You could add a few layers of thin glassfiber net when applying the concrete. This should improve the flexural and compressive strength of the concrete substantially. I personally use insect netting that can be found rather cheap.
There should be no real need to seal the wood when applying the concrete. But applying some oil to the ends of the wood before the concrete should make it not stick together.
For repair jobs where strength is an issue and if you don't need huge amounts. It can be worth looking into high performance concrete. It has superior properties and it bonds extremely well with regular concrete. When using HPC for a repair job its very important that the concrete its being applied on is already saturated with water.