Microorganism-based bioplasticizer for cementitious materials

A plasticizer resulting from mixed culture of microorganism with beneficial effect that co-exist in a liquid environment has been evaluated as potential admixture for cement. The bioplasticizer MEF (Microorganism-based bioplasticizer) contains fermentation products from liquid cultures of lactic bacteria, phototrophic bacteria and yeast of more than 80 different species. The material was tested in pastes and mortar using a rheology protocol, and compared with series made with one commercial superplasticizer (SP). Cement pastes were prepared with different dosage of MEF (4%, 6% and 8%). The experimental program included the evaluation of the plasticity index from the minicone test; viscosity through the Marsh cone, and setting time with the Vicat needle. Further, mortars with the same dosage were prepared and their rheology, water absorption and mechanical properties were assessed. Results indicate that MEF has plasticizing properties; however the effect is lower than commercial SPs. The main reasons appear to be the high dilution rate. Concentration through roto-evaporation brings about an increase in plasticizing properties. Separation by polar fractions shows that apparently the plasticizing principle is related to the presence of lactic acid. MEF seems to influence hydration of the aluminates, and in high dosages it may have some retarding effect. It has proven to contribute to decrease viscosity of cement pastes and no major differences in performance were found with commercial SPs. Tests carried out in mortars confirm the results obtained in pastes. Mortars made with MEF show similar mechanical properties than those of the reference.