COMPONENTS OF CONCRETE PAVEMENT

A. Concrete slabs with a determinedthickness

Concrete is a construction material that is made of portland cement ,aggregate s and water mixed in predetermined

proportions. Concrete solidifies and hardens after mixing and placement due to a chemical process known asb

hydration.

B. Joints (both transverse and longitudinal)Concrete slabs will crack randomly from natural

actions such as shrinkage or curling. Therefore, joints are vital elements introduced into

CP to control cracking and horizontal movements of the slabs.

Transverse Joints Perpendicular to Lane Lines and Longitudinal Joints

Longitudinal Joint at Lane Line

Tie bars are typically used at longitudinal joints and transverse construction joint in a nondoweled

shoulder addition/reconstruction to hold tight the faces of abutting concrete in contact.

C. Tie bars

Load transfer is the ability of a joint to transfer a portion of an applied load (the truck wheel)

from one side of the joint to the other.

Dowel Bars in a Transverse Joint

Slab Movements in Non-doweled SlabSlab Movements in Doweled Slab

E. Base layer~It can provide a stable platform for the

concrete paving, provides for additional load distribution, and contributes to drainage (if permeable base is used) and frost resistance.

F.Subbase layer (if required),~the subbase layer is a planned thickness of

specified material that is placed on the subgrade or under the basement material.

G.Subgrade~greater subgrade structural capacity can

result in more economical pavement structures.

The general pavementConstruction

practices involve:

• subgrade, base and subbase preparation conforming to the thickness and cross section requirements,

• proper placement of tie bars and dowel bars to be embedded, carefully examining for bending which could injure the material, oil, dirt, rust and other coatings that would prevent or reduce bonding to concrete.

• proper concrete placement including consolidation, finishing, texturing, curing and jointing essential for a strong durable pavement

Sub-grade, Sub-base and Base Preparation

Sub-grade Preparation

~ minimum depth of 0.5 feet below the grading plane for the width between the outer edges of shoulders, or

~ minimum depth of 2.5 feet below the finished grade for the width of the traveled way and auxiliary lanes including 3 feet on both sides as specified in Section 19-5.03 of the Standard Specifications

Sub-base Layer Preparation

•The Department uses Aggregate Sub-base (AS) for use in JPCP construction to provide a foundation or working platform for the base when the sub-grade R-value is less than 40.

•The maximum thickness of any one layer should not exceed 0.50 foot after watering and compaction. Where the required thickness is more than 0.50 foot, spreading, watering and compaction should be conducted in 2 or more lifts of approximately equal thickness.

Base Layer Preparation

The Department uses Hot Mix Asphalt (HMA) Type A, Lean Concrete Base (LCB), Asphalt Treated Permeable Base (ATPB), and Aggregate Base (AB) to provide a construction platform underneath the CP.

•Hot Mix Asphalt Type A (HMA-A)HMA-Type A consists of one or more layers

placed on a prepared sub-base or sub-grade in conformity with the alignment and grades shown on the project plans. HMA-A is placed at a 20 temperature of no less than 310 °F and only when the sub-base or sub-grade surface is dry and in satisfactory condition.

•Lean Concrete Base (LCB) ~ LCB is placed, constructed and finished in no less than 12-foot widths separated by contact joints. Widths that are greater than 26 feet are constructed with longitudinal weakened plane joints at no more than 3 feet from the centerline of the width being constructed.

•Aggregate Base (AB) ~ where the required thickness is 0.50-foot or less, is spread and compacted in one layer. If the required thickness is more than 0.50-foot, spread and compact AB in two or more lifts in approximately equal thickness, and each lift shall not exceed 0.50-foot.

Steel Placement

Tie Bar Placement

Tie bars are not to be used at a joint where concrete and asphalt concrete pavements abut. Tie bars are placed:(a) along longitudinal weakened

plane in multilane paving, and(b) at longitudinal and transverse contact joint in a nondoweled lane/shoulder addition or reconstruction. These tie bars are placed at mid depth of the concrete slab.

• Dowel Bar PlacementDowel bars are placed as shown on the plans

by using either dowel bar baskets, drilling and bonding, or mechanical insertion.

• Bar Reinforcement PlacementAlthough CP does not typically have bar

reinforcement, bar reinforcement can be found in a few situations such as pavement transitions ,gore areas, and around drainage inlets.

• Concrete Placement ~ Concrete is transported to the paving site by dump trucks or ready-mix trucks with the goal to deliver a uniform, well-mixed and workable concrete from batch to batch.

• Consolidation ~ it is the process that compacts fresh concrete to mold it within the forms and around steel reinforcements and to remove undesirable voids.

