Highway & Airport Engineering

CT 231
Dr. Mohamed Reda
Department of Civil Engineering
Ain Shams University
mohamedahmedreda@yahoo.com

Spring 2019
 Overall aims of course
To provide the basics of highway engineering this
includes:-
- Sight distance.
- Horizontal alignment, vertical alignment.
- Intersections design.
- Soil classification, soil strength.
- Pavement response under loads.
- Structural design of flexible pavement.
- Asphalt materials and design of hot asphalt
mixtures.
 Intended learning outcomes of course
a. Knowledge and understanding
a1. Knowledge of sight distance, horizontal alignment, vertical alignment,
and intersections design.
a2. Knowledge of soil classification, material strength, pavement response
under loads, and structural design of flexible pavement
b. Intellectual skills: Learn the students to:-
b1. Calculate the stopping and sight distance on highways
b2. Select appropriate horizontal alignment according to the standard
specifications
b3. Select appropriate vertical alignment according to the standard
specifications
b4. Choose the suitable type of intersection
b5. Characterize the different soils according to measurable properties
b6. Evaluate the soil as subgrade
b7. Evaluate the pavement materials
b8. Calculate the pavement responses under the loads
b9. Prepare the required data for design of flexible pavement
 Intended learning outcomes of course (cot.)
c. Professional and practical skills
c1. Studying the sight distance on all geometric elements of highways
c2. Design of the Horizontal Curves
c3. Design of the Vertical Curves
c4. Design of At-Grade Intersection
c5. Classifying the soil of subgrade and the other courses
c6. Evaluate the pavement responses under the different load
configurations
c7. Design of flexible pavement
c8. Conducting the quality control tests of pavement materials
c9. Design of Hot Asphalt Mixtures
d. General and transferable skills
d1. Preparing design reports for highways projects
d2. Preparing study plan for any of the highways problems
 Teaching and learning methods

1. 36 one-hours lectures.

2. 24 one-hours problems classes and tutorials.

3. 13 one-hour practical tests.

 Student assessment methods

1. Semester first mid term exam, to asses the

dynamics of trains.

2. Semester second mid term exam, to asses the

track alignment.

3. Final written examination, to asses the whole

course
 Weighting of assessments

• First Mid-Term Examination 20%

• Second Mid-Term Examination 20%
• Final-term Examination 40%
• Semester Work 20%
• Total 100%
 Course schedule
Topic No. of
week hours
Lecture Tutorial practical

Introduction to Geometric and Structural Design of

1 6 3 2 1
Highway
2 Sight Distance 6 3 2 1
3 Soil Classification 6 3 2 1
4 Horizontal Alignment 6 3 2 1
5 Soil Strength and Soil Stabilization 6 3 2 1
Semester first exam
6 6 exam 2 1
Horizontal Alignment
Pavement Response under Load (Stress and
7 6 3 2 1
Deflection)
8 Vertical Alignment 6 3 2 1
9 Vertical curves 6 3 2 1
Semester second exam
10 Specifications o Road Layers or Structural Design 6 3 exam 1

Design of Intersection and Sight Distance at

11 6 3 2 1
Intersection
12 Design of Flexible Pavement 6 3 2 1
Asphalt Materials and Design of Hot Asphalt Mixtures
13 6 3 2 1
14 Final Exam 2 - - -
 List of references

1. Course notes
Available (handed to students part by part).

2. Text books
Highway Engineering Volume 1 and Volume 2, Gerber.
 Important Notes
– Students should not attend in sections other than their own.
– Considerable percentage of the mark will be deducted for messy
assignments.
– Students will be expected to submit cover page to the sheet with
name, bench number, sheet number and title.
– Due dates will be strict. Any delay in sheets (even the next day)
will cause deduction in marks. 20% can be deducted per day late to
a maximum of 60% deduction.
– Copied sheets will be monitored and marks will be deducted.
– Students are expected to attend both lectures and sections.
-Not all subject material is covered in both and students are
responsible for all material. Sections will mainly focus on problem
solving.
– Tables/ Figures handbook is available in the Department and
needs to be with the students in all lectures and sections.
 Chapter (1)

