Recycled Concrete Update

"We are committed to witness through the good quality of our work and careful stewardship of our resources."

-From the Statement of Values of the Appalachia Service Project

The first week of work on the recycled concrete project is over, and I have an update. First of all, I need to re-issue the formula. Finally, here's the formula for making one cubic foot of concrete from recycled concrete aggregate.

To Make One Cubic Foot of Concrete From Recycled Concrete Aggregate
(combine these ingredients)

Ingredient	Volume	Weight	"Density"
	(Cubic Feet)	(Pounds)	(Pounds per Cubic Foot)
Cement:	0.14	13.16	94
Water:	0.12	7.44	62
Coarse Aggregate: (gravel)	0.39	46.8	120
Fine Aggregate: (sand)	0.35	35	100

Now, it seems obvious that this is a great idea which will help to preserve our natural environment while cutting costs, but we mustn't be hasty and presumptuous environmentalists. For this purpose, a cost-benefit analysis is necessary.

To make one cubic foot of concrete using Quickrete ready-mix bags costs $7.42.
To make one cubic foot of concrete using the recycled concrete method costs $1.32.

This is based on using 80-pound bags of Quickrete at $4.45 per bag, and using 94-pound bags of Portland cement at $9.45 per pound. These are the prices at the ACE Citizens Building Supply store here in Bluefield, WV.

And if you consider that using recycled aggregate keeps 82 pounds of aggregate from going to the dump (per cubic foot of concrete needed), $1.91 is saved in dump fees. This assumes a dump fee rate of $46.75 per ton, which is the Mercer County Landfill fee.

If you include the cost of dumping the old concrete, making one cubic foot of concrete from Quickrete Ready-mix bags costs $9.33.

That makes for a savings factor of 705%, and a savings of $8.01 per cubic foot of concrete needed. On our project, where 16.5 cubic feet were needed, we saved a total of $132.12 by going with recycled concrete.

What's missing? Labor. Here at ASP, labor is free. This would obviously be a major contributing factor to the cost of recycled concrete for a non-volunteer organization. I have no way of telling how much extra labor we put into breaking up the concrete blocks as opposed to the labor of loading it into a truck and hauling it to a landfill. We used sledge hammers and digging poles (a.k.a. "God Rods") to smash the blocks, and a clothes hamper with 1/2" hardware cloth over it to separate the fine from the coarse aggregate. Another thing to consider is that on a larger site, pneumatic or hydraulic tools would typically be used to break up the concrete into aggregate. That might speed up the process.

Another major variation from the conventional recycled concrete process is that we used aggregate from broken-up concrete blocks (a.k.a. "cinder blocks") instead of breaking up reinforced concrete, which would have been too difficult without the help of pneumatic or hydraulic tools.

If you're curious as to the performance of the final product, I'm sorry to say that we don't have the facilities to do stress tests here at ASP. I'm not concerned, though, because our recycled concrete will be going into post-holes. I wouldn't recommend making a structural member from recycled concrete without testing it first.

Environmental Impact: Making concrete from recycled aggregate eliminates the need to mine gravel. Gravel quarries strip land of vegetation and habitat, allow sediment runoff into streams, and require lots of energy to extract the gravel. Loss of vegetation and use of carbon fuels is double-trouble for climate change (if you're into that kind of thing).

Finally, I would like to address the educational impact of our project. Using this simple, sustainable method of making concrete, we were able to teach volunteers and community members how to really "think green." I urge you to involve others when you do cool things. They may have helpful input. For example, I didn't come up with the specifics on how to break up blocks, but the volunteers came up with a great system for doing it, and for separating the coarse and fine aggregates. So take the time to grab the people around you and teach them.

And remember: "These things won't fix themselves, and most of them can't be fixed alone."