PRINCIPLES FOR
FLEXIBLE PAVEMENTS
The primary function of the pavement structure is to reduce and distribute the
surface stresses (contact tire pressure) to an acceptable level at the subgrade.
A flexible pavement reduces the stresses by distributing the traffic wheel
loads over greater and greater areas, through the individual layers, until the
stress at the subgrade is at an acceptably low level.
LOAD DISTRIBUTION
STRESS DISTRIBUTION
SERVICEABILITY
CONCEPT
Pavement failure is an important factor in
considering the serviceability of a pavement. Its
occurrence affects the structural and functional
performance of a pavement.
Structural performance relates to the physical
condition of the pavement while the functional
performance pertains to the riding quality.
To quantify the performance of a pavement,
The Pavement Serviceability-Performance
Concept of Carey and Irick [1962] was
developed.
PAVEMENT PERFORMANCE TRENDS
Pavement performance, at any point in
time, is known as the present
serviceability index, or PSI
It has been found that new pavements
usually have an initial serviceability
index rating of approximately 4.2 to 4.5.
The terminal serviceability index (TSI)
varies by type of highway. Highway
facilities such as interstate highways or
principal arterials usually have TSIs of
2.5 or 3.0, whereas local roads can have
TSIs of 2.0.
FLEXIBLE-PAVEMENT
DESIGN EQUATION
WHERE:
W 18 = 18-kip–equivalent single-axle load (ESAL)
Z R = standard normal deviate
S o = overall standard deviation of traffic,
SN = structural number,
Δ PSI = loss in serviceability from the time the
pavement is new until it reaches its TSI, and
MR = soil resilient modulus of the subgrade in
2
lb/in
INPUTS
The predicted loading (W 18 )
Reliability ( Z R , So )
Pavement structure (SN)
Serviceable life ( Δ PSI)
Subgrade support (M R )
INPUTS
Reliability
Predicted loading
The predicted loading is simply the
predicted number of 18-Kip ESALs
that the pavement will experience
over its design lifetime.
The reliability of the pavement
design-performance process is
the probability that a pavement
section designed using the
process will perform
satisfactorily over the traffic and
environmental conditions for the
design period (AASHTO, 1993)
Pavement structure
The pavement structure is
characterized by the Structural
Number. The structural number, SN,
represents the overall structural
requirement needed to sustain the
design’s traffic loadings.
INPUTS
Serviceable life
Subgrase support
The difference in present serviceability
index (PSI) between post construction and
end-of-life is the serviceability life. Loss of
serviceability is caused by pavement
roughness, cracking, patching, and rutting.
Subgrade support is characterized by the
subgrade’s resilient modulus(MR).
Intuitively, the amount of structural
support offered by the subgrade should
be a large factor in determining the
required pavement structure.
STRUCTURAL
NUMBER
Function
Relationship to Pavement Layers
Coefficients
FUNCTION
The primary purpose of any pavement design is to protect the subgrade
soil from the stresses due to the loading, as well as penetration of
surface water into the subgrade soil. Structural number of a pavement is
defined as a criterion to measure the ability of pavement to withstand
the applied load.
The structural number of a pavement is a function of type, thickness, and
drainage capability of different materials used in the pavement structure.
The weaker the subgrade soil the higher the required structural number
will be for the same loading and climatic conditions.
RELATIONSHIP TO
PAVEMENT LAYERS
As previously mentioned, there are many pavement material combinations and
thicknesses that will provide satisfactory pavement service life. The following
equation can be used to relate individual material types and thicknesses to the
structural number:
SN = a 1 D 1 + a 2D2 M2 + a3 D3 M 3+ .....
Where:
a 1 , a2 , a3 = structural-layer coefficients of the wearing
surface, base, and subbase layers, respectively
D1 , D2 , D3 = thickness of the wearing surface, base, and
subbase layers in inches, respectively, and
drainage coefficients for the base and subbase,
M2 , M3 =
respectively.
