Silicon fluorescence from microcracks in cement, revealing signs of damage | Hacker News Reader

Silicon fluorescence from microcracks in cement, revealing signs of damage

nature.com

62 pointstech_timc12 comments

It would be relatively easy to setup a CCTV rig that would monitor and report stress changes over time on bridges and such. Would be cheap and low maintainence.

The magnitude of this fluorescence is likely way below the noise floor under normal conditions. They're fluorescing the cement with a laser under presumably not-extremely-bright conditions.

What about conditions when it’s the middle of a moonless night and the number of cars actively on the bridge is low?

Seems it might be not-extremely-bright / pretty dark during such intervals.

Then the fluorescence will be equally dark.

Bridges have complicated shapes, are often huge, and would need a rather crazy number of cameras + laser to get full coverage. This might be one of the few times a drone with a camera is actually a reasonable solution. Doing a full inspection every 2-6 months would normally be fast enough so it could wait for good weather.

Could this be done by a drone that flies around the structure once a week, month, etc - and that footage could be then reviewed? It could be a combo of video and still photos taken in the same approximate location on a routine basis.

The fluorescence is so weak that the ambient conditions need to be dark and the concrete needs to be hit with only a narrow band of the light spectrum. Then you need a tuned detector to pick up the weak fluorescence, after which the SNR is still so low that the raw data must be processed to produce a meaningful result.

All very doable, but I don't think this would work using a standard CCTV looking at an area bigger than a metre (few feet) across.

A long time ago in a place far far away, I was part of a team that did exactly this to differentiate between healthy and possibly pre-cancerous tissue.

> A long time ago in a place far far away, I was part of a team that did exactly this to differentiate between healthy and possibly pre-cancerous tissue.

How did those techniques pan out? Did patients ingest fluorescent dyes that got ingested and metabolized faster by cancerous cells, or do some types of cancer cells naturally fluoresce with a unique spectra you can detect?

Epithelial and endothelial cells only?

In paper they actually propose general light, possibly construction ones, and an near IR camera with NBP filter for 1140nm. Seems reasonable to me.

Box girders in a concrete bridge are hollow, meaning a measurement system could be inside where it is dark.

It seems to me very much (yet) theory only.

From experience in actually building reinforced concrete structures (both bridges and tunnels) and following later checks/inspections the amount of dirt (be it smog, pollution, dust, spiderwebs, whatever) on a structure that has been built only a few years before is impressive and would probably make this kind of microcracks detection not feasible/ineffective, let alone via a camera (or a drone).

Typically (talking of box girders where you could walk inside the bridge) you would normally check areas where you would suspect a (macro) crack to possibly develop by brushing with a hard brush the area and (not always, but it happened) pressure wash it.

Seems like it would also be possible to detect mixture differences, undocumented patches, pour boundaries and anything else that would lead to a non-homogenous mixture.

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