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RAR RUS 3701-3701 Usov Alexey Sergeevich 0000-0002-5262-6609 Lisyatnikov Mikhail Sergeevich 0000-0003-0356-1383 Roshchina Svetlana Ivanovna 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 The object of research is to investigate the mechanical properties of concrete incorporating carbon black as a novel filler material, with a focus on compressive and tensile strength—a topic previously underexplored in literature. Method. Carbon black, a hydrocarbon-derived soot (Type 660N), was added at 2%, 4%, 8%, and 12% by weight of cement, with water-cement ratios (W/C) of 0.40, 0.45, and 0.5. A total of 150 samples were tested at 7 and 28 days using ASTM-standardized methods, including the Brazilian tensile test. Result. Outcomes demonstrated that 4% carbon black optimally enhanced tensile strength (up to 24.3% increase at W/C=0.40 and 35.9% at W/C=0.45), while higher percentages (8–12%) degraded performance due to pore-filling inefficiencies. Compressive strength followed a similar trend, peaking at 4% replacement. The study highlights carbon black’s potential to improve concrete durability, reduce cement consumption, and mitigate environmental impacts, proposing an optimal dosage for industrial applications. ***ARTICLE IN PRESS*** 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. 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. ***ARTICLE IN PRESS*** 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 This comprehensive study investigates the relationship between the number of foaming agents and the increase in shear strength of concrete under various parameters, including cement grades (C300, C350, C400), water-to-cement ratios (0.4, 0.45, 0.5), and curing times (3, 7, 14, 21, and 28 days), and the shear strength at the interface of old and new concrete under successive freeze-thaw cycles. This research analyzes how increasing the concentration of foaming agent (0 to 0.45 wt%) affects the mechanical properties of concrete, with special emphasis on the trend of decreasing shear strength. After 3, 7, 14, 21 and 28 days of curing, 300 consecutive freeze-thaw cycles were used in this study to investigate the effect of these cycles. The temperature of the samples decreased from 4 to -18°C and increased from -18 to 4°C during the freeze-thaw cycles. This was done alternately and at a 4-hour interval for each cycle. After three hours of freezing, the samples were immersed in water for one hour to defrost. The results show that with increasing foaming agent content, a continuous decrease in shear strength occurs, and the rate of decrease is significantly affected by cement grade, water-to-cement ratio, and curing time. The shear stress increases with increasing weight percentage of foaming agents and decreases with increasing melting and freezing cycles. Higher grade cement (C400) shows greater resistance to strength loss compared to lower grades (C300), especially at longer curing periods. The water-cement ratio plays an important role, with higher ratios (0.5) accelerating strength loss due to increased porosity. The study shows that early stages of curing (3–7 days) experience the most rapid strength loss, while longer curing (28 days) partially mitigates this effect through continued hydration. A nonlinear relationship is observed between foaming agent content and strength loss, with critical thresholds identified at 0.25–0.35% foaming agent, beyond which the strength loss becomes greater. In the concrete sample with a curing period of 7 days and a foam consumption of 0.45 and zero, the shear strength after applying the temperature cycle decreased by 81.63% and 1.36% for different water-cement ratios and cement grades, respectively. In the concrete sample with a curing period of 28 days and a foam consumption of 0.45 and zero, the shear strength after applying the temperature cycle decreased by 82.48% and 7.09% for different water-cement ratios and cement grades, respectively. Water-cement ratios of 0.45 and 0.5 are associated with the highest and lowest percentage reduction in shear strength per weight percent of foaming agent, respectively. These findings provide valuable insights for optimizing foam concrete mixtures in applications that require a balance between lightweight properties and structural integrity. Practical implications for mix design, durability considerations, and performance-based specifications are discussed, which will help improve material selection for insulation, non-load-bearing foam concrete, and semi-structural foam concrete applications. ***ARTICLE IN PRESS*** 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 to investigate 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 reinforcing. 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. ***ARTICLE IN PRESS*** 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