COEFFICIENT
STRUCTURAL-LAYER COEFFICIENT
Since the layer coefficient represents
the strength of the material, this is the
primary variable that factors in the
type of material you plan to use for
each layer.
For design purposes, layer coefficients
are typically determined empirically
based on the performance of the
material.
COEFFICIENT
DRAINAGE COEFFICIENT
A drainage coefficient is a value assigned
to a pavement layer that represents its
relative loss of strength due to drainage
characteristics and exposure to moisture
saturation. A value of 1.0 for a drainage
coefficient represents a material with
good drainage characteristics (a sandy
material).
Assume a value of SN
Let SN = 4
Convert the given loads into 18-Kip ESAL
For cars, pickups, light vans; 18-Kip ESAL = 0.0004
2-kip single-axle equivalent = 0.0002
For single-unit truck, 18-Kip ESAL = 2.131
8-kip single-axle equivalent = 0.041
22-kip single-axle equivalent = 2.090
10-kip single-axle equivalent = 0.102
For tractor semi-trailer truck, 18-Kip ESAL = 0.928
16-kip tandem-axle equivalent = 0.057
44-kip triple-axle equivalent = 0.769
Use :
Table 4.1 for single-axle equivalent
Table 4.2 for tandem-axle equivalent
Table 4.3 for triple-axle equivalent
Solve for Total 18-Kip ESAL, W18
0.0004 x 30,000 + 2.131 x 1000 + 0.928 x 350 = 2467.8 18-Kip ESAL (Daily)
W18 = 2467.8 x 365 x 10 = 9,007,470 18-kip ESAL
Solve for SN
ZR = - 1.645
SN = 3.94
So = 0.4
PSI = 4.2 - 2.5 = 1.7
Solve for base thickness, D2
a 1 = 0.44
D = 10.0 inches
a 3 = 0.11
M3 = 1.0
a 2 =30.20
M2 = 1.0
D1 = 4.0 inches
SN = a 1 D 1 + a 2D2 M2 + a3 D3 M 3+ .....
3.94 = 0.44(4) + 0.20D2(1.0) + 0.11(10.0)(1.0)
D2 = 5.4 = 5.5 inches
RIGID PAVEMENT
PRINCIPLES OF
RIGID PAVEMENTS
What is rigid pavement?
Composition and structure of rigid pavement
WHAT IS RIGID
PAVEMENT?
Rigid pavements support loads through rigidity and high
modulus of elasticity of concrete slab.
Rigid pavements are constructed of Portland cement
concrete slabs resting on a prepared sub-base of
granular material or directly on a granular subgrade.
COMPOSITION OF
RIGID PAVEMENT
The reinforcement is provided in the slab depending upon the soil
strength and loading conditions.
The strength of Rigid pavement is mostly depending upon the concrete slab so, it
should be laid strongly while the bottom layers are constructed using low cost
materials to make it economical.
TYPICAL RIGID
PAVEMENT STRUCTURE
CONCRETE
PAVEMENT
This is also called as surface course or
concrete slab
It is water resistant and prevents the water
infiltration into the base course.
It offers friction to the vehicles to provide
skid resistance.
Concrete slab laying
BASE COURSE
This is also called as base course or granular
base or stabilized base
This course helps the surface course to take
additional loads
It provides stable platform to construct rigid
pavement
Laying of base course
SUBBASE
COURSE
This is also called as Granular Subbase or
Stabilized Subbase Course
Its primary function is to provide support for
the top layers and it also serves as frost
action controller and prevents the intrusion
of fines from subgrade to top layers
Laying of subbase course
SUBGRADE SOIL
The subgrade is nothing but the existing soil
layer which is compacted using equipment to
provide stable platform for rigid pavement.
