ABSTRACT
The efficient strengthening of concrete structures using fiber composite materials (FRP’s) is largely dependent on the bond properties between the FRP and the concrete. The concrete substrate is the primary component facilitating the transfer of forces from the FRP to the global structure and is also a zone of relative weakness commonly initiating debonding failure and preventing the full utilization of FRP material. The current paper summarizes the results from an experimental study conducted to increase strength of FRP-to-concrete joints by introducing a series of 30–40 mm wide × 20 mm deep concrete chases within the concrete cover zone in both transverse and longitudinal orientations in order to strengthen the substrate to which the FRP is bonded. Furthermore, FRP spike anchors are evaluated to transfer the forces from an FRP laminate to the concrete via dowel action. In all cases tested, the mechanically strengthened substrate anchors and spike anchors significantly improved the strength of the FRP bond.
The experimental program devised was designed using 400 x 400 x 250 mm reinforced concrete blocks, reinforced with 3 x 8 mm diameter closed links in each direction with 20 mm cover. Four groups of specimens were designed consisting of 2 specimens in each group. The first group consisted of control specimens consisting of 100 mm wide x 1.4 mm thick FRP laminates bonded to the concrete with epoxy resin (without anchorage) over a 370 mm bond length. The second group (anchor type M1) consisted of a 40 mm wide x 20 mm deep longitudinal chase installed directly below the FRP laminate and filled with laminate adhesive. The third group (anchor type M2) involved constructing three rows of 30 mm x 20 mm mechanical chases running transverse to the FRP laminate. The transverse chases were filled with epoxy resin and acted as a mechanical key which distributed the FRP forces to a wider area of concrete. The last group of specimens (anchor type M3) tested consisted of two TYFO SCH composite spike anchors installed at 75 mm spacing with the dowel end of the anchor drilled into the concrete with a 75 mm deep embedment and the fan end of the anchor bonded directly to the FRP laminate. A detailed summary of the properties for each specimen is shown in figure 1. Specimen summary. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig58_1.tif"/>
Table 1 summarizes the results from the experimental program. The longitudinal chase increased the anchorage strength of the joints by 135–138% compared with 69–72% for the transverse chase anchorage and 86–93% for the spike anchors respectively. Results summary.
Specimen
Exp. Failure Load (kN)
Max Laminate strain (με) (SG)
0.1
55.2
2097
0.2
62.0
2201
M1.1
129.9
5184
M1.2
147.9
5952
M2.1
109.6
3891
M2.2
93.1
3669
M3.1
106.7
3918
M3.2
115.5
4284
