the tree has several things going against it. from the photos it appears to be planted too deep and that is causing a compromised root system and an inability for the root system to maintain the top. it also is surrounded by rock which holds heat and does not allow the root system to stay cool (about 85 degrees soil temp the fine roots start to die.) and the rocks also bounce both sunlight and heat onto the stem so it is like a convection oven on the stem. The pavers that surround the tree also cause damage to the root system as most of the roots want to be in the top 12 inches of soil andin general maple trees/pavers don't play well together. if this were my tree i would remove it , the stone, and the pavers and plant  a new tree. make sure you plant the tree so it shows the root flare on the surface. trees that look like a telephone pole coming out of the ground are planted 3-6 inches too deep ( fatal to a maple in 5-10 years). Also, potted trees all have girdling roots (the roots that wrap around the inside of the pot) and if not corrected before planting they will girdle the tree and kill it in 5-10 years. Sorry to be the bearer of bad news but this is the most common problem we see with young trees.
Jesse