PSI - Issue 68

Zoi S. Metaxa et al. / Procedia Structural Integrity 68 (2025) 184–189 Z.S. Metaxa et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 2. Flexural strength versus: (a) density ( d ) of XPS-modified mortar mixtures and (b) thermal conductivity ( λ ) of XPS-modified mortar mixtures, at 28 days.

3.3. Thermal performance The diagram in Fig. 2b shows the relationship between flexural strength (in MPa) and thermal conductivity ( λ , in W/mK) for XPS-modified mortars at 28 days. As thermal conductivity decreases, which corresponds to an increase in XPS content, the flexural strength also decreases. The regression line, shows a strong correlation between these two parameters, indicating that as thermal conductivity decreases, so does the flexural strength. The 100 vol.% XPS mixture exhibits the lowest thermal conductivity (~0.61 W/mK) and the lowest flexural strength (~5.42 MPa), while the 0 vol.% XPS mixture demonstrates the highest values for both thermal conductivity (~1.17 W/mK) and flexural strength (~7.32 MPa). Despite the flexural strength decrease as XPS content increases and thermal conductivity improves, all mixtures remain above the 5 MPa threshold indicating the feasibility of achieving thermal insulative properties while still maintaining sufficient strength. Mortar mixtures with 90 vol.% and 100 vol.% XPS content achieved thermal conductivity values below the RILEM Class II threshold for structural and insulating lightweight cement composites. This positions XPS-modified mortars as a viable material for energy-efficient buildings, where thermal insulation is critical (Dixit et al., 2019). 4. Conclusions The present investigation has demonstrated the effectiveness of incorporating XPS waste into cement-based mortars as a sustainable solution for lightweight and energy-efficient construction materials. The inclusion of XPS affects the mechanical and thermal properties of the mortars, but the mixtures still maintain key performance criteria suitable for structural applications. The following conclusions can be drawn: • As XPS content increases, both flexural strength and stiffness decrease, indicating a trade-off between lightweight properties and mechanical performance. • All mixtures, regardless of XPS content, exceed the minimum flexural strength requirement of 5 MPa, confirming their suitability for structural applications. • The mechanical strength development pattern remains consistent across all mixtures over time, showing that XPS does not alter the overall curing and strength gain behavior. • XPS-modified mortars show reduced density as XPS content increases, with values ranging from 2115 kg/m³ (0 vol.% XPS) to 1482 kg/m³ (100 vol.% XPS), highlighting their lightweight characteristics. • Higher XPS content significantly improves thermal insulation, with thermal conductivity decreasing from 1.170 W/mK to 0.610 W/mK. Mixtures with 90 vol.% and 100 vol.% XPS meet the requirements for both structural and insulating applications.