Introduction to Geometric and Structural

Design of Highway
 Introduction and Course Overview
Employment in Transportation:
– Transportation represents one of the broadest opportunities for
employment. It involves many disciplines and modes.
– As a civil engineer you can work in planning, design, construction,
operation, and maintenance of transportation systems.
- You consider also the efficiency of the system in an economic point of
view, and the external requirements concerning energy, air quality, safety,
congestion, noise, and land use.
 Opportunities for engineering careers in transportation
Careers related to civil engineering include:-
• Planning: selection of projects for design and construction through
defining the problem, gathering and analyzing data, and evaluating
alternatives based on social, economic, and environmental considerations

• Design: designing all physical components to ensure smooth, efficient,

and safe operation
• Construction: use of machinery and labor and managing time and
Resources

• Traffic operation: integration of vehicle, driver, and pedestrian

characteristics to improve the safety and capacity of roads

• Maintenance: involves all work necessary to ensure that the highway

system is kept in proper working order and includes maintenance
What is Transportation?
- Transportation is concerned with the movement of goods and
people from one location to another in an environmentally
conscience manner.
– Transportation systems are now complex networks of modes and
Facilities.
– Highway transportation is one of the most important components
of the overall transportation system.

Main Components of the Transportation System

Where are we (Highway Engineering)
in the big picture
A-Geometric Design Overview
Highway Design Control Factors
1. Highway Function
2. Design speed of the facility
3. Design vehicle (i.e., the largest vehicle that is likely to use the
facility with
considerable frequency
4. Acceptable degree of congestion (LOS)
5. Percentage of Heavy Vehicles
Road Classification
– The orderly grouping of roads into systems according to the type
and degree of service they provide to the public
– Many classification systems have been developed be based on:-
 Function
 Median
 Location (rural or urban)
 Road service
 Design speed
 Local Streets
• To provide land access

• Have “Stop”, “Yield”, or signalized

controls

• Connect other locals and collector

streets

• Account for about 70% of the total

length of urban streets
 Collector Streets
• Provide both traffic service and land access
• Connect between local and arterial streets
• Design yearly traffic volume: 1,000 to 12,000 vpd
• Have more than 2 lanes and can be divided

Representative collector in a rural area Representative collector in a urban area

 Arterial Streets
• Carry large volumes of traffic moving at medium to high speeds

• Serve the major traffic flows between the principal traffic

generators and connect between collectors and freeways

• Design yearly traffic volume: 5,000 to 30,000 vpd

• May have interchanges

Representative urban arterial

 Urban Freeway
• Class for urban roads only

• Uninterrupted flow except at signals

• Speeds ≥ 80 km/h

Representative urban freeway

Roadway Function
– The first step in the design process is to define the
function that the facility is to serve.
– Roadway systems provide two fundamental functions:-
Mobility & Accessibility
 Mobility: The ability to move goods and passengers to their
destination. (in a reasonable time)
 Accessibility: the ability to reach desired destination.
Arterials
Higher degrees of Mobility Low degree of access
Collectors
Balance between Arterials and Collectors
Locals
Lower degrees of mobility High degree of access
Road cross section element
B-Structure Design Overview
Main Classes of Pavements
Flexible Pavement
Rigid Pavement
Source of Asphalt
Part (A): Geometric Design
Chapter (2)

Sight Distance
 Introduction
• Sight distance is a fundamental criterion in the
design of any road or street.
• It is essential for the driver to be able to perceive
hazards on the road, with sufficient time in hand
to initiate any required action safely.
• On a two-lane two-way road it is also necessary
for him or her to be able to enter the opposing
lane safely while overtaking.
Perception-Reaction Process
–PIEV is important for safety of cars, drivers, and
pedestrians.

