Pool coping repair

We have a fibreglass pool with 400x400 pavers for copings. When they installed it, they used mortar on the concrete beam and some adhesive on the fibreglass to set the coping. Two pavers have cracked at the interface between fibreglass and concrete beam. I've removed the excess mortar and now have a good surface to put down replacement pavers. Is there an adhesive I can use to stick to paver to the concrete and fibreglasses? Probably two different adhesives I'd imagine. But something that can flex a bit to prevent a recurrence.