PSI - Issue 74

Maciej Gruszczyński et al. / Procedia Structural Integrity 74 (2025) 25 – 32 Maciej Gruszczyński / Structural Integrity Procedia 00 (2025) 000–000

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The addition of a highly porous material such as activated carbon to the cement-based composite increases and stabilizes the adsorption of NO 2 and other harmful air pollutants as a result of an increase in the inner surface of the matrix, Krou, et al. (2015), Horgnies et al. (2015). By Horgnies et al. (2014), the NO 2 adsorption rate for the reference concrete (without the addition of AC) was below 3%. While for concrete with AC (0,5% of c.m.), it was within 20 - 26% (values determined on the basis of measurement of NO 2 concentration (ppbv) at input and output in the condition of the prototype garage) and was independent of the age of concrete (3, 9, 12 months). On this basis, it was concluded that the addition of activated carbon (AC) causes that the carbonation of the cement slurry does not significantly affect the level of NO 2 adsorption, which was confirmed by other studies, Krou, et al. (2015). On this basis, it was concluded that the addition of activated carbon (AC) causes that the carbonation of the cement slurry does not significantly affect the level of NO 2 adsorption, which was confirmed by other studies. Moreover, the addition of activated carbon to the cement-based composite reduces the dependence of the NO x adsorption rate on the temperature (within the temperature 20 - 50°C, the adsorption practically did not change. Moreover, small amounts of AC addition (1.5% c.m., Horgnies et al. (2015), 2% c.m., Lekkam et al. (2019) do not significantly affect the porosity of the cement-based composite, its consistency and mechanical strength. The following research program is a pilot, preliminary program to determine the NO x adsorption under real conditions of a busy road tunnel located in the center of Cracow, Poland. Therefore, preliminary research was carried out, including: development of the sample preparation technology, subjecting them to carbonation and determining the degree of NO x absorption by the cement-based composite with 4% c.m. activated carbon addition and without it. 2. Materials and Methods Two types of mortars with 4% AC additive and mortars without this additive were made. The following materials were used to make the mortars: • cement CEM I 52.5 R with 4% addition of activated carbon, • cement CEM I 52.5 R, • ground quartz sand of 0 / 0.3 mm fraction, • distilled water. Distilled water was used due to the limitation of the influence of foreign microelements, normally found in tap water. For the same reason, no release agents were used to cover the steel molds (Fig. 3a). The test samples were prepared from mortars with the composition (mass proportions) C:W:S = 1:0.5:0.5. The mortars were prepared in a laboratory mixer for mortars according to an experimentally established mixing program, based on the generally accepted mixing procedure presented in PN-EN 197-1. The modified mixing procedure included: automatic mixing of the cement slurry at a speed of 140 rpm for 180 seconds, adding sand and mixing for 90 seconds also at a speed of 140 rpm, then manual mixing of the components for 60 seconds and final automatic mixing of ingredients at a speed of 285 rpm for 180 sec. Samples were prepared from the mortars made in this way in the form of tiles with dimensions of 100 × 100 × 10 mm in the amount of 12 pieces for each series (Fig. 3). The mortar samples were stored in the molds for 24 hours and then transferred to the chamber with 95% humidity and 20°C temperature. The samples were cured under these conditions for 28 days. Then, the samples were placed in a chamber at 20°C and 90% humidity for 21 days. There they were stored in an atmosphere consisting of 10% CO 2 and 90% nitrogen. The above conditions were to ensure the carbonation of the mortar samples. The sample carbonation treatment was aimed at reducing NO x adsorption by strongly alkaline cement slurry minerals (C-S-H and Ca(OH) 2 ) and thus demonstrating the ability to adsorb nitrogen oxides by the addition of activated carbon. Tests carried out with the use of phenolphthalein confirmed that all tested samples obtained a pH below 9.