I would like to inclose a carport and need to raise the concrete 3 inches. Would it by advisable to pour over existing concrete which has a few cracks and is 30 plus years old? I live in AZ where the ground is rock hard and don't see any point in breaking out the old. Also there are 3 6X6 posts mounted to existing concrete with old style corner brackets that were poured over and buried in the original concrete. Can I just pour around the posts and use the same type of system. Thanks for your input