Geopolymer and ordinary Portland cement interface analyzed by micro-Raman and SEM

Geopolymers are a class of material that could potentially be used for sealing and repair of damaged concrete structures. This application is important for both decommissioning activities and standard industrial applications. The purpose of this article is to investigate the interface between ordinary Portland cement and geopolymer. The surface microstructure of the cement is investigated by SEM, EDX, and micro-Raman after embedding in geopolymer or immersion in the activation solution of a geopolymer for various durations. It is found that immersion in the solution induces a dendritic carbonation profile into the cement structure following the CSH gel. On the contrary, embedding in the geopolymer creates a dense, impermeable interface with a thickness of a few micrometers. This interface is found to be dense and brittle and it decreases the permeability of the surface, preventing the penetration of silicates into the cement structure. However, this brittle interface is sensitive to dehydration and can rupture under intense drying. This phenomenon can be utilized to separate the geopolymer and cement but is concerning if the integrity of the material must be guaranteed under extreme conditions.

地质聚合物（Geopolymer）是一类有望用于受损混凝土结构密封与修复的材料。该类材料的应用场景对于退役作业与常规工业应用均具有重要意义。本文旨在研究普通硅酸盐水泥与地质聚合物之间的界面特性。研究人员通过扫描电子显微镜（SEM，Scanning Electron Microscope）、能量色散X射线光谱（EDX，Energy Dispersive X-ray Spectroscopy）与显微拉曼光谱（Micro-Raman），对经不同时长埋入地质聚合物基体或浸泡于地质聚合物活化液后的水泥表面微观结构进行表征。研究发现，浸泡于活化液会在水泥结构中沿水化硅酸钙（CSH）凝胶形成枝晶状碳化分布特征。与之相反，将水泥埋入地质聚合物基体后会形成一层厚度为数微米的致密、不透水界面。该界面致密且质脆，可降低水泥表面的渗透性，阻止硅酸盐类物质渗入水泥结构内部。但该质脆界面对脱水作用较为敏感，在强干燥条件下易发生断裂。该现象可被用于分离地质聚合物与水泥，但在极端工况下需保障材料整体完整性时，该特性则存在安全隐患。