PSI - Issue 74

Lucyna Domagała et al. / Procedia Structural Integrity 74 (2025) 17 – 24 Lucyna Domagała / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 3. Fractures of fine-aggregate concretes with: polystyrene granulate (S), perlite (P), expanded glass (G), expanded clay (C), sintered fly ash (V) and natural sand (R).

The bending strength of the tested composites turned out to be proportional to their compressive strength and constituted from 17% to 31% of its value. The influence of the type of fine aggregate used turned out to be of secondary importance here. The demonstrated correlation of both values confirms the generally known principle that an increase in the compressive strength of concrete composites is accompanied by a decrease in the ratio of bending strength to compressive strength. The thermal conductivity coefficient of lightweight concretes tested in the oven dry condition ranged from 0.07 W/(m·K) for concrete with perlite aggregate to 0.17 W/(m·K) for composite with sintered fly ash aggregate. The corresponding values determined in the natural moisture condition (9–13%) were higher by 19–27% and ranged from 0.09 to 0.20 W/(m·K). Fig. 4 presents the relationships between the density of lightweight concretes tested in the oven dry and natural moisture condition and the thermal conductivity coefficient tested and estimated according to the Valore formula (1). The analysis of these relationships confirms the general effect of increasing the density of composites on the increase in their thermal conductivity. However, these relationships are not exponential, as indicated by the Valore report (1980) and ACI 122R-14 guidelines (2014). More importantly, the obtained results of the thermal conductivity coefficient of lightweight concretes in the dry condition turned out to be significantly lower than those estimated based on formula (1). The values estimated from this formula were higher by 32 to as much as 104% compared to the values determined in the tests. In the case of composites in the natural moisture condition, even greater discrepancies were obtained between the values tested and estimated based on formula (2). The estimates according to (2) gave values higher by as much as 61 to 151%. To sum up, the commonly used models (1) and (2) in the case of the lightweight concretes tested overestimate the values of the thermal conductivity coefficient to an unacceptable level.