PSI - Issue 64

Mahdi M.K. Zanjani et al. / Procedia Structural Integrity 64 (2024) 1134–1141 Zanjani et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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3.1. Structural constraint

The NRG&STRUCT-foam is thought to replace, not only the insulation but also, the structural materials of the BESTEST walls. Therefore, the following inequality constraint is prescribed for structural reasons: ( 1 ) +⋯+ ( ) ≥ + + = ̅ = 870.68 kg/m 3 , (8) i.e., the average density of the NRG&STRUCT-foam layers multiplied by a factor <1 must not be smaller than the average density ̅ of the insulation and structural layers in BESTEST 900. The factor is defined as: =1− − 1+( − −1) , (9) and introduced to account for the unfavourable effect of the mPCM content on the structural response of NRG&STRUCT-foams; we adopted =0.5 in Eq. (9). 3.2. Compressive strength decay and foam density The mechanical properties of cementitious materials are strongly influenced by their micro- and meso-scale structure which in turn, are defined by the components and relative contents of the mix proportion and, by the mixing, pouring and curing processes. Therefore, any change in the above-mentioned aspects, conducts to a different composite with different physical and mechanical properties. Among other properties, porosity is a fundamental parameter and is directly related with the compressive strength, and with the tensile strength of the cementitious composite. It is well known that for improving compressive strength it is necessary to reduce open porosity (Li and Aubertin, 2003; Chen et al., 2012). However, porosity is not easy to be measured and, moreover, there are different methods for its determination. Consequently, results in the literature are not enough for determining approximation functions of strength-porosity rules. An alternative is to evaluate another physical property as water absorption (Gopalakrishnan et al., 2020) or dry density (Othman et al., 2021), which are easy to be determined and are data usually provided in most of the experimental scientific papers in the field. In the frame of the research in this paper, density seems to be the most suitable property regarding that other properties, as thermal conductivity, can be related with it. Therefore, a large set of data obtained from papers in the literature was analyzed and can be seen in red dots in Fig. 3, where f ’ c in the vertical axis is the compressive strength in MPa and  in the horizontal axis is the density in kN/m 3 . It is remarked that the considered data include different concrete types, as foam, lightweight, recycled aggregates, normal- and high-strength concretes. Then, the simple approximation in Eq. 10 for obtaining a medium value of compressive strength in terms of density is proposed: 3 ' 0.17  = c f (10)

Fig. 3. Compressive strength vs. density: experimental data in red dots, approximation functions represented by lines.