Can a tag be cast into concrete?
Yes, and the two cases are not alike. In a precast factory the tag goes into the mould under controlled conditions. In a pour on site it meets wet alkaline concrete, a steel cage that fights the field, and the certainty that nobody will ever reach it again.
Two very different pours
A precast element is made in a factory, in a mould, with the tag positioned deliberately near the surface it will be read from. That is an industrial process with a fixture, a depth and a repeatable result, and it is the version that works.
An in situ pour is a building site. The tag is fixed to formwork or to reinforcement by someone with gloves on, concrete arrives from a truck, and the position it ends up in is approximate.
Both are the moulding problem the moulding page describes, with the same conclusion: qualify the process on the real material rather than on a sample of the tag.
What fresh concrete is
Wet and alkaline, and both matter. Water attenuates the field while the element is curing, which the water page covers, so a tag that reads perfectly in a cured element may read nothing in the first days.
The chemistry attacks anything not sealed against it, so the tag is an encapsulated product rather than an inlay, which the natural materials page puts alongside stone and ceramic for the same reason.
Depth costs range on top of that. A tag ten millimetres under the surface and a tag at the centre of a slab are not the same deployment, and only one of them is readable with a phone.
The steel in the way
Reinforced concrete contains a steel cage, and steel cancels the field exactly as the metal page describes. A tag behind a mesh, or flat against a bar, is a tag that will not read.
So the position is decided by the reinforcement rather than by convenience: in the cover zone between the surface and the first bar, away from a bar rather than on one, and with the antenna parallel to the face it will be read from, which the orientation page explains.
An on metal construction helps where the tag has to sit near steel, at the cost of thickness, and it is the same trade the on metal page sets out.
It is never coming out
This is the part that decides the design. A tag in concrete cannot be replaced, rewritten in place if it has been locked, or repositioned if it turns out to be unreadable. Everything that might change has to live on a server behind a stable identifier, which is the argument the storage page makes and which is absolute here.
Test before the pour and after it, on the first elements rather than on the hundredth, and keep the rejects. A read that works on the bench and fails in the element is the normal outcome of a first attempt.
And ask what happens in twenty years, since a structure outlives the company that tagged it, the address it points at, and usually the format of the register. A printed identifier on the surface costs nothing and survives all three.
Frequently asked questions
Will a tag survive being cast in?
An encapsulated tag built for it will. An inlay or a label will not survive the water, the alkalinity or the handling.
Can a phone read a tag in concrete?
Only if it sits in the cover zone near the surface, clear of reinforcement. A tag deep in an element needs a dedicated reader or nothing at all.
Does the steel stop it working?
It can. The bars cancel the field where they sit, so the tag goes between the surface and the first bar, away from steel, facing the reading side.
What should be written on it?
An identifier. Nothing else can be corrected once the element is cast, and a printed number on the surface is worth having as well.