Microstructural analysis of cement paste blended with blast furnace slag using 1H NMR relaxometry

Abstract

1H NMR is a powerful technique for characterizing the microstructure of cement pastes; however the analysis of the data poses significant challenges. This work presents a comparative analysis of the microstructure evolution in cement pastes using 1H NMR relaxometry, MIP and thermoporometry. We developed and implemented a cumulative T2 distribution to improve the reproducibility and robustness of the results obtained from the CPMG raw data. Although NMR and thermoporometry measured similar pore sizes, MIP measured considerable deviations at pores>10 nm for matured white cement pastes, but blends with slag were more comparable. Nevertheless, deviations were observed in the blends when the degree of slag hydration was low. These discrepancies are attributed to the C/(A + S) ratio of C–S–H which decreases with slag hydration. The findings suggest that the pore refinements typically measured with MIP for blended cement compared to reference Portland cement may be an artefact of sample preconditioning.