> In what sense is it strongest, strength-to-weight

Weight, size, and cost. The galvanized wire was the clear winner (hairline crack at 300lbs), but also cost significantly more than the acrylic yarn. Would be interesting to revisit this experiment with different densities of the acrylic weave to see where the limits are. We used a very sparse weave, but I could see tripling the weave density raising the weight limit closer to 300 than 225.

Also probably need to prestress it for best results :)

If it's stretchy or wavy, the concrete may crack before it starts to produce tension

I wonder.

I hypothesize that one of the reasons the yarn performed so much better than the deer net is because it is more permeable and thus formed a better bond with the concrete.

In this scenario, I would imagine that it would be "locally tensioned" because the cement is effectively tightly bonded across any point of stress. Would be an interesting experiment!

Isn't the point of pre-tensioning is not the actual tension on the reinforcement, but the pre-loading of the concrete - so it needs to happen everywhere in the volume of the concrete, not just next to the reinforcement?

Interesting point; I see what you are saying like during the curing process, the tension in the yarn weave itself would pre-tension the dried slab. But I wonder if acrylic yarn would have a sufficient effect and to what extent.

If anyone has science fairs coming up, these seem like excellent experiments!

I was thinking about this. The yarn is fuzzy and so has a lot more surface area for bonding

It wouldn't work well: Coefficients of thermal expansion: Nylon: Typically ranges from 80-100 x 10^-6 per °C Steel rebar: Typically around 11-13 x 10^-6 per °C Comparison: The coefficient of thermal expansion for nylon is significantly higher than that of steel rebar - about 6-9 times greater. This means nylon expands and contracts much more with temperature changes compared to steel. That's not even taking into consideration the tensile strength of nylon and steel. But an interesting thought, for sure.

I would just call this "peak parenting". Half the world is Asian and doing experiments like this is rare.

Good things are always rare, the question is whether they are less rare in some cases compared to others