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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properties. In particular, it was important to compare the properties of composites with sintered aggregates (expanded clay, sintered fly ash), traditionally used for insulating and structural purposes, and with ultra-light aggregates, rarely used in such applications. In the latter group of aggregates, expanded glass deserves special attention, which has appeared on the market relatively recently and for which there are no comparative studies that would allow for the assessment of its suitability for insulating and structural concretes against the background of other fine lightweight aggregates. 2.1. Constituent materials and mix compositions Five types of lightweight fine aggregates were selected for the tests, and the reference aggregate was natural standard sand meeting the requirements of EN 196-1 (2016). The types of aggregates used are shown in Fig. 1, and their basic characteristics are given in Table 1.

Fig. 1. Selected fine-aggregates: polystyrene granulate (S), perlite (P), expanded glass (G), expanded clay (C), sintered fly ash (V), reference natural sand (R).

Table 1. Properties of selected fine aggregates. Aggregate designation Aggregate type

Fraction, mm

Loose bulk density, kg/m 3

S P

Polystyrene

0.5/2.0 0.5/2.0 0.25/1.0

180 100 290 490 830

Perlite

G C V R

Expanded glass Expanded clay Sintered fly ash Natural sand (ref.)

2/4 2/4 0/2

1800

Lightweight aggregates, due to their significant water absorption, were pre-moistened to a moisture content corresponding to their water absorption after 30 minutes of saturation in water before being used in the concrete mix. Due to the structure of the fine aggregates used and their size not exceeding 4 mm, their water absorption determined in the time interval from 30 minutes to 3 hours practically did not change. While in the case of expanded glass, expanded clay and sintered fly ash aggregates this moisture content was 15-17%, for perlite it was as much as 130%. Polystyrene granulate basically showed no tendency to absorb water. A series of concretes were made with the selected aggregates, characterized by a constant water-cement ratio w/c = 0.8. Due to the applied procedure of pre-wetting of aggregates, the adopted w/c ratio corresponded to the values of effective coefficients (w/c) eff according to EN 206 (2021). A relatively high w/c ratio, not used in the case of structural concretes, allowed for meeting the strength criterion of insulating and structural concretes, and ensures substantially lower cement consumption and lower composite density. The cement matrix in the prepared lightweight concretes was a cement paste consisting of CEM I 32.5 R cement, tap water and Centripor SK120 foaming admixture in the amount of 0.25% of the cement mass. On the one hand, this admixture allowed for an additional reduction in the composite density, and on the other hand, ensured the stability of mixtures with lightweight aggregates, eliminating their susceptibility to segregation. The foaming admixture was not used in the case of the reference concrete with natural sand. A total of 6 different fine-aggregate concretes were made, the compositions of which are presented in Table 2.