Deterioration of concrete ppt

Deterioration of concrete and causes of concrete deterioratios

1. Module 4 Deterioration of concrete structures Wasim Shaikh AIKTC, New Panvel

2. D eterioration of concrete structures

3. Deterioration of concrete structures Defect : An identifiable, unwanted condition that was not part of the original intent of design. Deterioration : A Defect that has occurred over a period of time.

4. SCALING Scaling is referred to the loss of the surface portion of concrete (or mortar) as a result of the freezing and thawing . This problem is typically caused by the expansion of water due to freezing and thawing cycles. Scaling happens when the hydraulic pressure from water freezing within concrete exceeds the tensile strength of concrete It is a physical action that usually leaves the aggregates clearly exposed. Usually it start with localized area then extend to larger areas. Concrete having decent amount of entrapped air can prevent scaling damage.

5. DISINTEGRATION Disintegration is the physical deterioration (such as scaling) or breaking down of the concrete into small fragments or particles. The deterioration usually starts in the form of scaling and, if allowed to progress beyond the level of very severe scaling is considered as disintegration. Severity Light – Loss of surface mortar to a depth of up to 5 mm without exposure of coarse aggregate; Medium - Loss of surface mortar to a depth of 6 to 10 mm with exposure of some coarse aggregates; Severe - Loss of surface mortar to a depth of 11 mm to 20 mm with aggregate particles standing out from the concrete and a few completely lost. Very Severe - Loss of surface mortar and aggregate particles to a depth greater than 20 mm.

6. EROSION Erosion is the deterioration of concrete surface as a result of particles in moving water scrubbing the surface . Similar, damage may be caused by flowing ice. Erosion is generally an indication that the concrete is not durable enough for the environment in which it has been placed. Erosion is sometimes combined with the chemical action of air and water-borne pollutants which accelerate the breakdown of the concrete.

7. CORROSION OF REINFORCEMENT Corrosion  is the deterioration of steel reinforcement in concrete. Corrosion can be induced by chloride or carbonation. The alkali content in concrete protects the reinforcement from corrosion. when chloride ions above a certain concentration are dissolved in water and penetrate through the concrete to the reinforcement this protection breaks down and corrosion starts. The formation of rust requires iron, water and oxygen . Although it's a complex process, the chemical equation is, 4Fe + 3O 2  + 6H 2 O → 4Fe(OH) 3 .

8. CORROSION OF REINFORCEMENT 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.   The alkaline environment of concrete (pH of 12 to 13) provides steel with corrosion protection. At the high pH, a thin oxide layer forms on the steel and prevents metal atoms from dissolving

9. Role of chloride ions in corrosion of Rebars The risk of corrosion increases as the chloride content of concrete increases. When the chloride content at the surface of the steel exceeds a certain limit, called the threshold value, corrosion will occur if water and oxygen are also available. a threshold limit of 0.20 percent total (acid-soluble) chloride by weight of cement.

10. Role of Carbonation in corrosion of Rebars Carbonation occurs when carbon dioxide from the air penetrates the concrete and reacts with hydroxides, such as calcium hydroxide, to form carbonates. T he reaction with calcium hydroxide, calcium carbonate is formed. Ca(OH) 2  + CO 2  → CaCO 3  + H 2 O This reaction reduces the pH of the pore solution to as low as 8.5, at which level the passive film on the steel is not stable.s

11. Causes of concrete Deterioration Causes Chemical Physical Mechanical Defects

12. Chemical Deterioration by carbon dioxide Deterioration by sulphates Deterioration chlorides Deterioration Alkali-aggregates reaction

13. Deterioration by carbon dioxide 1) Carbonation Carbonation is due to the penetration of CO2 into the concrete. This phenomenon consists in the transformation of the lime (Calcium Hydroxide) This lime (Calcium Hydroxide ) then converts into Calcium carbonate. If the concrete gets carbonated it reduces the p h of the concrete .

14. Effect of corrosion

15. Leaching of the concrete Formation of lime on the surface 50 to 60 % humidity is very bad. Can be prevented using air entrapped concrete.

16. Deterioration by sulphates The most common soluble sulphates in the ground, in water and in industrial processes are calcium and sodium. may also be found directly in the aggregates as impurities They react with calcium hydroxide to form gypsum This process increases the volume of the concrete by lamination process.

17. Lamination of concrete

18. Deterioration by chlorides Chlorides causes the corrosion of the rebars by reducing the alkalinity of concrete. a structure completely immersed in seawater will have a higher chloride content. However, the porosity in the concrete will be completely saturated with humidity, and the oxygen will not be able to penetrate. Corrosion of the reinforcement rods will not occur, or will be negligible

19. Deterioration Alkali-aggregates reaction Some types of aggregate, such as those which contain reactive silicon, react with two alkalis contained in the cement, potassium and sodium An alkali-aggregates reaction may cause considerable expansion and serious deterioration of concrete structures. This reaction forms a gel which is highly expansive if exposed to humidity, and the gel creates forces which break the concrete around the aggregates.

