PSI - Issue 64

Reza M. Fioruz et al. / Procedia Structural Integrity 64 (2024) 1142–1151 Firouz R. M. et. al./ Structural Integrity Procedia 00 (2019) 000 – 000

1147

6

1000 1200

0 200 400 600 800 Temperature [ ° C]

Experiment

ISO 834

0 10203040506070

Time [min]

Fig. 3. Heating regimes adopted experimentally vs. standard fire curve of ISO 834.

4.1. Bond performance Three identical pullout tests were carried out for evaluating the bond strength of NSM CFRP strips in the ambient temperature with CBA and GPA adhesives. The average of the maximum pullout force for samples with CBA matrix was 20.53 kN (COV 4%), and the average bond strength based on the 100mm bond zone was 9.0 MPa. For the samples of NSM CFRP with GPA, the average of the maximum pullout force and the average bond strength were 18.62 kN (COV 8%) and 8.2 MPA, respectively. As a comparison with previous works in the literature, the average bond strength of about 6 MPa for NSM CFRP with cement-based adhesives (Al-Saadi et al. 2018) and up to 21 MPa when using epoxy resin adhesive (Benedetti et al. 2016) were reported. An average bond strength of 15 MPa was reported by (Al-Abdwais 2023) using epoxy adhesive to bond NSM CFRP to geopolymer substrate. Table 1 presents the results of the pullout tests for each of the samples. Results show a difference of about 10% between the bond strength of CBA and GPA samples. This indicates a promising potential of geopolymer material as an adhesive for NSM CFRP strengthening. The scattering of results was slightly higher in the GPA adhesive.

Table 1. Pullout bond tests results.

Adhesive type

Maximum pull out force [kN]

Slip at max pull out force [mm]

Average bond strength [MPa]

Sample label

P-CBA-1 P-CBA-2 P-CBA-3 P-GPA-1 P-GPA-2 P-GPA-3

CBA CBA CBA

19.7 20.3 21.6 19.1 16.7 20.1

0.54 0.46 0.46 0.55 0.64 0.23

8.6 8.9 9.5 8.4 7.3 8.8

Geopolymer Geopolymer Geopolymer

4.2. Bond performance at high temperatures The results of pullout tests at ambient temperature were used to calculate the constant service load for thermo mechanical tests. Therefore, the values of 6.2 kN and 5.6 kN, ±0.2 kN, were selected for samples with CBA and GPA matrices, respectively (30% of the average peak value). Table 2 presents the main outputs from the thermo mechanical pullout tests and the recorded temperatures in CFRP (middle and top), surface of concrete/NSM grooves, and the controller of the furnace, when of the failure of the sample was reached, i.e. slipping of the CFRP strips out of the adhesive medium (CBA or GPA). This table also includes the time until failure (TUF), which is calculated from the instant when heating started, up to the instant when failure of the sample was reached. The average temperature at the instant of failure in CBA samples was 150°C, 181°C, 618°C, and 795°C, respectively at CFRP-middle, CFRP-top, concrete surface, and the furnace controller. These values for GPA samples were 147°C, 183°C, 717°C, and 840°C, respectively. These results show that both adhesives could provide a delay to the