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Here is an excerpt from the Asphalt Contractor magazine concerning Intelligent Compaction: To-date, equipment manufacturers have been unable to consistently relate the measurement of buildup of stiffness beneath a drum to an actual density value; instead they use their own measurement values for stiffness, and are trying correlate stiffness data acquired during intelligent compaction activity with nationally accepted density specifications. Every maker has its own nomenclature: Hamm calls its stiffness measurement value the HMV. The inability to directly relate stiffness measurement values from the accelerometer or other process to actual engineering values stands in the way to use of IC for asphalt compaction for quality assurance or acceptance. “ Consistently rHere is an excerpt from the Asphalt Contractor magazine concerning Intelligent Compaction: To-date, equipment manufacturers have been unable to consistently relate the measurement of buildup of stiffness beneath a drum to an actual density value; instead they use their own measurement values for stiffness, and are trying correlate stiffness data acquired during intelligent compaction activity with nationally accepted density specifications. Every maker has its own nomenclature: Hamm calls its stiffness measurement value the HMV. The inability to directly relate stiffness measurement values from the accelerometer or other process to actual engineering values stands in the way to use of IC for asphalt compaction for quality assurance or acceptance. “ Consistently reliable correlation between intelligent compaction measurement values (ICMV) and in situ density readings have not been established,” said FHWA’s Michael Arasteh, Office of Technical Services, Baltimore, at a workshop in January 2014. “On many projects, there has been a ‘relationship’ between ICMV and density,” he added, but the firm, reliable link is not yet there. The major purpose of the FHWA/state DOT-sponsored projects from 2012-14 has been to see if the stiffness measurement values of different manufacturers can be correlated into density readings.
When the requirement in a specification is density, what exactly is the value of a stiffness measurement? Who realizes this value (project owner, project contractor, etc)?
bmarx: Yes, indeed. The requirement for compaction is density [g/cm³]. The value of stiffness is [N/m]
Definition:
The stiffness, C, of a body is a measure of the resistance offered by an elastic body to deformation.
C = F / l [N/m]
F is the force applied to the ground with the roller [N]
l is the displacement produced by the force, for instance, the change in layer thickness before and after compacting. [m]
Actually, there is no system on the market which you could measure density during the compaction process. At least not in a reasonable speed.
The systems on the rollers are measuring accelerations. The assumption is: The higher the density of the material, the higher the reaction force from the ground will be. Therefore, the higher the reaction force, the higher the acceleration.
– Compare compaction of sand vs. concrete.
When applying these considerations to compaction with rollers it comes to the point that you could say also: The thinner the mat after compaction, the higher the density of the material.
This means: acceleration is proportional to density
Look at the formula. With a given force, stiffness will increase when the change of layer thickness decreases.
The other way around: When compacting a given mass of material [kg] on a fixed area [m²] you will achieve higher density by decreasing the height [m]
Density = mass / (A x h) [kg/m³]
Stiffness, in this case, is a synonym for density.
Stiffness is proportional to density
These facts make it possible to draw a correlation curve under the assumption that the material characteristics, weather conditions, water content and temperatures stay constant during compaction.04.12.2015 0 points