Very-Low-Density Porous Aggregate Produced by Organomineral Surface Dusting with Kyzylorda TPP Ash and Ground Rice Husk

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.