Under water Repair of large cavities in Concrete & Masonry Dam by Hybrid Polyurethane Injection Resin

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    Milon Mukhopadhyay Managing Director, Normet India Pvt. Ltd.Concrete/ masonry water retaining structures like dam, barrages, aqueduct are often get damaged by abrasion from flowing water along with materials like silt, boulders etc. in the river during monsoon which often  creates major cavities in the body of the structure. Such damages needs to be repaired in underwater during  lean season of winter when there is no turbidity in  water .

    Underwater repair remains always a challenge to engineers as it is highly technical and very costly. It needs  sophisticated equipment , divers , costly materials  & experienced team.

    Before going for such repair , proper assessment of distress is necessary to plan for a systematic and successful repair.

    Why to do repair

    Such UW repair become essential in water retaining structure to avoid  problems like water leakages , further deterioration, to bring the structural safety and for increasing its service life. Some times it is necessary to upgrade certain facilities to  enable some change in use of the structure.

    Basic objective  of such repair is to :

    –    Restore Durability
    –    Structural strength
    –    Its Function & to bring appearance as per original

    How to Approach for such UW repair

    Preliminary Investigation:-

    Non Foaming PU–    Studying Drawings
    –    Interacting with concerned supervisor
    –    Identifying Vulnerable location for further  study
    –    Planning the whole survey and diagnosis
    –    Visual inspection  by an expert who has past experience on such repair
    –    Recording photographs of distress and analysis of the problem , extent of damage
    –    Testing at site and in laboratory
    –    Non Destructive Testing(NDT)- as proposed by expert
    –    Destructive Testing (DT)-t as necessary to assess the cause of distress.

    Selection of materials and repair methodology

    Selection of any such repair materials is dependent on problem specific and thus needs an expert advice who has experience in this field. In general, criteria for selection of materials & techniques can be  described as follows:-

    Good binding and adhesion with aggregate–    Causes of distress and its nature
    –    Recommendation from expert
    –    Availability of materials & equipment/ manpower
    –    Material properties and its testing  in laboratory as per relevant code
    –    Importance of the structure
    –    Time  available for repair/strengthening
    –    Life expectancy
    –    Feasibility

    Material Properties

    Repair material should possess  following properties and its data needs to be collected from its manufacturer along with test documents certifying the properties so that it can be verified with the supplied materials before its use.

    Good adhesion and bond strength under tension and pullout.–    Viscosity  should be within 1500Cps at @30oC  and  no mixing with water during its placing under water
    –    Ability  for penetration into  voids, cracks  under water
    –    Gel time & expansion for PU resin at room temperature
    –    Shrinkage value of the hardened materials
    –    Matching co-efficient  of thermal expansion
    –    Good adhesion to substrate
    –    Desired compressive & Flexural strength of the grouted mass
    –    Resistant to aggressive chemical
    –    Low permeability & high durability
    –    Ease of application

    For underwater repair of large cavities , generally Moisture insensitive epoxy or polyurethane resin are preferred as such materials have following beneficial properties over cement based materials.

    –    Moisture insensitive epoxy or silicate modified non-foaming PU resin does not mix with water and thus there is least chance of water contamination
    –    Its adhesion or bond with substrate under water is very good and achieve high mechanical strength of the mass
    –    Can be placed easily by using appropriate grout pump from top
    –    Good material for prepacked aggregate grouting which reduces the cost and heat generation of the mass.
    –    Achieve good impermeability and abrasion resistant surface after repair

    Main sequence for such UW repair can be considered as below

    –    Removal of Defective & loosely adhered materials from substrate which will receive the repair materials  .
    –    Preparing the substrate by cleaning with high pressure air-water jet or other appropriate tools.
    –    Fixing of any form work, fixtures, grout pipes etc as necessary  to place repair materials in cavities.
    –    Restoration to original section  by  placing/application of  the repair materials as per method statement.

    TamPur 115,116  is a Non Foaming PU Resin which is used  for cavity filling in concrete in both under water and above water. It’s a silicate modified PU resin and two component system.

    It has following Unique properties

    –    No water reactivity –  and thus very good material for underwater repair works on concrete , cavity filling, grouting.
    –    Ensure excellent bond with concrete, rock and even with aggregate underwater.
    –    Environmentally safe and does not mix with water during its placing in under water condition.
    –    Non-toxic when cured and thus safe for human beings during handling and its service.
    –    Flame retardant and Fire proof solid materials without toxic chemicals.
    –    No detrimental heat generation to adjoining concrete during gel formation of this PU underwater.
    –    Long shelf life and can be used over one year if stored below 35oC and not under direct sun.
    –    50% mineral unlimited resources and Saving fossile resources.
    –    Test on under water placing. No mixing with water. Normal hardening of the mass after 24hrs at 30oC.

    Conclusion

    TamPur 115 & 116 can be used for any big cavity filling in Masonry or Concrete dam in underwater by using a twin piston PU pump from top. However, trained diver is needed for such repair under supervision from an experienced Engineer who has knowledge of such materials and its application. Its not so costly materials as it is  produced in India by Normet under technology from UK R&D. The properties of the materials are declared in its Technical data sheet . However, for long distance pumping , its gel time can be modified locally by Normet India as & when it will be necessary for specific application.

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