- PIEV distance = PIEV time × Speed

- AASHTO (American Association of State Highway

and Transportation Officials) recommended 2.5
sec for stopping sight distance.
 Example
• A driver with a PIEV time of 2.5 sec is driving at
100 km/h when she observes that an accident
has blocked the road ahead.
• Determine the distance the vehicle would move
before the driver could activate the brakes.
Table of length equivalent units
Sight Distance Classification
1- Stopping Sight Distance (SSD)
1- Stopping Sight Distance (SSD)
Example
A student trying to test the braking ability of her
car determined that she needed 18.5 ft more to
stop her car when driving downhill on a road
segment of 5% grade than when driving downhill
at the same speed along another segment of 3%
grade.
Determine the speed at which the student
conducted her test and the braking distance on
the 5% grade if the student is traveling at the test
speed in the uphill direction.
Solution
Example
A motorist traveling at 65 mi/h on an expressway
intends to leave the expressway using an exit
ramp with a maximum speed of 35 mi/h.
At what point on the expressway should the
motorist step on her brakes in order to reduce her
speed to the maximum allowable on the ramp just
before entering the ramp, if this section of
the expressway has a downgrade of 3%?
Solution
Example
A motorist traveling at 55 mi/h down a grade of 5%
on a highway observes a crash ahead of him,
involving an overturned truck that is completely
blocking the road.
If the motorist was able to stop his vehicle 30 ft
from the overturned truck, what was his distance
from the truck when he first observed the crash?
Assume perception reaction time =2.5 sec
Solution
2- Passing Sight Distance (PSD)

– The distance required by an overtaking vehicle on a

two-lane, two-way highway to pullout, pass, and return
to the driving lane

– Percentage of length with enough PSD is a measure

of quality of two-lane highways
Elements of and Total Passing Sight Distance on Two-Lane Highways
3- Sight Distance at Horizontal Curves
Example
Solution
Example
A horizontal curve with a radius of 800 ft connects
the tangents of a two-lane highway that has a
posted speed limit of 35 mi/h. If the highway
curve is not super elevated, e =0.
Determine the horizontal sightline offset (HSO)
that a large billboard can be placed from the
centerline of the inside lane of the curve, without
reducing the required SSD. Perception-reaction
time is 2.5 sec, and f 0.35.
Solution
4-Decision Sight Distance (DSD)
• Decision Sight Distance (DSD) defined by
AASHTO as the “distance required for a driver to
detect an unexpected or otherwise difficult-to-
perceive information source or hazard in a
roadway environment that may be visually
cluttered, recognize the hazard of its threat
potential, select an appropriate speed and path,
and initiate and complete the required safety
maneuvers safely and efficiently.”
-The decision sight distances depend on the type
of maneuver required to avoid the hazard on the
road, and also on whether the road is located in a
rural or urban area.
-Table below gives AASHTO’s recommended
decision sight distance values for different
avoidance maneuvers, which can be used for
design.
Decision Sight Distances for Different Design Speeds and
Avoidance Maneuvers
 Chapter (3)
Horizontal Alignment
 Horizontal Alignment
Horizontal alignment consists of straight section (tangents) connected by horizontal curves.
Horizontal curves are used in horizontal planes to connect two straight tangent sections.
Horizontal Curve Elements – (1)Simple Curves
Minimum Curvature of a Horizontal Curve
Example

The intersection angle of a 4° curve is 55°25, and

the PC is located at station 23844.75.
Determine the length of the curve, the station of
the PT, the deflection angles and the chord lengths
for setting out the curve at whole stations from the
PC.
Solution
Example
An existing horizontal curve on a highway has a
radius of 80 m which restricts the maximum speed
on this section to only 60% of the design speed of
the highway.
If the curve is to be improved so that the
maximum speed will be as that of the design speed
of the highway, determine the minimum radius of
the new curve. Assume the coefficient of side
friction is 0.15 and the rate of super elevation is
0.08 for both the existing curve and the new curve
to be designed.
Max Super elevation (e)
Controlled by 4 factors:-
1. Weather conditions in area (amount of ice and
snow)
2. Type of terrain (flat, rolling, mountainous)
3. Highway Location (rural or urban)
4. Frequency of slow moving vehicles (may be affected
by higher super elevation rates:-
o Highest in common use = 10%, 12% with no ice and
snow.
o 8% is logical maximum to minimize slipping by
stopped Vehicles, considering snow and ice.
 Horizontal Curve Elements – (2) Spiral (transition) curves
Spiral (transition) curves are curves with changing radii, and are
placed between tangents and circular curves or between two
successive circular curves.
Advantages
1. Provides a vehicle path that gradually increases or
decreases the radial force as the vehicle enters or
leaves a curve. (lateral force increases and decreases
gradually)
2. Provides location for super elevation runoff (not
part on tangent/curve)
3. Aesthetic
Development of Super elevation
– Highway cross section on straight segments is “normal crown”.

