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DAMC > T3-3: Planning Investigations and Thermal Cracking > Flashcards

T3-3: Planning Investigations and Thermal Cracking Flashcards

1
Q

What are the five steps in the initial investigation process?

A
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2
Q

Describe the five different types of main investigation, in the detailed investigation process

A
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3
Q

What are the five steps in the final stage (actions) investigation process?

A
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4
Q

In concrete inspections, name different types (x7) of defects and probable causes to inspect for

A
  • Cracking related to construction
  • Other defects related to construction
  • Load induced cracking and design inadequacies
  • Environmental effects
  • Deterioration related to aggregate properties
  • Chemical attack
  • Reinforcement corrosion
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5
Q

What are the aims (x6) of concrete investigations?

A

To obtain sufficient information on the:

  • Condition of structure
  • Causes of deterioration
  • Extent of deterioration
  • Likely future deterioration
  • Remedial options
  • Extent of repair
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6
Q

What are indications of potential durability problems (x7) from a visual inspection/defect survey?

A
  • Surface shrinkage crazing
  • Blow holes
  • Cold joints
  • Honeycombing
  • Grout loss
  • Segregation
  • Scaling
  • Spalling
  • Corrosion of steel
  • Hollow (delaminated surface)
  • Varying colour
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7
Q

What are blow holes?

A

Air voids in the concrete surface

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8
Q

What are key investigation questions for cracks?

A
  • Is it structural (S) or non-structural (NS)?
  • Is it significant?
  • Is it recent?
  • Is it moving?
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9
Q

What is the range of crack widths for a hairline crack?

A

< 0.05mm

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10
Q

What is the range of crack widths for a crack that is likely in the structural range?

A

≤ 0.3mm

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11
Q

What is the range of crack widths for an excessively wide crack?

What are two causes/features of these cracks?

A

0.3mm - 5mm

  • structural overload (e.g. yield of bar)
  • non-structural cracks
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12
Q

What are possible causes (x4) of excessive cracking?

Classify into structural or non-structural

A
  • Insufficient allowance for structural movement (S)
  • Impact damage (S)
  • Settlement/differential movement (S)
  • Thermal shrinkage cracks (NS)
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13
Q

Why does thermal cracking occur?

A
  • The outer surfaces are cooler, which sets up a thermal gradient
  • The temperature increases by 14C per 100kg of cement, if the pour is < 0.5m minimum dimension
  • 400 kg/m^3 mix can reach 60C in its centre
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14
Q

Due to temperature differentials, what happens in thermal cracking?

What width can the cracks exceed?

A
  • Temp. differentials sets up tensile strains, and cracking occurs in the young, weak concrete if δC ≥ 20C
  • Cracks can exceed 1mm or more
  • Once cracked, can lead to salt ingress, carbonation (other durability problems)
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15
Q

What are two examples of low heat cements?

A
  1. GGBS
  2. PFA
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16
Q

In thermal cracking, what happens when the new concrete heats up?

A

It expands and, with the weak bond, slips along the larger mass (e.g. wall on slab)

17
Q

In thermal cracking, what happens when the new concrete cools?

A

It contracts against the larger mass, producing restrained thermal cracking

18
Q

How do you prevent thermal cracking due to a core/surface differential (x3)?

A
  • Use ‘quilt insulation’ to maintain δC < 20C
  • Use low heat cements, minimising T_core
  • Monitor the concrete core temperature
19
Q

On top of the causes of excessive cracking below, name other types of excessive cracking (x5)

  • Insufficient allowance for structural movement (S)
  • Impact damage (S)
  • Settlement/differential movement (S)
  • Thermal shrinkage cracks (NS)
A
  • PSe (plastic settlement) cracks (NS)
  • PSh (plastic shrinkage) cracks (NS)
  • Drying shrinkage cracks (NS)
  • ASR/AAR (alkali silica reaction) (S)
  • Underlying corrosion (S)
20
Q

[NAQ] identification of ASR and PSe/PSh cracks

21
Q

Rank the types of cracks from quickest appearance (after placing concrete) to longest appearance:

  • AAR/AMR
  • Plastic shrinkage
  • Early thermal contraction
  • Plastic settlement
  • Corrosion
  • Drying shrinkage
22
Q

[NAQ] example feature mapping, including identification of a rust stain, hollow area and exposed bar

23
Q

What does this image show?

A

Delamination/hollowness
- hammer tap survey of delaminated surface concrete

24
Q

What does this image show?

A

Surface spalling

25
Q

What are things to consider (x5) when planning for stage 2?

A
  • Types of test
  • Types of sample
  • Number of tests and samples
  • Locations of tests and samples
  • Access requirements
26
Q

What are two example things that in-situ testing on concrete is for?

A
  • Compressive strength
  • Density changes

DAMC (20 decks)

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