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this is about durability of concrete

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  1. 1. Durability of concrete Made by – Satya mishra. MIT 11-A-03 –G-CIVIL -7339
  2. 2. a) Durability –introduction of the durability concept. b) The factors affecting durability of concrete c) Different attacks on concrete affecting durability . i) sulfate attack. ii) origin of problems. d) Loss of strength and mass e)ACI building code 318 i) negligible attack ii)moderate attack iii)severe attack iv)very severe attack f) History of concept g)Examples of major damaged monuments. h) Prevention for factors affecting durability. i) bibliography/references. contents
  3. 3. Durability concept ->Definition-Durability of concrete :ability to resist weathering action ,chemical attack , abration or any process of deterioration. -> A durable concrete will retain its original form quantity and serviceabilty when exposed to its environment . Water causes – a)Chemical processes of degradation . b)Physical processes of degradation.
  4. 4. Factors affecting durability of concrete Physical causes concrete deterioration deterioration by surface wear a) Abration :dry attribution (wear on pavements and industrial floors by traffic. b)Erosion :wear produced by abration action of fluids containing solid particles in suspension.(canal lining ,spillways and pipes.) c) cavitation: loss of mass by formation of vapor bubbles and their subsequent collapes.
  5. 5. Abration; erosion •The deterioration starts at the surfaces there fore special attentions should be given to quantity of concrete surface. •Avoid laitance (layers of lines of cements and aggregate) Deterioration by frost action When water freezes ,there is an exopansion of 9% however, some of the water may migrates through the boundary ,decresing the hydraullic pressure. •Hydraullic pressure depends on •Rate at which ice is formed •Permeabilty of the material •Distance to an “escape boundary”. •Problem: the transformation of ice from liquid water generates a volumetric dilation of 9% .if the transformation occurs in small capillary pores ,the ice crystal can damage the cement pastes by pushing the capillary walls and by generating hydraullic pressure
  6. 6. Solution to the problem- Air voids can provide an effective escape boundary to reduce this pressure. Picture showing the effect caused by frost action
  7. 7. Frost action by aggregate Factors controlling frost resistance of concrete.
  8. 8. Deterioration by fire Consequences:- Fire in chunnal->
  9. 9. Effect of temperature Corrosion Reinforce concrete
  10. 10. Electrochemical process of steel corrosion in concrete Volumetric changes Carbonate of concrete->
  11. 11. Alkali –silica reaction ASR chemistry
  12. 12. Repairing ASR Damage to a concrete Dam ASR damage examples
  13. 13. Sulfate attack *sulfate attack on concrete has been reported from many other parts of the world . •As early as 1936 the concrete construction in annual published by US bureau of reclamtion warned that concentrations of sulfate greater tha 0.1% in siol may have a deleterious effect on concrete ,and more tha 0.5 % soluble sulfate in soil may have a serious effect. Origin of the problem •most soil contains some sulfate in form of gypsum (typically 0.01% to 0.05% expressed as So4 ); this amount is harmless to concrete . • higher the concentrations of sulfate in ground water are generally due to presence of magnesium and alkali sulfates. •Ammonium sulfate is frequently present in agriculture soil and water effluents from furnances that use high sulfur fuels and from chemical industries may contain sulfuric acid.
  14. 14. Expansion of concrete •When concrete crack ,its permeability increases and aggressive water penetrates More easily into the interior thus accelerating the process of deterioration . •Sometimes the expansion of concrete causes serious structural problem. Loss in strength and mass * sulfate attack can also take the form of progressive loss of strength and loss of mass due to loss of cohesiveness in the cement hydration product. Expansion reaction sulfate attack •gypsum formation leads to reduction of stiffness and strength •,then by expansion and cracking. •Sodium sulfate attack
  15. 15. Sodium sulfate attack •The formation of sodium hydroxide as a by product of the reaction ensures the •continuation of high alkalinity in the system which is esential for the stability •of cemetitious material C-S-H. Magnesium sulfate attack
  16. 16. Factors influencing sulfate attack •Amount and nature of the sulfate present •Level of the water table and its seasonal variations. •Flow of ground water and soil porosity. •Form of construction, •Quantity of concrete. ACI building code 318 •Negligible attack : when the sulfate content is under 0.1% in soil ,under 150 ppm (mg/liters) in water ,there shall be no restriction on the cement type and water /cement ratio. *moderate attack: when the sulfate content is 0.1 to 0.2% in soil ,or 150% to 1500 ppm In water ,ASTM type 11 portland cement or portland pozzolan or portland cement shall Be used ,with less than on 0.5 water /cement ratio for normal –weight concrete. •Severe attack: when the sulfate content is 0.2 to 2% in soil ,or 1500 to 10,000 ppm •in water ,ASTM type V portland cement ratio ,shall be used 0.45 water /cement ratio, Shall be used. •Very severe attack: when the sulfate content is over 2% in soil ,or over 10,000 ppm in water, ASTM type V cement plus a pozzolanic admixture shall be used ,with less than an 0.45 water /cement ratio.
  17. 17. freeze thaw •expansion and cracking occurs when water in paste Freezes . Volume expansion Hydraullic pressure. Ice lens
  18. 18. Reactive aggregates *Amorphous silica (glass ,opal). Unstable crystalline polymorphs of silica.(tridymite,cristobalite , strained quartz).
  19. 19. PREVENTIONS * Recognize and avoid susceptible aggregates . *use low alkali cement. •Use supplement cementing material. Making durable concrete •Make good –quality concrete low w/c . •Test materials. •Use air entrainment if concrete will be frozen. •Recognize and avoid material known to cause deterioration (D- cracking ASR)