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

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MPa were obtained, respectively. Further details about the CBA development can be found in (Mohammadi-Firouz et al. 2023). The alternative adhesive developed is a geopolymer-based (GPA) mixture, consisting of sodium silicate (Na 2 SiO 3 ), sodium hydroxide (NaOH), metakaolin, water, and fine sand. The sodium silicate was provided as solution with a content of sodium oxide (Na 2 O) of 13% and a ratio (SiO2/Na 2 O) of 2.03. The sodium hydroxide was originally supplied in pearl form and dissolved in water until a concentration of 10 M was achieved. The activator was composed of sodium silicate solution and sodium hydroxide solution, with a mass proportion of 2:1, which was mixed with the metakaolin precursor in a mass proportion of 1:1. The water to binder mass ratio was 0.34 and the aggregate to binder volume ratio was 0.15. A flow table test was performed similarly to previous adhesives, and the recorded value for the fresh GPA mixture was 165 mm in diameter. An average compressive and flexural strength of 45.0 MPa and 6.2 MPa was obtained, respectively. 2.2. The NSM reinforcement CFRP reinforcements of 1.4×10 mm 2 cross-section with smoothed surfaces, provided by S&P Clever Reinforcement Ibérica, Lda., were used in this work. According to the experimental tests executed with 3 CFRP strips, the tensile strength ( f fu ) and modulus of elasticity ( E f ) were 1909 MPa (COV 1.7%) and 171 GPa (COV 1.8%), respectively. To create a mechanical bond with the CBA and GPA adhesives, the CFRP strip surfaces were coated by a sand layer. Uniformly distributed sand particles of quartz with about 0.2 mm were used to provide a rough surface to these CFRP reinforcements. The coating layer covered the whole bond length of the strips, i.e. 100 mm. Vinyl ester with high glass transition temperature ( Tg about 190°C) was used as the bonding agent to attach the sand layer to the CFRP strips. To control the standardized process for different sand-coated CFRP strips, they have been weighted after each step. The production process is described in more detail in (Mohammadi-Firouz et al. 2023). Fig. 1 shows CFRP reinforcements with and without sand-coating.

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Fig. 1. (a) Smoothed surface CFRP strip, (b) sand-coated CFRP strip [Adapted from (Mohammadi-Firouz and Barros 2023)].

3. Pullout bond tests The sand-coated CFRP strips were introduced into the grooves of concrete blocks filled with the adhesive (CBA/GPA), forming an NSM bond zone of 100mm. The samples were then kept in the lab condition, covered by a wet cloth for testing after 4 weeks. 3.1. Ambient tests To measure the bond strength of NSM CFRP with CBA and GPA adhesives, direct pullout tests were performed by applying monotonic loading under a displacement control of 2µm/s using an actuator with maximum capacity of 200 kN. Linear Variable Differential Transformers (LVDTs) were used to register the displacements at loaded-end and free-end slip of NSM CFRP strip. Fig. 2 shows the setup for performing the direct pull-out tests.