@article{PartschefeldTutalHalmansederetal.,
  author    = {Partschefeld, Stephan and Tutal, Adrian and Halmanseder, Thomas and Schneider, Jens and Osburg, Andrea},
  title     = {Investigations on Stability of Polycarboxylate Superplasticizers in Alkaline Activators for Geopolymer Binders},
  series = {Materials},
  volume    = {2023},
  journal   = {Materials},
  number    = {Volume 16, issue 15, article 5369},
  publisher = {MDPI},
  address   = {Basel},
  doi       = {10.3390/ma16155369},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20231026-64809},
  pages     = {1 -- 14},
  abstract  = {Calcined clays are interesting starting materials to be used as SCMs (supplementary cementitious materials) in cements or to be converted to geopolymers by activation with a high alkaline activator. The adjustment of the properties in the fresh state, especially regarding the consistency of these binders, is almost exclusively achieved by the addition of water, since commercially available superplasticizers seem to be ineffective in low-calcium geopolymer systems. The aim of this study was a systematic investigation of various PCE (polycarboxylate ester/ether) superplasticizers (methacrylate ester PCE: MPEG, isoprenol ether PCE: IPEG, methallyl ether PCE: HPEG) with respect to their stability in different alkaline activators (NaOH, KOH, sodium and potassium silicate solutions). The effectiveness of superplasticizers (SPs) in low-calcium geopolymer binders was verified by rheological tests. Size exclusion chromatography was used to investigate if structural degradation of the superplasticizers occurs. The investigated PCE superplasticizers showed a thickening effect in the low-calcium geopolymer system. Depending on the alkalinity of the activator solution, a degradation process was detected for all the PCEs investigated. The side chains of the PCEs are cleaved off the backbone by basic ester and ether hydrolysis. The highest degree of degradation was found in sodium and potassium silicate solutions. In alkaline hydroxide solutions, the degradation process increases with increasing alkalinity.},
  subject      = {Geopolymere},
  language  = {en}
}
@article{SchirmerOsburg,
  author    = {Schirmer, Ulrike and Osburg, Andrea},
  title     = {A new method for the quantification of adsorbed styrene acrylate copolymer particles on cementitious surfaces: a critical comparative study},
  series = {SN Applied Sciences},
  volume    = {2020},
  journal   = {SN Applied Sciences},
  number    = {Volume 2, article 2061},
  publisher = {Springer},
  address   = {Heidelberg},
  doi       = {10.1007/s42452-020-03825-5},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210804-44729},
  pages     = {1 -- 11},
  abstract  = {The amount of adsorbed styrene acrylate copolymer (SA) particles on cementitious surfaces at the early stage of hydration was quantitatively determined using three different methodological approaches: the depletion method, the visible spectrophotometry (VIS) and the thermo-gravimetry coupled with mass spectrometry (TG-MS). Considering the advantages and disadvantages of each method, including the respectively required sample preparation, the results for four polymer-modified cement pastes, varying in polymer content and cement fineness, were evaluated. To some extent, significant discrepancies in the adsorption degrees were observed. There is a tendency that significantly lower amounts of adsorbed polymers were identified using TG-MS compared to values determined with the depletion method. Spectrophotometrically generated values were ​​lying in between these extremes. This tendency was found for three of the four cement pastes examined and is originated in sample preparation and methodical limitations. The main influencing factor is the falsification of the polymer concentration in the liquid phase during centrifugation. Interactions in the interface between sediment and supernatant are the cause. The newly developed method, using TG-MS for the quantification of SA particles, proved to be suitable for dealing with these revealed issues. Here, instead of the fluid phase, the sediment is examined with regard to the polymer content, on which the influence of centrifugation is considerably lower.},
  subject      = {Zement},
  language  = {en}
}
@article{TutalPartschefeldSchneideretal.,
  author    = {Tutal, Adrian and Partschefeld, Stephan and Schneider, Jens and Osburg, Andrea},
  title     = {Effects of Bio-Based Plasticizers, Made From Starch, on the Properties of Fresh and Hardened Metakaolin-Geopolymer Mortar: Basic Investigations},
  series = {Clays and Clay Minerals},
  volume    = {2020},
  journal   = {Clays and Clay Minerals},
  number    = {volume 68, No. 5},
  publisher = {Springer},
  address   = {Heidelberg},
  doi       = {10.1007/s42860-020-00084-8},
  url       = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210804-44737},
  pages     = {413 -- 427},
  abstract  = {Conventional superplasticizers based on polycarboxylate ether (PCE) show an intolerance to clay minerals due to intercalation of their polyethylene glycol (PEG) side chains into the interlayers of the clay mineral. An intolerance to very basic media is also known. This makes PCE an unsuitable choice as a superplasticizer for geopolymers. Bio-based superplasticizers derived from starch showed comparable effects to PCE in a cementitious system. The aim of the present study was to determine if starch superplasticizers (SSPs) could be a suitable additive for geopolymers by carrying out basic investigations with respect to slump, hardening, compressive and flexural strength, shrinkage, and porosity. Four SSPs were synthesized, differing in charge polarity and specific charge density. Two conventional PCE superplasticizers, differing in terms of molecular structure, were also included in this study. The results revealed that SSPs improved the slump of a metakaolin-based geopolymer (MK-geopolymer) mortar while the PCE investigated showed no improvement. The impact of superplasticizers on early hardening (up to 72 h) was negligible. Less linear shrinkage over the course of 56 days was seen for all samples in comparison with the reference. Compressive strengths of SSP specimens tested after 7 and 28 days of curing were comparable to the reference, while PCE led to a decline. The SSPs had a small impact on porosity with a shift to the formation of more gel pores while PCE caused an increase in porosity. Throughout this research, SSPs were identified as promising superplasticizers for MK-geopolymer mortar and concrete.},
  subject      = {Geopolymere},
  language  = {en}
}