Urbanite: Using old concrete for new construction

There’s a much better alternative to breaking up a concrete slab and hauling it off to the landfill. That old slab can become low dry stacked retaining walls or act like flagstones, depending on how its surface was treated.

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Urbanite paving

Larger pieces work best, with smaller pieces between them. They’re less likely to tip or moved when stepped on, and can be installed more quickly.

The trick with this material is that the thickness is not always uniform, so you need to check the maximum thickness before you begin, if possible, then dig down at least an inch deeper than your thickest piece.

The next step is to put down some geotextile fabric, then whatever base you’re using for the urbanite. The base can be compacted sand, aggregate base or crushed rock, as used here. Sand is easy to modify in case there’s a bump or thicker side to the concrete; aggregate base less so, because it’s harder to dig into once it’s been compacted – although once you’ve got it, the stuff doesn’t move. The fabric is there to prevent fine particles from the soil from mixing with the aggregate, since they would reduce permeability over time and support weed growth better than pure gravel.

If you’re using aggregate base or sand, you’ll need another more decorative material for the joints. It can be crushed rock, tumbled recycled glass (expensive), pebbles or whatever you find interesting as long as it lets water through and isn’t toxic.

The crushed rock used here, 3/8″ Ione Gold, does not compact into an almost solid surface, so smaller slabs can move around if they’re not placed close to one another to form a more continuous surface. The advantage of the rock is that water passes through it instantly, and the spaces between the rocks can become a reservoir for rain water.

If you’re not setting the urbanite slabs in soil, you’ll need to install headers efore you place the base material. The headers (the gray-brown divider between the plants and gravel) will keep the gravel out of your landscape, more or less.

This header is recycled plastic, but is subject to heat expansion and contraction that eventually flips the thing out of the ground. Not good. It might be a “green” material, but it’s not the best solution – aluminum headers would be better, and they’re almost certainly more recyclable.

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Header to contain gravel
Narrow path paved with urbanite
Narrow path paved with urbanite

This used to be a silly, too-narrow path that didn’t work well at all. It was one of the first things to go when we redesigned the front yard. The path now works – in the sense that it goes where we really want to walk, not where someone thought we’d walk. It’s the same concrete, but in a more useful layout – and we didn’t have to pay to haul it off to the dump.

Yeah, those are weeds in the cracks – along with a ground cover euphorbia that’s gradually moving in. This path used plantable soil between pavers, in an attempt to grow creeping thyme. The thyme died; the weeds didn’t – but the euphorbia (left) is gradually moving in.

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This root can grow without restrictions, and no pavement gets heaved

Urbanite works where solid concrete might be problematic, too – as in this case. The tree root has already grown about 1/2″ since the urbanite and gravel went in. This way, the root just becomes a stepping element, and we can fill in gravel to keep it more or less level with the walking surface.

If you’re feeling really ambitious, you can stain or color the concrete – or go even crazier (maybe too crazy) and add mosaic. We’re not quite that crazy… yet.

Don’t limit yourself

Urbanite can be used with other landscape elements, working very well in eclectic or artists’ gardens (or sustainable artist’s gardens).

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urbanite paving combined with narrow modular pavers

The linear texture of the deck transitions to the decorative arcs in the step, ending with the random angles and shapes of the urbanite. Since there’s a lot of deck and urbanite, the step functions as a decorative transition between the two, keeping the design from getting too “busy”.

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Transition from low deck to step to urbanite

Remember to keep large expanses of one paving type – urbanite, deck, gravel – and use transitions and accents where they’ll have the most effect, generally between garden areas or where you’re moving from one surface to another.

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Urbanite, gravel and a recovered cast iron drain grate give a more industrial look to the paving.

A lot of old concrete is now being ground up and used for road base, so even if you want pristine new paving, your old concrete may have found a better life that doesn’t involve a landfill.

 

4 thoughts on “Urbanite: Using old concrete for new construction

  1. There is a layer of weed barrier / geotextile (filter) fabric on the soil, then a layer of aggregate, then the urbanite with aggregate between the cracks. The geotextile keeps the soil from infiltrating the gravel – so the spaces between the gravel particles stay open and dry. The result is that although some weeds do grow between the cracks, there’s not much for them to grow in (no soil) and they’re easy to pull out if they do start.

    We’re also in a climate that doesn’t get a lot of rain and the urbanite is generally not irrigated – if this were a wetter climate, this would not be as effective due to constant moisture between the gravel particles.

  2. Urbanite is just broken-up concrete. We found some when a neighbor tore out a driveway, but most of it was from demolishing existing concrete paths.

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