In this study, the multi-spray lay-up process using normal spray
lay-up method was used to control a volume fraction of fibers and
consistent thickness of layer. Spray lay-up operation was carried
out in accordance with layer-by-layer technique by the multispray
lay-up process up to a specific thickness to control a consistent
thickness (cf. [16]). Details of spraying operation by the multilay-
up process can be found in Ha [16]. The eight concrete specimens
were retrofitted and rehabilitated with the sprayed FRP composite
containing 25% volume fractions of fibers with fiber length
of 30 mm. Finally, proper roll-out work using a rigid aluminum
roller was carefully taken into consideration in the multi-lay-up
process to reduce any entrapped air voids and to make sure the
wet ability of glass fibers in matrix, as recommend by Banthia
and Boyd [5].
The sprayed FRP composite consisted of randomly oriented
glass fibers with length of 30 mm in commercial epoxy resin matrix.
In this study, commercial epoxy resin, called Solvent Free
Epoxy Lining Clear (SFELC) developed by Noroo Company in South
Korea was used to fabricate the sprayed FRP composite. In detail,
SFELC with specific gravity of 1.1 and a boiling point of 74 C was
formulated in bisphenol A resin with modified amine, where a
mix ratio was 2:1 (bisphenol A resin: modified amine) (cf. [16]).
The fibers used in this process was 359A Gun Roving format with
multi-filament E-glass strands where diameter of a single filament
was 11 lm, manufactured by Owens Corning (cf. [16]).
In general, primer resin can act as a bond coat layer at interface
between concrete substrate and sprayed FRP composite which can
enhance bond behavior and performance of retrofitting or rehabilitation
materials on concrete substrate [17]. A commercialized primer
resin, DNY-200 formulated with polyamide resin (specific
gravity of 0.94) from Noroo Company was used.