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Durability of Concrete

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Concrete Durability

Definition

The ability of concrete to withstand the conditions forwhich it is designed without deterioration for a longperiod of years is known as durability

OR

Durability of concrete may be defined as the ability ofconcrete to resist weathering action chemical attackand abrasion while maintaining its desiredengineering properties

Durability is defined as the capability of concrete toresist weathering action chemical attack andabrasion while maintaining its desired engineeringproperties It normally refers to the duration or lifespan of troubleshyfree performance Different concretesrequire different degrees of durability depending onthe exposure environment and properties desiredFor example concrete exposed to tidal seawater willhave different requirements than indoor concrete

Concrete will remain durable if

The cement paste structure is dense and of low permeability

Under extreme condition it has entrained air to resist freezeshythaw cycle

It is made with graded aggregate that are strong and inert

The ingredients in the mix contain minimum impurities such as alkalis Chlorides sulphates and silt

Factors Affecting Durability of Concrete

Durability of Concrete depends upon the following factors

Cement content

Mix must be designed to ensure cohesion and prevent segregation and bleeding If cement is reduced thenat fixed wc ratio the workability will be reduced leading to inadequate compaction However if water isadded to improve workability water cement ratio increases and resulting in highly permeable material

Compaction

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The concrete as a whole contain voids can be caused by inadequate compaction Usually it is beinggoverned by the compaction equipments used type of formworks and density of the steelwork

Curing

It is very important to permit proper strength development aid moisture retention and to ensure hydrationprocess occur completely

Cover

Thickness of concrete cover must follow the limits set in codes

Permeability

It is considered the most important factor for durability It can be noticed that higher permeability is usuallycaused by higher porosity Therefore a proper curing sufficient cement proper compaction and suitableconcrete cover could provide a low permeability concrete

Types of Durability of Concrete

There are many types but the major Concrete Durability types are

1 Physical durability2 Chemical durability

Physical Durability

Physical durability is against the following actions

1 Freezing and thawing action2 Percolation Permeability of water3 Temperature stresses ie high heat of hydration

Chemical Durability

Chemical durability is against the following actions

1 Alkali Aggregate Reaction2 Sulphate Attack3 Chloride Ingress4 Delay Ettringite Formation5 Corrosion of reinforcement

Causes for the Lack of Durability in Concrete1 External Causes

a Extreme Weathering Conditionsb Extreme Temperaturec Extreme Humidityd Abrasione Electrolytic Actionf Attack by a natural or industrial liquids or gases

2 Internal Causesa) Physical

Volume change due to difference in thermal properties of aggregates and cement paste

Frost Action

b) Chemical

Alkali Aggregate Reactions

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i Alkali Silica Reaction

ii Alkali Silicate Reaction

iii Alkali Carbonate Reaction

Corrosion of Steel

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