PSI - Issue 81

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

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In addition, the recycling of concrete waste as recycled aggregates has been the focus of many studies aimed at reducing construction and demolition waste generation. Research has demonstrated the feasibility of using coarse recycled concrete aggregate for various applications (Rocha et al. (2024)). Recent studies have also shown the possibility of successfully producing high-strength cement-based materials using fine recycled concrete aggregate (Wu et al. (2023)). However, during the production of recycled aggregates, the fine fraction (less than 150 μm), known as Waste Concrete Powder (WCP) or Recycled Concrete Powde r (RCP), is often discarded without any specific use. In recent years, the potential of RCP as a supplementary cementitious material has been proposed due to its chemical and physical properties (Duchesne (2021)). Previous studies indicate that RCP exhibits pozzolanic characteristics and filler effects, enabling it to partially replace cement (Cantero et al. (2022)). Furthermore, RCP significantly reduces the environmental impact associated with CO ₂ emissions and energy consumption compared to conventional cement (Wu et al. (2021)). While WCP or RCP has been extensively studied as an additive to cement or as an aggregate in concrete, its application in the production of pressed materials and products remains insufficiently explored. Considering the promising potential of semi-dry pressing technologies, the investigation of materials based on dispersed concrete waste and the development of appropriate mix designs represent a relevant scientific task, capable of combining resource conservation with the production of high-quality construction products. It should be noted that pressed composites based on dispersed concrete waste are inherently similar to well-known binders and contact-hardening materials (Dvorkin et al. (2024)) used in construction practice, which belong to the broader group of geopolymeric materials (Davidovits (2022)). Geopolymer binders can be classified as energy-efficient types of mineral binders, produced from highly dispersed mineral products (various rocks and industrial by-products). The hardening of such materials occurs under so- called “compressed conditions” (as defined by Sychov (Dvorkin et al. (2023))) throug h the establishment of adequate contact between particles as a result of pressing. When pressing materials based on WCP, the prerequisites arise for a complex mechanism of structure formation, determined by the composition of concrete waste: hydration hard ening in the presence of a certain “potential” of unhydrated cement paste particles, contact (contact-condensation) hardening of amorphized cement hydration products (Runova et al. (2018)), as well as contact crystallization processes in the “compressed conditions” of particles of different nature, primarily the aluminosilicate components of concrete aggregates (Dvorkin et al. (2024)). The aim of this study is to investigate the possibility of using concrete waste powder as a component for the production of pressed composites, to identify the most promising types of concrete waste for pressing, and to determine the technological parameters of their manufacture. 2. Materials and Methods For the study, the fine fraction of concrete waste obtained from the crushing of hardened concrete of different ages and design strengths was used. Four types of concrete were produced with granite coarse aggregate and quartz sand. Concrete samples were crushed in a jaw crusher, and then particles smaller than 1 mm were sieved out. From these, the fraction smaller than 0.14 mm was further separated and selected for subsequent investigations as a kind of “binder” for pressed composites. For the obtained fractions, the particle size distribution of the crushed concrete waste was determined by sieve analysis, while the granulometric composition of the dispersed fraction (0 – 0.14 mm) was analyzed using a laser granulometer. Additionally, the hydrogen ion concentration (pH) was measured (Table 1, Figs. 1 – 2).

Table 1. Characteristics of concrete waste samples, fraction <0.14 mm. Concrete samples Concrete class Approximate age

Compressive strength of concrete, MPa

Residue on sieves, % pH 0.045 mm 0.08 mm

B1 B2 B3 B4

2 months

55.4 72.1 21.6 34.1

64.2 65.3 62.2 61.8

49.3 48.4 52.3 51.2

11.7 10.2 10.9

С40/50 С40/50 С 16/20 С 16/20

3 years

2 months

3 years

8.9

Table 2. X-ray diffraction analysis data of the dispersed fraction of concrete waste samples, %. Concrete samples C 3 S C 2 S C 4 AF Ca(OH) 2 CaCO 3

SiO 2 11.7 10.2 10.9

B1 B2 B3 B4

2 months

55.4 72.1 21.6 34.1

64.2 65.3 62.2 61.8

49.3 48.4 52.3 51.2

С40/50 С40/50 С 16/20 С 16/20

3 years

2 months

3 years

8.9