– On curved segments, it is “super elevated”.

– To change a normal crown section into a super elevated

section, a Super elevation runoff length is required.

– Super elevation runoff length equals the length of the spiral

curve.

– If no spiral curve is used, super elevation runoff length is

distributed as 60% on tangent and 40% on curve.

– Super elevation can be attained by rotating crowned

pavement about the centerline(C.L).
Super elevation
Example
Solution
Example
Solution
 Chapter (4)
Vertical Alignment
Vertical Curve
Values of K for Crest Vertical Curves Based on Stopping Sight Distance

Values of K for Sag Vertical Curves Based on Stopping Sight Distance

Example
Solution
Example
Solution
Example
Design a crest vertical curve that will connect a
highway segment with a 3% grade to an adjoining
segment with a -1% grade. Assume that the
design speed is for the highway is 100 km/h.
Example
Compute curve elevations and offsets from
tangents at +25 m interval points for a 350m
vertical curve joining a +2.7% grade with a –1.5%
grade. Assume the P.V. I. is at station 150+00 and
elevation 25.00 m. Results should be in tabular
form, with columns for stations, tangent
elevations, offsets, and curve elevations starting at
the BVC and ending at the EVC of the curve.
 Chapter (5)
Intersections design
 Intersections criteria
Highway engineers intersections design has the following
criteria: -
• Provide adequate sight distance – for approach and
departure maneuvers

• Minimize turning and through conflicts

• Avoid geometry (sharp curves/steep grades) that

adversely impact acceleration/deceleration
 Design Objectives
“To reduce the severity of potential conflicts
between motor vehicles, pedestrians, and facilities
while facilitating the convenience, ease, and
comfort of people traversing the intersection.”
AASHTO
Provide ease/control of access consistent with the
function of intersecting roadways

125
 Intersections
 More complicated area for
drivers
 Main function is to provide
for change of direction
 Source of congestion in urban
areas
 Concern for safety (fender
benders in urban, fatals in
rural)

126
 Intersection conflict points
There are three types of c as follows:-
- Merging points
- Diverging points
- Crossing points
 Types of Intersections
 Grade separated with ramps (freeway interchange)
 Grade separated without ramps (over or underpass with
no access)
 At-grade
 Conventional
 Roundabouts
 New concepts (e.g., “continuous flow”)
At Grade Intersection
Grade Separation Intersection.
 Operational Requirements

 Provide adequate sight distance – for approach and

departure maneuvers.

 Minimize turning and through conflicts.

 Provide natural paths for permitted movements

 Avoid geometry (sharp curves/steep grades) that

complicates the driving task and adversely impacts
acceleration or deceleration
 Intersection Sight Distance – ISD

- Definition: Required ISD is the length of cross

road that must be visible such that the driver of a
turning/crossing vehicle can decide to and
complete the maneuver without conflict with
vehicles approaching the intersection on the cross
road.

- ISD allows drivers to have an unobstructed view

of intersection.
 Adequate ISD
 Sight Triangle – area free of obstructions necessary to
complete maneuver and avoid collision – needed for
approach and departure (from stop sign for example) .

 Allows driver to anticipate and avoid collisions

 Allows drivers of stopped vehicles enough view of the

intersection to decide when to enter
 Sight Triangle
 Area free of obstructions necessary to complete
maneuver and avoid collision – needed for
approach and departure (from stop sign for
example).

 Consider horizontal as well as vertical, object

below driver eye height may not be an
obstruction.

 AASHTO assumes 3.5’ above roadway.

