Penetrability due to filtration tendency of cement-based grouts

Abstract

ii iii SummaryGrouting as a method of strengthening and sealing rock, soil and concrete is widely used. The possibilities of sealing structures are of great importance from both an economical and environmental point of view. The cost of grouting has in certain projects been as high as the cost for the blasting and excavation of the tunnel. To improve the technique of grouting with cement based material, it is necessary to focus on the properties of the used grout mixture. The ability of a grout to penetrate cavities, channels and porous material, the penetrability, depends on two things, the theology and the filtration tendency. Extensive laboratory tests on stable, low w/cratio, injection grouts show that the most significant limitation to their penetrability is the tendency of cement grains to agglomerate into an impermeable filter cake. The properties of a grout that may prevent passing obstructions in the flow path without the cement grains clogging and preventing further penetration is in this work called filtration tendency. An inert material mixture and a cement-based mixture are used for the investigations in this work. The inert material, which is crushed dolomite stone, does not react with the added water in the mixture. The used cement grouts are based upon three types of commercial available Portland cements and four Portland cements with modified grain size distribution curves.Performed tests show that the grain size and grain size distribution is of great importance for the filtration tendency. According to performed experiments with inert and cement material, it seems to be advantageous for the penetrability to have a grain size distribution that contains neither too many fine or coarse grains. It is reasonable to believe that the grain size distribution should be relatively steep (narrow grain size range) between minimum and maximum grain size. The maximum grain size is of importance in terms of for example d 95 . Too large maximum grain size will prevent penetration of the mixture through obstructions in the flow path. According to performed tests, the value of d 95 , should be between 4-10 times smaller than the aperture to be penetrated by the cement based mixture. The small grain sizes are also of importance in order to achieve a low filtration tendency of the grout. This is because of the increased tendency for the small grains to flocculation into larger agglomerates, compared to larger grain sizes.The filtration experiments with cement based grouts show that influences of parameters like surface chemistry (use of superplastisisers) and cement chemistry (hydration of cement grains) will strongly affect the filtration tendency of the mixture.To visualize the phenomenon of filtration tendency it can be investigated on a larger scale than usually takes place. Filtration experiments in the scale of approximately 100:1 have been performed in order to see influences of grain concentration, grain shape and the penetrated slot aperture. It can be seen that used grain sizes (monodisperse and inert m...

Effectiveness of Microfine Portland Cement Grouting on the Strength and Permeability of Medium to Fine Sands

“…With the increase of fine sand content, the penetration performance of cement suspensions decreased but with the increase of W/C ratio, the penetration performance of cement suspensions increased. Similar findings were also reported by Zebovitz [2], Eklund and Stille [17] and Markou et al [18].…”

“…The ability of a grout to penetrate porous material is a function of the rheological properties of the grout suspension and the physical characteristics of the cement, as well as the physical characteristics of the soil [15][16][17].…”

Swedish grouting design: hydraulic testing and grout selection

“…The value of b filter should be related to the value of b critical obtained using a penetrability meter (or similar) since they both describe the initiation of the filtration process of a grout (e.g. Eklund and Stille, 2008). …”

“…Axelsson, 2009;Funehag, 2007;Funehag and Gustafson, 2008;Gustafson et al, 2013) and at the Royal Institute of Technology in Stockholm (e.g. Eklund and Stille, 2008;Eriksson, 2002;Håkansson, 1993;Hässler, 1991) show that the developed theories can be used to estimate the penetration length for both a gelling Newtonian fluid such as silica sol and a cement-based grout with Bingham fluid properties. This paper deals with grouting of sparsely or moderately fractured rock, and in this case a radial flow approach as presented here is reasonable.…”

Uncertainties in Grout Penetrability Measurements; Evaluation and Comparison of Filter pump, Penetrability Meter and Short Slot

“…Hjertström (2001) using the NES method, a smooth slot approximately similar to Short slot, and Eriksson and Stille (2003) using Penetrability meter illustrated that the penetrability is independent of water to cement (w/c) ratio. However, Hansson (1995) by comparing the results of Filter pump with the ones on the sand column and the smooth slot, Eklund and Stille (2008) using Penetrability meter, Axelsson et al (2009) using the sand column, and Draganovic and Stille (2011) using Short slot disclosed that increasing the (w/c) ratio improves the penetrability. According to Hansson (1995), adding super plasticizer improves the grout penetrability using the smooth slot and Filter pump.…”