Highway Construction And Maintenance

Highway Construction and Maintenance • Highway materials, test and construction p practices • Routine maintenance, periodic maintenance • Common causes of failure 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 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; – 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, • shaping the finished surface to design levels, and • excavating for drainage works. Th earthworks The th k is i often ft the th largest l t task t k in i the th roadd building b ildi process and therefore careful planning and organisation are essential. Speed and efficiency depend very much upon the quantity and types of earthmoving plant available available.

Sequence of Operations •

The normal sequence of operations in cut and fill work is: – In Cut • excavate to the depth p necessaryy to reach formation level,, • 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 • thoroughly h hl compact these h layers l to required i d density. d i

Pavement Construction •

•

Gravel and Crushed Rock Pavements – Source: pits,quarries. 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-tyred pneumatic-tyred. – Usually final layer thin to achieve good riding surface.

Pavement Construction •

Cement Concrete Pavements – Manufacture: ready-mixed ready mixed batching plant 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 trimmingg oof underlying u de y g gravel g ve or o crushed c us ed rock oc pavement. p ve e . For o existing bituminous surface: patching. Steps: – Sweep surface - drawn rotary broom + hand sweeping. – Prepare P bi binder d - transport t t to t job j b by b roadd or rail il tanker, t k or in i 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 and start and finish. – Apply aggregate - quick incorporation into hot bitumen b f before excessive i cooling; li spreaders d required; i d drag d broom b to t correct spreading inconsistencies. – Roll surface - to bed stone; pneumatic-tyred or static steel drum rollers. – Drag broom – Record work - quantities bitumen sprayed, sprayed aggregate spread, spread etc. – Traffic control - throughout steps 1 to 10; minimise traffic d l delays.

Construction of HMA Road

Preparation for a Sprayed Bituminous Surfacing Left: Sweeping a gravel pavement prior to the application of a prime. Sweeping is usually carried out with drawn mechanical brooms, although some hand sweeping is often required as well.

Preparation for a Sprayed Bituminous S f i Surfacing Right: Damping the pavement. It is found that a prime or seal will adhere dh better b tt to t an underlying d l i gravel pavement if the pavement is slightly g y damp. p Left: A bitumen road tanker. Transport of bitumen to the job site will usually be by rail tanker or road tanker.

Asphalt Production Right: Batching Plant, Toowoomba. The mix falls through a series of inclined vibrating screens and the various size f i fractions are storedd in i hot h storage bins. bi The plant operator then weighs out the correct proportions of each size for a single batch. The sizes are mixed and then the required q amount of hot bitumen is added and mixing continued. The batch is then discharged from the mixer into a waiting truck, and the batching process repeated.

Left: Hot Storage Bins, Brisbane Plant. In the Brisbane plant, the batches of hot mix are stored in insulated storage g bins, and this means that arriving trucks can be filled more rapidly.

Asphalt Paving. Left: Paving Machine, Front View. This is a view of the front of a typical self-propelled, p p , floating g screed,, ppaving g machine. Tip trucks discharge the hot asphalt into the front hopper and it is then conveyed to the rear of the machine hi by a chain and slat conveyor. Right: Paving Machine, Machine Rear View. View This picture shows a truck with its tray tipped, 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 pplate which vibrates to act as a tamper, 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 paved. paved

Construction of RCC Road

Placement of dowels and tie bars

Dowel bars location

PCC thickness

Roofing paper

Roofing paper-1

Tie bars

Dowel basket

Placement of reinforcement

Dowels images

Forms,Steel form Figure 7.113: Steel Forms

Wooden Form

Removal of Form

Vibrator