Deformation in load and damage process:Damage type under compressive

loadOriginal crackDamage process-one-axis static

compression

§4.4.2 Deformation under load §4.4.2 Deformation under load and damage processand damage process

Damage type under compressive load

Damage type Reason PossibilityHardened cement

damage Cause by low grade cement

appear often

Interface damageCaused by interface cracks

appear often

Coarse aggregates damage

Normally, frock>f cu appear seldom

Tab.4.4.1Damage Types under Load, Reason and Possibility

There are three damage types of concrete under compressive load. Damage types, the reason and possibility of this kinds are illustrated

in Tab.4.4.1 and Fig.4.4.1.

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Damage type under compressive load

Fig.4.4.1 Damage types under compressive load

The interface damage is likely to happen because there are original cracks in interface.Original cracks refer to the cracks formed in the interface of coarse aggregates and mortar before the concrete is loaded Sketch map of original crack is illustrated in Fig.4.4.2.

Original crack

Fig.4.4.2 sketch map of original crack

Types of original crackTypes of original crack

Dry shrinkageCold contractVolume decreaseSettlementPlastic shrinkage Bleeding path forming

Method Method

The relation between deformation and interior crack development can be found by mechanical test and microscope observation

Damage process under one-axis static compression

MechanismMechanism

With load increasing, concrete deformation increases with micro-cracks appearing and developing in the concrete until the concrete is damaged.Compressive strength experiment is shown in the video.Concrete compressive instrument is shown in Fig 4.4.3.

Damage process under one-axis static compression

compressive strength of concretecompressive strength of concrete

• Compressive strength experiment is shown in the video.

Fig 4.4.3 Picture of Concrete Compressive Instrument

Compression-deformation curve of Compression-deformation curve of concrete (deformation, ultimate concrete (deformation, ultimate

load)load)

Ⅰ interface cracks develop slowly;ⅡIiterface crack increase; Ⅲcracks appear in mortar and continuous cracks appear; Ⅳcontinuous cracks develop quickly; Ⅴcracks develop slowly; Ⅵcracks develop quickly

Sketch map of concrete interior cracks in different stress periods

Relation between damage process Relation between damage process and interior crack developmentand interior crack development

Period Load σ〜 ε Interior cracks

Ⅰ-OA Elastic limit

(30% of ultimate load)σ=ε Not obviously develop

Ⅱ-AB Critic load (70%-90%

of ultimate load)σ<ε

More cracks appear (only at interface)

Ⅲ-BC Ultimate load σ<<ε Cracks develop to mortar

and continuous cracks appear

Ⅳ-CDExceeding ultimate

loadε increases

largely

Continuous cracks develop and concrete is

damaged

Tab.4.4.2 Relation between damage process and interior crack development

The following Tab.4.4.2 illustrated the relation between damage process and interior crack development .