[HN Gopher] Princeton engineers create new oyster-inspired cemen...
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Princeton engineers create new oyster-inspired cement 17X more
crack-resistant
Author : toss1
Score : 66 points
Date : 2024-06-27 01:44 UTC (21 hours ago)
(HTM) web link (engineering.princeton.edu)
(TXT) w3m dump (engineering.princeton.edu)
| robertlagrant wrote:
| Someone smarter than me can answer this: how would this be
| applied? If you normally pour cement, which presumably wouldn't
| work with this layered structure, how do you practically use it?
| surfingdino wrote:
| It's a variation on the idea of reinforced concrete. It will
| take time to understand the interaction between cement and
| polymer. It took us time to understand that if moisture gets to
| the steel rods, the reinforced concrete beams crack.
| toss1 wrote:
| >>if moisture gets to the steel rods, the reinforced concrete
| beams crack.
|
| Exactly; and the crucial intermediate step in there is the
| moisture causing the steel to oxidize, the iron oxide
| increasing the volume of the rebar, and thus putting the
| concrete in tension from the inside, and since concrete
| really sucks in tension (but is great in compression), the
| concrete cracks.
|
| I'm mystified that iron-based rebar is even still allowed in
| construction, when fiberglass-based rebar is readily
| available and proven to work better.
| riversflow wrote:
| I asked this question here a while back and the answer I
| got was that at failure steel rebar stretches rather than
| breaks catastrophically and thats a very important safety
| factor when calculating dynamic loads, a fiberglass rebar
| structure would fail far more catastophically.
| toss1 wrote:
| At, finally an answer that makes sense --Thx!
|
| I'm sure adding a bit of kevlar in the rods would solve
| that problem, but modeling will still be difficult...
| surfingdino wrote:
| We have no data on such solutions and we keep building
| bigger, taller, more complex structures so there may be
| some resistance to new solutions, but I'm sure someone is
| working on them, as we reach the limits of the old ones.
| SturgeonsLaw wrote:
| Precast concrete is often made at a factory then transported to
| the work site, a factory environment would enable all sorts of
| processes and this one doesn't look too difficult in principle
| - not to sell them short, it's great research and biomimicry is
| rad, but layering plates in polymer seems like it's definitely
| automatable.
| passwordoops wrote:
| The actual paper is posted in another thread:
|
| https://news.ycombinator.com/item?id=40796770
|
| Can we close this Princeton PR as a dupe and have the discussion
| over there instead?
| klysm wrote:
| I expect this one to perform much better due to the headline
| being more comprehensible
| toss1 wrote:
| thx! I worked on making the headline comprehensible in
| 80chars, and made sure the link to the original paper was in
| the article if people wanted to easily find that level of
| detail.
| CharlieDigital wrote:
| ...creating alternating layers of tabulated cement paste and thin
| polymer can significantly increase crack resistance and the
| ability to deform without completely breaking (ductility)
|
| A few years ago, my daughter and I did a science fair project[0]
| based on a question she asked while we were crossing bridge in a
| car and she noticed the rebar poking out out of an adjacent
| bridge which was under construction.
|
| In our experiment, we tried various reinforcements to concrete
| and tested the weight loading capacity before cracking. Quite
| surprising, at #2, was basic acrylic yarn layered perpendicularly
| in an overlapping "weave". By far the cheapest, lightest,
| strongest reinforcement that we tried!
|
| [0] https://youtu.be/9QlzRT69X-I
| alexpotato wrote:
| Super cool!
|
| I'm always looking for fun STEM things to do with my kids and
| will keep this in mind.
| alexey-salmin wrote:
| Very impressive! Even with an explicitly stated hypothesis.
| Peak asian parenting :)
|
| > By far the cheapest, lightest, strongest reinforcement that
| we tried
|
| In what sense is it strongest, strength-to-weight? Not sure the
| weight matters much compared to the weight of displaced
| concrete.
|
| Also would be really curious to try nylon instead, could even
| beat the steel potentially
| r2_pilot wrote:
| It wouldn't work well: Coefficients of thermal expansion:
| Nylon: Typically ranges from 80-100 x 10^-6 per degC Steel
| rebar: Typically around 11-13 x 10^-6 per degC 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.
| CharlieDigital wrote:
| > 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.
| alexey-salmin wrote:
| 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
| CharlieDigital wrote:
| 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!
| hammock wrote:
| I was thinking about this. The yarn is fuzzy and so has a
| lot more surface area for bonding
| ajb wrote:
| 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?
| CharlieDigital wrote:
| 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!
| IncreasePosts wrote:
| I would just call this "peak parenting". Half the world is
| Asian and doing experiments like this is rare.
| xnx wrote:
| Mesh can even dramatically increase the load bearing capacity
| of sand: https://m.youtube.com/watch?v=0olpSN6_TCc
| BobaFloutist wrote:
| Did you try other yarns in the same weave? I'd be interested to
| see how wool, cotton, hemp, etc would compare.
| loudmax wrote:
| My father went to Princeton for a year for post graduate work
| when I was in kindergarten in the 1970's. We went to a Concrete
| Canoe race (like this one
| https://paw.princeton.edu/article/throwbackthursday-racing-c...),
| and for years afterward I remember him wearing a Concrete Canoe
| t-shirt.
|
| It wasn't until I was much older that I realized that the
| impracticality of building a canoe out of concrete was the whole
| point of the endeavor. For years my childhood brain assumed that
| concrete was just one of the materials people commonly used to
| build boats. Want to build a canoe? Likely options are wood,
| animal hides, or concrete.
| hinkley wrote:
| Our local one when I was in school was milk carton races. Those
| boats were quite odd.
| tomcam wrote:
| I wish my old neighborhood was more crack-resistant
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