AMERICAN CONCRETE
PAVEMENT ASSOCIATION
MnROADs Low Volume Road Variable
Depth Grooving Experiment
Draft Workplan
Prepared by
Larry Scofield
American Concrete Pavement Association
December 10, 2007
MN Roads Low Volume Road Variable Depth Grooving Plan
Background
The IGGA and ACPA have been working with Purdue University to develop a
diamond grinding texture with improved noise characteristics. The result of this effort is
a diamond ground and grooved surface that provides a reduced overall noise level. The
new surface, referred to as Next Generation Concrete Surface (e.g. NGCS), is indicated
in Figure 1. Field trials of this surface began in the fall of 2007 and should continue
during the spring of 2008. The expected acoustic performance of this surface has been
obtained in the as constructed state. Performance for friction, winter storm operations,
and changes in acoustic properties will continue to be evaluated.
Traffic
Figure 1 Next Generation Concrete Surface
In addition to the acoustic performance of roadways, splash/spray and removal of
surface water during inclement weather are always concerns for pavement designers.
Traditionally, for non porous pavements, removal of surface water has been
accomplished by providing sufficient cross slope to the roadway to drain water to the
shoulder(s). For interstate type pavements, the cross slope is typically 2% for straight
and level roadways.
One means for accelerating roadway drainage is to increase the slope of the
drainage path. For new roadways this could be accomplished by increasing the roadway
cross slope. For existing roadways, this is only possible by installing grooves of variable
depth which allow the “groove channels” to improve the “groove” cross slope such that
increased water movement occurs. With the use of grooves, the roadway surface is
unaltered from a vehicle perspective, yet the hydraulic flow of water can be improved
through increased gradient.
The most obvious advantage of this would be for transverse grooving where the
groove slope could be increased beyond the normal roadway cross slope. However,
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transverse grooving is generally quite noisy and would probably result in an unacceptable
consumer reaction due to tonal issues.
For longitudinally grooved roadways, however, this could provide some benefit.
Longitudinally grooved roadways typically intercept the normal roadway sheet flow
every ½ to ¾ of an inch with the grooves. The water is then held in the grooves or drains
to the transverse joints where it escapes to the shoulder of the roadway. Historically, the
grooves and transverse joints have not been designed for or considered part of the
hydraulic solution in water removal.
Through the use of variable depth grooving, it may be possible to improve
drainage of existing roadways. Figure 1 indicates a potential means by which this can
occur. Figure 1A indicates a transverse cross section of the roadway, at mid slab, with
1/8 inch grooves spaced every one half inch. Figure 1B represents the longitudinal cross
section of that same roadway indicating the variable depth of the grooves. That is, the
groove is 1/8 inch deep at mid slab and increases in depth to one inch at the transverse
joints. The groove depth increases in both directions towards each of the transverse
joints for the slab.
Figure 1 B Longitudinal Cross Section View
One issue with having longitudinal grooves with slopes increasing towards the
transverse joints is that traffic will be going in the opposite direction of the rearward
water flow. With the air turbulence that surrounds a tire in motion, it is not known
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whether this would impede the drainage and perhaps even exacerbate the splash spray
issue. To resolve this question it will be necessary to construct a field test section and
evaluate this condition.
Proof of Concept
To evaluate the effectiveness of a variable depth longitudinal grooving approach,
it is necessary to construct a field test section and then evaluate the resulting splash spray.
To accomplish this, it is desirable to groove 8 consecutive slabs to enable sufficient
distance to observe the splash spray effect.
Test Section Construction
For the field validation it is proposed that cell 40, indicated in Figure 2 below be
used to conduct the variable depth grooving experiment. Each of the slabs would be
longitudinally grooved in the same manner. Figure 3 indicates the layout of the grooving
patterns with two, 4 ft wide wheelpaths being grooved for each of eight consecutive slabs
in the east bound direction. The groove depth would vary in depth from 1/8 inch at the
center of the slab to 1 inch deep at each of the transverse joints as indicated in Figure 1 B.
The grooves would all be 1/8 inch wide, spaced on ½ “ centers, as indicated in Figure 1
A.
Within the test area (e.g. 8 slabs) the transverse sealant will be removed to
provide a location for the water to drain to. If it appears the water cannot drain into the
transverse joints sufficiently after sealant removal, it may be necessary to provide core
holes in the shoulder alongside of the transverse joints. At this time it is not believed this
will be necessary.
Performance Evaluation
Field evaluation will consist of both a noise evaluation, using On Board Sound
Intensity Equipment, and a splash/spray evaluation using an artificial water source and
both passenger and truck vehicles.
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Figure 2 MnROADS Low Volume Road Concrete Test Sections
Figure 3 Layout of Wheeltrack Grooving in Cell 40 EB Direction
OBSI Evaluation
Since it will not be possible to evaluate the existing wheelpaths prior to
construction of the grooving, the between wheelpath location will be tested at the same
time as the wheelpath location. Three replicate runs of one wheelpath and the between
the wheelpath location will be conducted using the ACPA OBSI equipment. This testing
will compare the pre-grooved condition to the post grooving condition. Both overall
level and one third octave spectrum plots will be developed.
Splash Spray Evaluation
A water truck will be used to apply a constant amount of water to the test area just
prior to vehicular travel with a test vehicle. Both a passenger car and heavy truck will be
used to travel over the surface. The amount of splash and spray will be observed and
recorded on video. The same process will then be repeated on the adjoining random
transverse tined section to see if a difference is observable between the two sections.
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