The subgrade soils are subjected to lower
stresses than the top layers since the
stresses will reduce with depth
Preparing subgrade soil
TRADITIONAL AASHTO
RIGID-PAVEMENT
DESIGN PROCEDURE
1. Develop effective Modulus of Subgrade Reaction
(k-value)
2. Determining the required slab thickness
1. DEVELOP EFFECTIVE MODULUS
OF SUBGRADE REACTION
(K-VALUE)
MODULUS OF SUBGRADE REACTION
(K-VALUE)
The modulus of subgrade reaction (k) is used as a primary input for rigid
pavement design.
The modulus of subgrade reaction came about because work done by
Westergaard during the 1920s developed the k-value as a spring constant to
model the support beneath the slab
MODULUS OF SUBGRADE REACTION
(K-VALUE)
1. Identify the combinations or levels that are to be
considered
a. Subbase types
b. Subbase thickness
c. Loss of support LS
d. Depth to rigid foundation
MODULUS OF SUBGRADE REACTION
(K-VALUE)
1. he combinations or levels that are to be considered
2. Identify the seasonal roadbed soil resilient modulus values
3. Estimating the effective k-value is to assign subbase elastic
(resilient) modulus values for each season
4. Estimate the composite modulus subgrade reaction for each
season, assuming a semi-infinite subgrade depth (ie depth to
bedrock greater that 10ft)
5. Develop a k-value which includes the effect of a rigid foundation
near the surface
4. Estimate the composite modulus subgrade reaction for each season, assuming a semi-infinite subgrade depth
(ie depth to bedrock greater that 10ft)
a. If the slab is placed directly on the subgrade (ie no subbase), the composite modulus of subgrade
reaction is defined using the following theoretical relationship between k-values from a plate bearing
stress and elastic modulus of the roadbed soil
5. Develop a k-value which includes the effect of a rigid foundation near the surface
a. Note: this step should be disregarded if the depth to a rigid foundation is greater than 10 ft
MODULUS OF SUBGRADE REACTION
(K-VALUE)
6. Estimate the thickness of the slab to get the relative damage in each
season
7. Add all Relative damage and divide the total by the number of
seasonal increments to determine the average, then k-value will be
determined
ROADBED MODULUS
SUBBASE MODULUS
COMPOSITE K-VALUE
K-VALUE ON
RIGID
FOUNDATION
RELATIVE DAMAGE
2. DETERMINING THE REQUIRED
SLAB THICKNESS
BY THE USE OF NOMOGRAPH
SLAB THICKNESS EQUATION
WHERE,
W18 = 18-kip - equivalent single-axle loads,
Estimated future traffic for the performance period
The 18-kip–equivalent single-axle load is the same concept as
discussed for the flexible-pavement design procedure. However,
instead of being a function of the structural number, this value is a
function of slab thickness.
WHERE,
Zr = Reliability (z-statistic from the standard normal curve),
As in flexible-pavement design, the reliability, ZR, is defined as the
probability that serviceability will be maintained at adequate levels
from a user’s point of view throughout the design life of the facility
(the PSI will stay above the TSI).
WHERE,
So = Overall standard deviation of traffic,.
D = PCC slab thickness in inches
TSI = Pavement’s terminal serviceability index,
The pavement’s terminal serviceability index, TSI, is the point at
which the pavement can no longer perform in a serviceable manner,
ΔPSI = Loss in serviceability from the time when the pavement is new
until it reaches its TSI,
ΔPSI = PSI - TSI
WHERE,
S’c = Concrete modulus of rupture in lb/in2
The concrete modulus of rupture, S’c, is a measure of the tensile strength of
the concrete and is determined by loading a beam specimen, at the third
points, to failure.
Cd = Drainage coefficient,
The drainage coefficient in rigid-pavement design, it accounts for the
drainage characteristics of the subgrade. A value of 1.0 for the drainage
coefficient represents a material with good drainage characteristics (such
as a sandy material). Soils with less-than-ideal drainage characteristics
will have drainage coefficients less than 1.0.
