FEATURE
Passaic Valley Water Commission ( NJ ) uses a maneuverable 1.5 ton CR271 roller for utility work patching .
is only as good as what lies beneath it . Base material is the support structure for the asphalt surface , distributing loads and providing stability . Poorly , nonuniformly compacted base material can permit rutting , crack propagation , uneven wear , potholes , frost heave from water intrusion , and at worst , base failure resulting in the need for complete tear out . Mix moisture is under the plant ’ s control but contractors should control moisture in the base before laying the mat , as well as ensuring that the mix isn ’ t subjected to rain before application . Ensure that the base design accounts for the anticipated loads . For example : no amount of compaction will prevent pavement failure under a heavy truck for which the base is not prepared .
Beyond the Basics : Temperature Considerations
Beyond the standard practices of selecting the right roller and following recommended pass patterns , experienced contractors should consider not only the temperature of the mix before beginning but during compaction . Monitoring asphalt temperature is crucial for achieving optimal compaction . Rolling at too low or too high temperatures can affect compaction quality and the long-term performance of the pavement . Rolling should cease in the “ tender zone ” and finish before the mix cools . Rolling in the “ tender zone ” can cause shoving of the mat and checking . Rolling at too cool a temperature will be ineffective and damage the mat . Temperature ranges will vary with your local plant mix . A general guideline for the tender zone of hot mix asphalt ( HMA ) would be 250F-140F . Don ’ t rely solely on a temp gun ; use a probe to check the internal temperature of the mat .
Assessing Density Success
While formal density testing may not be common for smaller paving projects , experienced contractors can use observations and practical techniques to assess compaction quality :
• Visual inspection : Look for signs of aggregate segregation , unevenness ( smoothness ), depressions around stop-and-start areas , roller edge marks , shoving , checking and cracking . Are joints smoothly compacted and minimally detectable ?
• Operator feel : After the fifth to seventh pass , an operator may detect the vibrating drum changing from bounces to random vibrations as compaction progresses . However , the easiest way to achieve uniform compaction from the operator perspective is to accurately count the number of passes ( equally covering the entire job ).
• Tools : Where a density target is required , electromagnetic density or non-nuclear gauges ( i . e . Transtech ) are simpler , less expensive and require no licensing compared to nuke gauges . Intelligent Compaction is usually reserved for larger projects and larger rollers due to the investment expense . Core samples and nuke gauges are more commonly used on larger projects .
A TW354 combination (“ combi ”) roller combines drum + tires to replace the need for separate breakdown & finish rollers .
Example of washboarding
Common Symptoms of Compaction Issues & How to Prevent Them
The following are symptoms of improper compaction . To deliver a long-lasting finished product , contractors should become familiar with these and take preventative measures for the next job :
• Washboarding : - Cause : over-speeding a vibratory roller ( space between impacts ) - Prevention : slowing roller , turning up vibratory frequency or a mix of both
• Rutting , depressions and potholes : - Causes : improper base compaction , incomplete mat compaction , lift too thin - Prevention : ensure an even , compacted base for proper support of the mat . Ensure proper compaction of the mat by utilizing temperature-based rolling with a sufficiently weighted roller for the lift thickness .
• Alligator cracks : - Causes : improper or non-uniform base compaction , insufficient lift thickness - Prevention : ensure thorough and uniform compaction of the entire base , select a mat thickness appropriate for the intended load
• Raveling : - Cause : aggregate not bonded well with the binder - Prevention : compaction should begin at hot temperatures ( 290F + but depends on the mix type ) to ensure proper binding
• Crushed surface aggregate ( white capping ): - Cause : vibratory force too high - Prevention : reduce the roller ’ s amplitude setting
Additional Considerations
• Equipment maintenance : Regular maintenance of compaction equipment is essential for ensuring optimal performance and longevity . Follow the manufacturer ’ s recommended maintenance schedule and address any issues promptly .
• Operator training : Ensure that operators are properly trained on the use of compaction , implementing best practices and addressing common challenges , experienced contractors can deliver high quality work that meets or exceeds client expectations . Delivering projects with proper compaction will ensure long term performance of the mat , which is crucial to the reputation of an asphalt paving contractor .
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