I am building a minetrack to a blaze farm in the nether and everytime I go through the portal to my base and come back to the nether a chunk of the tracks and blocks I placed in the middle are gone and this has happened multiple times. This is on a single player world.
This sounds very much like a corrupted chunk in your world. You can't solve corrupted chunk issues within the game. You can alter your world files manually, but I would highly recommend you to NOT do this, as you can easily corrupt other chunks.
Your best bet would be to use a program like mcedit to delete that specific chunk for your world, so that it can be regenerated by the game.
There is also a thread on the minecraft forums about world repairs: http://www.minecraftforum.net/forums/minecraft-java-edition/discussion/297844-official-corrupted-save-recovery-thread