Highway and Railroad Engineering - Pavement Types
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Questions and Answers

Dynamic pavement response is easier to analyze than static response.

False (B)

Passenger cars typically have dual wheels on their axles.

False (B)

Doubling the load magnitude will always double the rate of pavement deterioration.

False (B)

Higher tyre pressures in trucks lead to faster deterioration of the pavement surface.

<p>True (A)</p> Signup and view all the answers

Predicting future traffic growth is always accurate, ensuring precise pavement design.

<p>False (B)</p> Signup and view all the answers

Environmental conditions have no effect on the properties of pavement materials.

<p>False (B)</p> Signup and view all the answers

Trucks typically have tyre pressures between 100 - 115 psi.

<p>True (A)</p> Signup and view all the answers

Different axle configurations do not influence pavement performance.

<p>False (B)</p> Signup and view all the answers

Slab thicknesses for PCC highway pavements typically range from 8 to 12 feet.

<p>False (B)</p> Signup and view all the answers

A flexible pavement reduces stresses by transmitting traffic loads directly to the subgrade.

<p>False (B)</p> Signup and view all the answers

The material for the base course in a flexible pavement is typically stabilized aggregates.

<p>False (B)</p> Signup and view all the answers

The average lifespan of a flexible pavement is estimated to be between 10 to 15 years.

<p>True (A)</p> Signup and view all the answers

Subbase layers are always used in the construction of flexible pavements.

<p>False (B)</p> Signup and view all the answers

Rutting and fatigue cracking are examples of distresses that can accumulate over the lifespan of flexible pavements.

<p>True (A)</p> Signup and view all the answers

A cone of distributed loads helps to concentrate stresses at the subgrade level.

<p>False (B)</p> Signup and view all the answers

Hot-mix asphalt is also known as asphalt concrete in flexible pavement design.

<p>True (A)</p> Signup and view all the answers

An 18-kip single-axle load is equivalent to 18,000 pounds.

<p>True (A)</p> Signup and view all the answers

A 44-kip tandem-axle load has a W18 value of 1.44.

<p>False (B)</p> Signup and view all the answers

ZR represents the probability that serviceability will be maintained from a user’s perspective.

<p>True (A)</p> Signup and view all the answers

The z-statistic is derived from a uniform distribution.

<p>False (B)</p> Signup and view all the answers

Reliability values for local roads can be as high as 90%.

<p>False (B)</p> Signup and view all the answers

Transverse cracks are important for evaluating the distress of flexible pavements.

<p>False (B)</p> Signup and view all the answers

Highways such as interstates require a low reliability level due to the high cost of reconstruction.

<p>False (B)</p> Signup and view all the answers

Tables 4.1, 4.2, and 4.3 present axle-load equivalency factors for flexible pavement design.

<p>True (A)</p> Signup and view all the answers

Joint faulting in rigid pavements is an indicator of erosion or fatigue beneath the slab.

<p>True (A)</p> Signup and view all the answers

The impact of an axle load on pavement is measured only in terms of weight.

<p>False (B)</p> Signup and view all the answers

Punchouts occur in Continuously Reinforced Concrete Pavements due to widely spaced transverse cracks.

<p>False (B)</p> Signup and view all the answers

The International Roughness Index is used to measure the impact of faulting on pavement smoothness.

<p>True (A)</p> Signup and view all the answers

Rigid pavements are built with expansion and contraction joints to allow for thermal movement.

<p>False (B)</p> Signup and view all the answers

Fatigue damage in rigid pavements is assessed through the measurement of transverse cracks only.

<p>False (B)</p> Signup and view all the answers

The overall standard deviation, So, only accounts for the statistical error in the equations used in pavement design.

<p>False (B)</p> Signup and view all the answers

The terminal serviceability index, TSI, indicates the maximum performance level of the pavement.

<p>False (B)</p> Signup and view all the answers

Increased roughness from punchouts can affect the overall performance of the pavement.

<p>True (A)</p> Signup and view all the answers

The spacing of transverse cracks is not relevant to the structural integrity of the pavement.

<p>False (B)</p> Signup and view all the answers

The amount of serviceability loss, ∆PSI, is calculated as the difference between the initial PSI and the TSI.

<p>True (A)</p> Signup and view all the answers

The average 28-day strength of concrete is typically measured in units of psi rather than lb/in2.

<p>False (B)</p> Signup and view all the answers

A drainage coefficient, Cd, value of 1.0 indicates poor drainage characteristics of a material.

<p>False (B)</p> Signup and view all the answers

Most highway agencies perform detailed tests to measure the modulus of subgrade reaction, k.

<p>False (B)</p> Signup and view all the answers

Typical values for the concrete modulus of elasticity, Ec, range between 3 and 7 million lb/in2.

<p>True (A)</p> Signup and view all the answers

The load transfer coefficient, J, is used to account for the load transfer capability of pavement across slab joints.

<p>True (A)</p> Signup and view all the answers

Rain and freeze-thaw cycles weaken the HMA materials and reduce the load carrying capacity of the subgrade.

