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pavement evaluation

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PAVEMENT EVALUATION
Pavement
evaluation
Functional
evaluation
Structural
evaluation
Present
serviceability
index
Pavement
roughness
Skid resistance
Destructive
testing
Flexible
pavements
Coring /Bitumen
extraction
Non destructive
testing
Rigid pavements
Crushing
srength,flexural
strength
Static creep
deflection
method
Steady state
deflections
Wave
propagations
Impulsive
loading
• Pavement evaluations are conducted to
determine functional and structural conditions
of a highway section either for purposes of
routine monitoring or planned corrective
action.
• Functional condition is primarily concerned
with the ride quality or surface texture of a
highway section.
• Structural condition is concerned with the
structural capacity of the pavement as
measured by deflection, layer thickness, and
material properties.
Need of evaluation
• At the network level, routine evaluations can
be used to develop performance models and
prioritize maintenance or rehabilitation efforts
and funding.
• At the project level, evaluations are more
focused on establishing the root causes of
existing distress in order to determine the best
rehabilitation strategies.
Functional evaluation
• Visual inspection /Present serviceability Rating
• Roughness
• Skid resistance
Present serviceability rating
• Visual condition surveys cover aspects of both
functional and structural pavement condition,
but generally serve as a qualitative indicator of
overall condition
Roughness
• Profilometer is a measuring instrument used to
measure a surface's profile, in order
to quantify its roughness.
• Roughness is a component of surface texture.
• The profile of a road consists of road slopes,
called grades, connected by parabolic vertical
curves.
• The road profile is the cross-sectional shape of
the road surface in relation to the road corridor
traversing the surrounding
profilometers
Cont..,
• The data collected by a profilometer is used to
calculate the International Roughness Index
(IRI) which is expressed in units of inches/mile
or mm/m.
• IRI values range from 0 (equivalent to driving
on a plate of glass) upwards to several
hundred in/mi (a very rough road).
• The IRI value is used for road management to
monitor road safety and quality issues.
Cont..,
• The IRI was defined as a mathematical
property of a two-dimensional road profile (a
longitudinal slice of the road showing
elevation as it varies with longitudinal
distance along a travelled track on the road).
As such, it can be calculated from profiles
obtained with any valid measurement
method, ranging from static rod and level
surveying equipment to high-speed inertial
profiling systems.
• Some profilers take
digital photos or videos while profiling the
road. Most profilers also record the position,
using GPS technology.
• Some profilometer systems include a ground
penetrating radar, used to record asphalt layer
thickness.
Dipstick profilometer
• Dipstick, “measures profiles (relative elevation
differences) at a rate and accuracy greater
than traditional rod and level surveys.”
Skid resistance
• Skid resistance is the force developed when a
tire that is prevented from rotating slides
along the pavement surface
• Skid resistance depends on a pavement
surface’s microtexture and macrotexture
• Microtexture refers to the small-scale texture of the
pavement aggregate component (which controls contact
between the tire rubber and the pavement surface) while
• macrotexture refers to the large-scale texture of the
pavement as a whole due to the aggregate particle
arrangement (which controls the escape of water from
under the tire and hence the loss of skid resistance with
increased speed) . .
• For example, a road which has gravel spread on top
followed by an asphalt seal coat will have a high
macrotexture, and a road built with concrete slabs will have
low macrotexture. For this reason, concrete is often
grooved or roughed up immediately after it is laid on the
road bed to increase the friction between the tire and road.
Variation of skid resistance
• Skid resistance changes over time. Typically it
increases in the first two years following
construction as the roadway is worn away by
traffic and rough aggregate surfaces become
exposed, then decreases over the remaining
pavement life as aggregates become more
polished.
• Skid resistance is also typically higher in the fall
and winter and lower in the spring and summer.
Importance of skid resistance
• Skid resistance is generally quantified using
some form of friction measurement such as a
friction factor or skid number.
• In general, the friction resistance of most dry
pavements is relatively high; wet pavements
are the problem. The number of accidents on
wet pavements are twice as high as dry
pavements (but other factors such as visibility
are involved in addition to skid resistance).
Lock wheel tester
• The most commonly used method for skid resistance testing uses some
form of a lock wheel tester . Basically, this method uses a locked wheel
skidding along the tested surface to measure friction resistance. A typical
lock-wheel skid measurement system must have the following:
• A test vehicle with one or more test wheels incorporated into it or as part
of a towed trailer.
