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RAR RUS 3701-3701 0000-0001-6160-9889 Usov Alexey Sergeevich 0000-0002-5262-6609 Lisyatnikov Mikhail Sergeevich mlisyatnikov@mail.ru 0000-0003-0356-1383 Roshchina Svetlana Ivanovna rsi3@mail.ru Physical and mechanical properties of wood-polymer composite based on polylactide and aspen wood flour The object of research is a wood-polymer composite (WPC) containing 75% polylactide and 25% aspen wood flour (hereinafter referred to as WPC composite). This work aimed to experimentally determine the numerical values of the physical and mechanical characteristics of the WPC composite to form a finite element model. Method. The study includes physical experiments to determine the physical and mechanical properties of the obtained WPC, as well as their comparison with the generally accepted physical and mechanical properties of pure polylactide and pure aspen wood. The experiments include determining the compressive strength, tensile strength and bending strength, according to accepted standards. Results. The compressive strength of the test material was 53.6 MPa, the tensile strength was 23.4 MPa, and the bending strength was 47.3 MPa. The determined values will allow calculating the supporting structure in a software package based on the finite element method Compared with pure polylactide and pure wood, the compressive strength increased by 36% and 18%, respectively. This comparison indicates the need to introduce a reinforcement element into the calculated section to increase the strength limits. 10.57728/ALF.37.1 69 Wood-polymer composite Polylactide Aspen wood flour Compressive strength Tensile strength Flexural strength Ecoplastic https://alfabuild.spbstu.ru/article/2026.37.1/ 3701.pdf

RAR RUS 3702-3702 Nasimi Shahin Ehsani Armin Shambina Svetlana Lvovna Impact of adding carbon soot on the tensile strength of concrete Concrete has high compressive strength but low tensile strength, which limits its structural applications. Carbon‑based nanomaterials have shown promise in improving concrete properties, yet the effect of carbon soot (carbon black) on tensile behavior remains underexplored. The object of research is the influence of carbon soot (Type 660N) as a partial cement replacement on the tensile strength of concrete, considering different water‑cement ratios and replacement levels. Methods. Carbon soot was added at 0%, 2%, 4%, 8%, and 12% by weight of cement. Three water‑cement ratios (0.40, 0.45, and 0.50) were tested. A total of 150 concrete specimens were cured for 7 and 28 days. Tensile strength was measured using the Brazilian (splitting) test according to ASTM standards. Results. The optimal carbon soot content was 4%, which increased 28‑day tensile strength by up to 24.3% (W/C=0.40) and 35.9% (W/C=0.45) compared to the control. Higher dosages (8–12%) reduced tensile strength by up to 37.8%, indicating a clear performance threshold. The best overall performance was achieved at W/C = 0.45 with 4% carbon soot. Carbon soot can effectively enhance concrete tensile strength when used at an optimal dosage of 4%, while higher replacements degrade mechanical performance. This approach also reduces cement consumption, offering both mechanical and environmental benefits for sustainable construction. 10.57728/ALF.37.2 69 Carbon soot Tensile strength Concrete compressive strength Brazilian tensile test Cement replacement materials Concrete durability enhancement Carbon black concrete https://alfabuild.spbstu.ru/article/2026.37.2/ 3702.pdf

RAR RUS 3703-3703 Ehsani Armin Nasimi Shahin Shambina Svetlana Lvovna Hybrid effect of carbon nanotubes and silica aerogel on mechanical, durability, and thermal properties of concrete Silica aerogel improves the thermal insulation of concrete but typically reduces its compressive strength. Carbon nanotubes (CNTs) were incorporated to compensate for this strength loss. Sixteen concrete mixtures containing 0–8% silica aerogel (by volume) and 0–0.5% CNTs (by weight of cement) were tested for compressive strength, electrical resistivity, chloride ion penetration, and heat transfer coefficient. The object of the research is to investigate the hybrid effect of carbon nanotubes (CNTs) and silica aerogel (SA) on the mechanical (compressive strength), durability (electrical resistivity, chloride ion penetration, permeable porosity), and thermal (heat transfer coefficient) properties of concrete. Additionally, the study aims to determine the optimal dosages of these two materials to balance strength, durability, and thermal insulation. Method. An experimental study was conducted with 16 concrete mix designs containing different amounts of silica aerogel (0, 4, 6, 8% by volume of concrete) and carbon nanotubes (0, 0.2, 0.3, 0.5% by weight of cement). Cubic specimens (15 cm) and cylindrical specimens (10 cm diameter × 5 cm height) were prepared. The following tests were performed: 1. Compressive strength at 7 and 28 days (according to EN 12390-3 standard); 2. Electrical resistivity (two-point method with 2 kHz frequency), 3. Chloride ion penetration (according to ASTM C1202), 4. Permeable porosity (saturation method), 5. Heat transfer coefficient (using a thermal sensor device). Results. The results demonstrate that the hybrid combination of CNTs and silica aerogel simultaneously enhances durability, mechanical strength, and thermal insulation. The optimal mixture (0.3% CNTs + 4% silica aerogel) increased 28-day compressive strength by 21% and reduced the heat transfer coefficient by 73% relative to control concrete. The highest compressive strength (58 MPa, 35% increase) was recorded for 0.3% CNTs with 6% silica aerogel, while the lowest thermal conductivity (0.451 W/m·K) was achieved with 0.2% CNTs and 8% silica aerogel. CNTs effectively mitigated the aerogel-induced increase in porosity and chloride ion permeability, producing a high-performance concrete suitable for energy-efficient construction. 10.57728/ALF.37.3 69 Carbon nanotube Silica aerogel Durability Compressive strength Heat transfer https://alfabuild.spbstu.ru/article/2026.37.3/ 3703.pdf

