Pavement System Design
Thickness
Learning Objectives:
- Define pavement thickness and its significance in the design and construction of roadways.
- Identify the primary functions of pavement thickness in providing structural support to traffic loads.
- Familiarize oneself with key terminology related to pavement thickness, such as structural number, subgrade, base course, and surface course.
- Sufficient thickness to spread loading to a pressure intensity tolerable by subgade
- Sufficiently strong to carry imposed stress due to traffic load.
- Sufficient thickness to prevent the effect of frost susceptible subgade.
- Pavement material should be impervious to penetration of surface water which could weaken subgade and subsequently pavement.
- Pavement mat. shd be non-frost susceptible.
- Pavement surface should be skid resistant.
- The surface course is the layer in contact with traffic loads and is made of PCC or RCC. It provides characteristics such as friction, smoothness, noise control and drainage. In addition, it serves as a waterproofing layer to the underlying base, sub-base and sub-grade.
- The surface course can vary in thickness but is usually between 150 mm (6 inches for light loading) and 300 mm (12 inches for heavy loads and high traffic).
Solved Example: 9068-01
Minimum thickness of the base of a flexible pavement is:
A. 15 cm
B. 20 cm
C. 10 cm
D. 5 cm
Correct Answer: C
Subgrade
Learning Objectives:
- Define the subgrade in the context of pavement design and construction.
- Describe the role and importance of the subgrade in providing structural support for pavements.
- Explain the factors that influence subgrade soil properties, including soil type, compaction, and moisture content.
In transport engineering, subgrade is the native material underneath a constructed road, pavement or railway track. It is also called formation level. The term can also refer to imported material that has been used to build an embankment.
The subgrade is the area of the earthen roadbed that receives the base or surface material after being built in pretty close compliance with the lines, grades, and cross-sections shown on the plans. The subgrade in a fill section is the top of the fill or embankment.
- Preperation of Sub-grade Subgrades are commonly compacted before the construction of a road, pavement or railway track, and are sometimes stabilized by the addition of asphalt, lime, portland cement or other modifiers.
- The subgrade is the foundation of the pavement structure, on which the subbase is laid. Preparation of the subgrade for construction usually involves digging, in order to remove surface vegetation, topsoil and other unwanted material, and to create space for the upper layer of the pavement. This process is known as "subgrade formation" or "reduction to level".
- Subgrade shall be free from all foreign debries and rock outcrops.
Trio3D, CC BY-SA 3.0, via Wikimedia Commons
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Solved Example: 9067-01
Given the load, warping and frictional stresses on a cement concrete pavement slab as 220 N/mm$^2$, 300 N/mm$^2$ and 10 N/mm$^2$ respectively, the critical combination of stresses during summer season is:
A. 300 N/mm$^2$
B. 530 N/mm$^2$
C. 520 N/mm$^2$
D. 510 N/mm$^2$
Correct Answer: D
Solved Example: 9067-02
The contact pressure P$_C$, tyre pressure P, and rigidity factor R are related by:
A. $\dfrac{{\rm{P}}}{{{{\rm{P}}_{\rm{C}}}}} = {\rm{R}}$
B. $\dfrac{{{{\rm{P}}_{\rm{C}}}}}{{\rm{P}}} = {\rm{R}}$
C. P $\times$ P$_C$ = R
D. ${\rm{R}} = {\rm{\;}}\sqrt {\left( {{\rm{P}} \times {{\rm{P}}_{\rm{C}}}} \right)}$
Correct Answer: B
Solved Example: 9067-03
Calculate spacing between expansion joints, if the expansion joint gap is 2.0 cm in a cement concrete pavement. The laying temperature is 10 C and the maximum slab temperature in summer is 50 C.($\alpha$ = 10 $\times$ 10$^{-6}$)
A. 30 m
B. 25 m
C. 100 m
D. 20 m
Correct Answer: B
Drainage
Learning Objectives:
- Recognize different types of drainage systems, including surface drainage, subsurface drainage, and cross-drainage structures.
