What are some easily-undertaken reactions that will precipitate or restore the iron from rust, in a non-lab context? Unusually, this question arises in a DIY context rather than a chemistry one.

I'm doing some work in my garden with reinforced concrete (a retaining wall against a  high bank of soil). As some will know, it usually doesn't matter if the steel used in reinforced concrete  gets rusty, because it will still have its inner bulk of steel for strength, still be gripped when concrete pours around it, and won't corrode further provided it is deep enough inside the body of concrete.

There's one exception. If the steel is used to join two sections of concrete below ground level that are poured separately, without a "water stopper", water will inevitably enter the point where the two sections of concrete meet, and in favourable conditions can slowly corrode the steel there. It's a low risk, and a long term issue, but can happen.

That's the situation I'm in, and I didn't realise the issue early enough to take precautions. Having already poured one section with its steel last year, I'm trying to retrospectively prevent possible issues before pouring the second part.

To counter any corrosion issues, I plan to use a zinc based galvanising coat to retrospectively protect the steel in the region of the join between the two lots of concrete. But there's a problem. Galvanisation relies on electrical conductivity to create the sacrificial aspect, and rust doesn't conduct. Physically stripping rust back to steel is also hard on these bars, as they are designed with an irregular surface, to enhance grip. 

So I'm wondering if there is a solution via chemistry - some easily accessible way to revert a rust coat back to metallic form, or remove rust to expose metal. Most rust removal products as far as I suspect, attempt to passivate or stabilise rust, not actually return a surface to metallic conductive form.

Is there anything I can easily do to return the rust layer to an electrically conductive/metallic layer? If not, any ideas how else I might chemically reduce the scope for future corrosion over the years?

Update: noting for clarity, the join is below groundwater level, with some degree of hydrostatic pressure behind it (it's a 1m retaining wall where a soil slope in the garden was cut away, and I can't add drainage below the joint because the bottom slab is already set and the joint will be 30cm below ground level even on the lower side, hence below groundwater level). Also the concrete mix is self-consolidating/self-compacting (SCC) so air bubbles as mentioned in one answer are not an issue - both mixes are luckily, specifically designed to preclude them, and the formulation sets pre-compacted without vibrating.
If you have a plastic bowl or container large enough to accommodate your item, fill it with water with with some salt (e.g., kitchen salt).  Then you need Aluminum foil lightly wrapping your rusty piece of iron which altogether are immersed in this said solution (luke warm is enough).  One important detail is that the foil is in mechanical contact to the iron, while the solution is able to be in contact with the foil and the cast iron simultaneously.

Over the course of the next hours, Aluminum will be "eaten away" -- or, more chemically speaking, Aluminum will be oxidized, and the rusty iron will be reduced.  To facilitate the process, it does not harm to scratch the Aluminum surface with a brusch on the surface exposed toward your iron pieces.

To direct the work of this oxy-reduction reaction toward your rusty iron pieces, it is important that the container for this setup itself is not made of metal.  Depending on the size of the item "to recover" things like a glass / china bowl, or a plastic bucket are suitable.  After half a day or so, remove your item, rinse it with water and a brush; dry it and protect it against new corrosion.  As already mentioned by you, this may be done by galvanizing, or by galvanic anodes.

An alternative to using a salt solution is the addition of vinegar to the water.  The key point of both (salt or vinegar) is that they increase the electric conductivity of the solution, hence accelerating the process.  If using vinegar, however, do not forget to protect your hands with gloves and eyes (goggle) against the acid.