RAR RUS 3704-3704 Ehsani Armin Nasimi Shahin Shambina Svetlana Lvovna Shear strength at the interface of old and new concrete: Foaming agent content and freeze-thaw cycles impact The object of research is the interfacial shear strength between old and new concrete under the coupled effects of foaming agent content, mix proportion parameters, and repeated freeze-thaw cycles, with the aim of identifying critical thresholds for durable repair systems in cold climates. Method. A total of 540 specimens were prepared using three cement grades (C300, C350, C400), three water-to-cement ratios (0.4, 0.45, 0.5), and five foaming agent dosages (0–0.45 wt% of cement). After curing periods of 3, 7, 14, 21, and 28 days, the samples were subjected to 300 freeze-thaw cycles (from −18°C to 4°C, 4‑hour cycle, following ASTM C666 Procedure A), and interfacial shear strength was measured and compared with non‑cycled controls. Results. Increasing foaming agent content continuously reduced shear strength under standard conditions (average drop of 7.1–10.1% at 0.45% dosage), but under freeze-thaw exposure it significantly enhanced frost resistance, with strength gains up to 571% at 0.45% dosage. A critical dosage threshold of 0.25–0.35 wt% was identified, beyond which further improvements diminished. Higher cement grade (C400) and longer curing (28 days) notably reduced frost-induced degradation, while W/C = 0.45 exhibited the highest sensitivity to foaming agent content. The most severe strength loss occurred at early curing ages (3–7 days), whereas 28‑day cured aerated mixtures retained over 80% of their initial shear strength after 300 cycles. These findings provide quantitative design parameters for optimizing lightweight foam concrete mixtures that balance structural durability with thermal insulation performance in freeze-thaw environments. 10.57728/ALF.37.4 69 Freeze-thaw cycles Old-new concrete joints Cement grade effects Frost resistance Shear strength degradation https://alfabuild.spbstu.ru/article/2026.37.4/ 3704.pdf

RAR RUS 3705-3705 Nasimi Shahin Ehsani Armin Shambina Svetlana Lvovna Impact of fiber usage, high heat, and fire resistance on the mechanical properties of reactive powder concrete (RPC) The object of research is the composition, processing methods, and mechanical behavior of Reactive Powder Concrete (RPC), highlighting its superior durability, impermeability, and resistance to environmental degradation. Reactive Powder Concrete (RPC) is an advanced high-performance construction material developed to overcome the limitations of conventional concrete, such as low strength, poor durability, and susceptibility to chloride and sulfate attacks. RPC achieves exceptional mechanical properties with compressive strengths ranging from 170–800 MPa and flexural strengths up to 250 times that of ordinary concrete through ultra-dense particle packing, elimination of coarse aggregates, and the incorporation of steel fibers. Methods. The mechanical properties and processing techniques of powdered concrete are compared with the characteristics of different kinds of concrete currently in use. This study emphasizes RPC's revolutionary potential in contemporary building by combining research on mix designs, curing regimes, and fiber reinforcement. It addresses robustness in harsh environments as well as sustainability (by utilizing industrial byproducts). Results. Key findings indicate that heat treatment (90°C–250°C) and pre-setting pressure significantly enhance compressive strength, while steel fibers improve flexural toughness and ductility. Additionally, RPC exhibits remarkable thermal stability, with minimal weight loss and retained strength at high temperatures (up to 800°C), making it suitable for extreme environments. Comparative analyses with ordinary and high-performance concrete demonstrate RPC's advantages, including reduced porosity (2–6%), enhanced resistance to chloride penetration, and superior performance under fire exposure. However, optimal fiber reinforcement and curing conditions are critical to mitigating brittleness and ensuring structural reliability. 10.57728/ALF.37.5 69 Reactive Powder Concrete (RPC) High-Performance Concrete Steel Fibers Heat Treatment Durability Mechanical Properties Thermal Resistance https://alfabuild.spbstu.ru/article/2026.37.5/ 3705.pdf