METHOD OF STATEMENT FOR LARGE VOLUME REPAIRS TO DAMAGED REINFORCED CONCRETE ELEMENTS

METHOD OF STATEMENT FOR LARGE VOLUME REPAIRS TO DAMAGED REINFORCED CONCRETE ELEMENTS

Summary:   This Method of Statement includes the following;

1. For large volume repairs to damaged reinforced concrete elements particularly where access is restricted and where vibration of the placed material is difficult or impossible.

1. Preparation  

1. Defective concrete surfaces must be cut-back to a sound base. Smooth surfaces should be roughened, corroded reinforcing bars should be exposed around its full circumference  and remove all loose scale and corrosion deposits. It is important to clean the steel to a bright condition.
2. The unrestrained surface area to be repaired must be kept to a minimum. The formwork should be rigid and tight to prevent loss of material and have an impermeable face to prevent drying out. It should include drainage outlets fro pre soaking and if beneath a soffit, provision for air-venting must also be made for suitable access points to pour or to pump the mixed micro-concrete into place.
3. Several hours prior to placing the prepared concrete substrates should be saturated with clean water. Immediately prior to placing any free water should be removed.
4. For repair sections deeper than 125 mm it may be necessary to fill out the “Renderoc HF” with properly graded 8 mm to 12 mm silt free aggregate to minimize temperature rise. Aggregate should be in a saturated surface dry condition and should be tested to ASTM C-289-81. The quantity of aggregate may vary depending in the nature and the configuration of the repair location. The mixture for 125 mm to 250 mm depth sections shall be 25 kg of Renderoc HF to 4.30 kg of clean water and 10 kg. of 8 mm to 12 mm approved aggregate. For sections deeper than 250 mm the mix design should be changed. However the quantity of aggregate should never exceed one part of aggregate to one part “Rendoroc HF” by weight (dry).
5. Actual water demand may vary depending on the condition of the aggregate. Trial mixes should be made in order to ensure the optimum addition to both water and aggregate.
6. Expose fully any corroded steel in the repair area and remove all loose scale and corrosion deposits. Steel should be cleaned to a bright condition paying particularly the back of the exposed steel painted by approved rust cut materials.

2. Material for Application.

 Renderoc HF  Transmittal # C4A &4B-C-

• Mixing

• A force-action mixer  will be used in mixing the material to have a even mixing in a suitable drum using spiral paddle in a slow speed of 400rpm rotary drill fitted with a mixing paddle.
  • Place 4.3 to 4.5 liters of quality water per 25 kg bag of “Renderoc HF” in the drum with the drill running at slow speed and mix for 3 to 5 minutes until even consistency is achieved.
  • Where the addition of a graded aggregate has been specified, this should be added after the water an “Renderoc HF” are properly mixed. Mixing should then  

Continue for further one minute to ensure correct dispersion.

3. Application

• The mixed material should be placed immediately if placing by pump, standard concrete pumping practice should be followed. The pump and pipeline must be grouted with a cement slurry mortar discharging the grout as waste pumping should be commenced immediately after grouting.
  • In cold temperature down to 2 deg. C, the use of warm water (up to 30 deg. C) is advisable to accelerate strength development.
  • At ambient temperature above 35 deg. C, the material should be stored in the shade and cool water is used for mixing.

4. Curing Immediately after finishing like common Cementous materials,  “Renderoc HF” must be cured by spraying water on the surface of application for 2 days.