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- Superplasticizers (2) (entfernen)
Besides their plasticizing effect, superplasticizers (SPs) are known to retard the hydration of inorganic systems such as cement. Despite their frequent use, the understanding of these highly complex systems is still limited and the relevant parameters, which control the interaction between SPs, and cement components and reaction products are in the focus of ongoing research activities.[1] Optical methods have been successfully used for the analysis and monitoring of the interactions between a broad variety of nanoscale and molecular systems like nanoparticles of various chemical composition and different types of organic ligands or biomolecules. The potential of these methods to study processes at the interface between (hydrated) particles and the fluid phase at a very early stage of concrete formation could reveal possible mechanisms of interaction.
This investigation focuses on the study of organic/inorganic mixtures consisting of cement (CEM) and cement phases (C3S and C3A) in the presence of polycarboxylate ether and organic dyes in aqueous solution (particularly alkali resistant dyes) at a water to powder ratio of 1. Diffuse reflectance as well as steady state and time resolved fluorescence spectroscopy of the above mentioned mixtures were evaluated. Based upon changes of the intensity of the reflectance and fluorescence signal and spectral changes of the dye, acting as optical reporter, a model for the interactions of dye, PCE and cement (including different cement phases) was derived which describes the very first stage of cement hydration.
Chemical admixtures like superplasticizers or stabilizing agents are of ever increasing importance for modern concrete technology. Although such admixtures have meanwhile become common practice in many applications of concrete technology, the understanding of these highly complex systems is still limited and the relevant parameters, which predominantly control the interaction between the superplasticizer and the cement components, have not been identified yet.
Optical methods have been successfully used for the analysis and monitoring of the interactions between a broad variety of nanoscale and molecular systems like nanoparticles of various chemical composition and different types of organic ligands or biomolecules. This encouraged us to assess the potential of these methods, and particularly reflectance and fluorescence measurements, for the study of the interactions that occur at the interface between particle or hydrate surfaces and the fluid phase at a very early stage of concrete formation. Special emphasis is dedicated to search for and identify differences between commonly used superplasticizers.
Here, we focus on hydration effects using commercial comb shape polycarboxylate ethers (PCEs) with different charge densities, which are known to allow a very low water/cement ratio (w/c of 0.20 or less) while maintaining good workability. Based upon changes of the intensity of the reflectance and fluorescence signal and spectral effects of a dye, acting as optical reporter, a model for the interactions of dye, PCE molecules and cement nanoparticles in the very first phase of cement hydration is derived