PSI - Issue 81

Oleh Bordiuzhenko et al. / Procedia Structural Integrity 81 (2026) 78–83

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Analysis of the obtained data indicates the predominance of the 0.14 – 0.5 mm fraction in the particles of concrete waste smaller than 1 mm. At the same time, the content of the fraction <0.14 mm ranges from 25 to 32%, with higher values observed for lower grade concretes and, accordingly, lower strength (B3 – B4). The granulometric analysis results show a generally similar pattern for all samples. The content of the fraction smaller than 0.08 mm is about 50%, again with a slight predominance for the lower-strength concretes. The chemical – mineralogical composition of the dispersed fraction of concrete waste samples was determined using X-ray diffraction analysis (Table 2).

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B1 B2 B3 B4

50

40

30

20 Content, %

10

0

0.5-1

0.14-0.5

<0.14

Sieve size, mm

Fig. 1. Sieve analysis data of concrete waste particles smaller than 1 mm.

b

a

Fig. 2. Granulometric analysis data of concrete waste particles (<0.14 mm): (a) sample B1; (b) sample B4. Based on the results of the mineralogical analysis of concrete waste samples, it can be noted that specimens with higher strength and, evidently, a higher cement content are characterized by an increased amount of alite (C ₃ S). The content of this clinker mineral in sample B1, which had cured for 2 months, exceeds 14%, which is almost twice the amount found in sample B2 of the same class but with an age of 3 years. A similar trend is observed for concrete samples B3 – B4 of lower classes, where in the 3-year-old sample the content of unhydrated C ₃ S decreases almost to zero. This can be explained both by the longer curing time and by the lower cement content compared to samples B1 – B2. It is also worth noting a certain regularity regarding the Ca(OH) ₂ content in relation to the age and strength (cement content) of the concrete. As shown by the data in Table 2, the decrease in calcium hydroxide content occurs both due to its carbonation over time and as a result of the transition from higher-strength concretes to lower-strength ones. In addition, the Ca(OH) ₂ content from Table 2 correlates quite clearly with the pH of aqueous solutions of the dispersed fraction of concrete waste samples (Table 1). Cylindrical specimens (25 mm in diameter and height) were produced from the dispersed fraction of concrete waste by pressing using a FP 100/1 testing machine. The molding moisture depended on the pressing pressure and amounted to about 12 – 13% at 20 MPa. The specimens were stored under air-dry conditions, above water (in a desiccator), and directly in water (after preliminary curing in air for 1 day). Strength, bulk density, and water resistance were determined according to standardized methods.