Influence of fine aggregate characteristics on the rheological properties of mortars

This paper presents results from a laboratory study on the influence of crushed fine aggregate on the rheological properties, i.e., yield stress and plastic viscosity, of the mortar phase of concrete. The effect of grading, particle shape, etc. of the fine aggregates has been evaluated with the use of a viscometer suited for coarse particle suspensions. The evaluation has been done at different dosages of superplasticizer and paste volumes by the use of an inert artificial “cement paste”.The results show that the properties and amount of fine aggregate have a strong influence on the water demand and workability of the mortar, i.e., the rheology. The large amounts of fines often found in crushed fine aggregate primarily increases the yield stress of the mortar. The amount of fines also contributes to the plastic viscosity by increased interparticle friction. However, the results clearly show that the particle shape of the fine aggregate strongly contributes to the plastic viscosity.The influence of the properties of the fine aggregate is largely dependent on the paste volume of the mortar. Thus, by increasing the paste volume, negative effects of poorly graded and shaped aggregates can be eliminated or significantly reduced.