GFRP rebar is used to reinforce foundation all over the worlds. Application of fiberglass rebar is considered acceptable for both strip and slab foundations in buildings up to 4 floors.
An example of GFRP rebar use in strip foundation is shown in the video:
The choice of composite rebar for the foundation reinforcement is stems from its advantages over metal:
savings on transportation due to fiberglass light weight and packing in coils;
composite rebar is shipped in coils of 50 and 100 meters, which allows easy cutting the bars of the required length (welded joints of metal rebar, as you know, are a trouble spot);
easy handling;
no cracks in the foundation due to difference of thermal expansion coefficients of concrete and metal (they are similar for fiberglass and concrete);