Effect of fineness variation on the chemical reactivity of Metakaolin

Abstract

Metakaolin (MK) affects the cement matrix physically, due to its filler effect, and chemically through the generation of additional C-S-H compounds. These actions are closely linked to the fineness of the material. In the literature, the effect of MK fineness on the evolution of mechanical strength is widely studied. However, the effect of fineness variation on the pozzolanic reactivity of MK, measured by chemical tests, is not well discussed. The aim of this study is to contribute to the clarification of the relationship between the fineness of a MK and its pozzolanic reactivity evaluated by chemical tests of Frattini, modified Chapelle and saturated lime. To do this, two MKs (obtained by appropriate calcination of two kaolins from Algeria) were used. Both materials were ground to several Blaine finenesses, which vary between 4000 and 8000 cm²/g, before their pozzolanicity was assessed. The results obtained showed that the reactivity of MKs increased absolutely with the increase in their fineness, regardless of the chemical test used. The fineness of MK favours its chemical reaction with lime in the different chemical test systems despite their differences in temperature, time and MK-lime ratio. It was concluded that these tests are more sensitive to the variation in the fineness of the MK than the classic compressive strength test.