Fractal characterization on pore structure and analysis of fluidity and bleeding of fresh cement paste based on 1H low-field NMR

In this study, a novel method for calculation of surface fractal dimensions (D-f) of pore structure based on H-1 low-field NMR was proposed. Influencing parameters including water cement ratio and specific areas of cements on the fractal dimensions were investigated. In addition, the relationship between pore structure and fluidity value as well as bleeding velocity was also discussed in this paper. Results confirm that the pore structure of fresh cement paste has a significant fractal feature, and fractal regions, region i (2.0 < D-f < 2.2) and ii (2.6 < D-f< 3.0), are found for the pore structure in the distribution of the transverse relaxation time (T-2). It is found that the D-f for region ii is sensitive to both water cement ratio and specific surface of cements. Moreover, the initial fluidity of fresh cement paste increase with the T-2 position, and with identical T-2 position, fresh cement paste with high D-f can generate a low fluidity. Results also suggest that high D-f of pore structure lead to a low velocity of bleeding, and D-f can be a main factor for migration of the bleeding water when the T-2 positions are close. (C) 2017 Elsevier Ltd. All rights reserved.