Imagine that you are managing an asphalt paving job. You are onsite, and compaction has begun. It is an overnight job, and there is much work to be done. Although you trust your team, you would normally be more than a little concerned about finishing the job in time and ensuring adequate asphalt density. However, you recently began using intelligent compaction (IC) on your projects, and today you are much more confident that the job will be completed efficiently and effectively.
On projects like this, IC is a valuable tool that presents location and compaction data in real time. Useful for soils, aggregates, and asphalt, it can improve the quality of pavement, save money, and expedite construction through continuous compaction control (CCC). An emerging technology, IC provides solutions to challenges frequently encountered with traditional compaction.
Although key to pavement performance, it is difficult to consistently achieve adequate, uniform compaction. Uncertainty exists from different environments, equipment, operators, and materials. Experienced roller operators may be able to tell how many passes are necessary for a job, but a change to one variable or reduced visibility (as in our hypothetical night paving scenario) could affect whether or not the density required by the contract is met.
IC facilitates greater consistency, regardless of the operator, location, or other factors. Continuous stiffness measurements are taken and used to optimize compaction. From the real-time data, operators immediately know areas that need more work or where additional work could lead to overcompaction and should be avoided. The compaction effort can be adjusted manually or automatically based on feedback from the system. This helps ensure uniform compaction and optimum density. For hot-mix asphalt (HMA), temperature readings verify that operations occur within the optimal temperature range while avoiding tender zones. All of these factors contribute to improved pavement performance, which leads to longer pavement life.
Higher-quality, longer-lasting pavement translates to cost savings. The pavement will not need to be replaced as frequently and will require less maintenance. For contractors, high-quality pavement means maximum pay, without any penalties or rework required on the job.
IC also helps expedite construction. The compaction process is optimized, reducing the time required. In addition, by showing when an acceptable compaction level has been reached, an IC system eliminates unnecessary passes. Avoiding extra passes saves time and reduces the risk of overcompaction that may reduce densities and damage aggregates. IC is a perfect tool to detect areas of weak support or soft spots. In some cases, the soft spots may not even be compactable, which is crucial to know before attempting compaction.
Another benefit of IC is documentation. Stiffness measurement values and location data are continuously logged. With this information, there is a permanent record of any problem areas that were inadequately compacted. This increases operator accountability, since results at a particular location can be traced back to recorded compaction data.
Various vendors make IC systems – single-drum vibratory rollers for soils and double-drum vibratory rollers for asphalt – including Ammann/Case, Bomag, Caterpillar, Dynapac, Sakai, Hamm/Wirtgen, and Volvo. Regardless of the manufacturer, certain components are standard. Most IC systems are outfitted with an accelerometer-based compaction measurement system. This is attached on the axle of the front drum to measure the vibration between the drum and compacted materials, and then translate it into levels of applied compaction effort. A GPS unit is placed on top of IC rollers and is critical to track location, speed, and number of passes. An onboard display computer provides valuable information to the operator, most notably the real-time data collected. For HMA pavement, the system includes one or two infrared sensors for surface temperature measurement. Feedback control may or may not be part of the system. If included, it is used to adjust the amplitudes and/or frequencies automatically to optimize the compaction effort.
Information from IC systems is color-coded and map-based, making it easy to interpret the results. It is possible to view the location, roller passes, material stiffness, and temperature (for asphalt compaction). Other variables that are recorded include frequency, amplitude, and speed of IC rollers. The data can be viewed with vendor-specific software in real time or during post-processing. The Federal Highway Administration (FHWA) and some departments of transportation recommend a geospatial software tool, Veda, for standardized viewing, analysis, and reporting.
IC is an evolving technology, so there is still room for improvement and further progress. Currently, there are various roller measurement values and file formats, different for the assorted IC roller vendors. An IC Road Map was developed under the FHWA/Transportation Pooled Fund (TPF) IC project to aid with IC implementation. Among other goals, the IC Road Map calls for standardization of IC roller measurement systems and data storage. It also suggests IC workshops and certification. Following through on this recommendation, the first of three FHWA National IC workshops will be held this winter in Atlanta.
In addition to creating the Road Map, the FHWA/TPF IC project – "Accelerated Implementation of Intelligent Compaction Technology for Embankment Subgrade Soils, Aggregate Base, and Asphalt Pavement Materials" – conducted 16 IC field demonstrations nationwide. The final report for the project is available at www.intelligentcompaction.com/downloads/Reports/FHWA-TPF_IC_Final_Report.pdf
As IC continues to evolve, its implementation will become even more widespread. End results include improved pavement performance, lower costs, expedited construction, and your peace of mind as you begin a busy night at the jobsite.
To learn more about IC, visit www.intelligentcompaction.com
Jennifer Rutledge is a FHWA/TPF IC research team member and administrative manager for The Transtec Group Inc. George Chang, Ph.D., P.E., is principal investigator for the FHWA/TPF IC research team and project manager for Transtec. Austin, Texas-based Transtec (www.thetranstecgroup.com) is a specialty engineering firm with expertise in pavements and pavement materials.
Get the latest from the RAI NewsBlog in your inbox!