Transcript Slide 1
UNIT IV TECHNIQUES FOR REPAIR AND DEMOLITION GUNITE or SHOTCRETE: •Gunite can be defined as mortar conveyed through a hose and pneumatically projected at a high velocity on to a surface. •Recently the method has been further developed by the introduction of small sized coarse aggregate into the mix deposited to obtain considerably greater thickness in one operation and also to make the process economical by reducing the cement content. •Normally fresh material with zero slumps can support itself without sagging or peeling off. •The newly developed "Redi-set cement" can also be used for shotcreting process. EPOXY COATED REINFORCEMENT: •The object of coating to steel bar is to provide a durable barrier to aggressive materials, such as chlorides. •The coatings should be robust to withstand fabrication of reinforcement cage, and pouring of concrete and compaction by vibrating needle. •Simple cement slurry coating is a cheap method for temporary protection against rusting reinforcement in storage. •Central Electro Chemical Research Institute, (CECRI) Karaikudi have suggested a method for preventing of corrosion in steel reinforcement in concrete. •The steps involved in this process are 1. Derusting: •The reinforcements are cleaned with a derusting solution. •This is followed without delay by cleaning the rods with wet waste cloth and cleaning powder. •The rods are then rinsed in running water and air dried. 2.Phosphating: •Phosphate jelly is applied to the bars with fine brush. •The jelly is left for 45-60 minutes and then removed by wet cloth. •An inhibitor solution is then brushed over the phosphate surface. 3.Cement coating: •Slurry is made by mixing the inhibitor solution with Portland cement and applied on the bar. •A sealing solution is brushed after the rods are air cured. •The sealing solution has an insite curing effect. •The second coat of slurry is then applied and the bars are air dried. 4.Sealing: •Two coats of sealing solution are applied to the bars in order to seal the micro-pores of the cement coat and to make it impermeable to corrosive salts. •The above is a patent method evolved by CECRI and license is given to certain agencies. CATHODIC PROTECTION: Principles of Cathodic Protection: • Metal that has been extracted from its primary ore (metal oxides or other free radicals) has a natural tendency to revert to that state under the action of oxygen and water. • This action is called corrosion and the most common example is the rusting of steel. Corrosion is an electrochemical process that involves the passage of electrical currents on micro or macro scale. The change from the metallic to the combined form occurs by an“anodic” reaction. Advantages and Uses of Cathodic Protection •The main advantage of cathodic protection over other forms of anti-corrosion treatment is that it is applied simply by maintaining a dc circuit and its effectiveness may be monitored continuously. •Cathodic protection is commonly applied to a coated structure to provide corrosion control to areas where the coating may be damaged. •It may be applied to existing structures to prolong their life. •Cathodic protection can, in principle, be applied to any metallic structure in contact with a bulk electrolyte (including concrete). In practice, its main use is to protect steel structures buried in soil or immersed in water. •It cannot be used to prevent atmospheric corrosion on metals. •However, it can be used to protect atmospherically exposed and buried reinforced concrete from corrosion, as the concrete itself contains sufficient moisture to act as the electrolyte. Structures that are commonly protected by cathodic protection are the exterior surfaces of: •Pipelines •Ships' hulls • Storage tank bases • Jetties and harbor structures • Steel sheet, tubular and foundation pilings • Offshore platforms, floating and sub sea structures DEMOLITION TECHNIQUES DEMOLITION MANAGEMENT: A construction removal and demolition company of tem of engineers, project managers and demolition technicians providing effective and efficient work. SELECTIVE DEMOLITION: •Hydro demolition • Marine demolition • Underwater demolition • Bridge demolition • Building demolition • Nuclear demolition • Runway demolition METHODS OF DEMOLITION: 1.Pneumatic and hydraulic breakers 2.Dismantling 3.Pressure bursting 4.Explosives 5.Ball and crane for demolishing masonry and concrete structures.