Construction activities

Step IV. Pavement Construction

At last, the road bed is ready for paving. Planners and engineers study such factors as the cost of maintaining the road, the amount and type of traffic, the cost of paving material.

A formula that includes all these factors tells engineers to use either asphalt (bituminous) or concrete pavement.

Asphalt uses bitumen, a petroleum product, to glue together sand and crushed rock. This mixture is heated to approximately 300 degrees at the asphalt plant. At the construction site, workers spread and compact the hot mixture onto the roadbed.

Concrete uses cement and water as the glue between sand and crushed rock. Workers place concrete into steel molds called forms. A finishing machine vibrates and trims it to the necessary height. To prevent cracks, workers cut joints between the concrete slabs.

At each joint, wire baskets and steel dowels connect the slabs. These allow the slabs to expand and contract as the temperature changes. The slabs can slide from side to side along the dowels, but not up and down.

Step V. Open to traffic

With the new surface in place, quality testing is conducted. Testers use seismology equipment to measure vibrations of the new pavement. If there is too much vibration, the contractor must grind the pavement to ensure a smooth surface. The final steps are:

· another drainage test;

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· applying the permanent pavement markings.