 Sight triangles
• There are two types of sight triangles, approach sight
triangles and departure sight triangles.
• The approach sight triangle allows for the drivers on both
the major roads and minor roads to see approaching
intersecting vehicles in sufficient time to avoid a potential
collision by reducing the vehicle’s speed or by stopping.
• The decision point on a minor road of an uncontrolled or
yield control intersection is the location where the minor
road driver should start his/her braking or deceleration
maneuver to avoid a potential conflict with an
approaching major road vehicle.
• The departure-sight triangle allows for the driver of a
stopped vehicle on the minor road to enter or cross the
major road without conflicting with an approaching
vehicle from either direction of the major road.
Sight Triangles at Intersections
Sight Distance Obstruction

Hidden Vehicle
 ISD Cases
A. No control: vehicles adjust speed.

B. Stop control: where traffic on minor roadway must

stop prior to entering major roadway.

C. Yield control: vehicles on minor roadway must yield

to major roadway traffic.

D. Signal control: where vehicles on all approaches are

required to stop by either a stop sign or traffic signal.

E. All way stop: Stopped: major roadway left-turn

vehicles – must yield to oncoming traffic
 Case A– No Control
 Minimum sight triangle sides = distance traveled in
3 seconds (design or actual?) = 2 seconds for P/R
and 1 second to actuate brake/accel.

 Assumes vehicles slow ~ 50% of midblock running

speed .
 Case A– No Control
• In this situation, the intersection is not controlled by a yield sign,
stop sign, or traffic signal, but sufficient sight distance is provided
for the operator of a vehicle approaching the intersection to see a
crossing vehicle and if necessary to adjust the vehicle’s speed so
as to avoid a collision.

• This distance must include the distance traveled by the vehicle

both during the driver’s perception reaction time and during
brake actuation or the acceleration to regulate speed.

• In this situation, we assumes vehicles slow ~ 50% of midblock

running speed.
 Case A– No Control
 Prefer appropriate SSD on both approaches
(minimum really)

 Provided on lightly traveled roadways

 Provide control if sight triangle not available

 Assumes vehicle on the left yields to vehicle on the

right if they arrive at same time.
 Can use
table or
graph

Modify for grade

142
 using similar triangles

can set critical speed to

d
available stopping distance, db  a  a
da  b
Example
Large
Tree 25 mph
72’

47’

50 mph

Is sufficient stopping sight

distance provided?
 Large 25 mph
Tree
b = 72’
db

a = 47’

50 mph da

da
db  a 
da  b
da = 220 feet
 Large 25 mph
Tree
b = 72’
db

a = 47’

50 mph da

da = 220 feet
da
db = 47’ (220’) = 69.9’ db  a 
da  b
220’ – 72’
db = 69.9 feet
corresponds to 15
mph
 Large 25 mph
Tree
b = 72’
db

a = 47’

50 mph da

25 mph > 15 mph, stopping sight

distance is not sufficient for
25 mph
 Example

• A tall building is located 45 ft from the centerline of the

right lane of a local road (b in Figure 7.20) and 65 ft
from the centerline of the right lane of an intersecting
road .
• If the maximum speed limit on the intersecting road is
35 mi/h, what should the speed limit on the local road
be such that the minimum sight distance is provided to
allow the drivers of approaching vehicles to avoid
imminent collision by adjusting their speeds? Approach
grades are 2%.
Solution
 Case B –Sight Distance Requirement for Stop-
Control Intersections on Minor Roads
Three Sub Cases – Maneuvers
 Turn left on to major roadway (clear traffic left,
enter traffic right)
 Turn right on to major roadway (enter traffic from
left)
 Crossing (clear traffic left/right)
Case B –Sight Distance Requirement for Stop-Control Intersections on Minor Roads

