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Title: Phosphated Superplasticizers as Effective Water Reducing Agent for α-Calcium Sulfate Hemihydrate Systems

Author(s): My Linh Vo, Johann Plank

Publication: Symposium Paper

Volume: 354


Appears on pages(s): 165-176

Keywords: calcium sulfate, hemihydrate, superplasticizer, phosphate, dispersion, workability, fluidity, comb polymer, polycarboxylate

DOI: 10.14359/51736070

Date: 7/1/2022

In this work, the suitability of phosphate group containing, comb-shaped superplasticizers was tested in α-calcium sulfate hemihydrate paste as well as in a fully formulated α-hemihydrate-based self-leveling floor screed. The phosphated superplasticizers, more specifically a 100% phosphated one and two mixed phosphated carboxylated ones, were compared with a MPEG-based polycarboxylate superplasticizer and a commercial melamine-formaldehyde polycondensate (PMS) sample. The polymers were characterized via size exclusion chromatography and their plasticizing effectiveness and water-reducing capability were investigated in both paste and screed. Adsorption measurements were carried out to explain the working mechanism and the compressive strength of the screed formulations was determined. It was found that the introduction of phosphate groups into PCE comb polymers greatly improves their dispersing effectiveness and allows extremely high-water reductions of up to 40%. However, the content of phosphate groups has to exceed a certain minimum value to show effect. Owed to this exceptional water-reducing capability, unprecedented gains in compressive strength were observed and after 28 days values of ~ 55 N/mm2 (570 tf (short)/ft2) as compared to 40 N/mm2 (420 tf (short)/ft2) for the reference floor screed were recorded. A mechanistic study revealed that the superior effectiveness of phosphated comb polymers is owed to their higher adsorbed amounts on α-hemihydrate as compared to a conventional MPEG-PCE.