Effects of flocculation of cement slurry on groutability of porous media

Considering the groutability of porous media using cement slurry, the following phenomenon remains explained: although cement powder particles are smaller than the pore diameter of the porous medium to be grouted, cement slurry cannot be effectively grouted into the porous medium under some conditions. To better understand this unexplained phenomenon and the correlation between particle sizes and pore diameter, a focused beam reflectance measurement (FBRM) system was used to analyse the in-situ particle state characteristics of cement slurry. Further, the grouting depth of the slurry in sand columns was tested. Results showed that cement powder particles have a significant flocculation effect on the slurry and the chord size of the flocculent particles is 2-4 times greater than the powder particle size. The relationship between changes in chord size, water-to-cement ratio, and flocculation time were established. The primary factors affecting groutability were the presence of ultra-large flocculent particles, friction between large particles and pores, and particle arrangement within the pores. Finally, flocculent chord size can be employed as an index for evaluating groutability and develop a new criterion, as it particularly considers the blocking effect of large flocculent particles on porous media. This new and improved criterion can be used to predict groutability of cement grouts in sand as it more essentially reflects the groutability of porous media. (C) 2019 Elsevier Ltd. All rights reserved.