Which parts of an asphalt parking lot should be concrete?

Which parts of an asphalt parking lot should be concrete?

The places where something heavy stands still or turns hard, plus the low spots where water sits. Those get commercial concrete in Henderson, and the stalls and drive aisles between them stay asphalt. On a business lot along US 41 or Green Street the list is usually short:

• the dumpster spot and the stretch of lot the hauler’s truck stops on in front of it
• the apron at a dock door or an overhead door
• the entrance where delivery trucks swing in off the street
• the curb line those turns run over

Asphalt is a flexible pavement. A truck rolling across it presses the surface down and moves on, and the asphalt recovers. A load that sits for hours, or a tire that twists in place while the truck barely moves, pushes it sideways faster than it can come back. On a July afternoon, with the blacktop soft, it can happen in a single day. Concrete carries a parked load and a rolling one the same way.

Is the dumpster pad enough, or does the strip in front of it need concrete too?

The strip usually needs it more. The pad is where the container sits. The hauler’s truck stops on the asphalt in front of it, picks up a loaded can, and carries all that weight on the same few square feet of blacktop at every pickup. That approach is where a business lot ruts first, so the concrete gets sized to the truck’s approach, not the dumpster’s footprint.

A pad poured to the size of the enclosure and no bigger leaves its edge right where the truck’s tires stop. Within a couple of seasons the asphalt side of that edge sinks into two dished ruts, and the pad stands up out of the lot like a step. Ask the hauler which truck services the lot and where it stops when it lifts. The concrete runs out to there.

The pad itself is covered on the commercial page under what a dumpster pad is and why the hauler wants one.

What does a trailer parked at a dock door do to asphalt?

It punches holes in it. A loaded trailer dropped at a dock stands on two small landing-gear feet for hours or days, and in summer heat those feet sink into asphalt the way a kickstand sinks into a lawn. The trailer’s tires roll back into the same two ruts on every visit. A concrete apron in front of the door, long enough that the landing gear sets down on concrete, takes both.

The length comes from the trailers that actually use that door, measured from the dock face out to where the gear lands, with some room for a driver who backs in a little short.

Forklifts are the other load at Riverport and in the industrial parks off the bypass. Where one comes out of an overhead door at grade, its small hard wheels turn tight under a pallet and scuff the asphalt into loose stone. Concrete holds up to that turning.

Parked weight is harder on any pavement than rolling weight, new concrete included, which is part of why a loaded truck stays off a fresh slab longer than a car does.

Why does the entrance break up, and is that a curb problem?

The same turning truck usually breaks both. A box truck or a semi turning in off the street cuts the corner, and its rear tires climb the curb and scrub across the asphalt where the turn is tightest. The asphalt there shoves into ridges and the curb cracks off in pieces. Along US 41, a winter of plowing finishes off a curb the tires already loosened. A concrete curb and gutter run through the turn, or a concrete section across the entrance itself, stands up to that scrub where asphalt and an asphalt curb do not.

Curb and gutter is figured by the running foot, $30 - $45 per linear ft as a Henderson planning range, so the length of the turn the trucks actually use is the measurement that matters. Watch one delivery come in. The black tire marks on the curb face and the place where the asphalt edge starts to crumble show the line drivers really take, which is rarely the curve the curb was built to.

How does a concrete section meet the asphalt around it?

At a straight saw cut, finished flush. The asphalt is cut back to firm pavement in clean lines, the base underneath is dug out and rebuilt, and the concrete is placed level with the asphalt around it so a tire rolls over the seam and a plow blade rides across it instead of catching.

The sequence on most of these jobs:

1. Mark the cut past the damaged area, out to asphalt that is still tight. Rutted asphalt usually sits on base that has already been pushed around, and pouring on it carries the failure into the new section.
2. Saw the asphalt along the marks and lift it out.
3. Dig out the soft material and rebuild the base to the depth the concrete section needs.
4. Form, pour and finish the concrete to the height of the surrounding lot.
5. Patch the asphalt back up to the new concrete edge where the cut left a gap.

That last step is paving work. The crews we connect with do the concrete. The asphalt patch at the seam, and any sealcoat or striping afterward, belongs to a paving contractor, and lining the two trades up on one schedule keeps the spot from sitting open between them.

Will a concrete pad in an asphalt lot hold water?

It will if it gets poured into a low spot as a flat slab. A lot drains by falling toward its inlets or its edges, and the worst asphalt is often where that fall flattens out and water sits. A concrete section has to keep the lot’s existing fall, carrying water across it and on toward the drain, or the lot trades a pothole for a concrete puddle.

Standing water is part of why the asphalt in that spot gave out. It softens what is underneath, and the next loaded truck pushes it out the sides. Look at where the water stands after a hard rain, before anyone lays out the section. On lots toward the river, where the water table rises in spring, the ground under a low spot can stay wet from below, and that gets checked on the site visit before the section is dug.

How long before the hauler or a loaded truck can use the new section?

Cars are a matter of days. A loaded hauler or a trailer standing on its landing gear waits out the full cure, 28 days. The lot keeps working around the closed spot. The dumpster sits on the asphalt somewhere else for the month, or a dock door comes out of rotation while its apron cures. Pour day is the other closure, and pours scheduled outside business hours keep it out of the working day.

A spot that gives out in January waits. A winter pour takes blankets and carries risk a lot section does not need to take, so a rut that opens in plow season gets a temporary asphalt patch from a paving contractor until the pour season comes back in April.