4. Stability

This Chapter deals with the third basic component of grout’s injectability, i.e., the stability of the suspension against bleeding and segregation. The grout should keep its homogeneity up to its setting, as much as possible. When the bleeding remains lower than a certain limit, the grout can be used; otherwise, the grout may be unable to flow in and adhere to the internal surfaces of the discontinuities. Similarly, because of inadequate internal cohesion, larger solid particles of the gout may quickly settle, resulting in non-homogeneous layered structure of the mix. Excessive bleeding and segregation may produce blockage of the flow and sudden dangerous increase of pressure. The most prevailing parameters shaping stability characteristics, are water content and percentage of ultrafine materials. After a brief literature survey, an oversimplified predictive model of bleeding is firstly proposed and then its validity is confirmed using the results of an experimental study. The role of superplasticizers is also discussed. In both cases, with and without superplasticizer, semi-empirical formulae are proposed, that are useful for the design of a grout composition. Finally, the chapter presents experimental results demonstrating the role of water and superplasticizer content in the appearance of segregation; some empirical formulae are also proposed for the estimation of the critical water content initiating segregation.