3.0 ROAD CONSTRUCTION

TECHNOLOGY

ER. SABIN POKHREL

3.6 Construction of Cement Concrete

Pavement

• Construction of pavement slab

• Design and placement of joints

3.6 Construction of Cement Concrete

Pavement

• CEMENT GROUTED CONCRETE:

• Open graded aggregate mix of minimum size 18~25mm is laid on prepared

subgrade

• Dry rolled to provide 80% of rolled thickness.

• Grout: mix of cement, coarse sand and water

• Applied on the surface.s

3.6 Construction of Cement Concrete

Pavement

• ROLLED CONCRETE LAYER:

• Lean mix of aggregate, sand, cement and water is laid on prepared subgrade

or sub base course.

• Rolling similar to WBM

• Tandem rollers are preffered and rolled before final setting time.

• Both cement grouted and rolled concrete are suitable for base course

only.

3.6.1 Construction of Concrete Slab

• Basically 2 methods:

• ALTERNATE BAY METHOD

• CONTINUOUS BAY METHOD

3.6.1 Construction of Concrete Slab

• ALTERNATE BAY METHOD:

• Construction of one slab in alternate succession

• Next or intermediate bays are followed after a week or so

• Provides additional working convenience for laying slab

• Construction joints are easier to provide

• Numerous transverse joints are to be provided resulting in high cost for construction and smoothness in riding is reduced.

3.6.1 Construction of Concrete Slab

• Traffic has to be completely halted or diverted

3.6.1 Construction of Concrete Slab

• CONTINUOUS BAY METHOD:

• All slabs laid in sequence

• Construction joints provided at the end of day’s work

• Construction of half of the pavement width can be done at a time and

traffic can be diverted on the other half

• Generally in practice

3.6.1 Construction of Concrete Slab

• MATERIALS:

• Cement: OPC in general but RHPC may also be used

• Coarse Aggregate: Max size < ¼ of slab thickness

• Gradation of coarse aggregate range from 50 to 4.75 or 40 to 4.75 mm

• Free from harmful materials

3.6.1 Construction of Concrete Slab

• LIMITS:

• Crushing value< = 30%

• Impact Value <= 30%

• LAA <= 30%

• Soundness <= 12 % Na2SO4, <= 18% MgSO4

3.6.1 Construction of Concrete Slab

• Fine Aggregates: Natural sand or crushed stone

3.6.1 Construction of Concrete Slab

PROPORTIONING OF CONCRETE:

• Develop minimum compressive strength 280 kg/cm3 at 28 days or higher

values

3.6.1 Construction of Concrete Slab

• PLANTS AND EQUIPMENTS:

• Concrete mixer, batching equipment, wheel barrows, internal vibrators, float,

straight edge, brush, and other small tools

3.6.1 Construction of Concrete Slab

• CONSTRUCTION STEPS:

• Preparation of Subgrade and Sub base:

• Properly drained, plate bearing test result 5.54 kg/cm2 (Modulus of

subgrade reaction)

• Checked 2 days in advance and should be kept moist at the time of placing

concrete

3.6.1 Construction of Concrete Slab

• PLACING OF FORMS:

• Steel or wooden forms

• Depth = thickness of pavement

• Maximum deviation during entire work < 3mm from straight edge 3m in

length

3.6.1 Construction of Concrete Slab

• BATCHING OF MATERIAL AND MIXING:

• Proportion of coarse and fine aggregates are proportioned WRT no. of bags

of cement and put in the mixture

• Batch mixer mixes the materials in uniform manner with uniformity in color

and is homogeneous

• Water introduced within first 15 seconds of mixing

• Mixing completes approximately in 1 and half minutes

3.6.1 Construction of Concrete Slab

• TRANSPORTING AND PLACING OF CONCRETE:

• Mixed concrete should be used immediately, within the prepared form to a

required thickness

• No segregation should take place

• Redistribution can be done by shovels

3.6.1 Construction of Concrete Slab

• COMPACTING AND FINISHING:

• Compaction by power driven finishing machine or vibrating hand screed

• For smaller width of slab and corner of junction, hand consolidation is

considered

• Further compacted by longitudinal float

• Tested for grade and level

3.6.1 Construction of Concrete Slab

• CURING:

• For initial curing Covered with jute mats and water is poured

• Final curing is done by saturating by water for 14 days

• OPENING TO TRAFFIC:

• After concrete acquires adequate strength or after 28 days of curing

3.6.2 Construction of Joints

• Joints provided for expansion, contraction and warping of the slabs

• Expansion joints provided to allow for expansion

• Provided at interval of 50~60 m for smooth interface laid in winter and

90~120m for summer

• 140m spacing for rough interface

• Gap width of expansion joint: 20~25mm

3.6.2 Construction of Joints

• Contraction joints provided to permit the contraction

• Spaced closer than expansion joints

• Maximum spacing in unreinforced cement concrete 4.5 m and for RCC of

thickness 20cm is 14m

3.6.2 Construction of Joints

• LONGITUDINAL JOINTS:

• Provided for width more than 4.5 m

• Prevents longitudinal cracks

• Acts as hinge and helps maintaining the level of slabs

3.6.2 Construction of Joints

• TRANSVERSE JOINTS:

• Staggered arrangement, uniform arrangement and skew arrangement

• Allows interaction of water and ingress of stone grits

• If subgrade is clayey soil, mud pumping occurs

• Joint spaces should be filled with compressible joint filler first and sealed

with sealer.

3.6.2 Construction of Joints

• REINFORCEMENTS:

• In the form of welded wire fabric or bar mats

• Holds the cracked slab portions together

3.6.2 Construction of Joints

• The prestressing technique is used in continuous lengths upto 120m without

joints

• Advantage is the elimination of the joints w/o inducing cracks

• Low maintainance cost