Concrete and a tense situation

By Tom Gocze, BDN Staff
Posted Nov. 26, 2010, at 8:40 p.m.

There are times that serendipity crosses my path. We have been working on a new type of wood boiler. Part of its unique design is that you feed wood into it vertically. This allows for simpler handling of the wood, but smoke can spill out since the wood smoke will naturally rise out the open cover. I came up with an idea to solve the problem while busy with another project.

Of course, I forgot about it. I did not remember the change I wanted to try until late today while looking at a video of another boiler we are working on. I tried the change, which seems to work extraordinarily well. Sometimes things just fall into place.

Another serendipitous occasion occurred today while looking through some trade publications. There was an article touting the latest and greatest building products of 2010. There are things such as new “eco-green” insulation, “next generation” drywall and the newest engineered wood. This is rather ho-hum stuff since there was nothing really new there.

Then I came across a product called Bolt-A-Blok. It is basically a cement building block like you would use for a basement wall, but instead of mortar to hold the blocks together, they are bolted together with anti-corrosive steel fasteners: A cement block wall that bolts together!

This does not sound like a big deal, but structurally, you are creating what is known as a post-tensioned wall system, which is very strong.

Concrete and cement blocks are very strong in compression. You can squeeze them a lot and they take it. They are, however, weak in tension. If you push them sideways, they will buckle and fail. This is why we install reinforcement steel in concrete walls and cement block walls. The steel adds tensile strength to the wall. The combination of reinforcement bar, or rebar, and concrete make a very effective building system.

The dilemma is that there is some art to good masonry and there also is some serious time invested for the installation and for the mortar to cure.

This system starts with a concrete footing or base, but once that is done, the block is simply stacked and bolted together. It is fast and affordable. Reinforcement is not necessary since it is part of the construction.

The reinforcement is a little different in that the blocks are squeezed together with bolts instead of just installing pieces of rebar into concrete. The physical act of squeezing the block together with bolts is known as post tensioning. This concept is usually used in a slightly different fashion to built bridges. As you might imagine, it is quite strong.

Why get so excited about a concrete building block?

Well, it is truly something new that works better. There always is a better building block that shows up in the trade literature, such as the new-old variations on a theme that fill the “best of 2010” reports. This is truly something that is noteworthy.

I can see a lot of variations on the basic theme.

If we look at buildings that last, masonry and stone can be real survivors compared with wooden structures.

Masonry structures are not perfect. They need to be insulated properly or they will suffer in our climate, but in 2010, this is not a daunting task.

Questions for Tom Gocze should be mailed to The Home Page, Bangor Daily News, P.O. Box 1329, Bangor 04402-1329.

http://bangordailynews.com/2010/11/26/living/concrete-and-a-tense-situation/ printed on September 2, 2014