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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lowering blood pressure, and is irritating to the eyes, Latza et al. (2009). In plants, it damages chloroplasts and reacting with hydrocarbons in the atmosphere, peroxyacetyl nitrate is formed which inhibits photosynthesis, Baciak et al. (2018), Muneer et al. (2014). Moreover, NO 2 is a precursor of ozone formation in the lower atmosphere because the photochemical decomposition of NO 2 into NO and O, and then the reaction between O 2 and O, leads to the formation of ozone, Lawrence et al. (2005) , Wilkins et al. (2001). The main source of air pollution with nitrogen oxides (NO x ) is transport. At Fig. 2 there are the percentage share of individual sources of NO x emissions to the atmosphere that took place in Poland i n 2018 (own study based on statistical data contained in Statistics Poland Environment 2018).

Fig. 2. Sources of air pollution with nitrogen oxides (expressed in NO 2 ) in Poland in 2018.

As already mentioned, properly modified cement composites can absorb harmful pollutants with nitrogen oxides, Ramakrishnan et al. (2013). The two main directions of modification involve the use of titanium (IV) oxide (TiO 2 ), Fiore et al. (2013), Giosuè et al. (2020), or activated carbon in the composite, Aiswarya et al. (2019). Titanium dioxide causes photodegradation of NO x pollutants because it is characterized by high absorption of UV radiation, Guo et al. (2018). The disadvantage of this solution is the need to expose cement composites to solar radiation in order to activate the reaction of photodegradation of pollutants. The second direction of cement composites modification is the use of activated carbon. In this case, the NO x adsorption activity is not related to the need to expose the material to solar radiation. Hence, composites modified in this way can be used in tunnels and underground passages, Horgnies et al. (2014). Activated carbon is an organic substance, most often obtained from wood pulp, but also from peat, coal or nut shells, and it can be activated physically or chemically, Aiswarya et al. (2019). It is characterized by a very large external surface (over 3300 m 2 /g) and strong adsorption properties, Patil et al. (2012). It is widely used, among others in: chemical industry (as a catalyst), Veerakum aret al. (2018), in water treatment (to remove pollutants), Jiang et al. (2019), in technology (as a component of filters that absorb impurities or odors), Zhu et al. (2009), and in medicine, Roberts et al. (1997). It is also cheap to produce and readily available. The addition of activated carbon (AC) in the production of cement composites increases the natural NO x adsorption of concrete. The hardened cement- based composite is a highly alkaline and porous material containing calcium hydroxides Ca(OH) 2 and the C-S- H phase. Chemical neutralization takes place between NO 2 and surface alkaline forms, e.g. calcium hydroxides as was shown by spectrographic studies carried out by Ramakrishnan et al. (2014). In turn, the chromatographic studies accomplished by Krou et al. (2015) showed that adsorbed NO 2 is converted into nitrate and nitrite ions. Whereby Horgnies et al. (2014) suggests that in the presence of excess oxygen more nitrates will be formed than nitrites. Moreover, even 12-year-old concrete has the ability to adsorb NO 2 from the surrounding air, of course this adsorption is lower than for young concrete due to its ca rbonation (transformation of strongly alkaline hydrates into much less reactive calcium carbonate). The NO 2 adsorption rate is also strongly dependent on the temperature, with the temperature increase from 20 to 50°C, the NO 2 adsorption rate doubled.