HIGHWAY ENGINEERING II
HIGHWAY ENGINEERING II1
Instructor: Raeed Ali ([email protected])HIGHWAY ENGINEERING II
ICE-BREAKERWhat do you understand by Pavement Engineering?What kinds of problems did you notice on the roads of Ethiopia?List the materials used for the construction of roads.What do you think it takes to become a good pavement/material engineer?
Who wants to be a pavement engineer? Contents Introduction1.1 General1.2 Overview of pavement structures1.2.1 Flexible pavements1.2.2 Rigid pavements1.3 Basic design requirements Stress in pavements2.1 Stress in flexible pavements2.2 Stress in rigid pavementsTraffic Loading and Axle load SurveySub-grade soils4.1 Overview of soil data and site investigation4.2 Essential laboratory tests4.3 Soil classification for highway use
Contents contdUnbound pavement materials5.1 Source and properties of aggregate5.2 Aggregate for surfacing5.3 Base and Sub base courses5.4 Selected capping layersStabilization pavement materials6.1 Mechanical Stabilization6.2 Cement Stabilization6.3 Lime Stabilization6.4 Bitumen StabilizationBituminous materials and mixtures7.1 Bituminous binder and properties7.2 Bituminous mixtures
Contents contdStructural design pavements8.1 TRL method of flexible pavement design8.2 AASHTO method of flexible pavement design8.3 ERA and AACRA Pavement design procedures8.4 Design of gravel surfaced roadsHighway maintenance and rehabilitation (optional)
For our consumption Chapter 1IntroductionWhat is a pavement structure?A pavement is a layered structure that:has sufficient total thickness and internal strength to carry expected traffic loads, and distribute them over the subgrade soil without overstressing;have adequate properties to prevent or minimize the penetration or internal accumulation of moisture; andhave a surface that is reasonably smooth and skid resistant at the same time, as well as, reasonably resistant to wear, distortion and deterioration by vehicle loads and weather.
Types of pavement structuresEarth Roads Gravel Surfaced Roads Flexible Pavements Rigid Pavements
Earth RoadsDesigned for a very low traffic where the soil can be trafficableUsed when there is economic limitationThe natural sub grade soil can be made to carry the traffic load after clearing and shaping Such earth roads give seasonal services and Require reshaping after seasonal changes.
Gravel RoadsConstructed by spreading gravel over the subgrade, shaping and compacting to avoid excessive strain at the sub grade levelUsually provides services in all seasons with less frequent reshaping as compared to earth roads. Designed to carry low to medium traffic & serve as stage construction. The surface material should be kept to certain standard such as grading and plasticity.
Flexible PavementsA flexible pavement is one, which has low flexural strength, and the load is largely transmitted to the subgrade soil through the lateral distribution of stresses with increasing depth.
The strength of subgrade soil would have a direct bearing on the total thickness of the flexible pavement.
Types of flexible pavementsconventional flexible pavementfull-depth asphalt pavement
Question: Where do you think is each applicable?Rigid PavementsAre pavement structures constructed of cement concrete slabs, which derive their capacity to withstand vehicle loads from flexural strength or beam strength due to high modulus of elasticity. High flexural strength permits the vehicle load on cement concrete slab to be distributed over a relatively wider area and to bridge over minor irregularities of the soil than flexible pavements and thus, variation in the subgrade soil strength has little influence.
Types of rigid pavements
Composite pavementsComposite pavements are pavements composed of cement concrete as a bottom layer and hot-mix asphalt as a top layer to obtain an ideal pavement with the most desirable characteristics. The cement concrete slab provides a strong base and the hot-mix asphalt provides a smooth and non-reflective surface.
Question: How are they formed?Comparison between flexible and rigid pavementsThe manner in which vehicle loads are transmitted to subgradeDesign life and precisionMaintenance requirementsInitial costSuitability for stage constructionSurface characteristicsPermeability andTraffic dislocation during construction.
Airports vs. Highwaysgross-weight vs. number of load repetitionsarrangement and spacing of wheel loadstypical tyre pressureLoad applications (location)
Designing PavementsMajor Design factorstraffic loading, environment, materials and failure criteria.
Traffic Loadingloading configuration; number of repetitions (ESAL); tyre pressure; and speed of traffic loading
Environmenttemperature, Flexible pavement elastic/viscoelastic properties of bituminous materialsRigid pavement warping/curling stresses Frost in the subgrade - heave and stronger subgrade in the winter but a much weaker subgrade in the spring precipitation Water requirement during construction;Strength of pavement structure; andSurface water drainage.
MaterialProperties of soils, aggregates, bituminous binders, cement, and their mixtures under traffic loading in a given environmental conditionsStiffness, Poison Ratio, Strength, Durability, Permeability, Thermal-Volumetric Properties
Performance and Failure criteriaPavement failure/ distress/ defect is a condition of the pavement structure that reduces serviceability or leads to a reduction in serviceability.Defects of a road can be classified into two: Structural defect Surface defectPerformance and Failure criteriaGravel roads defects include: dustiness, potholes, stoniness, corrugations, ruts, cracks, ravelling, erosion, slipperiness, impassibility and loss of wearing course material function of properties of materials of construction, alignment, volume of traffic, and etc.Flexible pavement fatigue cracking ; rutting; and thermal cracking Rigid pavement - fatigue cracking; pumping ; and joint deterioration
Visual Depiction of failure modes
Closing RemarkWhich of the failure modes do most of the world design the pavements for???FATIGUE!!!
