CHAPTER 5 RIGID PAVEMENT Characteristic of Rigid Pavement

CHAPTER 5 RIGID PAVEMENT

Characteristic of Rigid Pavement Source: http: //www. pavement. com/Concrete_Pavement/Technical/Fundamentals/

Characteristic of Rigid Pavement Subgrade Subbase Toplayer

Subgrade Primary function is to support load transmitted from overlaying layer Compacted to maximum density

Subbase/base layer Is optional, depending on the engineering properties of the subgrade. If the subgrade soil is poor and erodable, then it is advisable to use a base layer. If the subgrade soil has good engineering properties and drain well, a base layer need not be used. Subbases provide uniform support to the pavement and a stable platform for construction equipment. Subbases also help prevent movement of subgrade soils at transverse pavement joints in roads subject to a large volume of truck traffic. Subbases may be gravel, stone, cement-modified soil or asphalt.

DIFFERENCES BETWEEN RIGID AND FLEXIBLE PAVEMENT 1. The manner in which the load is distribute over the subgrade. Rigid pavement, because of concrete’s rigidity and stiffness, tends to distribute the load over a relatively wide area of subgrade. Flexible pavement, built with weaker and less stiff material usually require more layers and greater thickness for optimally transmitting load to the subgrade.

DIFFERENCES BETWEEN RIGID AND FLEXIBLE PAVEMENT 2. MAJOR design factor The major factor considered in the design of rigid pavement is the structural strength of the concrete. For this reason, minor variations in subgrade strength have little influence upon the structural capacity of the pavement. The major factor considered in the design of flexible pavements is the combined strength of the layers.

Material Used in Rigid Pavement Portland Cement Coarse Aggregate Fine Aggregate Water Reinforcing Steel Temperature Steel Dowel Bar Tie Bar Garber & Hoel, 2009

Temperature Steel Bar mat or wire mesh : longitudinal and transverse welded at regular interval 3 in. below slab surface The amount of steel required depends on the Length of pavement between expansion joint Max allowable stress in pavement Pavement thickness Modulii of elasticity of Concrete and steel Garber & Hoel, 2009

Temperature Steel Purpose: not to prevent cracking but control the crack width because the steel acts as tie holding the edge of the cracks together. This helps to increase shear resistance of the slab Garber & Hoel, 2009

Dowel Bars Mainly as a load transfer mechanism across joints. Provides flexure, shearing and bearing resistance Diameter of 1 to 1. 5 in and length 2 -3 ft spaced 1 ft c/c across the slab width One end should be smooth and lubricated to facilitate free expansion Garber & Hoel, 2009

Tie Bar To tie two section together Diameter 0. 75 in and 3 ft spacing Garber & Hoel, 2009

Joint in Concrete Pavement Expansion Joints Contraction Joints Hinge Joints Construction Joints Garber & Hoel, 2009

Expansion Joints Place transversely, at regular intervals, to provide adequate space for the slab to expand Across full width of the slab and 0. 75 to 1 in wide in longitudinal direction The joint space filled with compressible material (e. g cork, rubber, bituminous material etc) Garber & Hoel, 2009

Contraction Joint Decrease in temperature , slab will contract if it is free to move. Prevention from moving will induce tensile stress in the concrete pavement. This joint will released the induced tensile stress Garber & Hoel, 2009

Hinge Joints To reduce crack at centre line of concrete pavement. Garber & Hoel, 2009

Construction Joint Placed transversely To provide suitable transition between concrete laid at different times Garber & Hoel, 2009

Types of Rigid Pavements Plain concrete pavement Simply reinforced concrete pavement Continuously reinforced concrete pavement Garber & Hoel, 2009

Jointed Plain Concrete Pavement (JPCP) No temperature steel or dowels for load transfer Steel tie bars are often used: To provide hinge effect at longitudinal joints To prevent the opening of these joints For low volume highway When cement-stabilized soils are used as subbase Joints at shorter distances (10 -20 ft) to reduce amount of cracking Garber & Hoel, 2009

Simply Reinforced Concrete Pavement Has dowels to transfer the traffic loads across the joints Joints spaced at longer distances (30 ft-100 ft) Temperature steel is used – it depends on the length of the slab Tie bars commonly used at longitudinal joints. Garber & Hoel, 2009

Continuously Reinforced Concrete Pavements (CRCP) No transverse joints (except construction joints or expansion joints when necessary such as at bridge approach) Has high percentage of steel (0. 6% of cross-section of slab) Tie bars across the longitudinal joints Garber & Hoel, 2009

