4 ms·

Probably because (among other reasons) structural reinforced concrete depends on cracking, both to develop internal strength and to prevent abrupt catastrophic

Probably because (among other reasons) structural reinforced concrete depends on cracking, both to develop internal strength and to prevent abrupt catastrophic failure. ACI building code (or a derivative) applies in most US jurisdictions, and it relies on heavily on the premise of concrete showing cracks before reaching the failure point of the internal steel. It ensures a failure mode that illicits a warning. (The internal strength development probably wouldn't be as much of an issue with the "rubbery" concrete, assuming the compressive strength is equivalent, but I'm sure there are other considerations I haven't thought of. You're changing fundamental properties of the material that is expected by most designers. Existing brittleness is accounted for and expected.) Civil Defense and Military applications don't necessarily have the same design requirements, or need to be as compliant with a particular building code, as they're typically exempt from local building regulations and/or have their own separate building standards. On the other hand, asphalt pavement design is based on principles that could benefit from such a material without having to completely re-invent the design code.

LegitShady 7y ago
There just isn't enough information in the article to judge the material. My guess is by lowering the amount of cement they're reducing overall compressive strength, but by including fibrous materials they're resisting cracking. The reported "rubbery" behaviour means the material is overall less stiff and I'm not sure that does good things for development lengths or reinforcing required. I don't know what to make of the statement that it's "impact proof". Steel yields and concrete crushes, but I guess this is a high strain material. My initial thought was that it sounded like a good paving material if its sufficiently stiff...
specialist 7y ago
Great explanation, thank you. A cogent answer to a question I would have never thought to ask. Maybe that visual inspection requirement will change as we develop non-destructive testing options.
- beerandt 7y ago
  Non destructive testing exists and is fairly mature for reinforced concrete. It's just more expensive. But it's not so much about testing, since once a structure is built, you're not going to get the owner to pay for any more testing, until signs of potential failure arise. You need an obvious reason to test in the first place. Testing also somewhat implies that the design or material is defective; but that's only two paths to failure out of many. More likely, the structure is overloaded, or supplemental supports are removed prematurely, as is what seems to be the case for the recent hard-rock hotel collapse in New Orleans. This isn't too say that new materials don't have a beneficial use. We would probably need to develop a new and separate sub-discipline, the same way pre-stressed and post-stressed concrete structures are designed, which have since been included into ACI code.

LegitShady 7y ago

There just isn't enough information in the article to judge the material. My guess is by lowering the amount of cement they're reducing overall compressive strength, but by including fibrous materials they're resisting cracking. The reported "rubbery" behaviour means the material is overall less stiff and I'm not sure that does good things for development lengths or reinforcing required. I don't know what to make of the statement that it's "impact proof". Steel yields and concrete crushes, but I guess this is a high strain material. My initial thought was that it sounded like a good paving material if its sufficiently stiff...

specialist 7y ago

Great explanation, thank you. A cogent answer to a question I would have never thought to ask. Maybe that visual inspection requirement will change as we develop non-destructive testing options.

beerandt 7y ago
Non destructive testing exists and is fairly mature for reinforced concrete. It's just more expensive. But it's not so much about testing, since once a structure is built, you're not going to get the owner to pay for any more testing, until signs of potential failure arise. You need an obvious reason to test in the first place. Testing also somewhat implies that the design or material is defective; but that's only two paths to failure out of many. More likely, the structure is overloaded, or supplemental supports are removed prematurely, as is what seems to be the case for the recent hard-rock hotel collapse in New Orleans. This isn't too say that new materials don't have a beneficial use. We would probably need to develop a new and separate sub-discipline, the same way pre-stressed and post-stressed concrete structures are designed, which have since been included into ACI code.