Investigation of early hydration of cement by hydrogen nuclear magnetic resonance (1H NMR): New insights into paramagnetic effect

The paramagnetic substances can affect the result accuracy of hydrogen nuclear magnetic resonance (1H NMR), which restricts the application of this technology in cement-based materials. In this study, the effect of paramagnetic substances (Fe2O3) with different content of 0-5 % on 1H NMR signals of cement paste within 72 h of hydration was quantitatively analyzed, and the influencing mechanisms were discussed. The degree of cement hydration was quantified by hydration heat using calorimetry simultaneously. The results showed that the influence of Fe2O3 is time-varying and reduced with hydration time. Based on this, a rational Taylor model fitting was applied to the reductions in 1H NMR signal intensities of various samples at different hydration times, and a correction coefficient omega for 1H NMR signal intensity was put forward to effectively eliminate the signal attenuation caused by paramagnetic iron. This result can provide some new insights into the application of 1H NMR in cement-based materials.