Concrete tubes: hemholtz resonators? tubes?

During a search on the web I found a blur about using concrete tubes, found at places like Home Depot as bass traps. Has anyone used this before? Will the hard shell reflect more than absorb?
It is the size of the cavities and the openings that determine the characteristics of these resonators. The shell of the cavities should be inert since they do not play a role as an absorber. The fact that they are concrete would be an advantage because they would not flex.
They are not talking about "concrete tubes". They are talking about the hard cardboard tubes that are used to form concrete pillars. You pour concrete into them, and when it dries, you cut the cardboard off, and you have a pillar or piling.

These tubes come in sizes from about 6" diameter to about 24" diameter, and they are thick hard cardboard. The most common size I see are 8" and 12". They are often used in DIY projects to make tuned "t-line" type enclosures for subwoofers. Unfortunately, the single diameter tube doesn't have the actual correct tapering for a true t-line, and winds up giving "one note bass". It's not really that bad, but tapered would be a lot better.

They could be used as bass traps, if you make them correctly.
A few years ago, there was an article about this at Headroom (the headphone people). Unfortunately, my company's firewall thinks the link to Room Tubes is about sex and won't let me open it. Maybe you will have better luck:
The hollow concrete tubes go by the trade name Sonotube. I've used 'em, but to build a deck and fence (I know, I've failed as a 'phile so far). The exterior of the tubes are shiny and if I had to guess, reflect more than absorb but I really have no practical audio experience with these. In any event you may want to check out HSU's subwoofers, I suspect they use Sonotubes in their design.

Tsouth, your company firewall blocking you is somehow amusing to me.
Good article and interesting information. I just think that implementing so many tubes may make my listening room look like a graveyard of sorts. It is worth exploring.