PSI - Issue 78

Francesco Bianco et al. / Procedia Structural Integrity 78 (2026) 41–48

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Fig. 4. Comparison between experimental and numerical results: a) bond length 400mm; b) bond length 100mm.

3. Bioleaching process for treatment of CFRP The objective of the experimental campaign was to study the process of bioleaching for the treatment of CFRP applied on concrete substrate. 3.1. Dark fermentation setup The experimental test, performed for about 45 days, involved the following conditions: concrete (C), concrete + primer (CP), fiber (F), fiber + resin (FR) and concrete + fiber + primer + resin (ALL). These samples (2 replicates) were subjected to an aging protocol involving 3 cycles of 24 h at ambient followed by 24 h at -20 °C in the dark to simulate the effect of aged fibers (Apitz et al. 1999). A dark fermentation (DF) process in fed batch mode (wet conditions, % total solids < 10%) was carried out using 250 mL serum bottles with a working volume of 60% to allow biogas (i.e., H 2 +CO 2 ) to accumulate in the headspace. As an inoculum, 7.5 mL of digestate pretreated in an oven at 100 °C for 1 h was used to allow inhibition of methanogenic microorganisms. The organic substrate consisted of 5.0 mL/L of a micronutrient solution, 13 g/L glucose, 0.764 g/L ammonium chloride, 4 g/L sodium bicarbonate, and 0.58 g/L potassium dihydrogen phosphate. To ensure anaerobic conditions, serum bottles were flushed with pure nitrogen for about 2 min. Finally, each bioreactor was shaken manually and placed in an oven at 38 °C to ensure mesophilic temperature conditions (Fig. 5). Quantitative analysis of the produced biogas was performed by a liquid displacement volumetric method (Filer et al., 2019). Qualitative analysis of biogas was carried out in terms of H 2 and CO 2 using a gas chromatograph 3400 GC TCD (Varian-Agilent, USA) using argon and nitrogen as carrier gases. Dissolved calcium analyses after bioleaching tests were conducted by a mass balance on concrete samples to assess weight loss (Trancone et al., 2019). The determination of pH was obtained via a Sentix/940 pH-electrode.