@inproceedings{HuebertHuenger, author = {H{\"u}bert, Cornelia and H{\"u}nger, Klaus-J{\"u}rgen}, title = {Strukturbildung und Eigenschaften von Alumosilicathydraten in Baustoffen}, series = {18. Internationale Baustofftagung IBAUSIL, F.A. Finger-Institut f{\"u}r Baustoffkunde, Bauhaus-Universit{\"a}t Weimar, Tagungsbericht, Teil 2}, booktitle = {18. Internationale Baustofftagung IBAUSIL, F.A. Finger-Institut f{\"u}r Baustoffkunde, Bauhaus-Universit{\"a}t Weimar, Tagungsbericht, Teil 2}, publisher = {F.-A.-Finger-Inst.}, address = {Weimar}, isbn = {978-3-00-034075-8}, pages = {2-0310}, language = {de} } @inproceedings{Huenger, author = {H{\"u}nger, Klaus-J{\"u}rgen}, title = {Zum Reaktionsmechanismus von Grauwacken im Beton}, series = {Tagungsbericht, IBAUSIL, 16. Internationale Baustofftagung, 20. - 23. September 2006, Weimar, Bd. 2}, booktitle = {Tagungsbericht, IBAUSIL, 16. Internationale Baustofftagung, 20. - 23. September 2006, Weimar, Bd. 2}, publisher = {F.-A.-Finger Inst. f{\"u}r Baustoffkunde}, address = {Weimar}, isbn = {3-00-018263-2}, pages = {2-0427 -- 2-0434}, language = {de} } @misc{MsinjiliVoglerSturmetal., author = {Msinjili, Nsesheye S. and Vogler, Nico and Sturm, Patrick and Neubert, Markus and Schr{\"o}der, Hans-J{\"u}rgen and K{\"u}hne, Hans-Carsten and H{\"u}nger, Klaus-J{\"u}rgen and Gluth, Gregor J. G.}, title = {Calcined brick clays and mixed clays as supplementary cementitious materials: Effects on the performance of blended cement mortars}, series = {Construction and Building Materials}, volume = {266}, journal = {Construction and Building Materials}, issn = {0950-0618}, doi = {10.1016/j.conbuildmat.2020.120990}, pages = {11}, abstract = {While calcined clays in general have been credited with a great potential to mitigate CO2 emissions related to cement production and consumption, calcined brick clays are currently understudied in this regard. In the present work, two brick clays, a low-grade kaolinitic clay, and a mixed clay composed of 50\% brick clay and 50\% low-grade kaolinitic clay were studied regarding transformations on calcination, and strength and durability performance as well as pore structure of mortars made with the blended cements. All calcined clays exhibited pozzolanic reactivity, with the performance of the brick clays inferior to the low-grade kaolinitic clay. However, the mixed clay performed very similar to the low-grade kaolinitic clay, which points to a viable option for optimal use of brick clays in cementitious systems. The carbonation resistance of the blended cement mortars was generally worse than that of the plain Portland cement mortar, as expected, but the former exhibited a significantly improved chloride penetration resistance. The latter improvement was due to pore structure refinement in the blended cement mortars, compared to the Portland cement mortar.}, language = {en} } @misc{HuengerKositz, author = {H{\"u}nger, Klaus-J{\"u}rgen and Kositz, Mario}, title = {Thermodynamic modeling of silica dissolution kinetics of quartzitic aggregates stored in highly alkaline solution}, series = {Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete}, journal = {Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete}, publisher = {LNEC}, isbn = {978-972-49-2315-4}, pages = {1447 -- 1458}, abstract = {Knowledge's on the dissolution behaviour of SiO2-containing aggregates are the basis for understanding damaging processes regarding ASR. Because of many influences, the solubility of aggregates has still needs to be determined by dissolution experiments. This article is about the reliably modeling of silica dissolution of relatively pure SiO2 containing aggregates in alkaline solutions. Therefore, quartz, quartzite, opal sandstone and flint with different silica modifications were chosen. A kinetic model based on the surface area was derived and numerous thermodynamic data from different authors were evaluated. The surface area of the aggregate grains were determined by an adapted BET method. For this measurement, the original grain sizes were used as they are also used so in concrete. These aggregates were stored in 0.1 mol and 1.0 mol KOH solution at 40°C and 80°C respectively. The dissolution experiments too were performed with grains in the original particle sizes. The concentration of silica in the liquid phase was measured by ICP-OES. The model based on a comparison of calculated and experimental determined silica concentrations, because some parameters of the differential equations are still unknown. The model includes the temperature and molarity dependence of the silica dissolution. The model also takes into account the influences of the SiO2 structures and can vary between crystalline and amorphous SiO2 in a wide range. Thermodynamic data suitable for modeling are recommended. In future, these dissolution calculations shall be extended to other non-pure quartzitic aggregates. Instead of time-consuming ASR concrete prism tests the silica dissolution rates may be used then to indicate quickly the ASR sensitivity of aggregates. Of course, it will be possible to distinguish between innocuous, medium and highly reactive grains.