WHERE,
J = Load transfer coefficient
The load transfer coefficient, J, is a factor that is used to account for
the ability of pavement to transfer a load from one PCC slab to
another across the slab joints. Many rigid pavements have dowel bars
across the joints to transfer loads between slabs. Pavements with
dowel bars at the joints are typically designed with a J value of 3.2.
Ec = Concrete modulus of elasticity in lb/ in2 , and
The concrete modulus of elasticity, Ec, is derived from the stressstrain curve as taken in the elastic region. Typical values of Ec for
portland cement concrete are between 3 and 7 million lb/in2
k = Modulus of subgrade reaction in lb/in3
PROBLEM SOLVING
PROBLEM
A rigid pavement is to be designed to provide a service life of 20 years and has an initial PSI of
4.4 and a TSI of 2.5. The modulus of subgrade reaction is determined to be 300 lb/in3 . For design,
the daily car, pickup truck, and light van traffic is 20,000; and the daily truck traffic consists of 200
passes of single-unit trucks with single and tandem axles, and 410 passes of tractor semi-trailer
trucks with single, tandem, and triple axles. The axle weights are
Reliability is 95%, the overall standard deviation is 0.45, the concrete’s modulus of elasticity is 4.5
million lb/in2 , the concrete’s modulus of rupture is 900 lb/in2 , the load transfer coefficient is 3.2,
and the drainage coefficient is 1.0. Determine the required slab thickness.
GIVEN
20 yrs life span
For design
the daily car, pickup truck, and light van traffic is
20,000;
the daily truck traffic consists of 200 passes of
single-unit trucks with single and tandem axles,
410 passes of tractor semi-trailer trucks with single,
tandem, and triple axles.
W18 = ?
PSI = 4.4
TSI = 2.5,
ΔPSI = 1.9
ZR = -1.645
So = 0.45
S’c = 900 lb/in2
Ec = 4.5 million lb/in2
Cd = 1.0
J = 3.2
k = 300 lb/in3
SOLUTION
Step 1 - Typical assumption for slab thickness D = 10inches
Step 2 - Determine the axle equivalent factor - 18-kip ESAL
For cars, pickups, and light vans is
2-kip single-axle equivalent = 0.0002 (Table 4.6)
This gives an 18-kip ESAL total of 0.0004 for each vehicle.
For single-unit trucks,
10-kip single-axle equivalent = 0.081 (Table 4.6)
22-kip tandem-axle equivalent = 0.305 (Table 4.7)
This gives an 18-kip ESAL total of 0.386 for single-unit trucks
For tractor semi-trailer trucks,
12-kip single-axle equivalent = 0.175 (Table 4.6)
18-kip tandem-axle equivalent = 0.132 (Table 4.7)
50-kip triple-axle equivalent = 3.020 (Table 4.8)
This gives an 18-kip ESAL total of 3.327 for tractor semi-trailer
trucks.
Step 3 - Compute for the traffic on this highway
Daily traffic = (0.0004 x 20,000 + 0.386 x 200 +
3.327 x 410) = 1449.27 18-kip ESAL
Traffic (total axle accumulations) over the 20year =
1449.27 x 365 x 20 = 10,579,671 18-kip ESAL
W18 = 10,579,671 18-kip ESAL
SOLUTION
Step 4 - Compute for slab thickness, D
SOLUTION
Step 4 - Compute for slab thickness, D
SOLUTION
Step 5 - Determine the axle equivalent factor - 18-kip ESAL using D = 9
For cars, pickups, and light vans gives
2-kip single-axle equivalent = 0.0002 (Table 4.6)
This gives an 18-kip ESAL total of 0.0004 (same as before) for each vehicle.
Step 6 - Compute for the traffic on
this highway
Daily traffic = (0.0004 x 20,000 +
0.390 x 200 + 3.249 x 410) = 1418.09
18-kip ESAL
For single unit trucks,
10-kip single-axle equivalent = 0.082 (Table 4.6)
22-kip tandem-axle equivalent = 0.308 (Table 4.7)
Traffic (total axle accumulations)
This gives an 18-kip ESAL total of 0.390 (up from 0.386) for single-unit trucks. over the 20-year =
1418.09 x 365 x 20 = 10,352,057 18-kip
For tractor semi-trailer trucks,
ESAL
12-kip single-axle equivalent = 0.176 (Table 4.6)
18-kip tandem-axle equivalent = 0.133 (Table 4.7)
D = 9 inches
50-kip triple-axle equivalent = 2.940 (Table 4.8)
W18 = 10,352,057 18-kip ESAL
This gives an 18-kip ESAL total of 3.249 (down from 3.327) for tractor semitrailer trucks.
D = 10 inches
W18 = 10,579,671 18-kip ESAL
MEASURING PAVEMENT
QUALITY AND
PERFORMANCE
1. International Roughness Index
2. Friction Measurements
3. Rut Depth
4. Cracking
5. Faulting
6. Punchouts
MEASURING PAVEMENT
QUALITY AND PERFORMANCE
The design procedure for pavements originally focused on the pavement serviceability index (PSI) as a
measure of pavement quality. However, the pavement serviceability index is based on the opinions of a
panel of experts which can introduce some variability into their determination.
As a result, efforts have been undertaken to develop quantitative measures of pavement condition that
provide additional insights into pavement quality and performance and that correlate with the traditional
pavement serviceability index.
1. INTERNATIONAL ROUGHNESS INDEX (IRI)
The International Roughness Index (IRI) has become the most popular
measure for evaluating the condition of pavements. The IRI evolved out of a
study commissioned by the World Bank [Sayers et al., 1986] to establish
uniformity of the physical measurement of pavement roughness. The IRI is
determined by measuring vertical movements in a standardized vehicle’s
suspension per unit length of roadway. Units of IRI are reported in inches
per mile (in/mi).
1. INTERNATIONAL ROUGHNESS INDEX (IRI)
The higher the value of the IRI, the rougher the
road. Tables 4.11 and 4.12 provide IRI and PSI
values corresponding to what is considered poor,
mediocre, fair, good, and very good for Interstate
and non-Interstate highways. due to the higher
design standards and performance expectations,
interstate highways are held to a higher standard
for fair, mediocre, and poor pavement
assessments.
2. FRICTION MEASUREMENT
Surface friction is critical because low friction values can increase stopping distances and the
probability of accidents. Given the variability of pavement surfaces, weather conditions, and tire
characteristics, determining pavement friction over the range of possible values is not an easy
task. To estimate friction, a standardized test is conducted under wet conditions using either a
treaded or smooth tire. Although other speeds are sometimes used, the standard test is
generally conducted at 40 mi/h using a friction-testing trailer in which the wheel is locked on
the wetted road surface, and the torque developed from this wheel locking is used to measure a
friction number.
3. RUT DEPTH
Rut depth, which is a measure of pavement surface deformation in
the wheel paths, can affect roadway safety because the ruts
accumulate water and increase the possibility of vehicle
hydroplaning . Because of its potential impact on vehicle control,
rut depths are regularly measured on many highways to
determine if pavement rutting has reached critical values that
would require resurfacing or other pavement treatments.
Usually, rut depths are considered unacceptably high when their
values reach between 0.5–1.0 inches, indicating that corrective
action is warranted.
Primary cause of rutting: 1. Asphalt layer problem, 2. Structural
layer Problem, 3. Weak subgrade layer problem
4. CRACKING
For flexible pavements, four types of cracking are usually monitored: longitudinal fatigue
cracking, transverse cracking, alligator cracking, and reflection cracking.
ALLIGATOR CRACKING
LONGITUDINAL FATIGUE
CRACKING
TRANSVERSE
CRACKING
REFLECTION CRACKING
LONGITUDINAL FATIGUE CRACKING
Longitudinal-fatigue cracking is a surface-down
cracking that occurs due to material fatigue in the
wheel path. Such cracking can accelerate over time
and require significant repairs to protect against
water penetration into the flexible pavement
structure.
