@inproceedings{HuengerKositzHuengeretal., author = {H{\"u}nger, Klaus-J{\"u}rgen and Kositz, Mario and H{\"u}nger, Maximilian and Krey, Juliane and M{\"u}hlst{\"a}dt, Mike}, title = {Surface coating of siliceous parts of aggregate grains by alumina containing SCM' in alkaline solutions}, series = {ICAAR, 15th International Conference on Alkali Aggregate Reaction, July 03-07, 2016, Sao Paulo, Brazil, abstracts}, booktitle = {ICAAR, 15th International Conference on Alkali Aggregate Reaction, July 03-07, 2016, Sao Paulo, Brazil, abstracts}, publisher = {ICAAR}, pages = {S. 42}, abstract = {It is well known that SCMs containing alumina can prevent the damaging alkali silica reaction in concrete. This paper deals with the direct interactions between aggregate grain surfaces (quartzitic rock material Q1) and the dissolved amounts of SCMs (metakaolin, aluminum hydroxide). Investigations have confirmed that the presence of such SCMs can strongly decrease the silica release from aggregates in comparison to solubility experiments without SCM addition. The reason for this effect is the formation of a thin alumina containing layer (some nanometers thick) on the grain surfaces. The existence of this layer could be determined by XPS. Only this method provides data of the strongly increased alumina concentration in a thin surface area and also of the layer thickness in dependence on reaction parameters. Dissolution experiments of grains coated with such layer demonstrate the effectiveness of this process and can give a further contribution for understanding the preventing mechanisms of SCMs.}, language = {en} } @inproceedings{KositzHuenger, author = {Kositz, Mario and H{\"u}nger, Klaus-J{\"u}rgen}, title = {A predicitve model for the assessment of aggregate sensitivity to ASR}, series = {ICCM, 10th ACI/RILEM International Conference on Cementitious Materials and Alternative Binders for Sustainable Concrete, 2017, Montreal, Kanada}, booktitle = {ICCM, 10th ACI/RILEM International Conference on Cementitious Materials and Alternative Binders for Sustainable Concrete, 2017, Montreal, Kanada}, publisher = {RILEM}, pages = {14}, abstract = {Different aggregates stored in alkaline solutions have different solubility of silica and alumina. The dissolved silica reacts with water and alkalis to form an alkali silica gel, which can swell. ASR swelling can be reduced or prevented, if enough space is available for the alkali silica gel formation. This "space" is the open porosity, which can also be determined directly at the aggregate grains. Concrete specimens made with different aggregates were produced. They all were stored in a fog chamber at 104°F (40°C) and the ASR swelling was measured for one year. At the same time, the aggregates were stored in 0.1 mol KOH solution at 176°F (80°C) for 56 d only. The solubility of silica and alumina was determined continuously by ICP-OES. The obtained dissolution rates, open porosity and expansion data were compared and a reliable model for predicting the ASR sensitivity of concrete aggregates was derived.}, language = {en} } @misc{KositzHuengerWeise, author = {Kositz, Mario and H{\"u}nger, Klaus-J{\"u}rgen and Weise, Frank}, title = {Regression analysis of ASR expansions and silica dissolution in the presence of NaCl}, 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 = {711 -- 723}, abstract = {The durability of concrete structures due to alkali-silica-reaction (ASR) is usually been assessed by ASR concrete prism tests (CPT). Therefore, the expansion of concrete specimens indicates an alkalisensitivity. In Germany these tests are performed at 40°C or accelerated 60°C. Nevertheless, ASR prism tests are expensive, power and time-consuming. For these reasons, an alternative chemical test ("mod. BTU-test") was developed in the past. The "mod. BTU-test" was correlated with German standard CPT. In this test, the solubility of silica and alumina in the liquid phase is measured by ICP-OES. For special requirements in concrete road construction, stricter test procedures are necessary. The specimens are repeatedly subjected to cyclic alternating storage in NaCl. On the one hand, the presence of NaCl increases the ASR expansion, on the other hand NaCl also changes the dissolution behaviour of silica and alumina. For now is not possible to correlate the solubilities of mod. BTU-test and ASR expansions influenced by NaCl. Therefore, four aggregates with different ASR sensitivities