BTCVSS801D Maintenance and Repair of Concrete Structures

MODULE 1 

Q1. Explain the necessity of maintenance activities in structural operations.

              To keep the structure in good and healthy condition.     

              To prevent serious damages in buildings.

             To prevent decay of structure caused due to adverse effects of weathering agencies.

             To strengthen the structures or to maintain the standard of structure.

             To make some needful improvements in the building so that it can preform its function properly.

            To improve the facilities depending on the modernization of that area.

            To maintain the utility value.

            To increase the durability of structure.

            To enhance the serviceability of a structure.

            To avoid crisis maintenance by doing regular and planned maintenance program. 

             Q2 .Elaborate the repair aspects in concrete structures.

1. Patch Repair Materials
2. Contentious mortar / concrete.
3.   Polymer modified contentious mortar / concrete.

4.  Injection Grouts., Contentious grouts (with or without fibers) Bonding Aids. • Polymer emulsion type.

   Resurfacing Materials. • Protective coatings and membranes. Other Repair Materials. • Corrosion inhibitors.

3. what is the significance of corrosion?

Steel corrosion in structures causes considerable losses to society due to maintenance and repair needs. A significant percentage of concrete structures are structurally deficient due to corrosion and are subjected to repair and rehabilitation to regain the functional and structural performance Corrosion may be defined as a destructive phenomena, chemical or elec -trochemical, which can attack any metal or alloy through reaction by the surrounding environment and in extreme cases may cause structural failure. Corrosion can be also defined as the deterioration of material by reaction to its environment. 

4. Explain corrosion of steel ?

The corrosion of structural steel is an electrochemical process that requires the simultaneous presence of moisture and oxygen. Essentially, the iron in the steel is oxidized to produce rust, which occupies approximately six times the volume of the original material. The corrosion of steel is a process that requires the presence of water or moisture and oxygen. The iron (i.e. iron ore) in the steel is oxidized or chemically changed to produce rust. This rust has no structure and occupies approximately six times the volume of the original steel.

5. Explain embedded metal corrosion.

Corrosion of reinforcing steel and other embedded metals is the leading cause of deterioration inconcrete. When steel corrodes, the resulting rust occupies a greater volume than the steel. This expansion creates tensile stresses in the concrete, which can eventually cause cracking, delamination, and spalling.

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6. Explain cracking phenomena in concrete structures.

This phenomenon occurs because some of the water in the concrete evaporates. Cracks occur when the shrinkage forces exceed the strength of the concrete. This can be seen as a race against the clock between two phenomena: the evaporation of water and the increase in the strength of concrete.

7. Elaborate corrosion induced cracking, de lamination and spelling in buildings.  Reinforcement corrosion is the most common deterioration mechanism of structural concrete. As the rebar corrodes, the iron in the steel is oxidised to produce rust, that occupies a larger volume than the original material. This expansion causes tensile stresses in the concrete which eventually lead to cracking. Spalling is a term used to describe areas of concrete which have cracked and delaminated from the substrate. There are a number of reasons why spalling occurs including freeze thaw cycling, the expansive effects of Alkali Silica Reaction or exposure to fire.Delaminations are separations of thin layers of the slab surface from the base concrete. Delamination typically results in break off of surface layers, 1/8 to ¼ inch (3 to 6 mm) in thickness, from a finished slab. 

8. Explain carbonation induced corrosion.

Carbon dioxide in the atmosphere enters the concrete and in pore solution forms weak carbonic acids. These acids react with calcium hydroxide in the pore solution and are deposited as calcium carbonates which line the internal surfaces of the concrete pores. In addition to chloride induced corrosion, the other commonly occurring type of rebar corrosion in reinforced concrete structures is that induced by the ingress of atmospheric carbon dioxide into concrete, commonly referred to as ‘carbonation induced corrosion’. 

9. Elaborate corrosion mechanism.

The metal on the surface gets ionized due to removal of electrons at anode and hydroxide ion is formed due to the reaction of oxygen and water molecules. The metal and hydroxide ions combine to form metal hydroxide and ultimately metal oxide from the reaction.

10. What are the different types of cracks in buildings?

. 3)Epoxy-Coated Rebar –Epoxy-coated rebar is black rebar with an epoxy coat. It has the same textile strength, but is 70 to 1,700 times more resistant to corrosion. However, the epoxy coating is incredibly delicate. The greater the damage to the coating, the less resistant to corrosion. 3)Galvanized Rebar-Galvanized rebar is only forty times more resistant to corrosion than black rebar, but it is more difficult to damage the coating of galvanized rebar. In that respect, it has more value than epoxy-coated rebar. However, it is about 40% more expensive than epoxy-coated rebar. 4)Glass-Fiber-Reinforced-Polymer (GFRP)-GFRP is a composite much like carbon fiber. As a result, field bends are not permitted when using GFRP. However, it will not corrode, period. In that respect, GFRP is an unparalleled concrete reinforcement bar. While it costs ten times as much as epoxy coated rebar per pound, it is extremely light, so the cost is only about double when considering talking linear feet. 5)Stainless Steel Rebar-Stainless steel rebar is the most expensive reinforcing bar available, about eight times the price of epoxy-coated rebar. It is also the best rebar available for most projects. However, using stainless steel in all but the most unique of circumstances is often overkill. But, for those who have a reason to use it, stainless steel rebar 1,500 times more resistant to corrosion than black bar. It is more resistant to damage than any of the other corrosive-resistant or corrosive-proof types or rebar and it can be bent in the field.For all of your rebar questions, wants, and needs – contact our team at BN Products. We are leaders in rebar benders, cutters, and tiers.

12. Explain FRP rebars.

FRP reinforcing bars and strands are made from filaments or fibers held in a polymeric resin matrix binder. FRP reinforcing can be made from various types of fibers such as glass (GFRP), basalt (BFRP) or carbon (CFRP).FRP rebars are widely used in the construction of highways, bridges, buildings, marine structures and waterfronts, water treatment plants, MRI rooms, tunnels, smelters, and chemical plants. FRP is a Fiberglass-Reinforced Plastic material that has the strength of steel at the fraction of the weight. FRP won’t corrode, rot, warp, attract insects, or rust, making it an ideal and long-lasting replacement for steel, wood and aluminum in a wide range of applications. 

13. Explain corrosion of pre-stressed concrete.

Prestressed concrete is a system devised to provide sufficient precompression in the concrete beam by tensioned steel wires, cables, or rods that under working conditions the concrete has no tensile stresses or the tensile stresses are so low that no visible cracking occurs. How is Prestressed Concrete Made?  Steel strands are pulled to a high tension force through formwork. Concrete is poured into formwork and cures around steel strands. Formwork is removed and steel strands are cut.