This study investigates the effect of rice husk content (0–60 wt.%) on the thermal, mechanical and rheological properties of polypropylene composites prepared by extrusion and injection molding. A temperature-invariant approach was applied to analyze the viscoelastic properties, allowing the combination of data obtained at different temperatures. The results show that as the husk content increases, the elastic modulus and hardness rise linearly, while the impact strength and elongation at break significantly decrease. Composites with 40–50% filler exhibit a balanced combination of strength and stiffness, as confirmed by the summary data in the table (provide references). The application of the temperature-invariant viscosity method confirmed its effectiveness in evaluating the flow properties of composite melts. The obtained results have practical significance for the development of eco-friendly polymer materials with natural fiber fillers.

This study evaluates sustainable dune-sand concrete produced using local dune sand, rice husk ash (RHA), and dried oil sludge. The experimental program included a control mixture (C0) and three modified mixtures (M1–M3). RHA was used as a partial replacement for Portland cement at contents of 20, 40, and 60 kg/m³, while dried oil sludge was introduced as a waste-derived additive at 10, 15, and 20 kg/m³, respectively. The total binder content, defined as Portland cement plus RHA, was maintained at 350 kg/m³, while the mixing-water content and water-to-binder ratio were kept constant at 185 kg/m³ and 0.53, respectively. The RHA was heat-treated at 800 °C for 60 min, immediately quenched in water, and subsequently dried at 105 ± 5 °C until a constant mass was achieved. Among the investigated compositions, M2, containing 310 kg/m³ Portland cement, 690 kg/m³ dune sand, 1110 kg/m³ crushed stone, 40 kg/m³ RHA, and 15 kg/m³ dried oil sludge, exhibited the most balanced overall performance. Its compressive strength reached 27.8 MPa at 7 days, 42.5 MPa at 28 days, and 47.7 MPa at 90 days, while its static modulus of elasticity was 32.7 GPa. M2 also showed the lowest water absorption (3.63%), the highest watertightness grade within the investigated series (W10), and the greatest measured freeze–thaw resistance, completing 223 cycles. Optical microscopy and X-ray diffraction observations indicated a visually more continuous matrix and lower relative intensities of several portlandite peaks in the modified concrete. For the replicate-based properties, mixture composition had a statistically significant effect (p < 0.001). Because RHA and dried oil sludge were varied simultaneously, the results represent their combined effect. M2 is therefore identified as the most balanced composition within the present limited test series, rather than as a universal optimum.

This study investigates the development of a composite material based on agricultural plant waste from Kazakhstan, utilizing a multicomponent binder incorporated with rice husk ash. The implementation of low-clinker binders enables the full utilization of ash dumps from the Kyzylorda thermal power plant (TPP) and rice husk residues from local rice-processing enterprises. Physical and chemical analysis of the ash–cement stone revealed a reduction in portlandite content compared to control samples. Phase composition analysis indicated the presence of hydroaluminate C₄AH₁₃ and a reduction in calcite, suggesting accelerated crystallization of calcium silicate hydrates. The formation of crystalline phases and intergrowth structures is assumed to contribute to the strengthening of the gel-like matrix. Experimental optimization of the ash–cement binder with rice husk ash yielded compressive strengths ranging from 3.03 to 4.10 MPa at densities of 790–900 kg/m³, depending on the type of organic filler. These results confirm the feasibility of using locally sourced agricultural waste for the production of heat-insulating and structurally stable composite materials.

This study evaluates a sintered lightweight aggregate produced from a 70:30 mass ratio of loess-like loam to hydraulic ash from the Kyzylorda thermal power plant (TPP), with an external 50:50 TPP-ash–ground-rice-husk dusting mixture. Four dusting regimes (C0–C3) were examined at 1000, 1030, 1060, and 1100 °C using 15 test specimens or portions per condition. C0 was the undusted control; the dusting-mixture-to-raw-granule mass ratios for C1, C2, and C3 were 1:2.5, 1:3.5, and 1:4.9, respectively. Dusting regime and firing temperature affected density, strength, water absorption, pore structure, and thermal conductivity. The selected C2 regime, corresponding to a dusting-mixture-to-granule ratio of 1:3.5, produced at 1060 °C an aggregate with a bulk density of 324 ± 18 kg/m³, cylinder crushing strength of 1.42 ± 0.08 MPa, water absorption of 15.8 ± 0.6%, and effective packed-bed thermal conductivity of 0.078 W/(m·K). Scanning electron microscopy (SEM) showed porous and consolidated regions; local energy-dispersive X-ray spectroscopy (EDS) indicated higher Ca, Al, and Fe in the examined shell region than in the examined core region. Lightweight concrete containing the developed aggregate achieved a dry density of 920 ± 5 kg/m³, 28-day compressive strength of 3.87 ± 0.22 MPa, water absorption of 19.4 ± 0.3%, and thermal conductivity of 0.215 ± 0.010 W/(m·K). The results identify 1060 °C and the C2 dusting regime as a preferred compromise among the tested conditions, based on a comparative assessment of density, cylinder crushing strength, water absorption, and thermal conductivity rather than a weighted numerical optimization.