Effect of Mineral Additions on Rheology and Fresh Properties of Cement Pastes and Mortars

Abstract

In this study the following mineral additions were used as 10% by weight cement replacement: silica fume SF, two types of metakaolin MK1 and MK2, and limestone powder LP. One type of cement CEM I 42.5R and one high range water reducing (HRWR) admixture were used in all mixes. Fresh properties of mortars with natural postglacial sand 0/4 mm were examined by mini-cone test and rotational viscometer Viskomat XL. In this instrument, when the cylindrical sample container rotates, the mortar flows through the blades of the impeller and exerts a torque which is measured by a transducer. As a result of the measurement, a set of data expressing the resistance of the mix subjected to the stresses induced by the rotation of the impeller was obtained. By linear approximation of the obtained results from the down-curve, the flow line of the mixture was obtained and compared with the modified Bingham Equation, which allowed to determine the rheological parameters of the tested mortars. All additions except for LP decreased rheological properties of the tested pastes and mortars. Not only particle size distributions (PSD), cumulative percentages and specific surfaces of the powders influence water and admixture demand of cement-based composites. Also shape and texture of the individual particles have an effect on the rheological properties.