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far enough down the core
Wednesday, November 12 2008
While I was out today getting things like concrete, I hit two of the places where I've been able to get free scrap iron of late. One of these places is the Citgo at the 9W shopping area that features Burlington Coat Factory, Staples, a dollar store, a pizza place, and a liquor store. This Citgo is currently undergoing massive rennovations, meaning there's at least a mile-long stretch of 9W without a gas station. As part of these rennovations, an enormous trench has been dug, and many cubic yards of reinforced concrete have been jackhammered apart and piled up. This leaves plenty of twisted pieces of rebar scattered around the site. Though the Citgo is fenced-off from the surrounding parking lot, I've been able to reach through or under the fence to grab pieces of the rebar, which I've then been able to use to reinforce the cores of the concrete block walls of my nascent greenhouse. At a price of a dollar per foot, it turns out that rebar is actually one of the pricier commodities that go into a reinforced concrete block wall, so it's been good to be able to get some of it for free.
The other place I can go for scrap iron is the wasteland immediately south of the Hudson Valley Mall (and immediately north of Home Depot). Into this wasteland, which is semi-forested, has gone all the leftover concrete and asphalt from various nearby development projects. I visited it in the past with Gretchen and noted the other detritus here, which includes things like industrial-grade cast iron pipes and odd bits of broken machinery. Today I went there looking for rebar or any heavy iron that I could use as a rebar substitute. I found a number of amazing pieces, including an old axle at least two feet in length and much sturdier than rebar. I also found some heavy bits of broken cast iron which I also took. One of these was of a shape and size that I thought perhaps it could be used as short structural girder or perhaps even an anvil.
This evening I found myself calculating the volume of each of my concrete block cores, which each seem to require an eighty pound sack of concrete to fill, but only if I augment the concrete with numerous cobblestones. I did a calculation of the volume of the cores, which measure approximately sixteen square inches in cross section and are eighty inches long. That's 1280 cubic inches, and eighty pounds of concrete yields about a half a cubic foot, or 864 cubic inches. This means that if I use a whole eighty poind bag on a full eighty inch core, I have 416 cubic inches leftover that I have to fill with something else like cobblestones. Otherwise that extra volume ends up being air, a non-structural component that is hard to avoid when filling a long narrow core. Cobblestones, no matter how small or smooth, seem to delight in lodging on the narrowest ledges they can find on their way down, where they can then catch other cobblestones, eventually forming a blockage. If it's far enough down the core, the only notice I'll receive is after it's too late: that I haven't used nearly enough of the concrete I've mixed.
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