TRANSVERSE CRACKING
Transverse cracking is generally the result of low
temperatures that cause fractures across the traffic lanes
(resulting in an increase in pavement roughness).
For rigid pavements, transverse cracking is a common
measure of pavement distress. Such cracking can be the result
of slab fatigue and can be initiated either at the surface or
base of the slab. The spacing and width of transverse cracks,
and the potential impact of severe cracking on the structural
integrity of the pavement, are critical measures of rigidpavement distress.
ALLIGATOR-FATIGUE CRACKING
Alligator-fatigue cracking is a consequence of
material fatigue in the wheel path, generally starting
from the bottom of the asphalt layer. Such material
fatigue creates a patch of connected cracks that
resembles the skin of an alligator (as with other
types of cracks, these can accelerate quickly over
time and generate the need for maintenance to
protect the integrity of the pavement structure).
REFLECTION CRACKING
Reflection cracking occurs when hot-mix asphalt
(HMA) overlays are placed over exiting pavement
structures that had alligator-fatigue cracking, or
other indications of pavement distress, and these old
distresses manifest themselves in new distresses in
the overlay. This results in surface cracking that
increases surface roughness and the need for
maintenance to protect water intrusion into the
pavement structure.
5. FAULTING
Faulting is an indicator of erosion or fatigue of the layers beneath
the slab and reflects a failure of the load-transfer ability of the
pavement between adjacent slabs.
Faulting is associated with increased roughness and will be
reflected in International Roughness Index measurements.
6. PUNCHOUTS
Fatigue damage at the top of the slab is often measured by
punchouts, which occur when the close spacing of transverse
cracks cause in high tensile stresses that result in portions of the
slab being broken into pieces. Punchouts are associated with
increased roughness and are reflected in International Roughness
Index measurements.
MECHANISTICEMPIRICAL
PAVEMENT DESIGN
Pavement Design
Mechanistic-Empirical Pavement Design
Software
Advantages
PAVEMENT DESIGN
Selection of materials and layer thicknesses so that the
pavement can withstand the traffic, environmental, and location
issues.
Process of developing the most economical combination of
pavement layers with respect to both material type and thickness
to suit the soil foundation and the traffic load during the design
period.
PAVEMENT DESIGN
Pavement design life is a term that engineers
use when they’re planning to build a new road
or maintain an existing roadway
MECHANISTIC-EMPIRICAL
PAVEMENT DESIGN
MECHANISTIC APPROACH
- Seeks to explain pavement responses
only by reference to physical causes
- Use of mathematical model
EMPIRICAL APPROACH
-Dependent onexperiments and
experience or a combination of both
-Observed performance to determine
relationships
MECHANISTIC-EMPIRICAL
PAVEMENT DESIGN
The design of the pavement structure is initially assumed on a trial
basis, along with inputs for traffic and climate.
Uses software to calculate all the data needed to design a pavement
that will be used for long and be an effective structure to use.
MEPDG
Mechanistic-Empirical Pavement Design Guide (MEPDG) is to provide
the highway community with a state-of-the-practice tool for the design
and analysis of new and rehabilitated pavement structures.
Mechanistic-Empirical design is an iterative process. Evaluating
alternatives helps increase confidence that the pavement design that is
ultimately selected is optimal for the circumstances.
MEPDG
Process analyzes the pavement design with respect to
performance indicators that reflect the projected impact of
stresses and strains on the pavement over time.
These performance indicators include pavement
roughness for all pavements, quantified according to the
International Roughness Index (IRI), along with specific
indicators according to the pavement type.
MEPDG
International Roughness Index (IRI ) – a measurement
of the roughness of a pavement, expressed as the ratio of
the accumulated suspension motion to the distance
traveled obtained from a mathematical model of a
standard quarter car traversing a measured profile at a
speed of 50mi/hr (80 km/h).
