INTERACTION BETWEEN CEMENT AND SUPERPLASTICIZER IN PRESENCE OF METAKAOLIN

摘要

Usage of metakaolin (MK) significantly improves properties of concrete, especially those related with durability. The addition of MK to concrete influences also rheological properties (and therefore workability) of fresh mix. It is due to high specific surface and chemical activity of MK itself and due to its influence on interaction of cement -superplasticizer (SP) system. The results of an investigation into the influence of MK on interaction of cement - SP system are presented and discussed in the paper. The interaction of cement - SP system in presence of MK was studied using Two Point Workability Test (TPWT) made on modified mortars according to EN 196-1:1996 which can be considered as a model of concrete. Additionally, influence of MK on setting times and compressive strength of concrete were determined. The results establish that the addition of MK significantly influences Theological properties of concrete mix. The character and range of this influence depends on the properties of the cement, properties of SP and MK content. Discussion of results covers the mechanism of MK influence on rheological properties of fresh concrete and comparison of effects of MK with effects of condensed silica fume and fly ash. On the ground of obtained results basic relationships of MK influence were elaborated. It is concluded that compatibility of cement - SP system must be tested taking into account the presence of mineral additives. TPWT made on modified standard mortars enables selecting optimal SP - mineral additive system and collecting data for adjusting concrete workability.