| Summary: | The article aims to present a research into the impact of dosage and effectiveness of commonly used plasticizing admixtures. More specifically, it focuses on rheological properties of the cement pastes (yield stresses and plastic viscosities) of different testing times (from 0 min to 90 min after mixing). The following materials were used in the study: Portland cement CEM I 42.5 R, plasticizer P (ligno-sulphonates based), superplasticizer SP1 (modified acrylic polymer based), superplasticizer SP2 (polycarboxylate esters based) and water. Experiments were carried out using rotational rheometer Rheotest RN4.1 with coaxial cylinders. It was observed that larger dosage of SP1 (0.6–1.2 %) results in slower increase in plasticizing effects until the 90 min margin. In conclusion, from the start of mixing until the 90 min margin, the best plasticizing effect and its retention are achieved by superplasticizer SP2. Recommended SP2 dosage varies within the range of 0.6 % to 0.8 %.
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