- Learn the principles governing the collection and removal of surface water from highways, including the design of road crowns, shoulders, and cross slopes.
Highway drainage is an essential part of highway design and construction which remove the surplus water with in the highway limits and dispose it.
Road way drainage is mainly due to surface runoff from adjacent area, precipitation of rain and moisture rising by capillarity from the ground water table.
Removal and diversion of surface water from road way and adjoining land is known as surface drainage.
Removal of excess sub soil water from the subgrade is termed as sub surface drainage.
Importance of Highway Drainage:- To prevent subgrade failure: Excess moisture reducing the stability of pavement which leads to subgrade failure.
- To prevent reduction in strength of pavement material: The strength of pavement material like stabilized soil and WBM (water bound macadam) is reduced.
- To prevent frost action: In flexible pavement the formation of waves and corrugation takes place due to poor drainage.
- To prevent pavement edge: Excess water on pavement edge cause considerable damage.
Pavement drainage channel, St Edward Street, Newport by Jaggery, CC BY-SA 2.0, via Wikimedia Commons
Rehabilitation
Learning Objectives:
- Identify and understand the various factors contributing to the deterioration of pavement systems, including traffic loading, environmental conditions, material properties, and construction practices.
- Learn about different rehabilitation strategies for addressing various pavement distress types, including cracking, rutting, potholes, surface deterioration, and structural deficiencies.
- Understand the principles, selection criteria, and applicability of rehabilitation techniques such as overlays, resurfacing, rehabilitation, reconstruction, and preventive maintenance.
Pavement rehabilitation refers to the process of restoring or improving the condition, performance, and service life of existing pavements to ensure safe and efficient transportation infrastructure. It involves addressing various types of distresses, such as cracking, rutting, potholes, surface deterioration, and structural deficiencies, to maintain pavement functionality and user satisfaction.
Pavements deteriorate over time due to factors such as traffic loading, environmental conditions (e.g., temperature variations, moisture infiltration), material properties (e.g., aging, oxidation), and construction practices (e.g., inadequate compaction, poor drainage).
Common rehabilitation techniques include overlays (e.g., asphalt concrete overlays, concrete overlays), resurfacing, rehabilitation (e.g., milling and overlay), reconstruction, and preventive maintenance treatments (e.g., crack sealing, seal coating).
Common evaluation methods include visual inspection, pavement distress surveys, pavement condition index (PCI) assessment, roughness measurement, and non-destructive testing methods such as Falling Weight Deflectometer (FWD) and Ground Penetrating Radar (GPR).
Well designed rigid pavement provides excellent performance for long term. Distresses may take place in rigid pavement and rehabilitation is required to get expected useful life. Repair/Rehabilitation requires understanding of causes and mechanics of distresses. In rigid pavement, distresses are limited and causes are well understood. This presentation is focused on specific repair/rehabilitation methods for these distresses.
Methods:- Bonded concrete overlay
- Diamond grinding
- Full depth repair
- Partial depth repair
- Dowel bar retrofit
- Cross stitching of longitudinal cracks
- Joint repair
- Thin asphaltic concrete overlay
Oregon Department of Transportation, CC BY 2.0, via Wikimedia Commons
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Solved Example: 9066-01
The design life of flexible pavement is _____ years.
A. 8
B. 10
C. 12
D. 15
Correct Answer: D
Solved Example: 9066-02
The interface treatment provided to plug in the voids of porous surfaces and to bond loose particles in bituminous pavements is called:
A. Tack coat
B. Seal coat
C. Prime coat
D. Surface dressing
Correct Answer: C
Solved Example: 9066-03
hich of the following is used in a regular pavement maintenance activity?
A. Tack coat
B. Prime coat
C. Fog seal
D. None of these are correct
Correct Answer: C
Solved Example: 9066-04
Which of the following it NOT a critical parameter to control cracking and rutting in a flexible pavement?
A. Tensile strain near the surface close to the edge of the wheel
B. Vertical sub-base strain
C. Vertical subgrade strain
D. Tensile strain at the bottom of bituminous layer
Correct Answer: B