• A standard tire for use on the test wheel. The standardized skid-test tire, a
tubeless, bias-ply G78x15 tire with seven circumferential grooves, is
defined by AASHTO M 261 or ASTM E 501. A newer tire, one with no
grooves, appears to be gaining acceptance as well. By defining the
standard test tire, the tire type and design are eliminated as variables in
the measurement of pavement skid resistance.
• A means to transport water (usually 750 to 1900 liters (200 to 500
gallons)) and the necessary apparatus to deliver it in front of the test
wheel at test speed
•
• A transducer associated with the test wheel that
senses the force developed between the skidding
test wheel and the pavement
• Electronic signal conditioning equipment to
receive the transducer output signal and modify
it as required
• Suitable analog and/or digital readout equipment
to record either the magnitude of the developed
force or the calculated value of the resulting Skid
Number (SN)
Operation of the equipment
• To take a measurement, the vehicle (or trailer)
is brought to the desired testing speed
(typically 64 km/hr (40 mph)) and water is
sprayed ahead of the test tire to create a
wetted pavement surface. The test tire
braking system is then actuated to lock the
test tire. Instrumentation measures the
friction force acting between the test tire and
the pavement and reports the result as a Skid
Number (SN).
Structural evaluation of pavements
• Destructive testing
1. Flexible pavements
Bitumen extraction test
• Rigid pavements
1. Flexural and crushing strength test
• Non destructive testing
Destructive testing
• Destructive testing provides more detailed
data about the pavement not possible to
obtain through non-destructive testing. Such
detailed data include:
• laboratory mechanical, physical, and chemical
properties (obtained through coring and
trenching), and
• visual inspection of pavement layers through
coring and trenching.
Destructive testing
• Bitumen extraction test:This test is done to
determine the bitumen content as per ASTM
2172. The apparatus needed to determine
bitumen content are –
i) Centrifuge extractor
ii) Miscellaneous – bowl, filter paper, balance
and commercial benzene.
A sample of 500g is taken.
Bitumen extraction
• If the mixture is not soft enough to separate with a trowel,place 1000g of
it in a large pan and warm upto 100oC to separate the particles of the
mixture uniformly.
• ii) Place the sample (Weight ‘A’) in the centrifuge extractor. Cover the
sample with benzene, put the filter paper on it with the cover plate tightly
fitted on the bowl.
• iii) Start the centrifuge extractor, revolving slowly and gradually increase
the speed until the solvent ceases to flow from the outlet.
• iv) Allow the centrifuge extractor to stop. Add 200ml benzene and repeat
the procedure.
• v) Repeat the procedure at least thrice, so that the extract is clear and not
darker than the light straw colour and record the volume of total extract in
the graduated vessel.
• vi) Remove the filter paper from the bowl and dry in the oven at 110 + 5oC.
After 24hours, take the weight of the extracted sample (Weight ‘B’).
• Bitumen content = [(A-B)/B]×100 %
Repeat the test thrice and average the results.
Non destructive testing
• Non-destructive testing is the collective term for
evaluations conducted on an existing pavement structure
that do not require subsequent maintenance work to
return the pavement to its pre-testing state.
• This is generally desirable to minimize disruption to traffic,
and is essential as a screening tool to determine locations
where selective material sampling should be conducted to
evaluate other material properties in the laboratory.
• As such, its focus is to assess in situ properties that can be
used to evaluate the need for further “destructive” testing
(i.e., coring, boring, trenching), location of that destructive
testing, and the current structural capacity of the highway
as related to layer stiffness
NDT
Modulii of pavement layer
Load transfer efficiency
1.
2.
3.
4.
Static creep deflection method
Steady state deflection method
Wave propagation method
Impulse loading method
Structural evaluation of pavements
• Static creep deflection method:
• Benkleman beam :
• is used to measure deflections of flexible pavements. The
light weight instrument is supplied in two parts for
assembling on site with easy hand tools.
• In use one end of the beam rests at a point under
investigation while the beam is pivoted at the centre. The
free end carries a dial gauge to record the deflections.
• The other end is kept on a stable platform.
• with a dial gauge 0. 01 x 25mm.
• This is a light weight dismantleable instrument and easy to
carry
Falling weight deflectometer
• A falling weight deflectometer (FWD) is a
testing device used by civil engineers to
evaluate the physical properties of pavement.
