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

反应性二氧化硅与碱的反应导致在混凝土中形成胶态碱-硅（ASR）凝胶，该凝胶吸水膨胀。这可能导致相当大的膨胀压力，从而损坏混凝土结构。破坏性ASR凝胶的形成需要高含水量、碱和碱敏感性的可用性、富含硅的聚集体。化学成分（Al/Si，Ca/Si，Na/Si bzw.通过使用含铝的矿物添加剂（粉煤灰、偏高岭土、煅烧粘土）改变凝胶的化学组成，从而改变凝胶的溶胀能力。然而，在何种程度上铝被纳入ASR凝胶及其对膨胀pressure.This研究项目的影响是未知的，旨在更好地了解在混凝土中的碱硅酸反应的化学条件的影响。特别注意ASR损伤，溶胀能力和化学组成和凝胶的纳米结构之间的关系。合成的ASR凝胶与不同的组合物的生产和分析使用光谱（NMR /红外/拉曼光谱）以及物理（热重）和化学方法（ICP-OES）。凝胶的溶胀能力在使用各种相对湿度的储存实验中测定。结果产生的纳米结构和ASR凝胶的化学组成和其膨胀behaviors.Concrete棱柱体的关系产生与杂砂岩，蛋白石砂岩和燧石以及硼硅酸盐玻璃模拟ASR凝胶在真实的混凝土中的形成。棱镜的膨胀进行监测，并使用薄切片光学显微镜和SEM/EDX研究它们的结构。进行拉曼光谱和激光烧蚀ICP-MS测量以更详细地分析凝胶。此外，实验室混凝土暴露在室外条件下长达14年进行了分析。这些实验使得研究结果能够转移到真实的结构中的混凝土中。这项工作旨在揭示一个破坏性的ASR，混凝土的膨胀和ASR凝胶的化学组成之间的关系。因此，上述研究结果与合成ASR凝胶转移到混凝土。ASR凝胶的纳米结构和化学组成对混凝土损伤的影响的研究结果，旨在作为未来的战略，预防和评估混凝土结构中的ASR损伤发展的基础。

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.