The compaction of road materials such as soils, aggregate bases or asphalt paving materials with vibratory rollers is an essential element in the construction of highways, airports, buildings, sewers, and bridges. On road and building construction sites, materials are compacted to properly support the structure built above it. Quality assurance tests are made traditionally with handheld instruments like density gauges or by cores. Tests for material density, thickness and uniformity are taken in isolated areas. In recent years, the awarding authorities have experienced low numbers of personnel to conduct the already scattered tests.

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Measuring of density on aggregats with nuclear gauge

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Measuring of density on Asphalt with nuclear gauge

With Vibratory rollers, equipped with a MOBA in-situ measurment, a GNSS based mapping system and a stiffness measurement system, based on accelerometer data and software that automates the documentation of the results, a full coverage of the site is possible. Everywhere the roller has been, we collect the information. Integrated measurment and ducumentation allows real-time monitoring and correction of the compaction process. The system also maintain continuous records of color-coded views whichs show the number of passes, stiffness measurements, the position of the roller and temperature if applicable.

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Samples of MOBA documentation views.

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Stiffness values on the left, passes with vibration on the right hand of ech picture.

Compaction with MCA exposes week compacted areas, allowing the operator to eliminate week spots before further construction. These increases reliability, decreases life cycle cost and increases the return of investment. As powerful MOBAs MCA is, it still cannot relate achieved stiffness with actual density! The system can measure the number of passes and lift temperature for any spot on a lift, it is unable to detect pavement density on the fly, - and current technologies on the market simply don’t allow it.

How to connect stiffness to density?

Lift density is being extrapolated from measurements of lift stiffness, which is generated from the accelerometer. MOBA calls its stiffness measurement value the ICV. (Intelligent Compaction Value).

In praxis, we try to correlate stiffness data with nationally accepted density specifications. Reliable correlation between intelligent compaction measurement values (ICMV) and in situ density readings have not been established jet. On many projects, there has been a ‘relationship’ between ICMV and density. In principal, the correlation curve can be developed as illustrated in the picture below.

The premises for such an evaluation is that the measurements with the gauge and those one with the Roller are taken from the same spot. See Picture below. Furthermore, it is essential that all relevant compaction parameters are unchanged during the whole process.

Relevant compaction parameters that have to be kept are at least:

• Material to compact
• Temperature during compaction
• Temperature of the asphalt
• Water content of the soil
• Rolling speed
• Roller properties

Summary

Stiffness measurement increases the compaction efficiency significant. Nevertheless, the operator is the decision maker and he must have capabilities and skills to interpretation the results during compaction. He must take action to guide the roller to its maximum performance.