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Eng Material > Lec 10 > Flashcards

Lec 10 Flashcards

1
Q

Properties if hardened concrete in general (5)

A

Safety
Volume stability
Durability
Economy
Ecology

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2
Q

Explain safety and volume stability

A

Safety: minimum compressive strength required by the designer

Volume stability:
intrinsic -> cement, aggregate, water, and admixtures
external -> construction operations, external forces, changes in temperature and humidity, exposure to environment

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3
Q

Explain durability

A

physical: changes in the surrounding environment, humidity, and temperature, causing abnormal deformation

chemical: eriotsion by impurities (dissolution, crystallization, sulfate attack, alkaline reaction)

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4
Q

Explain economy

A
  • less amount of cement, less material cost by using mineral admixture
  • long time accumulation cost (maintenance, operation, etc) will be higher than initial investment
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5
Q

Explain ecology

A

cement should be minimized for the reduction and recycling of construction and industrial waste -> better environment

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6
Q

What is the most important property

A

Compressive strength

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7
Q

Why is strength specified in construction design and quality control?

A
  • it is relatively easy to be measured
  • other properties are related to the strength
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8
Q

general index of concrete strength

A

28 days compressive strength determined by standard uniaxial compression test

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9
Q

https://ibb.co/CnMXjx7

A

pahami saja bagian ini -> kek pengaruh strength dan modulus elasticity terhadap concrete -> stiffnes dan yound modulus

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10
Q

Factors affecting the strength of concrete

A
  1. water/cement ratio
  2. cement type and content
  3. aggregate
  4. mixing water and porosity
  5. curing method
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11
Q

https://ibb.co/hHFXYt1

bagan untuk CONCRETE STRENGTH

A
  1. strength of component phases
  2. moisture state
  3. rate of stress
  4. degree of consolidation
  5. curing time, temp, humidity
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12
Q

Explain water/cement ratio

A
  • larger w/c, larger pores in the concrete and lower strength
  • principle: abrams law: fc = k1/k2^(w/c) -> k : constant
  • if the concrete contains fly ash or slag, etc. we change the w/c to water/binder
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13
Q

how to lower w/c ratio

A
  1. proper mixing proportioning
  2. use of superplasticizer
  3. use of pozzolans material
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14
Q

just explain this graph of w/c ratio vs age and strength vs strain

https://ibb.co/zSvLf17

A

the higher the w/c ratio, the lower the strength and the higher the strain

the higher the w/c ratio, the lower the strength, but as the day getting longer, the strength is higher

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15
Q

Explain aggregate to strength

A
  • rough surface has better bonding strength
  • irregular shape is not good for the workability
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16
Q

Explain mixing water and porosity to strength

A
  • too much mixing water -> more pores -> more bleeding -> less compressive strength, durability, and water tightness
17
Q

Explain curing to strength

A
  • proper curing temperature -> good quality improvement
  • high temp good for early strength development but worse effect for long term strength
  • low temp (> 0C) -> slowly hydrate, the crystal arrangement and growth of the hydration product are denser -> higher strength at last stage - LOW TEMP IS GOOD
  • POKOKNYA MAKIN KECIL TEMP CURING MAKIN TINGGI STRENGTH NYA -> DEBEST <3
18
Q

Compressive Strength of Concrete (what is the test, general characteristic, factors)

A
  • Cylindrical compression test (waktu lab) -> d = 150 mm h = 300 mm (ASTM C39) -> fc = P/A
  • The higher the compressive strength -> larger linear portion of the curve -> lower failure strain -> concrete is more brittle
    https://ibb.co/1zdcjFy
  • Factors: size. shape, water condition
  • the higher height/diameter -> lower fc
  • wet test specimen will be about 5-20% lower than dry specimen because EXISTENCE OF DISJOINTING PRESSURE WITHIN THE CEMENT
19
Q

Explain the size effect to compressive strength

A

bigger size -> bigger deficiencies (void and crack)

20
Q

Explain tensile strength (general, function, methods)

A
  • tensile strength is 1/10 to 1/15 of compressive strength
  • significant to resist shrinkage and deformation due to temp change
  • method: direct tension test, splitting tensile strength test, flexure test
21
Q

https://ibb.co/nfGqQCB

A
  1. direct tensile test
  2. splitting test
  3. flexure test
22
Q

Explain pure tension or direct tensile test

A
  • waktu lab yg pake mesin
  • the shape of stress-strain curve, elastic modulus, poisson’s ratio unixaial tension = uniaxial compression
23
Q

Explain the splitting tension test

A
  • the result is known to overestimate the tensile strength of concrete by 10-15% compare to direct tensile test
  • Stress tension = 2P/pi(L)(D)
24
Q

Explain flexure test

A
  • waktu lab yang manual
  • hasilnya modulus of rupture -> MOR = PL/BD^2
  • flexure strength is about compressive strength 10-25%, the higher the compressive strength, the smaller the ratio
25
Q

Correlation of concrete strength

A

Tensile strength: flexure test > splitting test > direct tensile test

meaning: flexure test has higher tensile/compressive strength and stiffer in the tension/compressive vs compressive strength graph

26
Q

Approximation range of tensile strengths of concrete

A
  1. direct test -> 3 to 5 (normal) and 2 to 3 (lightweight) dikali akar f
  2. splitting test -> 6 to 8 (normal) and 4 to 6 (lightweight) dikali akar f
  3. flexure test -> 8 to 12 (normal) and 6 to 8 (lightweight) dikali akar MOR
27
Q

Explain elasticity modulus of concrete

A

https://ibb.co/Qc8M1b0 IMPORTANT PIC

  • proportionality constant between stress and strain is called elastic modulus (17250 to 24100 MPa or 2,5 to 3,5 * 10^-6 psi)
  • important parameter to calculate stiffness in structural design
  • larger elastic modulus -> smaller amount of elastic deformation
  • depends on the elastic modulus of aggregate and cement paste, and the relative amount of aggregate and cement paste

https://ibb.co/RCKy1jK

28
Q

https://ibb.co/0nPHrLf

A

liat liat aja elastic modulusnya, pahami aja <3

Eng Material (13 decks)

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