<p>True (A)</p> Signup and view all the answers

The same road can be built over different subgrade materials without affecting pavement thickness requirements.

<p>False (B)</p> Signup and view all the answers

Channelized traffic load results in uniform deterioration across the pavement surface.

<p>False (B)</p> Signup and view all the answers

The distribution of stresses and strains in a multi-layer pavement system is independent of the material properties of the layers.

<p>False (B)</p> Signup and view all the answers

Pavement failure occurs when the applied stresses exceed the strength of the material.

<p>False (B)</p> Signup and view all the answers

The AASHTO Guide for Design of Pavement Structures is a key resource for flexible-pavement design procedures.

<p>True (A)</p> Signup and view all the answers

Pavement structure typically consists of a single layer built directly on the subgrade.

<p>False (B)</p> Signup and view all the answers

HMA ages over time, leading to increased flexibility and decreased susceptibility to cracking.

<p>False (B)</p> Signup and view all the answers

Flashcards

HMA Material Weakening

Rain and freeze-thaw cycles reduce the load-bearing capacity of asphalt layers.

Subgrade Variations

Different subgrade materials (soil) along a road affect pavement layer thicknesses for supporting uniform loads.

Channelized Traffic Load

Wheel traffic load concentrated in wheel paths leads to faster deterioration.

Multi-layer Pavement

Pavement consists of multiple layers with varying materials and properties.

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Unconventional Pavement Failure

Pavement deterioration, not collapse, is the indicator of failure when stresses gradually exceed limits.

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AASHTO Flexible Pavement Design

A widely used procedure for designing flexible pavement structures, as outlined in the AASHTO Guide.

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Stress and Strain Distribution

Different pavement materials and layers lead to varied stress and strain patterns throughout the structure.

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Aging of HMA

HMA (hot mix asphalt) becomes stiffer and more prone to cracking over time.

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Dynamic Pavement Response

The reaction of a pavement to a moving load, which is more complex than a static response.

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Variable Load Configuration

Different vehicle axle and wheel arrangements (e.g., single, tandem, tri-axle) affect pavement stress interactions.

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Load Magnitude & Deterioration

Increasing load magnitude (e.g., heavier truck) leads to a faster rate of pavement deterioration, not a linear relationship.

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Tyre Pressure & Deterioration

Higher tire pressure (e.g., truck tires) results in higher contact pressures and faster surface layer deterioration.

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Future Traffic Growth

Predicting future traffic volume is crucial for pavement design, but inaccuracies affect pavement performance predictions.

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Environmental Impact on Materials

Temperature changes (high/low) affect pavement material properties (softening/hardening), causing issues like rutting and cracking.

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Non-linear Pavement Response

Increasing load doesn't proportionally increase stress or strain in the pavement; the rate of deterioration increases exponentially.

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Pavement Design Considerations

Pavement design must account for future traffic and changing environmental conditions to ensure durability.

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PCC Slab Thickness

Highway pavement slabs typically range from 8 to 12 inches.

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Flexible Pavement Function

Reduces and distributes surface stresses (from tires) to the subgrade to prevent deformation.

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Flexible Pavement Stress Transfer

Loads are distributed through layers to the subgrade via aggregate-to-aggregate contact.

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Flexible Pavement Layers

A typical flexible pavement has surface, base course, and subbase layers on a compacted subgrade.

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Flexible Pavement Materials

Surface layer is hot-mix asphalt (HMA); base course is usually unstabilized aggregates; subbase is local aggregate.

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Flexible Pavement Failure

Pavement failure occurs when distress (like rutting, cracking) reaches an unacceptable level.

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Flexible Pavement Life Expectancy

Average life is 10-15 years, varying by case, and a good design considers this expected lifespan.

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Pavement Distress

Damage or problems that lead to the failure of the pavement.

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Equivalent Single Axle Load (ESAL)

A standardized 18,000-pound (or 18-kip) single-axle load used to account for the various traffic loads impacting pavement.

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W18 Value

A factor representing how much impact a specific axle load has compared to an 18-kip single axle load on pavement structure.

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Axle Load Equivalency

The way pavement engineers determine the impact of different axle loads on pavements using standardized values (e.g., W18).

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Terminal Serviceability Index (TSI)

A measure of the expected pavement quality at the end of a design period.

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Reliability (R)

The probability (expressed as a percentage) that pavement serviceability will meet or exceed the desired level during the design period.

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High Reliability

A high probability (e.g., 90% or higher) that pavement quality will meet or exceed the design standards.

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Mixed Traffic Loading

The use of a variety of axle weights and configurations on a road.

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Design Life

The projected time period that a road or section of road is expected to perform at an acceptable level of serviceability.

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Overall Standard Deviation (So)

A measure of variability in pavement design due to factors like estimated axle loads, materials, and construction practices.

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Serviceability Loss (∆PSI)

The difference between the initial serviceability of a pavement and its TSI, indicating how much it deteriorates over time.

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Concrete Modulus of Rupture (𝑆'𝐶c)

A measure of the tensile strength of concrete, representing its resistance to cracking.

