Because of experience with disruption from alkali-silica reaction with the aggregates in our area (unless necessary precautions are taken), I always feel a little bit nervous about contact of portland cement with anything that can set this reaction going, such as glass. Is there any danger of alkali-silica reaction with concrete when fiber-glass forms are used? Couldn't it damage or at least discolor the surface?
Forms that are often referred to as fiber glass are actually plastic forms that have been reinforced with fiber glass. Glass fibers can react with alkalies in the concrete to cause discoloration. For this reason it is necessary to be sure that the resin cover over the fibers is maintained, but this is no great problem. Fiber-glass-reinforced plastics are widely and successfully used for producing architectural concrete finishes.