 Deformation in load and damage process:  Damage type under compressive load  Original crack  Damage process-one-axis static compression §4.4.2 Deformation under load and damage process

Damage type under compressive load Damage typeReasonPossibility Hardened cement damage Cause by low grade cement appear often Interface damage Caused by interface cracks appear often Coarse aggregates damage Normally, f rock >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 and Fig Back

Damage type under compressive load Fig 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 Original crack Fig sketch map of original crack

Types of original crack Dry shrinkage Cold contract Volume decrease Settlement Plastic 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

Mechanism Mechanism  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 Damage process under one-axis static compression

compressive strength of concrete Compressive strength experiment is shown in the video. Fig Picture of Concrete Compressive Instrument

Compression-deformation curve of concrete (deformation, ultimate load)  Ⅰ interface cracks develop slowly;  Ⅱ Iiterface crack increase;  Ⅲ cracks appear in mortar and continuous cracks appear;  Ⅳ continuous cracks develop quickly;  Ⅴ cracks develop slowly;  Ⅵ cracks develop quickly

Sketch map of concrete interior cracks in different stress periods

Relation between damage process and interior crack development PeriodLoad σ〜εσ〜ε Interior cracks Ⅰ -OA Elastic limit (30% of ultimate load) σ=εσ=εNot obviously develop Ⅱ -AB Critic load (70%-90% of ultimate load) σ<εσ<ε More cracks appear (only at interface) Ⅲ -BC Ultimate loadσ<<ε Cracks develop to mortar and continuous cracks appear Ⅳ -CD Exceeding ultimate load ε increases largely Continuous cracks develop and concrete is damaged Tab Relation between damage process and interior crack development The following Tab illustrated the relation between damage process and interior crack development.