Pumping of Rigid Pavement Discharge of water and subgrade or subbase material through joints, cracks and edge of pavement Caused by repeated deflection of pavement slab in the presence of accumulation of water underneath it Garber & Hoel, 2009

Pumping of Rigid Pavement http: //training. ce. washington. edu

Design Consideration for Preventing Pumping Reduce or eliminate expansion joint Replace soil susceptible to the pumping with granular or sandy soils or Improve subase or subgrade with stabilization process Stabilization process? ? Garber & Hoel, 2009

Assignment 1 Describe one type of stabilization process of sub base or sub grade. Prepare your short report based on following format: Introduction Stabilization method Type of suitable soil Process (include pictures, flow chart, related graph or chart) Testing (include pictures, flow chart, related graph or chart) References (arrange accordingly) 3 -4 pages (minimum-not include references)

Stress in Rigid Pavement Stress due to wheel load Stress due to temperature effects Assumption made in determining the stress: Garber & Hoel, 2009

Stress Due to Wheel Load 3 critical location of wheel load on the concrete pavement: A. At the corner B. At interior of the slab C. At the edge of the slab Garber & Hoel, 2009

Stress Due to Wheel Load Garber & Hoel, 2009

Stress Due to Temperature Effect The edge curling stress is resisted by the weight of the concrete pavement. The resistance tends to keep the slab to its original position, resulting stress induced in the pavement. The stress may cause cracking of the pavement when it is very high Studies have shown that the stress increases as the width of the slab increases. Longitudinal joint may reduces the stress as it limits the slab width to 10 -12 ft Garber & Hoel, 2009

Stress Due to Temperature Effect The temperature difference also depends on the Slab thickness Season Latitude of slab location – higher as approaching equator Garber & Hoel, 2009

Stress Due to Temperature Effect Garber & Hoel, 2009

Stress Due to Temperature Effect Garber & Hoel, 2009

Stress Due to Temperature Effect Garber & Hoel, 2009

THICKNESS DESIGN OF RIGID PAVEMENTS Main objective: to determine thickness of the concrete slab that will be adequate to carry the projected traffic load for the design period Two methods: AASHTO Method PCA Method Garber & Hoel, 2009

AASHTO method Design consideration: Pavement performance Subgrade strength Subbase strength Traffic Concrete properties Drainage Reliability Garber & Hoel, 2009

Pavement Performance Structural performance: Functional performance: riding comfort Present servicebility index (PSI): Roughness, distress measured in terms of extent of cracking, patching and rut depth The scale: 0 (lowest) – 5 (highest) Initial servicebility index (Pi): servicebility index immediately after construction Terminal servicebility index (Pt): minimum acceptable value before resurfacing is necessary Garber & Hoel, 2009

Pavement Performance Recommended value for Pt = 2. 5 or 3. 0 (major highway) 2. 0 (lower class. ) Minimum Pt = 1. 5 Garber & Hoel, 2009

Subgrade Strength Measured by Westergaard modulus of subgrade reaction, k Plate bearing test k depends on: Seasonal effect on resilient modulus of subgrade Type and thickness of subbase material Effect of potential erosion of subbase Whether bedrock lies within 10 ft of the subgrade surface Garber & Hoel, 2009

CBR 5 -10 CBR greater than 10 Garber & Hoel, 2009

Garber & Hoel, 2009

Effect of Potential Erosion of Subbase

Effect of Potential Erosion of Subbase Garber & Hoel, 2009

Bedrock lies within 10 ft from subgrade surface Garber & Hoel, 2009

Subbase Strength Garber & Hoel, 2009

Traffic The traffic load is given in term of equivalent axial loads (ESALs). ESAL factors depend on: Slab thickness Terminal serviceability index, Pt Repeated process? ? ? Garber & Hoel, 2009

Garber & Hoel, 2009

Garber & Hoel, 2009

Fwa, 2006

Drainage Fwa, 2006 and. Garber & Hoel, 2009

Reliability design level Assurance level that the pavement section designed using the procedure will survive for its design period Fwa, 2006

Reliability design level So accounts for chance variation in the traffic forecast and chance variation in actual pavement performance for a given design period Fwa, 2006

Design Procedure Garber & Hoel, 2009

Design Procedure Garber & Hoel, 2009

Garber & Hoel, 2009

Thank You