}, language = {en} } @misc{HuengerKositzDanneberg, author = {H{\"u}nger, Klaus-J{\"u}rgen and Kositz, Mario and Danneberg, Matti}, title = {Influence of alkali supply from outside on the dissolution behavior of aggregates}, series = {Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete}, journal = {Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete}, publisher = {LNEC}, isbn = {978-972-49-2315-4}, pages = {63 -- 72}, abstract = {Reactive aggregates, humidity and alkalis are necessary for ASR in concrete structures. If alkalis come additionally from outside, the damaging reaction can be strongly accelerated. However, the reasons therefore are not completely understood. Some researchers discuss a direct attack of alkali ions on the Si-O-Si bonds of quartz structures. This paper provides another point of view to understand this phenomenon. Different aggregates (grain size 2-8mm) were stored in a highly alkaline KOH solution. Additionally to this solution, sodium chloride with different concentrations was added. The aggregates were selected on the one hand according to their reaction behavior in concrete structures, on the other hand to their dissolution behavior. Long-term dissolution experiments were performed over several months. The silica, the aluminum and of course the sodium concentrations were determined. It can be expected, that under the influence of sodium the silica concentrations in the alkaline solution raise up. The question here is: What happens with the aluminum concentration at the same time? Very surprisingly was, that Al reaches a maximum after some days and then it decreases. Exactly from this time when the Al concentration decreases the silica concentration raises up extremely. The reason therefore can only be a precipitation process. Obviously, there is a correlation between the aluminum content in the solution and the extreme silica release of aggregates, both affected by alkali ions from outside. Aggregates, which do not release aluminum because of their composition (e.g. quartzite), do not show this behavior. The conclusion is that such aggregates are not so sensitive against alkali attack from outside.}, language = {en} } @misc{HuengerKurth, author = {H{\"u}nger, Klaus-J{\"u}rgen and Kurth, David}, title = {Calcined Clays and Geopolymers for stabilization of loam structures for plaster and bricks}, series = {Proceedings 3rd International Conferende on Calcined Clays for Sustainable Concrete, 15. - 17 Oktober 2019, Neu Delhi}, volume = {III}, journal = {Proceedings 3rd International Conferende on Calcined Clays for Sustainable Concrete, 15. - 17 Oktober 2019, Neu Delhi}, publisher = {RILEM}, pages = {185 -- 194}, abstract = {Loam is a very ecological building material with a great potential. It is found worldwide and completely recyclable. Under dry conditions, loam develops high strength values. However, loam is not moisture-resistant. Permanently acting moisture reduces the strength dramatically. The idea to improve the water resistance of loams is adding materials to the loam with the same basic structure. Therefore, Metakaolin, Calcined Clay, here so called Metaclay and a specially developed Geopolymer were selected. Blends of 4 different loams with different amounts of these additives were produced and tested. Criteria for an evaluation are the dynamical modulus of elasticity and the water resistance. These studies were supplemented by structural investigations using a light and a scanning electron microscope and XRD. The results are very interesting and the effects depends strongly on the kind of loam too. Not all additives lead to an improving of the mechanical properties. Nevertheless, not the samples with the highest mechanical values show the best water resistance behavior. Obviously, a balanced structure between loam and additive particles is necessarily. Such structures are not so dense but enough resistant to water to guarantee the positive property of fast water absorption and delivery of natural loams. The service lives of the loam prisms could be increased from certain minutes to several days. Best results are obtained with geopolymer based materials as an additive. This is not so surprising because both the loam and the geopolymer form alumino silicate structures during hardening.}, language = {en} } @misc{MoJingHuengeretal., author = {Mo, Xiangyin and Jing, Yingjie and H{\"u}nger, Klaus-J{\"u}rgen and Kang, Cairong and Shen, Jian}, title = {Characteristics of alkali aggregate reaction}, series = {Gui suan yan xue bao}, volume = {36}, journal = {Gui suan yan xue bao}, number = {10}, issn = {0454-5648}, pages = {1385 -- 1389}, language = {mul} } @misc{HuengerKositzDannebergetal., author = {H{\"u}nger, Klaus-J{\"u}rgen and Kositz, Mario and Danneberg, Matti and Radnik, J{\"o}rg}, title = {Enrichment of aluminium in the near-surface region of natural quarzite rock after aluminium exposure}, series = {Surface and Interface Analysis}, volume = {53}, journal = {Surface and Interface Analysis}, number = {3}, issn = {1096-9918}, doi = {10.1002/sia.6918}, pages = {385 -- 391}, abstract = {Alkali-silica reaction (ASR) is an ongoing problem that causes damage to concrete constructions and reduces their durability. Therefore, minimizing this undesired reaction is of great interest for both safety and economic reasons. Additives containing high aluminium content are very effective in reducing the release of silica and enhancing the durability of concrete; however, the mechanism for this effect is still under discussion. In this study, an enrichment of aluminium in the near-surface region was observed for natural quartzite rock after storage in Al (OH)3 and metakaolin as aluminium sources, from which we conclude that the formation of aluminosilicate sheets of a few nanometres inhibits the silica release; this hypothesis is supported by high-resolution spectra of Al 2p, Si 2p and O 1s.}, language = {en} }