So why did they use a RPi for this? Why without ADC? Why not ESP if you really need the connectivity but at least then also get an ADC value instead of purely digital? Or simply any arduino with a light or anything to indicate the status right back to those applying the concrete? And why only one single line/point? Why not 20 all over the place? How large are these voids supposed to be that only one line (or even just point) of measurement is needed?

In other words: Is this actually relevant or just chinese trying to dealing with corruption etc. (tofu dreg)?