Durability

Question 1

What is the objective of durability?

Answer 1

To design and build concrete structures that meet their
Expected Service Lives with Minimum Repair

Question 2

What is deterioration?

Answer 2

Physical manifestation of failure of a material (e.g., cracking, spalling, delamination, pitting)
Decomposition of material (disintegration, weathering)

Question 3

WHAT ARE THE CAUSE OF CONCRETE DETERIORATION?

Answer 3

PHYSICAL DETERIORATION
CHEMICAL DETERIORATION
REINFORCEMENT CORROSION

Question 4

What causes PHYSICAL DETERIORATION?

Answer 4

Frost
Cracking
Fire
Abrasion

Question 5

What causes CHEMICAL DETERIORATION?

Answer 5

Sulphate
AAR
Sea water
Leaching

Question 6

What are the causes REINFORCEMENT CORROSION?

Answer 6

Chlorides
Carbonation

Question 7

How much of steel produced annually in the world is used to repair corrosion prob?

Answer 7

40% (25% to 30% for corrosion within reinforced conrete)

Question 8

What is corrosion?

Answer 8

it is a cycle caused by iron oxyde (rust) that expands the concrete –>cause stress–> causes failure —> causes spalling of concrete (écaillage) –>causes more rust (cycle goes back to expansion)

Question 9

What is passivation?

Answer 9

thin oxide film on reinforcement

Question 10

What causes de-passivation?

Answer 10

Entering of chlorides ION
Carbonation of concrete

Question 11

How much can volume increase with rust?

Answer 11

Up to 6 times

Question 12

How to differentiate carbonation from chloride infiltration?

Answer 12

Phenolphthalein test

Question 13

Phenolphthalein test –>PINK

Answer 13

NOT CARBONATED/Chloride infiltration

Question 14

Phenolphthalein test–> not pink

Answer 14

Carbonated

Question 15

What is the diffusion coeff?

Answer 15

rate of chloride ingress

Question 16

how to reduce diffusion coeff?

Answer 16

by reducing voids–>reducing permeability–>reducing water–>reducing diffusion coeff?

Question 17

What to use to reduce corrosion?

Answer 17

Epoxy coated bars (if defected in coat, it can accelerate the corrosion affect (concentrated in one pts))
Stainless Steel rebar ($$$)
FRP rebar (brittle)

Question 18

How to repair corrosion affected concrete?

Answer 18

Remove concrete–>corrosion inhibitors (adm) –> cover concrete –> coating–> impregnation
some cases, replace reinforcement/add new

Question 19

How much water expands as it freezes?

Answer 19

Expands up to 9% (tensile stress)

Question 20

What are the most common signs of freeze/thaw deterioration?

Answer 20

-Development of cracks sub-parallel to the surface
-Cracks throughout the concrete (delamination)
-Gaps around aggregates in the surface regions of concrete.

Question 21

How much freeze&froze cycle can concrete resists?

Answer 21

300 cycles before damages

Question 22

What is paste failure? (spalling)

Answer 22

Paste failure: Fracture surface consists of broken paste and occasionally undisturbed agg. faces

Question 23

What is agg. failure? (spalling)

Answer 23

spalled section contains a broken agg. at the bottom of fracture surface pit

Question 24

in sidewalks, where does D-cracking and scaling occurs bc of freeze-thaw?

Answer 24

expansion joints

Question 25

How to protect concrete from F-t?

Answer 25

keep concrete dry (not always possible) Reduce amt of freezable water Provide a relief for pressure (AEA) Combination of above

Question 26

Where does the Alkali in AAR comes from?

Answer 26

from cement

Question 27

Where does the silica in ASR comes from?

Answer 27

Agg (silica mineral)

Question 28

ACR or ASR worst?

Answer 28

ACR is worst (alkali carbonate reaction) Avoid it by using agg in Kingston (limestone)

Question 29

What are the field symptoms of ASR?

Answer 29

Longitudinal cracking Cracks starts from the 1st layer of agg Map cracking White powder (silica gel extracted from concrete)

Question 30

How to prevent AAR (ASR & ACR)

Answer 30

use non reactive agg (100% for ACR) selective aff Limit alkali in cement & concrete Lithium adm (earlier apply --> less damage) use SCM (SF, FA, Slag) Tight the concrete (confinement-->increase strength of struc; NOT permanent)

Question 31

How is the sulfate dangerous?

Answer 31

Sulfate is aggressive with water/moisture bc attack hydration product for cement

Question 32

Hydration products; what are the others?

Answer 32

Ettringite ---> Monosulfate (stable phase of ettiringite)

Question 33

How is ettringite and monosulfate created?

Answer 33

C3A + gypsum+water =ettringite (unstable) C3A+ettringite+water = monosulfate (stable) Volume ett> volume mono (about 700times)

Question 34

How can monosulfate go back to ettringite?

Answer 34

CH+sodium sulfate= GYPSUM +sodium hydroxide GYPSUM +monosulfate +Water= ettringite

Question 35

WHY is it a problem the conversion of ettringite to monosulfate?

Answer 35

Very large volume expansion and contraction

Question 36

How to prevent sulfate attacks?

Answer 36

prevent with type 20 and type 50 cement (low C3A) adding SCM (CH to CSH; pozzolanic activity)

Question 37

How to prevent plastic and drying shrinkage?

Answer 37

Wet curing Wind break Shade concrete surface

Question 38

What causes Drying shrinkage?

Answer 38

By volume change (decrease) due to loss of moisture in combination with restraint of soil or structure (struc applies stress by stoping mvt) Thermal effects(expansion)

Question 39

How to control shrinkage in sidewalks?

Answer 39

Seperation because of agg. that will restrain the slab (limit cracking)