PSI - Issue 64

Giovanni Pietro Terrasi et al. / Procedia Structural Integrity 64 (2024) 1347–1359 Giovanni Pietro Terrasi et al/ Structural Integrity Procedia 00 (2019) 000 – 000

1350

4

ISO 11357-2. This is slightly below the T g of over 140°C which was specified by Ciba-Geigy 1998 (considering a pultrusion in a 180°C heated dye with a dwell time of approx. 5 minutes at 180°C). Tensile testing was performed on an Instron 1251 servo-hydraulic tensile testing machine according to ISO 527-4 using an resin grout anchorage system (called LEIKA and described by Boloux et al. (2024)). All tensile specimens had a free length of 400 mm. Table 1 summarizes the results and shows that compared to the data established in 1998, the tensile strength of aged tendons has decreased by 9.7% in 25 years. The reason for this degradation is still under investigation and an embrittlement of the pultrusion epoxy resin is suspected. Micro-indentation experiments under a scanning electron microscope are planned for 2024.

Table 1. Comparison of the tensile properties of Kleine Emme recovered CFRP wires after 25 years of service/storage

CFRP wire properties

Wire recovered from Kleine Emme bridge (2023, N = 12)

Wire specimens after pultrusion (Stesalit Ltd) (1998, N = 5)

Difference in 25 years

Tensile strength [MPa] and (standard deviation) Tensile failure strain [%] and (standard deviation) E-modulus (0.01%-0.25%) and (standard deviation) E-modulus (0.01%-failure strain) and (standard deviation)

2941 (126) 1.74 (0.07) 154.1 (3.4) 169.4 (5.1)

3257 (43) 1.83 (0.02)

-9.7% -4.9% -2.5% -2.1%

158 (3.1) 173 (2.2)

2.2. New CFRP post-tensioning cables re-using 25 year old CFRP wires: Another world premiere The following sections summarize the design, verification and production of the two 26 m and 30 m long CFRP parallel wire cables using 25 years old regained wires the for post-tensioning a new bridge (Ilfis Bridge presented in chapter 3). Former Empa spin-off company Carbo-Link AG designed the novel filament wound CFRP anchor sleeves for the cables in collaboration with Empa, produced the resin-cast terminations of two full-scale cable specimens for creep and tensile testing before both bridge cables were built. 2.3. CFRP wire quality assessment for 25 years old reclaimed CFRP The original bridge cables were enclosed in a polyethylene shrink hose that had to be removed. For assessing the integrity of the 25-years old CFRP wires, each wire was continuously bent upwards and downward to a radius of curvature of approx. 0.5 meters corresponding to a bending strain on the faces of ±0.5% (equals bending proof stresses of ±800 MPa). This manual continuous proof bending allowed to sort out wires with surface cracks or interlaminar cracks introduced when decommissioning the bridge or during transport in 2016. A total of 10 wires with flaws were detected and sorted out of the total 182 wires that were checked meter by meter. 2.4. Filament wound CFRP anchor sleeves The novel anchor sleeves were produced in a wet lamination process by filament winding using IMS60 24k carbon fibres and a LY564/AD2954 resin by Ciba-Geigy (1998). Each conical CFRP anchor sleeve had a length of 600 mm, and inner diameter of 150 mm at the back end and of 80 mm at the front end (being the load introduction end).

Fig. 2: Filament winding of novel CFRP sleeves (courtesy of Carbo-Link AG)

To save production time, the two conical anchor sleeves are filament wound on one mandrel as shown in Figure 2. The total thickness of the filament wound sleeves is 22.5 mm. The sleeve is manufactured with a proprietary carbon fiber winding architecture for accommodating the axial and