Colloidal Grouts for Anchoring and Deep Soil Mixing 2

[SmokeyBear]

We are engaged in heated discussions about the need, or otherwise, of using true colloidal grouts (cement and water) for grouting soil or rock anchors and for deep mixing in soils.
One view is that it is not necessary, the opposing view is that it is essential.We are using an Obermann twin bowl mixer, but we do not seem able to produce colloidal grout.
Is colloidal grout essential and why?

 

[born2drill]

First off, no ordinary grout is truly colloidal - even in the best mixed batches the cement particles do settle. "Colloidal" mixers simply do a better job of dispersing clumps, separating air, and wetting individual grains.

Obermann mixers are not "colloidal" but can produce perfectly good quality grout. (Which model are you using? VS-63?) I personally do not like them for the simple fact that they have too many bells & whistles and are generally electrical nightmares, but when operational they are fine for mixing anchor grouts.

You stated "we do not seem able to produce colloidal grout." You are not using a "colloidal" mixer, so I'm curious as to what prompted you to say that. It seems as if you are trying to measure some property of the grout and determine if it is colloidal or not.

Finally, you asked "is colloidal grout essential?" No, it is not. I have installed thousands of anchors with paddle mixed grout with no problems. You may want to use a "colloidal" mixer for high volume applications (you mentioned soil mixing) because it is a faster process, or where higher strength grout is needed, but for rock & soil anchors I don't see any problems with paddle mixed grout.

 

[BigHarvey]

The properties of a grout mix depend also upon composition and characteristics of the components. For a cement water grout a high speed classical mixer will do the job as already stated. If you have problem with your mix design, you must check the quantity of cement ( you should have about 1200 kg of cement per m3 for anchors )because low cement content lead to unstable mix. You might have to use additives such as Intraplast or dispersive agents.

 

[PEinc]

I'm with born2drill on this one.

http://www.PeirceEngineering.com

 

[SmokeyBear]

Thanks for responses.
born2drill and PEinc, Using an Obermann 600 and agree completely re bells and whistles and that it's not a colloidal mixer. I should have added that we are using a high speed shear mixer in the agitator tank after batching in the Obermann.
For anchors I'm not concerned. I've been using paddle mixers for years without problems.
My query really related to grout for deep soil mixing, where we need large volumes (12m3/hour). Specifically, we use a cutter soil mixer forming a 0.5m by 2.4m panel to depths up to 23m.(Big Harvey)Grout mix is typically w/c 0.85 with 300+/-kg of OPC per cubic metre of untreated soil. The relatively high w/c is required to "fluidise" the soil. The grout is injected at the cutter head as it progresses down the panel. It is thought/considered that a "more colloidal" grout would be more effective and allow a reduction in the w/c, while still fluidising. It can be a real problem during mixing when stiff clays are encountered. Even with secondary, high speed shear mixing we can not get close to what I consider a "colloidal" mix.

 

[BigHarvey]

For CSM work, I am pretty sure that the influence of the type of grout mixer used will be nominal. You might be better off using a different type of cement than OPC ( maybe cements with high contents of PFA ) which will be less water demanding.