When vehicles are required to stop at an intersection, the drivers of

such vehicles should be provided sufficient sight distance to allow
for a safe departure from the stopped position for the three basic
maneuvers that occur at an average intersection.
These maneuvers are:-
• 1. Turning left onto the major road, which requires clearing the
traffic approaching from the left and then joining the traffic
stream on the major road with vehicles approaching from the
right ,Case B1
• 2. Turning right onto the major road by joining the traffic on the
major road with vehicles approaching from the ,Case B2
• 3. Crossing the intersection, thereby clearing traffic approaching
from both sides of the intersection ,Case B3.
Case B1 –Sight Distance Requirement for Stop-Control Intersections on Minor Roads
Example
A minor road intersects a major four-lane
undivided road with a design speed of 65 mi/h.
The intersection is controlled with a stop sign on
the minor road.
If the design vehicle is a single-unit truck,
determine the minimum sight distance required
on the major road that will allow a stopped
vehicle on the minor road to safely turn left if the
approach grade on the minor road is 2%.
Solution
 Case B2 Stopped Vehicle Turning Right into Two-Lane
Major Highway or Right Turn on a Red Signal

The computational procedure used for this case is similar to that for left turns discussed for
Case B1, but the values of the time gap for the minor road vehicle to enter the major road
(tg) are adjusted in consideration of the fact that drivers tend to accept gaps that are slightly
lower than those for left turns. AASHTO suggests that values shown on table of case B1
should be decreased by 1 second.
Case B3 Stopped Vehicle Crossing a Major Highway

Minimum requirements determined for right and left turns as presented for Cases
B1 and B2 will usually satisfy the requirements for the crossing maneuver.
 right turn
and crossing
 Case C - Yield Control
Minor Roadway Yields – must be able to see
left/right – adjust speed – possibly stop

Sight distance exceeds that of stop control

Similar to no-control
 Case C- Yield Control
Drivers on a minor road approaching a yield-controlled intersection
with a major road can enter or cross the intersection without
stopping if the driver does not perceive any conflict with oncoming
major road traffic.

Adequate sight distance on the major road therefore should be

provided for crossing the intersection (Case C1) and for making
right and left turns (Case C2).

For three-leg intersections, only case C2 exists as no through

movement can occur.
 Case C1: Sight Distance Requirement for Crossing a
Yield Controlled Intersection from a Minor Road
• The assumption made to determine the minimum sight distance
• for this maneuver is similar to that used for the no-control maneuver in
Case A, but with the following modifications:
• Drivers on minor roads approaching a yield sign tend to decelerate to
60 percent of the minor road design speed and not 50 percent, as
assumed for the no-control condition.
• The time tg to cross the intersection should include the time taken for
the vehicle to travel from the decision point where the deceleration
begins to where the speed is reduced to 60 percent of the minor road
design speed.
• The vehicle then travels at the reduced speed (60 percent of the minor
road design speed) until it crosses and clears the intersection.
• Based on these assumptions, the length of the sight distance (dISD) on
the major road can be obtained from the following equations:
tg
Example
An urban two-lane minor road crosses a four-lane divided
highway with a speed limit of 55 mi/h. If the minor road has a
speed limit of 35 mi/h and the intersection is controlled by a
yield sign on the minor road, determine the sight distance from
the intersection that is required along the major road such that
the driver of a vehicle on the minor road can safely cross the
intersection.
The following conditions exist at the intersection.
Major road lane width =11 ft
Median width =8 ft
Design vehicle on minor road is a passenger car length =22 ft
Approach grade on minor road 3%.
Solution
tg =ta +(w +La)/0.88vmin
Case C2: Sight Distance Requirements for Turning Right or Left from a
Minor Road at a Yield Controlled Intersection.

