Highway Construction andHighway Construction and Maintenance

• Highway materials, test and construction practices p

• Routine maintenance, periodic maintenance• Common causes of failure long life roads• Common causes of failure, long life roads

The Road Construction Process

• The type of road construction used varies from one job to another. The type of construction adopted for a particular road depends on: the volume and nature of traffic to useroad depends on: the volume and nature of traffic to use the road,

• the nature of the materials available, • the topography, • foundation conditions, • type and availability of construction equipment, and • financing arrangements and timing.

The Road Construction Process• Any road construction job consists of number of basic steps, although

the relevant importance and the interaction between these steps will vary from job to job. These steps can be summarized as: – planning, programming and pre-construction activities; – site clearance; – setting out;– setting out; – earthworks; – bridge construction; – drainage structures; – pavement construction; – placement of road surfacing; – placement of road furniture; and – landscaping.

Earthworks• The eventual aim of the earthworks phase of the construction is to

position the subgrade underlying the pavement layers in the right location and at the correct level, and to provide drainage. The operations to be performed are:

• formation of cuttings by excavating through high ground, • formation of embankments by filling over low ground,formation of embankments by filling over low ground, • shaping the finished surface to design levels, and • excavating for drainage works.

Th th k i ft th l t t k i th d b ildi• The earthworks is often the largest task in the road building process and therefore careful planning and organisation are essential. Speed and efficiency depend very much upon the quantity and types of earthmoving plant availableearthmoving plant available.

Sequence of Operations• The normal sequence of operations in cut and fill work is:

– In Cut • excavate to the depth necessary to reach formation level, p y ,• transport away from the site undesirable material such as organic

soils, • haul suitable materials from cuts to fill areas, and • suitably dispose of any excess cut material.

– In Fill • drain water from depressions and dispose of any unsuitable

underlying material, • spread fill material in horizontal layers not more than 250 mm thick,

and h hl h l i d d i• thoroughly compact these layers to required density.

Pavement ConstructionPavement Construction• Gravel and Crushed Rock Pavements

Source: pits quarries– Source: pits,quarries. – Haulage: trucks. – Spreading: grader or paver. – Compaction: higher compaction standard than subgrade; different

roller types used. – Accuracy of levels important.

• Asphalt Pavements– Manufacture: fixed plants (up to 400 tonnes per hour), or large

mobile plants. – Haulage: trucks. – Placement: paving machine. – Compaction: rollers - smooth vibrating drum and pneumatic-tyredCompaction: rollers - smooth vibrating drum and pneumatic-tyred. – Usually final layer thin to achieve good riding surface.

Pavement ConstructionPavement Construction• Cement Concrete Pavements

Manufacture: ready mixed batching plant– Manufacture: ready-mixed batching plant. – Haulage: agitator truck. – Large quantities: site manufacture + normal trucks. – Placement: slip-form paver. – Compaction: internal vibrators + external screeds.

Placement of Road Surfacing• May be gravel, sprayed bituminous seal, asphalt or cement

concrete. Construction of Sprayed Bituminous Surfacing• Pavement must be sound. For new work: compaction and

trimming of underlying gravel or crushed rock pavement. For g o u de y g g ve o c us ed oc p ve e . oexisting bituminous surface: patching. Steps: – Sweep surface - drawn rotary broom + hand sweeping.

P bi d t t t j b b d il t k i– Prepare binder - transport to job by road or rail tanker, or in drums.

– Flux and/or cutback binder. – Incorporate adhesion agent. – Prepare aggregate - stockpiles, precoating

– Spray binder - air temperature should be > 15 C; no rain should be threatening; mark out spray run- alignment andshould be threatening; mark out spray run- alignment and start and finish.

– Apply aggregate - quick incorporation into hot bitumen b f i li d i d d b tbefore excessive cooling; spreaders required; drag broom to correct spreading inconsistencies.

– Roll surface - to bed stone; pneumatic-tyred or static steel drum rollers.

– Drag broom – Record work - quantities bitumen sprayed aggregate spread– Record work - quantities bitumen sprayed, aggregate spread,

etc. – Traffic control - throughout steps 1 to 10; minimise traffic

d ldelays.

Construction of HMA RoadConstruction of HMA Road

Preparation for a Sprayed Bituminous Surfacing

Left: Sweeping a gravel pavementprior to the application of a prime.Sweeping is usually carried out with drawn mechanical brooms, althoughsome hand sweeping is oftensome hand sweeping is often requiredas well.

Preparation for a Sprayed Bituminous S f iSurfacing

Right: Damping the pavement.It is found that a prime or seal will dh b tt t d l iadhere better to an underlying

gravel pavement if the pavement is slightly damp.

Left: A bitumen road tanker.Transport of bitumen to the job

g y p

site will usually be by rail tanker or road tanker.

Asphalt Production

Right: Batching Plant, Toowoomba. The mix falls through a series of inclinedvibrating screens and the various size f i d i h bifractions are stored in hot storage bins.The plant operator then weighs out the correct proportions of each size for a single batch. The sizes are mixed and thenthe required amount of hot bitumen qis added and mixing continued. The batchis then discharged from the mixer into a waiting truck, and the batching processrepeated.

Left: Hot Storage Bins, Brisbane Plant. In the Brisbane plant, the batches ofhot mix are stored in insulated storage gbins, and this means that arriving truckscan be filled more rapidly.

Asphalt Paving.

Left: Paving Machine, Front View. This is a view of the front of a typicalself-propelled, floating screed, paving p p , g , p gmachine. Tip trucks discharge the hot asphalt into the front hopper and it is then conveyed to the rear of the

himachineby a chain and slat conveyor.

Right: Paving Machine Rear View ThisRight: Paving Machine, Rear View. This picture shows a truck with its traytipped, discharging mix into the paver.The operator sits on top and steers the machine to the required alignment.

Asphalt Paving.Right: Screed Unit. The screed unit consists of levelling arms,a screed plate which vibrates to act as a ptamper, and thickness controls. It is supported by the mix which gives it a floating action.

Left: Reference Beam Attached to Paver. A long moving reference beam, mounted on shoes (or skis) can be used to ensure the screed follows a smooth line regardless of irregularities in the surface being pavedbeing paved.

Construction of RCC RoadConstruction of RCC Road

Placement of dowels and tie bars

Dowel bars locationDowel bars location

PCC thickness

Roofing paper

Roofing paper-1

Tie bars

Dowel basketDowel basket

Placement of reinforcement

Dowels images

Forms,Steel form Figure 7.113: Steel Forms

Wooden FormWooden Form

Removal of Form

Vibrator