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.