TY - CONF A1 - Hu, Nanjie A1 - Hüsken, Götz A1 - Gluth, Gregor A1 - Kühne, Hans-Carsten T1 - The influence of activator composition on the strength, shrinkage and chloride migration resistance of alkali-activated slag mortars N2 - Alkali-activated slag materials are known for their high Chloride penetration resistance. This makes them potentially applicable as repair systems for damaged steel-reinforced concrete structures, which are exposed to chloride attack. For this purpose, the influence of the activator composition, i.e. the SiO2 and Na2O concentration of the alkaline solution on a) the compressive strength, b) shrinkage and mass change and c) the resistance against chloride penetration of four alkali-activated slag mortars (AASM) were studied. An ordinary Portland cement-based mortar was used as the reference sample. Increasing SiO2 and Na2O concentrations increased the strength, shrinkage and mass loss of the AASMs. The resistance of the mortars against chloride penetration was evaluated using the non-steady-state migration coefficient Dnssm obtained from NT BUILD 492. The results indicate that the Dnssm is related to differences in the pore solution of the AASMs rather than to differences in their microstructure. An upcoming study of the authors is going to evaluate this hypothesis by the accelerated chloride penetration (diffusion) test. T2 - 6th International Conference Non-Traditional Cement and Concrete 2017 CY - Brno, Czech Republic DA - 19.06.2017 KW - Alkali-activated slag mortar KW - Strength KW - Shrinkage KW - Chloride migration coefficient PY - 2018 DO - https://doi.org/10.4028/www.scientific.net/KEM.761.61 SN - 1662-9795 VL - 761 SP - 61 EP - 64 PB - Trans Tech Publications CY - Switzerland AN - OPUS4-43884 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gluth, Gregor A1 - Lehmann, Christian A1 - Rübner, Katrin A1 - Kühne, Hans-Carsten T1 - Hydration and strength development of calcite-rich wastepaper sludge ash N2 - In paper recycling large amounts of waste sludge, containing organics as well as inorganic fillers of the recycled paper, are produced. A large fraction of these sludges is incinerated; the ashes generated in this process, often referred to as wastepaper sludge ash (WSA), have the potential to be used as binder material, either alone or as supplementary cementitious material. However, ashes from different paper mills differ in their Chemical and mineralogical composition, thus, the reaction products and the properties of the hardened binders may vary s i gn i fi cantley. In the present study, a calcite-rich WSA was analyzed for reaction products and strength development. The WSA contained, besides calcite, hydraulic phases such as tricalcium aluminate (C3A) and belite (C2S), lime as well as inert phases. When activated with water, the WSA yielded a compressive strength of up to 12.3 MPa and the major hydration product was monocarboaluminate (C4A CO2 IIH2O or C4ACH11). Activation with 2M NaOH or 2M KOH solution caused a more rapid strength gain until one day of curing, but afterwards the strength development slowed down and the strength afiter 28 days was significantly lower than for the water-activated pastes. From TG analyses it is apparent that the higher strength of the alkaliactivated pastes after one day of curing was caused by a more rapid consumption of calcite and associated formation of C4ACH11. At later curing times the amount of calcite did not change substantially and consequently strength development almost ceased. The results demonstrate the complex influence of alkaline conditions on the hydration of WSA and show that the reaction products, which determine the durability properties of the hardened pastes (and materials made from it), of the calcite-rich WSA differ from the products of other WS As, as discussed in the article. T2 - CIC 2014 - Concrete Innovation Conference 2014 CY - Oslo, Norway DA - 11.06.2014 KW - Wastepaper sludge ash (WSA) KW - Alkali-activation KW - Strength KW - Tetracalcium monocarboaluminate PY - 2014 SP - 1 EP - 8 AN - OPUS4-31038 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gluth, Gregor A1 - Lehmann, Christian A1 - Rübner, Katrin A1 - Kühne, Hans-Carsten T1 - Reaction products and strength development of wastepaper sludge ash and the influence of alkalis N2 - Wastepaper sludge ash (WSA) from a newsprint paper mill was investigated for its mineralogical composition and its reaction products and strength development after activation with water and sodium and potassium hydroxide solutions. The results showed the WSA to consist of calcite, free lime, gehlenite, tricalcium aluminate, belite, talc, quartz and probably a glassy phase. The principle reaction product was monocarboaluminate (CO3–AFm) for the water- as well as for the alkali-activated WSA. Formation of monocarboaluminate and strength gain was more rapid for the alkali-activated WSA until 1 day of curing. However, afterwards reactions proceeded much slower when alkali solutions were used, leading to an about twice as high compressive strength for water-activated WSA mortars after 28 days of curing. The observed behavior is tentatively ascribed to a less uniform microstructure of the alkali-activated WSA. Significant differences between NaOH- and the KOH-activated WSA were not observed. KW - Wastepaper sludge ash KW - Reaction products KW - Monocarboaluminate KW - Strength KW - Alkali-activation PY - 2014 DO - https://doi.org/10.1016/j.cemconcomp.2013.09.009 SN - 0958-9465 SN - 1873-393X VL - 45 SP - 82 EP - 88 PB - Elsevier CY - Barking, Essex AN - OPUS4-29930 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gluth, Gregor A1 - Lehmann, Christian A1 - Haase, Oskar A1 - Rübner, Katrin A1 - Kühne, Hans-Carsten ED - Uzoegbo, H.C. ED - Schmidt, Wolfram T1 - Strength development and characterization of the reaction products of a one-part-geopolymer derived from a silica residue and sodium aluminate N2 - A silica-rich residue from waste-water treatment of chlorosilane production was tested for its applicability for the production of one-part geopolymers. The residue was blended with solid sodium aluminate, the blend activated with water and cured at 70 °C. The degree of reaction and strength were determined after 1,3, and 7 days. The reaction products were analyzed by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen Sorption, and small-angle X-ray Scattering (SAXS). Until the third day of curing the degree of reaction of the residue reached 51% and the strength reached 8.9 MPa. The reaction product was identified as geopolymer containing zeolite A. The results thus confirmed that the residue may be used in the production of geopolymers. However, from 3 to 7 days of curing no further progress of reaction was observed and the strength slightly decreased. It was observed that even harsh vacuum drying left some water, presumably zeolitic water and surface hydroxyl groups, in the hardened geopolymer, the volume fraction of the emptied pores was approximately 45%. The SEM and SAXS analyses showed the gel-like microstructure of the geopolymer with diameters of the gel particles of about 70 nm on average. In line with this colloidal particle size, the specific surface area of the geopolymer was measured by SAXS to be approximately 120 m2/g. On the contrary, nitrogen Sorption measurements yielded a specific surface area of only 13 mz/g and did not show the presence of micropores, which is attributable to the inaccessibility of the pores of the geopolymer and the zeolites for nitrogen at the measurement temperature. T2 - ACCTA - International conference on advances in cement and concrete technology in Africa 2013 CY - Johannesburg, South Africa DA - 28.01.2013 KW - Geopolymers KW - Waste materials KW - Sodium aluminate KW - Strength KW - Microstructure PY - 2013 SN - 978-3-9815360-3-4 SP - 253 EP - 259 AN - OPUS4-27758 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -