PSI - Issue 67

G. Goracci et al. / Procedia Structural Integrity 67 (2025) 30–38 G. Goracci/ Structural Integrity Procedia 00 (2024) 000 – 000

36

7

Concrete

20-40 50-70 70-80 80-90

Cool Pavement White Concrete

Highly Reflective Metal Roofing

Coating OPCCPS

80-100+

73 89

CSSC

Finally, the measured reflectance of the samples is illustrated in Figure 5. Within the sun wavelength – frequency range, highlighted in yellow, both carbonated samples exhibited a pronounced peak in reflectance (R). To ascertain the solar absorption (α) of the cementitious composites, the data were normalized to the solar spectra according to ASTM G173 Global Solar Spectrum. This normalization yielded calculated solar absorption values of α = 0.38 for OPCCPS and α = 0.26 for CSSC, significally lower than that of OPC cement paste (α = 0.38). This significant improvement (+62% and +93% respectively) can be attributed to the high presence of calcite formed due to the carbonation of the periwinkle shell and portlandite. Calcite acts as an effective whitening agent, substantially enhancing the reflectance properties. Furthermore, in the atmospheric window, carbonated samples demonstrated higher reflectance values compared to the reference, which is consistent with its elevated calcite content. A commonly employed method to quantify cooling efficiency is the estimation of the Solar Reflectance Index (SRI). SRI is calculated using solar reflectance and thermal emissivity values, which are then adjusted with wind coefficients. The active standard ASTM E1980 defines SRI through the following equation: 1. = 123.97 − 141.35 + 9.665 2 With 2. = ( − 0.029 ) 8.797+ℎ 9.52 +ℎ where α is the solar absorbance (1 – R), ϵ the emissivity, and hc the convective heat transfer coefficient. In order to calculate the SRI, the emissivity ϵ was calculated as 1 – ⟨ R ⟩ , where ⟨ R ⟩ is the average of R in the atmospheric window. Assuming a modest value of hc = 10 W/m 2 K, an SRI = 73 for OPCCPS and SRI = 89 for CSSC were obtained . These values are competitive with those of common cool materials employed to mitigate the Urban Heat Island effect, as shown in Table 1. The comparison reveals that the OPCCPS sample exhibits Solar Reflectance Index values comparable to those of white cement. Nevertheless, concrete incorporating carbonated aggregates demonstrates superior sustainability relative to commercially available white concretes. Conversely, the carbonated steel slag composite achieves SRI parameters on par with those of highly reflective metal roofing and coatings. This highlights its potential efficacy as a material for façades, pavements, and roofs in UHI mitigation strategies. 3. Conclusions This study demonstrates the promising potential of utilizing carbonated industrial by-products, specifically periwinkle shells and steel slag, for CO 2 sequestration and Urban Heat Island mitigation. The key findings include significant carbonation observed in both the carbonated periwinkle shell cement paste (OPCCPS) and carbonated steel slag composite (CSSC) samples, as evidenced by the formation of calcite in XRD patterns. The OPCCPS sample exhibited higher CO 2 capture efficiency compared to the CSSC sample. Reflectance measurements revealed high solar reflectance values for both carbonated samples, contributing to their effectiveness in UHI mitigation. The calculated Solar Reflectance Index (SRI) values were 73 for OPCCPS and 89 for CSSC, making them comparable to conventional cool materials such as white concrete and highly reflective metal roofing.