Hey there @MichaelGardner! Welcome to the community! As mentioned by both Techlord and Wind, Quixel is an amazing source of high quality concrete textures, and since they were generated with photogrammetry, they are rather accurate on their own.
One technique to look into when working with concrete and making convincing environments in general is having some visible wear on it. As you’re aware in your field, even perfect pours have some inconsistencies and with your knowledge on the subject you can accurately create realistic damage (or lack there-of). Using custom decals can give you a good lever to break up repeating textures and make the scene look more lived in.