• For this maneuver, it is assumed that a driver will reduce his

speed to about 10 mph.
• Based on this assumption, the length of the minor road leg of
the sight triangle is taken as 82 ft.
• The length of the major road leg is computed using the same
principles for the stopped control of Case B1 and B2.
• However, the tg values used are 0.5 seconds higher than those
shown in Table 7.8. Also, adjustment should be made for
major highways with more than two lanes.
• It should be noted that sight distance requirements for yield-
control intersections are usually larger than those for stop
control, which makes it unnecessary to check for the stopped
condition to accommodate those vehicles that are stopped to
avoid approaching vehicles on the major road.
 Case D -Sight Distance Requirements at
Signalized Intersections
The two main requirements at signalized intersections are:-
(1) the first vehicle stopped at the stop line of each approach
should be visible to the driver of the first vehicle stopped on all
other approaches.
(2) adequate sight distance should be provided for left-turning
vehicles to enable drivers of these vehicles to select adequate gaps.
However, when the signals are to be placed in a flashing operation
for all approaches during off-peak periods, then the sight distance
requirements for the appropriate condition of Case B should be
provided.
Similarly, if right turn on red is permitted, then the appropriate sight
requirement for right turns of Case B should be provided.
 Case E -Sight Distance Requirements at All-Way Stop
Controlled Intersections

The only sight distance required in this case is that

the first vehicle stopped at the stop line of each
approach should be visible to the driver of the first
vehicle stopped on all other approaches.
Part (B):Structure Design
Chapter (6)

Soil Classification
AASHTO Soil Classification System
Example
The results of the particle-size analysis of a soil are as follows:-
- Percent passing through the No. 10 sieve =100
- Percent passing through the No. 40 sieve =80
- Percent passing through the No. 200 sieve = 58
- The liquid limit and plasticity index of the minus No. 40 fraction
of the soil are 30 and 10, respectively. Classify the soil by the
AASHTO system.
Solution
Example
• Classifying a Soil Sample Using the AASHTO
Method .The following data were obtained
for a soil sample:-
Solution
Example
Solution
Example

Soil A Soil B
Sieve No 10 75 55%
Sieve No 40 55 40%
Sieve No 200 27 25%
L.L 30 4
P.L 10 NP
Solution
 Chapter (7)
Subgrade Strength tests
 Chapter (8)
Pavement Design
(I) Flexible Pavement
Flexible Pavement Traditional Structure
Example
Solution
Example
Solution
 Structure Number (SN)

R S ESAL Mr
229 ΔPSI SN
Example
Solution
Example
It is required to give full design for the highway flexible
pavement according to the following data:-
 Flexible Pavement
 ESAL = 2 x106
 Asphalt Concrete at 68oF Modulus = 45000psi
 CBR value of base = 100, Mr = 31000psi
 CBR value of sub base = 22, Mr = 13500psi
 CBR of Sub grade = 6
 Reliability (R) = 99%
 Standard Deviation (So) = 0.49
 Pi = 4.5
 Pt = 2.5
233
Solution
 ESAL = 2 x106
 Reliability (R) = 99%
 Standard Deviation (So) = 0.49
 PSI = 4.5-2.5 = 2.0
 a1 = 0.44 (Modulus = 450000psi, AC)
 a2 = 0.14 (CBR = 100,Base)
 a3 = 0.1 (CBR = 22, sub base)
 By using AASHTO graph
SN3 = 4.4 (Mr= 9000 psi)
SN2 = 3.8 (Mr = 13500 psi)
SN1 = 2.6 (Mr = 31000 psi)
234
 Structure Number (SN)
Log (W18) =(ZR * So)+ 9.36*LOG(SN+1)- 0.2+ LOG((P2- P1)/(4.2-
1.5))/(0.4+1094/(SN+1)^5.19)+2.32*LOG(MR)- 8.07

R S ESAL Mr
235 ΔPSI SN
D1 = SN1/a1 =2.6/0.44 = 5.9” (use 6”)
D1* = 6”
SN1*= a1 D1* =0.44 x 6 = 2.64
D2*≥ (SN2-SN1*)/(a2m2)≥(3.8-2.64)/(0.14x0.8)
≥10.36’’ (Use 12’’)
SN2*= 0.14x0.8x12+2.64=1.34+2.64 =3.98
D3* =(SN3-SN2*)/(a3m3)=4.4-(2.64+1.34)/(0.1x0.8)
= 5.25 ’’ (Use 6’’)
SN3*=2.64+1.34+6x0.8x0.1 = 4.46
Asphalt concrete surface = 6”
Granular base = 12”
Sub base = 6”

236
 Chapter (9)
Design of Hot Asphalt Mixtures
Asphalt Concrete Properties
 Stability
• The ability to withstand traffic loads without distortion or
deflection, especially at higher temperatures.

