Characterization of the Influence of an Accelerator upon the Porosity and Strength of Cement Paste by Nuclear Magnetic Resonance (NMR) Relaxometry

Designing of new cement-based materials, suitable for three-dimensional printing applications, requires accurate control of the porosity and strength development. This goal may be achieved by introducing the so-called accelerators in the cement mixture. One such accelerator, used in many commercial products, is calcium nitrate. In the present work, the effect of calcium nitrate on the kinetics of pore evolution and strength development was investigated using low-field nuclear magnetic resonance relaxometry and compressive tests. The presence of calcium nitrate in cement paste accelerates the hydration dynamics immediately after mixing but does not significantly affect the pore structure. Moreover, the presence of calcium nitrate increases the compressive strength at 7 days compared with the simple cement paste but the same compressive strength was reached following 28 days of hydration.