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Drainage Coefficient (Cd)

A factor that accounts for the ability of the subgrade to drain water, affecting the overall pavement performance.

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Load Transfer Coefficient (J)

A factor that describes how well the pavement transfers loads between concrete slabs.

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Concrete Modulus of Elasticity (Ec)

A measure of the stiffness of concrete, indicating how much it deforms under stress.

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Modulus of Subgrade Reaction (k)

A measure of the support provided by the subgrade soil to the pavement.

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Rigid Pavement Distress

Damage indicators in rigid pavements, including cracking, faulting, and punchouts, revealing structural weakness.

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Transverse Crack

Cracks running perpendicular to the direction of traffic in a rigid pavement, indicating stress and potential failure.

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Joint Faulting

Uneven slab elevations in jointed concrete pavements (JPCP), signifying movement and loss of load transfer between slabs.

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Punchout

Small pieces of concrete breaking off from a continuously reinforced concrete pavement (CRCP), caused by intense stress from closely spaced cracks.

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What does faulting indicate in JPCP?

Faulting indicates erosion or fatigue in the layers beneath the concrete slabs, leading to a weakened load transfer ability.

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What are punchouts a sign of?

Punchouts suggest fatigue damage at the top of the CRCP slab due to high tensile stresses from closely spaced cracks.

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How do transverse cracks affect pavement performance?

They increase roughness, leading to discomfort for drivers and potentially causing damage to vehicles.

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What is the relationship between cracking and roughness?

Cracking, especially in rigid pavements, contributes to increased roughness, impacting ride quality and potentially affecting pavement durability.

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Study Notes

Course Information

  • Course title: Highway and Railroad Engineering
  • Course code: HRE 313
  • Edition: First, 2021
  • Institution: President Ramon Magsaysay State University

Module Overview

  • Module introduces highway and railroad engineering
  • Covers topics in structural design of pavements
  • Includes discussion of flexible and rigid pavements
  • Sample: Typical flexible pavement consists of surface, base course, and subbase over compacted subgrade
  • Common distresses of pavements include fatigue cracking, rutting, roughness, and thermal cracking
  • Rigid pavements are commonly found in major highways and airports

Pavement Types

  • Two main types: flexible and rigid
  • Flexible pavements are built with layers of asphaltic cement and aggregates
  • Subgrade, subbase, base, and wearing surface are common layers in flexible pavements
  • Rigid pavements are constructed using portland cement concrete (PCC) and aggregates
  • Base layer is optional, depending on subgrade soil
  • Transverse contraction joints are built into the pavement to control cracking

Flexible Pavement Design

  • Pavement system design is aimed at reducing and distributing surface stresses to acceptable levels at subgrade
  • Stresses are transmitted through aggregate-to-aggregate particle contact
  • Confining pressures in subbase and base layers increase bearing strength
  • Cone of distributed loads reduces and distributes stresses to subgrade

Unique Properties of Flexible Pavements

  • Deterioration over time: Each load application contributes to distresses like rutting, fatigue cracking, disintegration, roughness, and bleeding
  • Repeated loads: Dynamic pavement response from traffic loads
  • Variable load configuration: Axles can be single, tandem, or multiple, while wheels can be single or dual.
  • Variable load magnitude: Increasing load significantly increases the rate of deterioration
  • Variable tyre pressure: Higher pressures result in increased contact pressure and faster deterioration of the surface layer
  • Traffic growth: Future traffic growth affects the accuracy of predictions of pavement performance and designed life

Rigid Pavement

  • Rigid pavements use portland cement concrete (PCC)
  • Drainage characteristics of subgrade are important, with drainage coefficients considered in design
  • Base layer is optional, depending on subgrade characteristics
  • Transverse contraction joints are built into the pavement to control shrinkage cracking
  • Load transfer devices like dowel bars help minimize deflection and stresses near edges of slabs

Pavement System Design

  • Traditional AASHTO flexible pavement design in the AASHTO guide
  • The amount of serviceability loss (APSI) over pavement life
  • The overall standard deviation (So) from variability in materials and construction practices
  • Structural number (SN) represents the overall structural requirement

Pavement Quality and Performance

  • International Roughness Index (IRI) measures surface roughness, important for safety
  • Pavement friction measurements are conducted, particularly under wet conditions, to estimate the friction number

Pavement Distress

  • Rut depth: Surface deformation in wheel paths affecting vehicle safety due to hydroplaning
  • Cracking: Material fatigue can lead to faulting, transverse cracking, alligator cracking, and others
  • Faulting: Different slab elevations in JPCP, an indicator of fatigue in layers or transfer ability
  • Punchouts: Fatigue damage in CRCP slabs

References

  • Includes materials from several texts, including "Principles of Highway Engineering & Traffic Analysis" and the "Handbook of Highway Engineering"

Assignment

  • Task: Explain the difference between flexible and rigid pavements

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HRE 313 Highway and Railroad Engineering PDF

Description

This quiz covers the fundamental concepts of highway and railroad engineering focusing on the structural design of pavements. It includes discussions on flexible and rigid pavements, their components, and common distresses. Test your knowledge on pavement types and their characteristics.

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