FWD data is primarily used to estimate
pavement structural capacity for
• 1) overlay design and
• 2) to determine if a pavement is being
overloaded.
Impulse load
•
•
•
•
An impulsive load
Short loading time
Weight falling on set of springs
With proper choice of drop weight ,spring
constant, falling weight, impulsive load
stimulating a real traffic load can be obtained.
deflection
• deflection is the degree to which a structural
element is displaced under a load. It may refer
to an angle or a distance.
• The deflection distance of a member under a
load is directly related to the slope of the
deflected shape of the member under that
load and can be calculated by integrating the
function that mathematically describes the
slope of the member under that load
geophones
• sensors (geophones; forcebalance seismometers) mounted radially from
the center of the load plate measure the
deformation of the pavement in response to
the load. Some typical offsets are 0mm,
200mm, 300mm, 450mm, 600mm, 900mm,
1200mm 1500mm. The deflections measured
at these sensors are termed D0, D200, D300
etc.
Cont..
• A geophone is a device that converts ground
movement (displacement) into voltage, which
may be recorded at a recording station.
The deviation of this measured voltage from
the base line is called the seismic response
and is analyzed for structure of the earth.
geophone
Elastic modulus
• An elastic modulus, or modulus of elasticity,
is a number that measures an object or
substance's resistance to being deformed
elastically (i.e., non-permanently) when
a force is applied to it. The elastic modulus of
an object is defined as the slope of its stress–
strain curve in the elastic deformation
region: A stiffer material will have a higher
elastic modulus.
Types of modulus
• Young's modulus (E) describes tensile elasticity, or the tendency of an
object to deform along an axis when opposing forces are applied along
that axis; it is defined as the ratio of tensile stress to tensile strain. It is
often referred to simply as the elastic modulus.
• The shear modulus or modulus of rigidity (G or ) describes an object's
tendency to shear (the deformation of shape at constant volume) when
acted upon by opposing forces; it is defined as shear stress over shear
strain. The shear modulus is part of the derivation of viscosity.
• The bulk modulus (K) describes volumetric elasticity, or the tendency of an
object to deform in all directions when uniformly loaded in all directions;
it is defined as volumetric stress over volumetric strain, and is the inverse
of compressibility. The bulk modulus is an extension of Young's modulus to
three dimensions
• Dynamic modulus is the ratio of stress to strain under vibratory
conditions (calculated from data obtained from either free or forced
vibration tests, in shear, compression, or elongation). It is a property
of viscoelastic materials.
Falling weight deflectometer
• FWD data is most often used to calculate stiffnessrelated parameters of a pavement structure. The
process of calculating the elastic moduli of individual
layers in a multi-layer system (e.g. asphalt concrete on
top of a base course on top of the subgrade) based on
surface deflections is known as "backcalculation", as
there is no closed-form solution. Instead, initial moduli
are assumed, surface deflections calculated, and then
the moduli are adjusted in an iterative fashion to
converge on the measured deflections. This process is
computationally intensive although quick on modern
computers. It can give quite misleading results and
requires an experienced analyst.
Types of deflectometer
• FWD data can also be used to calculate the
degree of load transfer between adjacent
concrete slabs, and to detect voids under
slabs.
• A Light Weight Deflectometer (LWD) is a
portable falling weight deflectometer. It is
used primarily to test insitu base and
subgrade moduli during construction.
Cont..,
• A Heavy Weight Deflectometer (HWD) is a falling weight
deflectometer that uses higher loads, used primarily for testing
airport pavements. The HWD can apply a loading in the range of
30-320kN, enabling it to simulate even the most extreme aircraft
wheel load such as the Boeing 777, the Airbus 340 or 380. The
HWD is highly versatile and can be used to test on both rigid, paver
block and flexible pavements used on roads and airports
• A Rolling Weight Deflectometer (RWD) is a deflectometer that can
gather data at a much higher speed (as high as 55 mph) than the
FWD. It is a specially designed tractor-trailer with laser measuring
devices mounted on a beam under the trailer. Another advantage of
the RWD over the FWD is that it can gather continuous deflection
data as opposed to discrete deflection data collected by the FWD.
Evaluation of load transfer efficiency of
rigid pavement
• By FWD
• Location of height of fall=close to joints of
pavement slab
• Deflection measured close to the joint =load
transfer efficiency of the joint
• Due to application of load close to the joint
both adjacent slab deflect by same amount
joint efficiency =100%
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