Pavement-quality concrete (PQC) yards

How does Pavement-quality concrete (PQC) yards work, step by step?

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   Step 1: Prove the formation and the drainage first

   A rigid pavement is only as good as what it sits on, and a container yard is usually built on filled or reclaimed ground with a settlement history. The formation is proven by testing to the designer's requirements, subbase and capping are placed and compacted in controlled layers, and the drainage is installed as a system that will survive point loading - channels, gullies, ducts and any interception the environmental permit requires. Falls are surveyed before any paving starts, because a yard that ponds is a defect the operations team will photograph forever.

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   Step 2: Complete everything that goes under the slab

   A container yard is an electrical and drainage distribution network with a pavement on top. Reefer power ducts, lighting and crane supply routes, communications, earthing, draw pits and chamber positions are all installed, surveyed and recorded before paving. Once a bay is cast, anything under it is effectively gone. On most projects the duct routes are deliberately kept out of the heaviest stacking rows and are recorded as-built in detail, because the operator will need to find them again.

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   Step 3: Set out the bay and joint layout

   The joint layout is the pavement design made visible. Bay sizes, joint positions and joint types are set by the pavement engineer and are coordinated with the yard markings, the crane runs, the drainage lines and any fixed obstruction, because a joint that clashes with a gully or ends at a re-entrant corner is where cracking will start. The layout is set out on site and checked against the design before any formwork or paving train is set up, and changes are referred back to the designer rather than resolved on the ground.

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   Step 4: Set the forms or the paving train and fix the reinforcement

   Bays are paved either between fixed side forms or by a slipform paver running to stringline or machine control. Dowels are set in cradles across transverse joint positions, aligned accurately and parallel to the direction of movement, and tie bars are placed along longitudinal joints. Dowel alignment is one of the few details that will wreck a concrete pavement quietly - a locked joint restrains movement and cracks the slab away from it. Where the design uses reinforcement it is fixed on supports to the specified position and cover, checked before the pour rather than after.

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   Step 5: Place, compact and finish the concrete

   Concrete is supplied at a controlled and consistent workability and placed continuously, compacted through the full depth by poker or by the paver's vibrators, and finished to the specified surface regularity and texture. Continuity of supply is critical - a paving train that stops leaves a cold joint that was never designed. The mix and its acceptance criteria come from the specification and the concrete supplier's design, and site trials are used to prove the mix, the placing method and the finish before production paving starts.

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   Step 6: Cure and protect the slab properly

   Curing controls early-age cracking, and early-age cracking is the most common serious defect in concrete paving. The slab is cured to the specification immediately after finishing, and protected against sun, wind, rain and temperature swings. Nothing is allowed onto the slab until the specified strength has been achieved and the designer or the specification permits it - not plant, not deliveries, not the following trade. The port operator's pressure to get onto a new bay early is a permanent feature of terminal work and is answered by the specification, not by judgement on the day.

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   Step 7: Cut and seal the joints on time

   Induced joints are saw-cut within the window the specification allows, because cutting too early ravels the edge and cutting too late means the slab has already cracked where it chose to. Joints are then cleaned out and sealed with the specified sealant so that water and grit stay out of the joint and away from the dowels. Joint sealing is often treated as a finishing item and it is not - it is the maintenance-critical detail of the whole pavement, and it is inspected and recorded like a structural element.

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   Step 8: Survey, mark and hand over

   Finished levels and surface regularity are surveyed against the specification, and any bay outside tolerance is dealt with before markings go down. Yard markings, stacking row numbering, lane lines and signage are applied, reefer points and lighting are energised and tested, and the completed area is handed to the terminal operator as a defined phase. The handover record includes the as-built service routes under the slab, the joint layout, concrete records and the level survey.