Thursday, September 8, 2011

INJECTION GROUTING

Definition
This is the basic process to use to stabilize any honeycombed structure, It is the injection into the structure of various materials which settle down in the cracks crevices and honeycombs and harden in the same making the structure denser and therefore watertight
.

Grouting Materials

Cement
This is the most common. However it has many disadvantages.

  • Does not get water after being grouted into the structure and therefore does not hydrate and gain strength,
  • Shrinks on losing water and therefore does not adhere well and naturally lets water through.

Epoxies
They are cost effective only when some structural restoration is to be done otherwise

  • They are too expensive
  • Are difficult to handle

Polymer Modified Cementatious Grouts
These are quick setting cements, which are admixed with fluidifiers, bonding agents, and expansive agents, which together help the grout to travel in the body of the concrete. They enable it to bond well with the cavities and by virtue of expansive action do not leave any weak points for water to penetrate.

Liquid Grouts
These are probably the best since they solidify on contact with water and therefore have very low rejection rate and also can penetrate even where the smallest particle of grout cannot resulting in very high degree of water tightness. This category is quite expensive to use and may be used as a supplement to the grouting with polymer modified grouts.

PROCESS

The process of injection grouting consists of the following steps.

  • Making of the holes in the structure
    Make the holes for the fixing of the nozzles always with a hammer and chisel and never with a drill machine since dust dislodged during drilling blocks the entrance to the porosity. Make the holes at every 0.75m2 for the concrete structure in a grid pattern and for the brick walls at every alternate joint.


(Click to Enlarge)

  • Fixing of the nozzles in the same.
    Always fix these after keeping a piece of stone aggregate below the nozzle in the hole made as above. This ensures that there is a cavity below the nozzle, in which the grout can go and accumulate and exert pressure on the side. Fix with a 1:3 mortar and cure for one day before grouting .If not properly fixed the nozzle will come out when pressure is exerted on them.
  • Injection grouting
    Always grout in batches of twenty five to thirty nozzles. First inject water in all nozzles. This will clean the pathway for the grout as well as ensure the wetting of the cavities

    Prepare the slurry in the first batch slurry with the material in 18-20 liters of water per bag of grout and then inject at a pressure of 140 psi for concrete and 40 psi for brick.. Just as this grouting is over for one batch of nozzles prepare second slurry with 14-16 liters of water per bag of grout and then reinject. Just as this stage is over further prepare slurry at 12-14 liters of water per bag of grout and reinject. Use a 140-psi machine for concrete and a 40 psi one for brick.
  • Removal of the nozzles
    Just after the grouting is over dislodge nozzles from their place by lightly stroking with a hammer. In case they are not easily dislodged leave in place and later cut with a welding machine.
  • filling of the holes
    Fill the holes formed or the tips jutting out with a polymer mortar over polymer slurry cure adequately FOR THREE DAYS. Often if this curing is not done cracks develop around the repair of the hole leading to weak points getting formed.

POLYMER REPAIRS

Essentially a polymer modified mortar is a normal mortar in which whole or part of the water is replaced by a polymer latex which gives it various additional properties like adhesion, cohesion, strength and as a concomitant of the same water tightness.

The method for making a polymer mortar is to mix one part of coacrylic polymer latex with two parts of water and then use the liquid so formed as a gauging liquid for making a cement sand mortar. A polymer modified bonding slurry can also be similarly made with pure cement being added to this gauging liquid.

To repair a surface with polymer modified mortar

  • clean it with wire brush ,

  • further clean it with an air jet or water stream

  • apply the polymer mortar on top of the polymer slurry made as above wet on wet basis.

This is a technique to be used for filling of cold joints, repair to areas of weak concrete and also to fill the holes made after removing the nozzles after grouting.

The materials to be used for the modification will range between PVA, coacrylic polymer mortars and SBR. These are in order of cost and effectiveness and for most common uses coacrylic latex based materials are sufficient.


FERROCEMENTING

Ferrocementing is an age-old practice and till the advent of the current crop of plastic tanks this as the most preferred system for making water tanks. Ferrocement is basically a reinforced rich plaster cast at a low water cement ratio and cured extensively to get high strength and impermeability.

The system for installing the same is

  • Nail wire mesh (for this use 26SWG ½”mesh) onto the surfaces in two layers
  • Impregnate by hand matrix so formed with a 1:2 mortar at a low water cement ratio over polymer bond slurry.
  • Profusely water to get a very hard surface.
  • Finish plaster with a 1:4 mortar.
This technique would find the most use wherever there is weak concrete or wherever the brick walls have to be waterproofed against pressure. Since the use of this technique for waterproofing is recent there are no fixed guidelines for this.

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