Is certification required to conduct runways repairs?
To the best of my knowledge, you do not require any certification to fix a runway/taxiway, and anyone with a proper equipment can do that. But to facilitate the process, the FAA has published a few checklists which have to be filled while doing this repair job. These checklists can be found Here. FAA also provides assistance in guiding the construction jobs and identifying risks, the link to which is in the same website as mentioned above.