OPTIMIZATION OF SUPERPLASTICIZER CONTENT IN SELF-COMPACTING CONCRETE
According to Okamura´s method for self-compacting concrete mix design, the dosage of superplasticizer is first determined in mortar mixtures and it is after adjusted in concrete mix trials. Other SCC mix proportioning methods rely on the definition of the superplasticizer saturation dosage in pastes. These approaches to mix design have advantages over the ones based exclusively on concrete batching because it is less expensive and material demanding to perform tests in mortar and paste than in concrete. Nevertheless, difficulties are being reported which concern to the lack of correlation between the amounts of superplasticizer determined in paste and mortar mixtures and the dosages necessary to produce SCC. This article presents the results of an experimental research carried out to investigate the use of tests performed in paste and mortar to define the dosage of superplasticizer for self-compacting concrete. The materials employed were cement of high initial resistance, limestone filler, fine and coarser sand as fine aggregate, a maximum 10mm diameter coarse aggregate and a policarboxylate based superplasticizer. The saturation point of the superplasticizer was determined in pastes by the use of Marsh cone and a coaxial cylinder viscometer. The amounts of superplasticizer for the mortar mixtures were determined with the use of Slump-flow and V-Funnel tests. The final superplasticizer dosage was determined in concrete, so it the requirements for Slump-flow, V-Funnel and the L-Box tests were satisfied. The results show a comparison of the admixture contents determined for the different phases. Better relationships were found between the amounts of superplasticizer determined for mortar and concrete. Poor relationship was observed between the dosages on paste and concrete. This allowed for the conclusion that in SCC mixture proportioning methods, the determination of the superplasticizer content in the paste phase is dispensable, and the amount of admixture is more reliably determined by testing mortar mixtures. Nevertheless, final adjustment of the superplasticizer dosage was always needed in order to produce SCC.
KeywordsFine Aggregate Plastic Viscosity Slump Flow Limestone Filler Saturation Dosage
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