If its done right, it should last for about 50 years. It should not show signs of cracking for 15 or 20 years. However, there are lots of variables. For example: where you live (climate), when it was poured, how thick was it poured, how it was mixed, many variables during the pour like how much water was used in the pour, how much morter was used, did you water it (keep it wet) after the pour during the cure, was it used befor it cured, what type of abuse it routinely goes through, the list goes on and on. So its hard to say why your's is cracking. Good luck with the contractor. I don't think anything can be done to improve the look.