Staining and adsorption of PCE superplasticizers in alkali-activated materials (AAM) investigated by fluorescence microscopy

The spatial-dependent adsorption of polycarboxylate ethers (PCE) in alkali-activated materials was analysed using fluorescence microscopy after coupling PCE with a fluorophore marker. The adsorption has been derived from the fluorescence with the consideration of the pH-dependence of the fluorophore marker using two different PCE superplasticizers and two different fluorescent markers. The synthetic route of a staining reaction was successfully applied to IPEG PCE and APEG PCE superplasticizers, verified and quantified by different spectroscopic methods. The derived adsorption values were compared with the flowability by mini-slump tests and total organic carbon measurements. It was shown that low activator concentrations can increase the adsorption of a superplasticizer on particles of different precursors. Additionally, it was shown that in alkali-silicate activated systems PCE adsorb on particles while the functionality is lost. • PCE molecule adsorption visualised with fluorescence microscopy. • Distinct PCEs on different precursors in an activator demonstrate an increase in adsorption at low excitation levels. • The observed loss of efficacy of PCE in a silicate activator does not appear to be related to its adsorption.