Effect of the chemical environment on the composition, structure and swelling behaviour of ASR gels

活性二氧化硅与碱发生反应，在混凝土中形成一种胶体碱-二氧化硅（ASR）凝胶，该凝胶吸水膨胀。这可能导致相当大的膨胀压力，从而破坏混凝土结构。形成具有破坏性的ASR凝胶需要高含水量、碱的可用性和碱敏感、富含二氧化硅的聚集体。化学成分(Al/Si, Ca/Si, Na/Si bzw。K/Si)和凝胶的相关纳米结构影响其膨胀能力。凝胶的化学成分，以及它的膨胀能力，通过使用含有铝的矿物添加剂（粉煤灰、偏高岭土、煅烧粘土）而改变。然而，铝在ASR凝胶中的掺入程度及其对膨胀压力的影响尚不清楚。本研究项目旨在更好地了解混凝土中的化学条件对碱硅反应的影响。特别关注了凝胶的化学成分和纳米结构与ASR损伤、膨胀能力的关系。生产不同成分的合成ASR凝胶，并使用光谱（核磁共振/红外/拉曼光谱）以及物理（热重法）和化学方法（ICP-OES）进行分析。凝胶的膨胀能力是在不同相对湿度的储存实验中确定的。研究结果揭示了ASR凝胶的纳米结构、化学成分及其膨胀行为之间的关系。混凝土棱镜由灰砂岩、蛋白石砂岩和燧石以及硼硅酸盐玻璃制成，以模拟真实混凝土中ASR凝胶的形成。利用薄层光学显微镜和扫描电子显微镜（SEM/EDX）研究了棱镜的膨胀和结构。拉曼光谱和激光烧蚀ICP-MS测量进行了更详细的分析凝胶。此外，还分析了暴露在室外条件下长达14年的实验室混凝土。这些试验使研究成果能够在实际结构中转化为混凝土。这项工作旨在揭示破坏ASR，混凝土膨胀和ASR凝胶的化学成分之间的关系。因此，上述合成ASR凝胶的研究结果被转移到混凝土中。关于ASR凝胶的纳米结构和化学成分对混凝土损伤的影响的研究结果旨在为未来预防和评估混凝土结构中ASR损伤发展的策略提供基础。

The reaction of reactive silica with alkalis leads to the formation of a colloidal alkali-silica (ASR) gel in concrete which swells on absorbing water. This can lead to considerable swelling pressures and thus damage to concrete structures. The formation of a damaging ASR gel requires high moisture content, the availability of alkalis and alkali-sensitive, silica rich aggregates. The chemical composition (Al/Si, Ca/Si, Na/Si bzw. K/Si) and the associated nanostructure of the gel affect its ability to swell.The chemical composition of the gel, and thus its swelling ability, is changed by the use of mineral additions (fly ash, metakaolin, calcined clay) which contain aluminium. However, the extent to which aluminium is incorporated into ASR gels and its effect on the swelling pressure is unknown.This research project aims at a better understanding of the effect of the chemical conditions in concrete on the alkali silica reaction. Particular attention is paid to the relationship between ASR damage, swelling capacity and chemical composition and nanostructure of the gel.Synthetic ASR gels with different compositions are produced and analysed using spectroscopic (NMR / Infrared / Raman spectroscopy) as well as physical (thermogravimetry) and chemical methods (ICP-OES). The swelling ability of the gels is determined in storage experiments using various relative humidities. The results yield relationships between the nanostructure and the chemical composition of the ASR gel and its swelling behaviour.Concrete prisms are produced with greywacke, opal sandstone and flint as well as borosilicate glass to simulate the formation of ASR gel in real concrete. The expansion of the prisms is monitored and their structure investigated using thin-section optical microscopy and SEM/EDX. Raman spectroscopic and laser ablation ICP-MS measurements are performed to analyse the gels in more detail. In addition, laboratory concretes exposed to outdoor conditions for up to 14 years are analysed. These experiments enable the transfer of the research results to concrete in real structures. This work intends to reveal relationships between a damaging ASR, the expansion of concrete and the chemical composition of the ASR gel. The results of the above studies with synthetic ASR gels are thus transferred to concrete.The findings on the effect of nanostructure and chemical composition of ASR gels on concrete damage are intended as a basis of future strategies for preventing and assessing ASR damage development in concrete structures.