08-16-2017, 09:18 PM
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introduction
Concrete expected to give trouble free service throughout design life.
Concrete decay is cancerous caused by carcinogenic agents.
Physical damage caused due to fire,explosion and restraints both external and internal.
Lack of maintenance has resulted in near loss of this irrigation structure.
PREVENTION OF CORROSION IN REINFORCEMENT
Seal the surface of the concrete
Modify the concrete to reduce its permeability
Protect the reinforcing bars to reduce the effect of chlorides
Corrosion controlling steps
Good concrete practice
Latex modified concrete
Silica fume concrete
Epoxy coated reinforcement
Providing membranes and sealers
Cathodic protection
Electro osmosis
Inorganic corrosion inhibitors
Organic corrosion inhibitors
Good Concrete Practice
Specify and introduce Chloride limit
Maintain a low water-cement ratio in concrete
Provide adequate cover to the reinforcing steel
Provide adequate curing
Use of water-reducing admixtures
Consolidating the concrete thoroughly
Use post tensioning
Include provision for immediate repair of cracks
Use of Latex Modified Concrete
Latex modified concrete is prepared by adding liquid styrene butadiene latex to conventional concrete
Latex modified concrete should be placed in the evening or at night to reduce cracking
Use of Silica Fume Concrete
Silica fume reacts with calcium hydroxide to form additional cementitious material
Silica fume is extremely puzzolonic material that reacts with calcium hydroxide
Performance of concrete is good to excellent
Epoxy Coated Reinforcing Bars
Pre-cleaned reinforcing steel bars are protected with a coating of powdered epoxy
Coating blocks chloride ions
Performance is poor to excellent
Post curing heating enclosure installed over an epoxy mortar repair area
A bucket mixer can be used to mix epoxy mortar for small repair areas.
Use of Membranes and Sealers
Membranes and sealers help prevent chloride entry
Urethanes, neoprene, or epoxies are usually used to built up in multiple layers of membranes
The performances of these materials vary depending upon the base of the sealer
Sealers- linseed oil and sophisticated silanes and siloxanes
Cathodic Protection
controls corrosion of steel by applying direct current
is a complicated process that requires extensive pre installation and monitoring
Corrosion of steel in concrete is a electrochemical process
Steel (reinforcement) inside the concrete act as cathode and provide protection
Concrete act as anode
Not recommended for carbonated concrete
Electro Osmosis
Electro Osmosis makes it possible to restore the initial alkalinity of the concrete
externally applied alkaline gel covering the external conductor is drawn
alkalinity increase of a carbonated concrete restores the passivation
The carbonate problem is solved
Organic Corrosion Inhibitors
combine other organic chemicals for successfully inhibiting corrosion
inhibitor forms a protective barrier on the reinforcing steel
barrier prevents reaction between the iron and chloride
REPAIR AND MAINTENANCE OF CONCRETE
. Experience has shown that there are certain portions of exposed concrete structures more vulnerable than others to deterioration from weathering in freezing climates
Concrete sealing compounds and coatings that provide good protection from weathering
Reclamation s concrete repair system
Determine the cause(s) of damage
Evaluate the extent of damage
Evaluate the need to repair
Select the repair method
Prepare the old concrete for repair
Apply the repair method
Cure the repair properly
Methods of concrete repair
Surface Grinding
Using Portland Cement Mortar
Dry Pack and Epoxy-Bonded Dry Pack
Preplaced Aggregate Concrete
Replacement Concrete
Epoxy-Bonded Epoxy Mortar
Polymer Concrete
Silica Fume Concrete
Surface grinding
It can be used to repair some bulges, offsets and other irregularities.
Grinding of sufaces subjected to cavitation erosion should be limited in depth so that no aggregate particles more than 1/16th inch in cross section are exposed to finished surface.
Grinding of surfaces exposed to public view should be limited in depth so that no aggregate particles more than 1/4 inch in cross section are exposed at the finished surface
Dry Pack and Epoxy-Bonded Dry Pack
Dry pack is a combination of Portland cement and sand passing a No. 16 sieve
Dry pack should be used for filling holes having a depth equal to, or greater than, the least surface dimension of the repair area; for cone bolt, she bolt etc.
Preplaced Aggregate Concrete
Preplaced aggregate concrete is made by injecting portland cement grout, with or without sand, into the voids of a formed, compacted mass of clean, graded, coarse aggregate
The preplaced aggregated is washed and screened to remove fines before placing into the forms
Replacement Concrete
Concrete repairs made by bonding new concrete to repair areas without use of an epoxy bonding agent or mortar grout applied on the prepared surface should be made when the area exceeds 1 square foot and has a depth greater than 6 inches.
Replacement concrete repairs are made by bonding new concrete to the repair areas without the use of a bonding agent or Portland cement grout
Portland Cement Mortar
Portland cement mortar may be used for repairing defects on surfaces not prominently exposed
Repairs may be made either by use of shotcrete or by hand application methods
Epoxy-Bonded Epoxy Mortar
Epoxybonded epoxy mortar should be used where the depth of repair is less than 1-1/2 inches and the exposure conditions are such that relatively constant temperatures can be expected
Epoxy mortars have thermal coefficients of expansion that may be significantly different from conventional concrete
epoxy injection equipment
difference in potential can result in the formation of a galvanic corrosion cell with accelerated corrosion at the repair perimeters
The epoxy bond coat and epoxy mortar create zones of electrical potential that are different from the electrical potential in the surrounding concrete
Polymer Concrete
Polymer concrete (PC) is a concrete system composed of a polymeric resin binder and fine and coarse aggregate
Water is not used to mix polymer concrete
PC is commonly used to repair potholes in concrete highway bridge decks,
thereby eliminating the necessity of long and costly road closures or detours
the monomer molecules are chemically linked and cross linked to form a hard, glassy plastic known as a polymer.
Placing polymer concrete in a repair area
Silica Fume Concrete
Silica fume concrete is conventional portland cement concrete containing admixtures of silica fume
Silica fume is a finely divided powder byproduct resulting from the use of electric arc furnaces
a small silica fume concrete repair
CONCLUSION
Repair and prepared corrected area should be carried out systematically
application of protective coatings are required to be properly supervised and carried out.
Surface defects like bugs holes and honey comb require immediate repairs