New scientific evidence of the effect of high temperatures and long curing times on MK-blended cement paste mineralogy

Abstract

This article reports new scientific evidence on the hydrated phases present in blended cement pastes formulated with 10%, 20% or 25% metakaolin (MK) and stored at 60 °C for 15 years. XRD-Rietveld, SEM/EDX, NMR, FT-IR and TG/DTG findings attested to substantial difference in the mineralogy and morphology of the phases present (C2ASH8, C4AH13 and hydrogarnet) between long-term and short-term curing. The predominant crystalline phases in OPC and 10% MK-blended pastes, portlandite, calcite and γ-C2S, were characterised by small, laminar crystals. Stable katoite and hydrogrossular were observed in the pastes with MK content ≥20%, although the cubic phase of the latter (tricalcium aluminate hydrate, Ca3Al2(OH)12) was found only in pastes with an MK content of 25%.