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
– 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:-
– 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
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.
– 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.
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.