Sleepers from renewal sites are all carted off to recycling, and graded. Those that are suitable for reuse on secondary routes or (more usually) in sidings are stored and then ‘sold’ when required. Sleepers not in suitsable condition, which is most of them, are chipped (timber) or crushed (concrete) and the end products sold on. Fittings to sleepers are similarly reuse s if in good nick, but most clips etc just go straight for recycling.
Rail is usually scrapped. Usually it is cut up on site prior to removal, the exception is the high output machines which thimble it out in full length. If the latter is to be reused it has to be ultrasonically tested for defects, have them fixed, and then th rail must be picked up and transported to where it is next needed. The effort (ie cost) of doing this meant that it didn’t make much sense, particularly with the cost of new steel so low. However I heard that there has been some of this happening recently.
The ‘scrap’ rail and sleepers that are often seen lying around are often actually spares placed deliberately. If you have a defect to fix then it is a lot quicker if you only have to shift a piece of rail or concrete sleeper half a mile on a trolley rather than cart it from the nearest depot.