved. "We've not been wrong yet about whether we would pass a test," Butler says. Land-based GPS The land-based global positioning system used by most manufacturers offers real-time kinematic (RTK) precision via a GPS base station, GPS radio and roller-mounted receiver and a GPS rover, all connected by radio signals. Hamm, however, eschews this system's setup by using the proprietary, subscription-based OmniSTAR HP system, which should provide location precision of up to 4 inches (10 cm) directly from the differential global navigation system satellites (DGNSS), operating in real time and without the need for lo- cal base stations or telemetry links. This eliminates the need to set up and move the base station and rover as work progresses. With the HCQ Navigator (for Hamm Compaction Quality), Hamm was one of the first manufacturers to launch a com- paction measurement and documentation system. The system links measurement data from various sensors on the rollers with the position information obtained via GNSS (global navigation satellite system) receivers. The HCQ Navigator uti- lizes these data to determine the progress of compaction for all rollers in a group in real time. A compaction map visual- izes the status for the roller drivers and site management. At the core of the application is a rugged panel touch- screen PC with USB interface. This computer provides pro- cessing power as well as a monitor and data storage facilities. It is based on military standards, has a fully enclosed metal case and is protected against water and vibrations. The differential global navigation system receiver in a heavy-duty version with magnetic feet only takes seconds to mount on the roller. This device receives the satellite signals, along with a DGNSS correction signal. Licenses for these sig- nals are available in different accuracy classes by subscription. The HCQ Indicator measures the stiffness of soil beneath the drum, and consists of an accelerometer inside the drum, a processor and a display. Based on these data, the processor calculates the HMV (Hamm measurement value) – indicating the degree of compaction derived from the measured signals – and displays this value to the driver in the cab. During the compaction process, the panel PC shows the op- erator how stiffness is progressing. Separate graphics depict, for example, the number of completed passes or the current asphalt temperature, and the operator has the ability to moni- tor two of these functions simultaneously on the split screen. Dynapac's compaction analyzer Advance mapping of a construction site sounds daunting, but preconstruction mapping is recommended for many IC applications. Project test strips are often calibrated in order to correlate the compaction index or stiffness/moduli values to conventional in situ measurements such as material modulus or density. The Dynapac Compaction Analyzer (DCA) and GPS allow operators to make a pre-compaction pass to chart ground conditions. The pass determines the properties of the material to be com- pacted, and also reveals weak areas before compaction begins. Dynapac's documentation system is built up in three levels. At the basic level there is the compaction meter. This can then be expanded with increasingly advanced documentation tools in the form of computers mounted on the roller with differ- ent positioning systems. The compaction meter consists of a sensor/accelerometer, a processor and a display. The sensor registers the vibratory movement of the roller, and this information is transferred to the processor where it's analyzed. This information is present- ed on the display as the CMV, or compaction meter value. v Dynapac Compaction Analyzer (DCA) supplies compaction control data with full area coverage for documentation and analysis. Illustration courtesy of Dynapac RoadScience_BR0614.indd 8 6/2/14 4:52 PM