Experimental studies of concrete materials for the restoration of hydraulic structures

Introduction. The objective of this research is to substantiate the application of advanced concrete materials for restoring hydraulic structures in Kazakhstan and Central Asia, where service conditions are severe due to sharp temperature swings, sulfate-chloride attack, and high seismicity. The relevance of the study is determined by the widespread deterioration of existing infrastructure and the demonstrated inadequacy of traditional repair methods. Methods and materials. To evaluate the properties of the original concrete and promising repair materials (polymer-modified mortars, geopolymer systems, and ultra-high-performance concrete- UHPC), a comprehensive set of laboratory tests was conducted. The research included: physico-mechanical tests (strength, elastic modulus, adhesion), durability tests (RCPT, NT Build 492, freeze-thaw resistance, sulfate resistance, abrasion–cavitation wear), and micro/nanostructural analysis (SEM/EDS, XRD, nanoindentation). Results and discussion. The original concrete exhibited high permeability (~5.2 thousand C according to RCPT), low adhesion, and significant strength loss under cyclic loading, which can be explained by pronounced porosity and cracking of the structure. UHPC demonstrated minimal permeability (<0.3 thousand C), high adhesion (2.2 MPa), low strength loss under freeze-thaw cycles (≤3%), and the highest local elastic modulus (40–50 GPa). Geopolymer materials showed strong sulfate resistance (expansion ≤0.038%) and a fine-pore structure with a low diffusion coefficient (5×10–12 m2/s). Polymer-modified mortars (PMM) exhibited intermediate characteristics, remaining the most economically feasible option. SEM confirmed the significant densification of the UHPC and geopolymer matrices compared to the original concrete; XRD revealed a reduction in portlandite content and the formation of sulfate-resistant phases in geopolymers, while UHPC showed a predominance of amorphous C–S–H phases. Conclusion. The comprehensive analysis demonstrated that the rational use of materials depends on the balance between durability, reliability, and economic–environmental indicators. UHPC is recommended for zones exposed to intensive cavitation and abrasion; geopolymers are optimal for structures in sulfate environments; and PMM are suitable for localized repairs under budget constraints. The results confirm the effectiveness of a multi-level approach: diagnostics → material selection → laboratory verification → durability prediction → practical recommendations. This provides a scientifically grounded basis for designing restoration measures for hydraulic structures.