Effective and efficient mixing of modern grouts for dam foundation grouting re-quires the use of high-speed, high-shear mixers, which, although they do not actually create a true colloidal suspension, commonly have been know n as"colloidal"mixers. Three basic types are available : the Colcrete and equivalent, which uses a tight tolerance between the pump rotor and casing to create a high shear ; the Hany which uses a high-curbulence chamber, presenting the advantage of less wear ; and the MAT, which uses rapidly rotating perforated mixing paddles to create shear forces. ChemGrout, which also manufactures grout agitators and pumps, is the only U. S. manufacturer of mixers o{(he Colcrete type.Some U. S. and foreign specialty contractors make shop-built versions of the original Colcrete mixer, and off-the-shelf variations of the basic mixer types are manufactured by several European firms, for example, Craelius.
Paddlle mixers, which consist of tanks with either vertically or horizontally mounted.slowly rotating (typically 40-60 rpm) paddles, have been in use for many year and are still use in a variety of applications. They commonly are set up in groups of two on skids or a trailer, allowing grout to be mixed in one unit while the other unit is being emptied by gravity now into an open-throat progressing cavity pump. Bussey suggested, even in 1973, that the only reason that they were still in use (for dam foundation grouting ) was that contractors had them on hand. They are less subject mechanical problems than high-speed, high-shear grout mixers and are relatively inexpensive to maintain. However, they are inferior to high-speed, high-shear mixers in almost all other respects. They are adequate for such applications as contact grouting of tunnel lining or cavern filling, where comminution and dispersion of the grout particles is not necessary. Nonetheless, their long batching times and the inhomogeneity of the grout produced by them can be disadvantageous even in those applications, and increasing frequency of line blockages can be anticipated.
On completion of mixing,grout is discharged into an agitator,which is usually placed close to the mixer.The function of the agitator is to keep the grout particles in suspension after thorough mixing has been achieved and to keep thick, thixotropic grouts in a fluid condition until injected. The agitator usually consists of a vertical cylindrical tank equipped with a rotating paddle mounted on a vertical shaft. Proper agitation cannot be accomplished with purely circumferential movement of the grout ; turbulent motion is required to prevent settlement of heavier particles to the lower part of the tank. In properly designed agitators, this turbulent motion is imparted by built-in baffles or deflectors. Some agitators, including those made by Atlas Copco and by Hany, introduce turbulence by mounting the paddle at a diagonal to the axis of the tank.
