NMR Study on the Pore Structure Development of Cement Paste with Bleeding during Hydration

Abstract

Previous studies focused on the determination and simulation of the bleeding extent of fresh cement paste and provided objective conclusions. However, few studies exist on the influence of bleeding on the final structure of cement paste. This study focused on the microstructure development during the hydration of cement paste with various bleeding caused by the water-cement ratio, the slag replacement, and the superplasticizer. To obtain information on the porosity profile and pore size distribution, the sample was measured using a low-field nuclear magnetic resonance (NMR) with Hahn spin sequence and Carr-Purcell-Meiboom-Gill (CPMG) sequence from top to bottom. The results showed that increasing bleeding thickness leads to a heterogeneous structure from top to bottom in terms of porosity profile and pore size distribution. Moreover, hydration can reduce the difference in the pore structure, especially when the bleeding depth is small. It was also found that the influence of bleeding depth on the pore size distribution of gels pores during hydration is minor compared with that of the capillary pores. Furthermore, detailed discussions on the connections between the bleeding and the final structure are presented in this paper.