Adsorption mechanism of PCE superplasticizers in alkali activated materials containing silica fume

Fluorescence and scanning electron microscopy were used to investigate hydroxide-activated slag-silica fume-based AAM mixes containing PCE superplasticizers. By applying two distinct fluorescent markers, the competitive adsorption of two PCEs with differing charge densities was observed. The results indicate that each PCE exhibits a location-specific affinity for certain topographical features of the precursor surface, as adsorption on the amorphous material is heterogeneous and varies significantly between the superplasticizers. Through the location-dependent investigations, the PCE on particle coverage levels of the particles were approximated at specific times and correlated with rheological measurements. A high charge density causes a high initial dispersion of the paste with a rapidly decreasing effect, while a lower charge density has a weaker but more persistent effect effect. A comparison of the spatially resolved adsorption derived from the fluorescence signal with the obtained scanning electron microscopy investigations shows that the tested PCEs used attach primarily to the early formed reaction products.