Effect of Mineral Additives on Cement Matrices Intended for Radioactive Waste Immobilization

Nurzhan Ye. Mukhamedov, A. S. Surayev, Nuriya Mukhamedova, Aisara Sabyrtayeva, Ospan Oken, S. A. Dolzhikov, Danil Kulbedin

2026

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DOI 10.3390/jcs10060305
Data confidence 70 medium
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Abstract

This study investigates the effect of mineral additives of different natures, namely blast-furnace slag, fly ash, and bentonite, on structure formation, phase composition, microstructure, and physicomechanical properties of cement matrices. The analysis included measurements of mass change and linear shrinkage during hardening, determination of density and microhardness, X-ray phase analysis, and microstructural examination by scanning electron microscopy. It was found that the introduction of mineral additives reduced linear shrinkage from 6.06 mm for the control composition to 0.25 mm for the composition with blast-furnace slag, 2.31 mm for the composition with fly ash, and 1.01 mm for the composition with bentonite. The maximum density and microhardness values were obtained for the matrix with blast-furnace slag and amounted to 1.99 ± 0.03 g/cm3 and 39.95 ± 1.12 HV1, respectively, whereas the overall range of values for the investigated compositions was 1.52–1.99 g/cm3 and 30.2–39.95 HV1. X-ray phase analysis showed that the amorphous component varied from 61 to 78%, reaching its maximum value in the composition with blast-furnace slag, which is associated with the formation of poorly crystalline C–S–H and aluminosilicate phases. According to the SEM data, the average size of visible pore-like defects was 2.4 μm for the control composition, 1.4 μm for the composition with blast-furnace slag, 1.3 μm for the composition with fly ash, and 1.7 μm for the composition with bentonite. The most favorable combination of high density, microhardness, developed amorphous component, and homogeneous microstructure was established for the composition with blast-furnace slag. The obtained results can be used as a materials-science basis for the development of cement matrices intended for further studies on the immobilization of solid radioactive waste.