We complete many paver repairs each year, and each pavement has its own set of issues that we address. Typically we repair new systems installed incorrectly or older systems that are starting to fail due to a lack of maintenance.
In this example, this concrete pavement is 15 to 20 years old. Over time with traffic, water and salt, pieces are now cracking and deteriorating. An important point to take note of, once holes and open-air cracks start to form in concrete paver pavements, water and dirt will begin to wreak havoc. Rain will start to erode the pavement in areas it's not meant to (meaning the pavement was only engineered to withstand wear and tear on the surface, not between or below), and dirt will allow a place for weeds to grow and push pavers when it freezes in the winter.
An important discovery we made on this particular job site is the condition of the pavers that were pulled up in another area of the property. These concrete pavers are similar in age and were pulled up in the entrance where some city road work was taking place.
You'll notice that the bottom of the pavers is bumpy and degrading. What has happened here is the concrete pavers have been chemically reacting with base material installed under the pavers. These pavers were more than likely installed on top of stone dust (stone chips) which is a material that has a lot of fine particles.
(This video demonstrates the moisture retention of stone dust (stone chips) compared to the industry standard sand & gravel base. Skip to minute 2:25 for the moisture demonstration.)
These fines hold moisture and do not allow water to drain freely beneath the pavers. It is likely that during the winter, compounds from de-icing products sat in the area beneath the pavers and over time ate away at the concrete.