Ukrainczyk Neven
Institute of Construction and Building Materials, Technical University of Darmstadt, Franziska-Braun-Str 7, 64287 Darmstadt, Germany.
Materials (Basel). 2021 Mar 15;14(6):1425. doi: 10.3390/ma14061425.
This paper investigates alkali leaching from geopolymers under various concentrations of acetic acid solutions. The effects of the raw metakaolin purity as well as fly ash-based geopolymer mortars and pastes are considered. A new methodology for (acetic) acid attack is proposed, adapting standard approaches, where the concentration of the leached alkali in the exposure solution is measured over time. The applicability of a simple diffusion-based mathematical model to determine the apparent diffusion coefficient () for geopolymer pastes and mortars was validated. At the end of the paste tests, microstructural alterations of the specimens' cross-sections were analyzed microscopically, revealing occurrence of degradation across the outermost surface parts and, especially under acid attack, the formation of long cracks that connect the surface with the intact inner zone. Drastically different are discussed in terms of the differences in the mix designs, principally resulting in different alkali-binding capacities of the geopolymers, while the acid promoted dissolution and increased porosity. As a result of this interpretation, it was concluded that is governed mainly by the chemistry of the alkali release from the gel, as it overruled the effects of porosity and cracks.
本文研究了地质聚合物在不同浓度乙酸溶液中的碱浸出情况。考虑了原料偏高岭土纯度以及粉煤灰基地质聚合物砂浆和浆体的影响。提出了一种新的（乙酸）酸侵蚀方法，采用标准方法，通过测量暴露溶液中浸出碱的浓度随时间的变化。验证了基于简单扩散的数学模型用于确定地质聚合物浆体和砂浆的表观扩散系数（）的适用性。在浆体试验结束时，对试样横截面的微观结构变化进行了显微镜分析，结果显示在最外层表面部分出现了降解，特别是在酸侵蚀下，形成了将表面与完整内部区域连接起来的长裂缝。根据混合料设计的差异讨论了截然不同的情况，主要导致地质聚合物的碱结合能力不同，而酸促进了溶解并增加了孔隙率。基于这种解释，得出的结论是，主要受凝胶中碱释放化学的控制，因为它排除了孔隙率和裂缝的影响。
