Surface Pre-Coating of Fly Ash Ceramsite for Interfacial Microstructure Evolution and Mechanical Enhancement of Lightweight Concrete

Le résumé fourni par la source

The widespread application of fly ash ceramsite as a lightweight aggregate in high-performance concrete is restricted by its inherent defects, including high porosity, high water absorption rate and weak interfacial transition zone (ITZ). In this study, a surface pre-treatment strategy is proposed, in which the ceramsite granules are pre-coated prior to mixing, followed by concrete preparation with the modified aggregates. A pre-coating formulation of micro–nano silica fume and modified acrylate emulsion was applied to improve the interfacial characteristics and mechanical/durability performance. The results show that the coating treatment improved 28-day compressive, flexural–tensile, and axial tensile strengths by 21.2%, 16.0%, and 20.6%, respectively, along with the elastic modulus and ultimate tensile strain. The coated concrete achieved an impermeability grade exceeding W14, retained over 85% of relative dynamic elastic modulus after 150 freeze–thaw cycles, and maintained compressive strength above 90.0% after 20 wetting–drying cycles, with a corresponding relative dynamic elastic modulus of 67.24%. Microstructural observation, pore parameter analysis, and microzone mechanical testing were performed to reveal the underlying mechanisms. The performance improvement is mainly attributed to the strengthening of the traditionally weak interfacial transition zone (ITZ). Additionally, the coating refines the pore structure, stabilizes its distribution, and acts as a physical barrier, further enhancing resistance to freeze–thaw and wetting–drying cycles.

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