Study of flow behavior of superplasticized cement paste systems and its influence on properties of fresh concrete

The composition of the cement paste system of concrete, consisting of cement, water, mineral admixtures and superplasticizers, practically governs its flow behavior, influencing workability, slump loss and other phenomena. Obviously, it also provides the cohesion necessary for the mechanical integrity and durability of concrete. The optimization of the composition of high performance concretes should therefore include the design of the paste phase, which should incorporate the selection of superplasticizer type and dosage. The present work deals with studies of the flow behavior of superplasticized pastes using the Marsh cone test. Saturation superplasticizer dosages and loss of fluidity with time have been determined using this test. In order to validate the use of data obtained from pastes for proportioning mortar and concrete, fluidity tests have been performed on mortars and concrete, and the results compared with those of the corresponding paste phases. It is seen that the superplasticizer saturation dosage may increase slightly due to the incorporation of sands with significant coefficients of absorption and that the loss of fluidity is much higher in mortar than in paste. The behavior of the concrete, characterized by slump and DIN flow tests, is similar to that of the mortar. However, when the concrete is maintained in movement (or remixed) as in truck transportation, the slump loss is more dramatic. Nevertheless, the loss in DIN flow is not very high indicating that some of the loss in workability can be compensated by vibration. The K-slump test data and those of compactability based on DIN flow show peak values that coincide with the paste composition with the superplasticizer saturation dosage. In general, the results demonstrate that for practical purposes the optimization of high performance concrete in terms of its flow behavior can be based on the behavior of its cement paste phase, permitting the selection of superplasticizer type and dosage from simple fluidity tests on pastes.