Experimental Study of Bond Strength between Existing Roof Slab and Concrete Support of Flat Roof Mounted Solar Arrays

Abstract

Rooftop mounted solar array systems are connected to the existing concrete roof using casting concrete blocks over the existing concrete roof surface or by using precast concrete blocks. Since fixing the mounting system directly on the roof surface using a bolted connection is not advisable since it can affect roof strength, concrete blocks, either precast or cast in situ, are desirable to support the mounting system. To better understand the bonding mechanism at the interface between old and new concrete surfaces, overlaid specimens were fabricated to measure the various bond strengths. Three different bonding methods, which include cement slurry, casting over existing concrete, and epoxy, were used. The tests performed found that epoxy bonding provides better bond strength for new and existing concrete. To withstand wind loads, the foundation of the solar system should resist horizontal drag and vertical lift forces safely. Self-weight of supporting concrete blocks significantly reduces drag and lift forces coming over the solar system due to wind loads. The bonding strength between the existing concrete roof surface and array supporting concrete blocks also plays a vital role in resisting drag and lift forces. Since the weight of concrete blocks cannot exceed the design load for the roof, drag and lift forces can be resisted by increasing bond strength either by increasing the surface area of blocks (which would increase weight thus may defy purpose) or by using a superior bonding agent.