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Last night I had a dream. I dreamed of a great bridge that spanned two peaks shaped like the Devil's Tower. The bridge was a single beam-like structure, black in color, but reflective like volcanic glass. It spanned a distance of many miles, and in my dream I thought "There is no substance strong enough to span this distance that would not collapse under its own weight." So I asked myself, "What material would be strong enough to support this span?"

The answer came into my head: "Pre-stressed carbon nanotubes in a diamond matrix." What I am asking all you engineers and scientists on Poal (stop laughing -- there may be a handful of you) is this:

Is a composite composed of pre-stressed nanotubes in a diamond matrix possible? Would it yield the strength that would allow a beam miles long to span the distance between two mountain peaks?

For those who have no idea what I'm talking about, we do much of our construction using pre-stressed concrete. This is concrete that contains steel rods that have been pre-stretched before the concrete is poured around them, then allowed to relax, which puts pressure on the concrete, holding it together. Pre-stressed concrete beams are much stronger than common comcrete beams would be and can support much greater loads.

I was able to find on carbon nanotube reinforcement of composits, but there was nothing in this chapter about a diamond matrix. Is it possible? Would it greatly increase the load-bearing strength of a beam made from it?

Last night I had a dream. I dreamed of a great bridge that spanned two peaks shaped like the Devil's Tower. The bridge was a single beam-like structure, black in color, but reflective like volcanic glass. It spanned a distance of many miles, and in my dream I thought "There is no substance strong enough to span this distance that would not collapse under its own weight." So I asked myself, "What material would be strong enough to support this span?" The answer came into my head: "Pre-stressed carbon nanotubes in a diamond matrix." What I am asking all you engineers and scientists on Poal (stop laughing -- there may be a handful of you) is this: Is a composite composed of pre-stressed nanotubes in a diamond matrix possible? Would it yield the strength that would allow a beam miles long to span the distance between two mountain peaks? For those who have no idea what I'm talking about, we do much of our construction using pre-stressed concrete. This is concrete that contains steel rods that have been pre-stretched before the concrete is poured around them, then allowed to relax, which puts pressure on the concrete, holding it together. Pre-stressed concrete beams are much stronger than common comcrete beams would be and can support much greater loads. I was able to find [this](https://www.intechopen.com/books/diamond-and-carbon-composites-and-nanocomposites/carbon-nanotube-cnt-reinforced-metal-matrix-bulk-composites-manufacturing-and-evaluation) on carbon nanotube reinforcement of composits, but there was nothing in this chapter about a diamond matrix. Is it possible? Would it greatly increase the load-bearing strength of a beam made from it?

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[–] • 5 pts

The short answer is no. Carbon nanotubes are not exceedingly strong under compression, so prestressing them doesn't yield great strength.

Concrete is absolutely terrible under tension and sheer. A quality concrete cylinder on which the weight of a car can be balanced can ripped apart by an average strength man. You prestress concrete to ensure the concrete stays under compression under all expected structure loads. Also

steel rods that have been pre-stretched before the concrete is poured around them

is not the way prestressing works. The pre is before the structure load is placed on the concrete. Not before it is poured. Usually, a steel rod with threaded ends is placed when there concrete is to be poured just like rebar. The concrete is allowed to sufficiently dry. Then fasteners are tightened on the end of the concrete to achieve proper compression of the concrete structure.

[–] • 0 pt

Actually you can pre-tension as well as post-tension concrete. Post-tensioning is done with cables in a sheath, tensioned after the concrete is set. Concrete can also be pre-tensioned with cables tightened before the concrete is placed. Post tensioning is handy since the pieces can be cast then transported with the tension load only added once the piece is in place.

[–] • 0 pt

Looks like you are correct. I've never seen stuff done this way, but I guess its usually used for prefabbed parts.