AASHTOWARE PAVEMENT ME DESIGN
It calculates pavement responses (stresses, strains, and deflections)
based on traffic, climate, and materials parameters to predict the
progression of key pavement distresses and smoothness loss over
time for asphalt concrete (AC) and portland cement concrete (PCC)
pavements.
Provides tools to optimize pavement designs based on given
requirements allowing the user to evaluate and fine-tune the design.
ADVANTAGES
It can be used for both existing pavement rehabilitation and new
pavement construction
It accommodates changing load types
It can better characterize materials allowing for:
- Better utilization of available materials
- Accommodation of new materials
- An improved definition of existing layer properties
ADVANTAGES
It uses material properties that relate better to actual pavement
performance
It provides more reliable performance predictions
It better defines the role of construction
It accommodates environmental and aging effects on materials
Reduce early failures and increase pavement life
THANK
YOU!
MECHANISTICEMPIRICAL
PAVEMENT DESIGN
Pavement Design
Mechanistic-Empirical Pavement Design
Software
Advantages
PAVEMENT DESIGN
Selection of materials and layer thicknesses so that the
pavement can withstand the traffic, environmental, and location
issues.
Process of developing the most economical combination of
pavement layers with respect to both material type and thickness
to suit the soil foundation and the traffic load during the design
period.
PAVEMENT DESIGN
Pavement design life is a term that engineers
use when they’re planning to build a new road
or maintain an existing roadway
MECHANISTIC-EMPIRICAL
PAVEMENT DESIGN
MECHANISTIC APPROACH
- Seeks to explain pavement responses
only by reference to physical causes
- Use of mathematical model
EMPIRICAL APPROACH
-Dependent onexperiments and
experience or a combination of both
-Observed performance to determine
relationships
MECHANISTIC-EMPIRICAL
PAVEMENT DESIGN
The design of the pavement structure is initially assumed on a trial
basis, along with inputs for traffic and climate.
Uses software to calculate all the data needed to design a pavement
that will be used for long and be an effective structure to use.
MEPDG
Mechanistic-Empirical Pavement Design Guide (MEPDG) is to provide
the highway community with a state-of-the-practice tool for the design
and analysis of new and rehabilitated pavement structures.
Mechanistic-Empirical design is an iterative process. Evaluating
alternatives helps increase confidence that the pavement design that is
ultimately selected is optimal for the circumstances.
MEPDG
Process analyzes the pavement design with respect to
performance indicators that reflect the projected impact of
stresses and strains on the pavement over time.
These performance indicators include pavement
roughness for all pavements, quantified according to the
International Roughness Index (IRI), along with specific
indicators according to the pavement type.
MEPDG
International Roughness Index (IRI ) – a measurement
of the roughness of a pavement, expressed as the ratio of
the accumulated suspension motion to the distance
traveled obtained from a mathematical model of a
standard quarter car traversing a measured profile at a
speed of 50mi/hr (80 km/h).
AASHTOWARE PAVEMENT ME DESIGN
It calculates pavement responses (stresses, strains, and deflections)
based on traffic, climate, and materials parameters to predict the
progression of key pavement distresses and smoothness loss over
time for asphalt concrete (AC) and portland cement concrete (PCC)
pavements.
Provides tools to optimize pavement designs based on given
requirements allowing the user to evaluate and fine-tune the design.
ADVANTAGES
It can be used for both existing pavement rehabilitation and new
pavement construction
It accommodates changing load types
It can better characterize materials allowing for:
- Better utilization of available materials
- Accommodation of new materials
- An improved definition of existing layer properties
ADVANTAGES
It uses material properties that relate better to actual pavement
performance
It provides more reliable performance predictions
It better defines the role of construction
It accommodates environmental and aging effects on materials
Reduce early failures and increase pavement life