• Finishing ~it involves any equipment or procedures used to impart desirable surface characteristics.

• Curing ~ it is the maintenance of satisfactory moisture and temperature in the concrete as it sets and hardens such that the desired properties can develop.

Flexible pavement design

This section describes the design for both asphalt concrete pavements and surface treatments which carry significant levels of traffic over the performance period

Modifications Included in Flexible Pavement design procedures

• The soil support number is replaced by the resilient modulus to provide a rational testing procedure that may be used by an agency to define the material properties.

• The layer coefficients for the various materials are defined in terms of resilient modulus as well as standard methods (CBR and R-value).

• The environmental factors of moisture and temperature objectively included in the Guide so that the environmental consdiderations could be ratioanally accounted for in the design procedure.

• Reliability is introduced to permit the designer to use the concept of risk analysis for various classes of roadways.

• Stage construction design procedures are incorporated.

Design Of Flexible Pavement

• Design Of Flexible Pavement By Group Index Method

Group Index is function of percentage material passing 200 mesh sieve (0.074mm), liquid limit and plasticity index of soil and is given by equation:

GI=0.2a+0.005ac+0.01bdHere, a=that portion of material passing 0.074mm sieve, greater than 35 And not

exceeding 75 % b=that portion of material passing 0.074mm sieve, greater than 15 And not

exceeding 35% c = that value of liquid limit in excess of 40 and less than 60 d = that value of plasticity index exceeding 10 and not more than 30

California Resistance Value Method

pavements thickness varies directly with R value and logarithm of load repetitions. It varies inversely with fifth root of Computer value.

T=K (TI) (90-R)/C1/5Here :T=total thickness of pavement, cm K=numerical constant=0.166 TI=traffic index R=stabilometer resistance value C =Cohesiometer value

Triaxial Method

HereT=Pavement thickness, cm Es=modulus of elasticity of sub grade from triaxial test

result, Kg/cm2 A=radius of contact area, cm ∆=design deflection (0.25 cm)

Other.....

Rigid pavement designAs the name implies, rigid pavements are rigid , they do not extend much under loading like flexible pavements. They are constructed using cement concrete. In this case, the load carrying capacity is mainly due to the rigidity and high modulus of elasticity of the slab (slab action).

Modifications Included in Rigid Pavement design procedures:

• Reliability concepts identical to those used for the flexible pavements are introduced.

• The environmental aspects of design are introduced in the same format as for flexible pavements.

• The design procedure is modified to include such factors as tied shoulders, subbase erosion, and lean subbase designs.

Rigid Pavement Response

• Curling stress– Differences in temperature between the top and

bottom surfaces of a PCC slab will cause the slab to curl. Since slab weight and contact with the base restrict its movement, stresses are created.

where:σt=slab interior warping stressE=modulus of elasticity of PCCe=thermal coefficient of PCC (» 0.000005/°F)Δ T=temperature differential between the top and bottom of the

slabµ=Poisson’s ratio for PCC (» 0.15)β=radius of wheel load distribution for corner loading

where:l=radius of relative stiffnessE=modulus of elasticity of PCCh=slab thicknessk=modulus of subgrade reactionm=Poisson’s ratio for PCC (» 0.15)

Load stress

Loads on a PCC slab will create both compressive and tensile stresses within the slab and any adjacent one (as long as load transfer efficiency is > 0).

a. Interior loading. Occurs when a load is applied on the interior of a slab s.urface which is “remote” from all edges.

b. Edge loading. Occurs when a load is applied on a slab edge “remote” from a slab corner.

c. Corner loading. Occurs when the center of a load is located on the bisector of the corner angle.

Shrinkage and expansion

• In addition to curling, environmental temperatures will cause PCC slabs to expand (when hot) and contract (when cool), which causes joint movement.

where:z=joint opening = change in slab length (inches)C=base/slab frictional restraint factor

= 0.65 for stabilized bases= 0.80 for granular bases

L=slab length (inches)

It is observed that flexible pavements are more economical for lesser volume of traffic.The life of flexible pavement is near about 15 years whose initial cost is low needs a periodic maintenance after a certain period and maintenance costs very high.

The life of rigid pavement is much more than the flexible pavement of about 40 years approx 2.5 times life of flexible pavement whose initial cost is much more then the flexible pavement but maintenance cost is very less.

References:

http://www.pavementinteractive.org/article/rigid-pavement-response/#sthash.ISwV8mbT.dpuf

pavement-procedures-construction-and-re-construction.pdf

“Start by doing what’s necessary;then do what’s possible;

and suddenly your are doing the impossible.”

~Francis of Assisi~

Prepared by:

FONTE, EDDIE REDZULUETA, ERWIN JOHN