• To get good stability, use strong, rough, dense-graded, cubical

aggregate with just enough binder to coat the aggregate
particles.

• Excess asphalt cement lubricates the aggregate particles and lets

them slide past each other more easily (which reduces stability).

• But a thick asphalt coating provides good flexibility to resist

cracking, which is desirable.
 Workability

• The ability to be placed and compacted with reasonable

effort and without segregation of the coarse aggregate.
•
• Too much asphalt cement makes the mix tender.
• Too little asphalt cement makes it hard to compact.
•
• Too much natural sand can also make the mix tender
because natural sand has smooth, round grains.
 Skid Resistance
• Proper traction in wet and dry conditions.
• To get good skid resistance, use smaller aggregate so
there are lots of contact points, use hard aggregate
that doesn’t polish and make sure you have enough
air voids to prevent bleeding.

• Some states now use an open-graded friction course

(OGFC) that allows water to drain to the sides of the
pavement, eliminating hydroplaning.

• But OGFC is not very durable because of the open

pores.
 Durability
• The ability to resist aggregate breakdown due to
wetting and drying, freezing and thawing, or
excessive inter-particle forces.
• To get good durability, use strong, tough, nonporous
aggregate and enough asphalt cement to
completely coat all of the aggregate particles (to
keep them dry) and fill all of the voids between
particles (to slow the oxidation of the asphalt
cement). But this reduces stability
 Stripping
• Separation of the asphalt cement coating from the
aggregate due to water getting between the asphalt
and the aggregate.

• To reduce stripping, use clean, rough, hydrophobic

aggregate and add enough asphalt cement to
provide a thick coating of asphalt on every
aggregate particle.

• This improves durability but decreases stability.

 Bleeding

• The migration of asphalt cement to the surface of the

pavement under wheel loads, especially at higher
temperatures.

• To prevent bleeding, incorporate enough air voids so

the asphalt can compress by closing air voids rather
than by squeezing asphalt cement out from between
the aggregate particles.
 Fatigue Cracking
• Cracking resulting from repeated flexure of the
asphalt concrete due to traffic loads.

• To minimize fatigue cracking, use the proper asphalt

cement grade and have a thick asphalt cement
coating to make the concrete flexible.

• This improves durability but decreases stability.

 Thermal Cracking
• Cracking that results from an inability to acclimate
to a sudden drop in temperature.

• To minimize thermal cracking, use the proper

asphalt cement grade
 Mix Design Basics
• The right grade of asphalt cement Relates to fatigue
cracking, thermal cracking, stability.
•
• The right type of aggregate Relates to stability,
durability, stripping, skid resistance .

• The right mix volumetric Relates to stability,

durability, stripping, bleeding, skid resistance
 Hot Asphalt Mixtures
Objective
Develop an economical blend of aggregates and asphalt
that meet design requirements.
Requirements

• Sufficient asphalt to ensure a durable pavement

• Sufficient stability under traffic loads
• Sufficient air voids:-
– Upper limit to prevent excessive environmental damage
– Lower limit to allow room for initial densification due to
traffic
• Sufficient workability
 Marshall Mix Design
Developed by Bruce Marshall for the Mississippi Highway
Department Steps involved: -
• Select and test aggregate
• Select and test asphalt cement
– Establish mixing and compaction temperatures
• Develop trial blends
– Heat and mix asphalt cement and aggregates
– Compact specimen (100 mm diameter)
 Marshall Design Criteria

These criteria can slightly vary between various regions

 Marshall Design Method
• Advantages
– Attention on voids, strength, durability
– Inexpensive equipment.
– Easy to use in process control/acceptance.
• Disadvantages
– Impact method of compaction – Does not
consider shear strength
– Load perpendicular to compaction axis
Mix design - Calculations
 Marshall Properties
Optimum Bitumen Content (OBC)
Marshall Design Use of Data
Asphalt Institute Procedure
Example
Solution
Example
Example
Solution
Благодарю за внимание!

Thank you!