Penetrablity for cementitious injection groups

Abstract: Grouting as a method of strengthening and sealing rock, soiland concrete is widely spread. The possibilities of sealingstructures are of great importance in both economical andenvironmental point of view. The costs of grouting have incertain projects been as high as the cost for the blasting andexcavation of the tunnel. To improve the technique of groutingwith cement based material, it is necessary to focus on theproperties of the used grout mixture.The ability of a grout to penetrate cavities, channels andporous material, the penetrability, depends on two things, therheology and the filtration stability. Extensive laboratorytests on stable, low w/c-ratio, injection grouts show that themost significant limitation to their penetrability is thetendency of cement grains to agglomerate into an impermeablefilter cake. The ability of a grout to pass constrictions ofthe flow path without clogging can be designated filtrationstability. An inert material is used for the investigations inthis work.The inert material, which is crushed dolomite stone,does not react with the added water in the suspension.Performed tests show that the grain size distribution is ofgreat importance for the filtration phenomenon. According toperformed experiments with inert material, it seems to beadvantageous for the penetrability to have a grain sizedistribution not containing too much fine grains and not toomuch coarser grains. It reasonable to believe that the grainsize distribution should be relatively steep (narrow grain sizerange) between minimum and maximum grain size.Correlations between different parameters have been studiedin order to identify possible connections. No clear correlationbetween the filtration stability (FS) and measured values asfor example grain size distribution or volumetric concentrationof grains has so far been identified. The best correlation forfiltration stability is found between the grain sizedistribution parameter d´ and filtration stability (FS).d´ [µm]is a grain size which corresponds to a amountof grains, normally about 50- 60 % of the total grain sizecontent for grouting cements. d´ is an output parameterfrom the Rosin Rammler Sperling Bennet (RRSB) distribution.Plotting the RRSB grain distribution is a way of describing thedistribution of different grain sizes in a mixture.