20. Deterioration due to alkali-aggregates reaction

21. Detection of deterioration due to alkali-aggregates reaction An initial, immediate assessment to detect the presence of an alkali-aggregates reaction is by carrying out a detailed visual check This type of deterioration shows up with cracking in the concrete distributed like a spider’s web, with an orderly or less orderly distribution pattern according to the reinforcement present (As shown in previous slide ) Chemical analysis by means of a colour test using sodium cobalt nitrite is a certain way to identify the presence of a reaction between alkalis and reactive aggregates The sodium cobalt nitrite reacts with the K (potassium) in the gel to form a coloured precipitate. Therefore, if there has been a reaction, its colour will change and will turn yellow, this indicates alkali aggregate reaction.

22. Deterioration by physical elements Deterioration by physical element can be subdivided into following three categories. Freezing and thawing (Effect of climate) High temperatures Shrinkage and cracking

23. Deterioration by Freezing and thawing (Effect of climate) Extreme change in change in climatic conditions have adverse effect on concrete, especially the freezing and thawing cycles. If the water present in the pores of concrete freezes, its volume gets increased by around 9% of volume. This increase in volume exerts stress on the concrete and causes cracks in the concrete as shown in figure below. Increase in humidity also increases the amount of water in the concrete which leads to hydrostatic pressure. This hydrostatic pressure may cause lamination of the concrete surface as explained before. To avoid the adverse effect of freezing and thawing use of aerating admixes is advised. The aerating admixtures fill the concrete pores with air pockets which do not allow the entrance of water in the concrete.  

24.   Deterioration by High temperatures The effect of high temperatures on concrete is destructive. The reinforcement rods resist at temperatures of up to 500°C, while concrete resists at up to 650°C. Even if the reinforcement rods are protected by concrete, when they heat up, their volume increases and they create stresses in the concrete, this may lead to parts of the concrete breaking off. Once the reinforcement is exposed to fire, it expand much more quickly than the concrete in which they are embedded, causing a loss of bond between concrete and reinforcement. Even if the failure temperature is not reached, the concrete may lose its performance characteristics if it is suddenly cooled down, a condition which usually occurs when fires are extinguished. In this situation, the oxide which forms due to the heat is transformed into lime, which disintegrates the concrete. If exposure to fire is prolonged, the reinforcement rods reach their failure temperature and there is a loss in tensile strength, which causes the entire structure to collapse.

25. Deterioration by mechanical elements Deterioration by mechanical elements can be subdivided into following parts Abrasion Impact Erosion Cavitation

26. Deterioration by Abrasion If a material is repeatedly struck by particles from a harder body, abrasion takes place. This is due to the friction which the harder powder particles exercise on the surface of the material. It is therefore quite clear that abrasion depends directly on the characteristics of the materials which make up the concrete. As a result, we can improve resistance to abrasion by reducing the water/ cement ratio or by sprinkling cement mixed with hard admixes and aggregates on the surface of the concrete

27. Deterioration by erosion Erosion is the deterioration of concrete surface as a result of particles in moving water scrubbing the surface. Similar , damage may be caused by flowing ice. Erosion is generally an indication that the concrete is not durable enough for the environment in which it has been placed. Erosion is sometimes combined with the chemical action of air and water-borne pollutants which accelerate the breakdown of the concrete. Effects of erosion can be seen in the figure.

28. Effect of loading on serviceability and durability: The response of concrete subjected to loading differs from type of loading, if the concrete is subjected to impact loading its strength reduces. Even under the sustainable loading which remains on concrete for long duration concrete undergoes deformation due to creep. Creep is the deformation in the concrete due to long term loading, the effects of creep are usually not visible in the fresh structure but it takes years to show up. Creep reduces the service life of the concrete structures. Another form of deterioration which arises due to cycling loading i.e. gradual removal and application of load on the concrete, is called as fatigue. Fatigue also a long term deformation usually found on concrete bridges

29. Deterioration by Defects: (Design and construction errors) These are the wide range of deterioration that arises due to design and construction errors, a list of few of these causes is given below. Defects due to bleeding and segregation Defects due to improver cover. Defects due to poor quality of materials. Defects due to poor/incorrect deign of the mix Defects due to the wrong composition Defects due to incorrect/poor quality installation

30. Examples of defects Inadequate Cover Segregation of concrete

31. Causes of leakage and seepage in concrete structures F ollowing are some major sources of leakage in the concrete structures. Structural Causes: Non-Structural Causes

32. Structural Causes Cracks due to differential settlement of foundations of a building . Cracks formed in the RCC slab, beam, walls due to poor design, deficiency, over loading or poor workmanship resulting in honey combing etc Cracks due to thermal extremes, expansion- contraction, shrinkage, creep including aggressive climatic conditions and lack of joints. Cracks due to vegetation growth. Cracks due to absence of structural elements like lintels, sill etc Cracks between two different materials particularly with different co-efficient of thermal expansion

33. Non-Structural Causes Improper slope of the terrace Defective Waterproofing Extreme Weather Conditions Sub Standard Work Practices Poor Quality of Materials Poor Quality of Bricks and Plaster: Broken tiles on Terrace Joints Between Flooring Tiles No Plinth Protection Leakage of Water from Water Storage Tanks Poor Plumbing

34. Non-Structural Causes  Poor Maintenance Chocked Pipes Broken Pipes  Lack of Periodic Checks and Cleaning Arrangements