Welcome to the Home Repair Forum
I have found some explanations to your problem...
quote:spalled concrete can happen for a number of reasons, the concrete mixture could have been bad, no way of knowing that unless you had it tested during the pour, when it was finished, the finishers may not have done a good enough job "muddling" the Crete, which moves the rocks down into the middle,In my own reading I believe that one possible cause is using ice melt. I found an article that might interest you if you want to tackle this yourselfquote:Concrete that has been on the truck too long and poured in hot weather will spall almost every time. Too much jitterbugging will also cause spalling sometimes.
If not call out a professional concrete repair company to do the work.
When getting bids always ask for references and total costs before paying any amount of monies!
I assume you will be tied up in litigation for quite some time trying to get anything out of your builder. As I understand it most builders only offer a 1 year warranty on a new home.