I'm trying to track down a book that I had that borrowed to a friend that lost it. I want to say it was from the 50's or 60's. It had a red cover.

I remember 3 stories. One about a blob that lands on Earth and absorbs matter exponentially. They launch it into space and blow it up, and now infinite pieces will land on more planets. The second is about a human-alien war where time freezes and there's a 1v1 duel in a sand pit with a barrier in the center. The alien is an armadillo type creature. The third is about a planet of robots who have no idea what humans are, finding a space shuttle and thinking it's another robot. They talk to it and then try to fix the damage, killing the man in the process by burning him alive.

I desperately wish to find this book again.