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ByProf Ir Dr Muhd Fadhil NuruddinCONCRETE TECHNOLOGYVCB 2023
Properties of Hardened Concrete
*Durability of hardened ConcreteThe durability of concrete may be defined as its ability to resist attack from the environment in which it is placed.Note : It is important to note that no material can be considered as inherently durable because its properties will change with time as a result of environmental interactions.
WHY IS DURABILITY IMPORTANT TO CONCRETE ?Concrete is capable of maintenance-free performance for decades without the need for protective coating, except in highly corrosive environment.Durability is an important factor in the life span of a concrete structure
LOW QUALITY- Methods of Construction(Honeycomb & low rebar cover)
LOW QUALITY Chloride-induced damage
LOW QUALITY Carbonation attack
LOW QUALITY Inadequate Compaction (Honeycomb)
LOW QUALITY Sheet spalling
LOW QUALITYInadequate cover (Mildew attack)
Flow Chart of the Factors that Governed the Quality Concrete
FACTORS AFFECTING DURABILITY
Durability of concrete
Physical
Mechanical
Chemical
Freezing and thawing
Wetting and drying
Abrasion
Sulphates
Acids
Sea Water
Chlorides
Temperature changes
What is permeability ?Permeability is the ease with which a fluid (liquids or gases) can travel thought concrete, under the action of a pressure differential.
Porosity and PermeabilityIllustration of permeability and porosity
Why Permeability is important in terms of durability of concrete ?Since chemical attack takes place within the concrete mass, the attacking agent must be able to penetrate through the concrete
Permeability affects the rate of entry of moisture which may contain aggressive chemicals and the movement of water during heating or freezing.
Water/Cement RatioWater/cement ratio has the greatest influence on durability because the permeability is dominated by large capillary porosity, rather than gel pores.Cement PasteConcrete
Water/ Cement Ratio
PermeabilityThe permeability decreases as the cement continues to hydrate and fills some of the original water space.The reduction in permeability will be faster for lower w/c ratio.
CarbonationChemical reaction between atmospheric carbon dioxide and the products of cement hydration.Reinforcing steel is no longer protected against corrosion at pH 9.5.Various factors significantly influence the rate of carbonation:Moisture TemperatureCarbon dioxide concentration.
PHYSICAL TEST
Test MethodsPrincipleMain applicationAbsorptionOven dried specimens with known dimension cooled in water for 30 minutesIndicates the quality and in particular the absorption of concrete in relation to durabilityPermeabilityMeasure the flow rate of the water through the concreteIndicates the degree of protection to reinforce offered by cover.Initial surface absorptionMeasure the flow rate of the water into the surface concreteIndicates the quality of the concreteLeak DetectionMeasure the clerical resistance between surface and reinforceDetects leakages in water proof membranesOxygen DillusionMeasure the rate of ingress of oxygen into the concrete structureEnables a maximum theoretical corrosion rate to be determinedCarbon Dioxide DillusionMeasure the rate of ingress of Carbon Dioxide into the concrete structureTo estimate the rate of carbonation and hence the time scale before possible reinforcement corrosionAir EntrainmentExamining a concrete sample Impregnated with dye under the microscopeEffective protection of cement paste from freezing and thawing cycles
TEST STANDARD
TestBritish StandardAmerican StandardOther StandardOther ReferenceAbsorptionBS1881 Part 122ASTM C642-82PermeabilityNBN748.18 ISO/DIS 7032Figg J.W. 1973Initial Surface AbsorptionBS1881 Part 208
Air EntrainmentASTM C457-82
Aggregate typeBS1881 Part 6BS 812 Part 1ASTM C856-83
Water/Cement ratioBS1881 Part 6
Chloride ContentBS1881 Part 6AASHTO T260-84Carbonation DepthRILEM CPC-18
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