Bio-Based Superplasticizers for Cement-Based Materials
The additives to regulate the fresh and solid properties of mortar and concrete are of enormous importance to the building materials industry. The superplasticizers with a proportion of 85% of all admixtures are the most frequently used type of additives. With a share of 60%, the polycarboxylate ethers dominate the market for building chemical additives. Starch, which can be modified by appropriate chemical modification in such a way that fluidizing properties are produced, represents an alternative basic material. For this purpose, it is necessary first to reduce the molecular weight of the natural polysaccharide and then to introduce anionic charges into the degraded starch molecules. The influence on the rheological properties of Portland cement pastes was determined by means of rotational viscosimeters and compared with commercially available superplasticizers. To determine the interaction mechanism with Portland cement, adsorption experiments and calorimetric studies were carried out. At the same concentration, the synthesized starch superplasticizers show comparable flow characteristics to the PCE superplasticizers. The interaction mechanism is based on adsorption at the first hydration products of the cement. A low degree of polymerization and a high amount of anionic charges showed the most intensive liquefaction effect.
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