Alkali Activated Materials (AAM) have a smaller climate footprint and are also generally more durable than cementitious systems. The increase in durability is due to the formation of strength-giving phases, which are chemically different from the calcium silicate hydrate (C-S-H) phases formed during the hydration of ordinary Portland cement (OPC). AAM basically consist of an aluminosilicate raw material such as granulated blastfurnace slag (HSM), metakaolin (MK) or fly ash (FA) and an alkaline activator. Activators can be aqueous solutions of alkali hydroxides, sulfates, carbonates or silicates (water glasses), which in turn have a high influence on the fresh concrete properties (rheology, setting times) and the reaction products (chemical composition, phase development, mechanical properties) of the possible formulations.

Important, highly effective admixtures for cementitious systems are polycarboxylate ether (PCE) superplasticizers, which is a polymer consisting of a polycarboxylate backbone with branching polyether (PEG) side chains. In aqueous solution, the carboxylate groups (-COOH) are negatively charged, allowing the molecule to attach to positively charged sites on binder particles. The attachment causes steric repulsion between the PEG side chains and consequently repulsion between the particles, resulting in liquefaction of a binder glue. However, the effectiveness of such superplasticizers in AAM is severely limited.

With the overall objective of being able to use effective superplasticizers in AAB, different superplasticizer types such as isopentenoxypolyethylene glycol (IPEG) or isobutenoxypolyethylene glycol (HPEG) of different molecular structures are being investigated for their adsorption properties in different excitation solutions on different binders. The knowledge gained will be used to estimate quantities for important parameters such as side chain density or molecular weight, which can optimize the use of PCE in AAM.

A new method is used to measure adsorption: in a first step, the PCE flow agents are covalently coupled to a fluorescent marker by a wet chemical procedure. The coupling allows a spatial distribution of the molecules on a binder substrate to be detected using fluorescence microscopy or confocal laser scanning microscopy (CLSM). In the second step, binder particles are fixed in a translucent flow cell so that excitation solution and PCE can be added and removed during a measurement procedure. This makes in situ observation of the adsorption behavior of the flow agent in a defined area possible. Measurement series can be compared with each other via the intensity of the signal; in addition, imaging can be used to qualitatively infer topographical or chemical influences of the particle surface on the superplasticizer adsorption.

The method is supported and verified by non-imaging measurements, comparisons are made to results from total organic carbon (TOC), zeta potential and dynamic light scattering (DLS) measurements.