@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{CappachionePartschefeldOsburgetal., author = {Cappachione, Clotilde and Partschefeld, Stephan and Osburg, Andrea and Gliubizzi, Rocco and Gaeta, Carmine}, title = {Modified Carboxymethylcellulose-Based Scaffolds as New Potential Ecofriendly Superplasticizers with a Retardant Effect for Mortar: From the Synthesis to the Application}, series = {Materials}, volume = {2021}, journal = {Materials}, number = {volume 14, issue 13, article 3569}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/ma14133569}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210804-44689}, pages = {1 -- 17}, abstract = {This article is focused on the research and development of new cellulose ether derivatives as innovative superplasticizers for mortar systems. Several synthetic strategies have been pursued to obtain new compounds to study their properties on cementitious systems as new bio-based additives. The new water-soluble admixtures were synthesized using a complex carboxymethylcellulose-based backbone that was first hydrolyzed and then sulfo-ethylated in the presence of sodium vinyl sulphonate. Starting with a complex biopolymer that is widely known as a thickening agent was very challenging. Only by varying the hydrolysis times and temperatures of the reactions was achieved the aimed goal. The obtained derivatives showed different molecular weight (Mw) and anionic charges on their backbones. An improvement in shear stress and dynamic viscosity values of CEM II 42.5R cement was observed with the samples obtained with a longer time of higher temperature hydrolysis and sulfo-ethylation. Investigations into the chemical nature of the pore solution, calorimetric studies and adsorption experiments clearly showed the ability of carboxymethyl cellulose superplasticizer (CMC SP) to interact with cement grains and influence hydration processes within a 48-h time window, causing a delay in hydration reactions in the samples. The fluidity of the cementitious matrices was ascertained through slump test and preliminary studies of mechanical and flexural strength of the hardened mortar formulated with the new ecological additives yielded values in terms of mechanical properties. Finally, the computed tomography (CT) images completed the investigation of the pore network structure of hardened specimens, highlighting their promising structure porosity.}, subject = {M{\"o}rtel}, 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} } @article{PartschefeldWiegandBellmannetal., author = {Partschefeld, Stephan and Wiegand, Torben and Bellmann, Frank and Osburg, Andrea}, title = {Formation of Geopolymers Using Sodium Silicate Solution and Aluminum Orthophosphate}, series = {Materials}, volume = {2020}, journal = {Materials}, number = {Volume 13, issue 18, article 4202}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/ma13184202}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:wim2-20210122-43378}, pages = {1 -- 16}, abstract = {This paper reports the formation and structure of fast setting geopolymers activated by using three sodium silicate solutions with different modules (1.6, 2.0 and 2.4) and a berlinite-type aluminum orthophosphate. By varying the concentration of the aluminum orthophosphate, different Si/Al-ratios were established (6, 3 and 2). Reaction kinetics of binders were determined by isothermal calorimetric measurements at 20 °C. X-ray diffraction analysis as well as nuclear magnetic resonance (NMR) measurements were performed on binders to determine differences in structure by varying the alkalinity of the sodium silicate solutions and the Si/Al-ratio. The calorimetric results indicated that the higher the alkalinity of the sodium silicate solution, the higher the solubility and degree of conversion of the aluminum orthophosphate. The results of X-ray diffraction and Rietveldt analysis, as well as the NMR measurements, confirmed the assumption of the calorimetric experiments that first the aluminum orthophosphate was dissolved and then a polycondensation to an amorphous aluminosilicate network occurred. The different amounts of amorphous phases formed as a function of the alkalinity of the sodium silicate solution, indicate that tetrahydroxoaluminate species were formed during the dissolution of the aluminum orthophosphate, which reduce the pH value. This led to no further dissolution of the aluminum orthophosphate, which remained unreacted.}, subject = {Geopolymere}, language = {en} }