were chosen and ASR concrete prism tests (in addition with NaCl) have been performed. According to the "mod. BTU-test" the solubilities of silica and alumina in presence of different NaCl concentrations were measured. This paper is about the regression analysis of silica and alumina dissolution and ASR expansion tests in presence of NaCl. The regression analysis shows the influence of a quasi-continuous and an interrupted cyclic alternating storage. Additionally the effects of temperature and NaCl concentration are investigated. In the end, a suitable NaCl concentration of the "mod. BTU-test" for dissolution experiments is recommended. The "mod. BTU-Test with NaCl might be a serious and reliable test method for ASR classification for concrete road construction.}, language = {en} } @inproceedings{HuengerKositzDannebergetal., author = {H{\"u}nger, Klaus-J{\"u}rgen and Kositz, Mario and Danneberg, Matti and Radnik, J{\"o}rg}, title = {XPS investigations on quartzite surfaces of natural rock samples for proof of Al exposure}, series = {27th Annual Conference of the German Crystallographic Society / Zeitschrift f{\"u}r Kristallographie. Supplement}, volume = {39}, booktitle = {27th Annual Conference of the German Crystallographic Society / Zeitschrift f{\"u}r Kristallographie. Supplement}, publisher = {De Gruyter}, address = {Berlin}, isbn = {978-3-11-065403-5}, issn = {0930-486X}, pages = {S. 110}, language = {en} } @inproceedings{HuengerKositzBrigzinskyetal., author = {H{\"u}nger, Klaus-J{\"u}rgen and Kositz, Mario and Brigzinsky, Maria and Ajami, Fouad}, title = {A fast testing method to characterize ashes and ash mixtures using the ultrasonic technique}, series = {Recent Advances in Concrete Technology and Sustainability Issues Proceedings Fourteenth International Conference Beijing, China October-November 2018}, booktitle = {Recent Advances in Concrete Technology and Sustainability Issues Proceedings Fourteenth International Conference Beijing, China October-November 2018}, pages = {19}, abstract = {Fly ash is a typical mortar constituent in Germany, other European countries and worldwide. If cement alone is used as a binder, then the mortar is too expensive and cannot provide all properties. That`s why many companies have special recipes with fly ash, especially hard coal fly ash components, in the mortar. The aim of this project is to substitute such fly ashes by lignite coal fly ashes, which are cheaper, available at every times or have better properties. However this means, that the calcium free or calcium poor ash should be substituted by calcium rich ashes, which are not certificated because of fluctuations. To compensate the fluctuations in the ash compositions, several ashes are mixed. The European standard EN 450, which contains requirements, for example for the chemical composition of ashes, has to be taken into account. Fly ash mortar compound prisms have been produced and the different mechanical and deformation values were determined in comparison to a reference material. The basis for all experiments was the recipe of the company for a special mortar. An ash compound could be developed with the same workability by considering the economic reasons of the company. An important result too is that the fluctuations of the fly ash batches can be controlled by special developed chemical (color test) and physical (Ultrasonic velocity) test methods.}, language = {en} } @misc{KositzHuenger, author = {Kositz, Mario and H{\"u}nger, Klaus-J{\"u}rgen}, title = {Untersuchungen zur Korrelation von AKR induzierten Dehnungen und der L{\"o}slichkeit von Gesteinsk{\"o}rnungen unter Ber{\"u}cksichtigung von NaCl; Teil 1}, series = {Beton : die Fachzeitschrift f{\"u}r Bau + Technik}, volume = {71}, journal = {Beton : die Fachzeitschrift f{\"u}r Bau + Technik}, number = {3}, issn = {0005-9846}, pages = {60 -- 65}, language = {de} } @misc{KositzHuenger, author = {Kositz, Mario and H{\"u}nger, Klaus-J{\"u}rgen}, title = {Untersuchungen zur Korrelation von AKR induzierten Dehnungen und der L{\"o}slichkeit von Gesteinsk{\"o}rnungen unter Ber{\"u}cksichtigung von NaCl; Teil 2}, series = {Beton : die Fachzeitschrift f{\"u}r Bau + Technik}, volume = {71}, journal = {Beton : die Fachzeitschrift f{\"u}r Bau + Technik}, number = {4}, issn = {0005-9846}, pages = {120 -- 124}, language = {de} } @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{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} }