For the current tests, eight concrete test specimens with
300 mm (width) 300 mm (length) 60 mm (thickness) were
made up of a domestically produced Portland cement Type I,
crushed stone of 25 mm in maximum size as coarse aggregates
(specific gravity: 2.65), sand as fine aggregates (specific gravity:
2.60) and an admixture (specific gravity: 1.20). The concrete mix
proportion is listed in Table 1. Cylindrical concrete specimens with
dimensions of 150 mm (diameter) 300 mm (height) were manufactured
in accordance with ASTM C 192 [24]. All cylindrical concrete
specimens were tested for splitting strengths of concrete
after 28 days of curing, these were undertaken in accordance with
ASTM C 39 [25]; the results are given in Table 2. In general, the
pull-off bond strength of retrofitting materials should be higher
than the splitting strength of concrete. As shown in the table, range
of tensile splitting strength is from 3.62 to 4.32 MPa.
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