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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1. Introduction Insulating and structural concrete is a type of lightweight concrete characterized by an average compressive strength of not less than 3.0 MPa and a thermal conductivity coefficient not exceeding 0.7 W/(m·K) (Roszak and Kubiczek (1989)). In practice, the condition for thermal insulation can be reduced to limiting the density of lightweight concrete in a dry condition to about 1800 kg/m 3 . According to the relationship (1) developed by Valore (1980) and the ACI 122R-14 (2014) guidelines, the thermal conductivity coefficient of concrete in a dry condition ( λ ) can be estimated based on its density ( D ) according to the following formula: =0.072 ⋅ 0 . 00125⋅ (1) where: λ - thermal conductivity coefficient of lightweight concrete in oven dry condition in W/(m·K); D - oven-dry density of lightweight concrete in kg/m 3 . Although the relationship (1) is universal and is valid for both normal and lightweight concretes, thermal conductivity values estimated according to (1) for concretes with densities ranged from 320 to 1600 kg/m 3 correlate better to tests than for composites outside this range. Valore (1980) also proposed the formula (2) which allows for correction of the estimation of the thermal conductivity coefficient of concrete with respect to its moisture content: = ∙ (1+6 ∙ ) (2) where: λ m - thermal conductivity coefficient of lightweight concrete in moist condition in W/(m·K); mc - moisture content of lightweight concrete in %. For the production of lightweight aggregate concretes with insulating and structural properties, mineral aggregates are most often used, primarily sintered shales, expanded clays and sintered fly ash. Concretes of this type can also be successfully made on lightweight aggregates characterized by significantly greater porosity, for example: perlite, polystyrene granulate or expanded glass (e.g. Clarke (1993), Chandra and Berntsson (2003), Domagała (2019)). Lightweight fine-aggregate concretes are a special type of insulating and structural concretes. They are used especially for the production of thin-walled products, such as protective, cladding or thermal insulation boards and coatings, hollow bricks, decorative elements, including renovation elements, and a wide range of so-called concrete haberdashery (e.g. Brooks and Meijs (2008), Feirabend at al (2014), Henriksen at al (2015)). Fine-aggregate insulating and structural concretes are also used in the increasingly popular 3D printing technology (Poraver (2025)). Due to the lack of standard guidelines for fine-aggregate insulating and structural concretes, the selection of lightweight aggregate, which is the most important component of these concretes, as well as the production process of these concretes and their quality control in different plants, are carried out according to different criteria. In some cases, the EN 206 (2021) standard is used, which takes into account lightweight aggregate concretes, but not fine aggregate concretes, only with a close structure and with aggregates of mineral origin. Therefore, more often with regard to fine-aggregate insulating and structural concretes, the EN 1520 (2014) standard is used, which takes into account fine-aggregate lightweight concretes, does not exclude the use of aggregates of organic origin, but refers only to composites with an open structure. In turn, due to the use of this type of concrete for the production of thin-walled elements, in many cases strength tests are carried out in accordance with the procedures described in EN 196-1 (2016). As a consequence, the results of studies available in the literature, conducted on fine-aggregate insulating-structural concretes according to different test procedures and on different types of specimens, cannot be compared and constitute a basis for assessing the suitability of individual lightweight aggregates for this type of concrete. Such an assessment is particularly necessary in the case of new ranges of lightweight aggregates. 2. Experimental details The aim of the undertaken research was to assess the suitability of lightweight aggregates available on the market for their application in fine-aggregate insulating and structural concretes with specific thermal insulation and strength