Lec 10 Flashcards
Properties if hardened concrete in general (5)
Safety
Volume stability
Durability
Economy
Ecology
Explain safety and volume stability
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
Explain durability
physical: changes in the surrounding environment, humidity, and temperature, causing abnormal deformation
chemical: eriotsion by impurities (dissolution, crystallization, sulfate attack, alkaline reaction)
Explain economy
- less amount of cement, less material cost by using mineral admixture
- long time accumulation cost (maintenance, operation, etc) will be higher than initial investment
Explain ecology
cement should be minimized for the reduction and recycling of construction and industrial waste -> better environment
What is the most important property
Compressive strength
Why is strength specified in construction design and quality control?
- it is relatively easy to be measured
- other properties are related to the strength
general index of concrete strength
28 days compressive strength determined by standard uniaxial compression test
https://ibb.co/CnMXjx7
pahami saja bagian ini -> kek pengaruh strength dan modulus elasticity terhadap concrete -> stiffnes dan yound modulus
Factors affecting the strength of concrete
- water/cement ratio
- cement type and content
- aggregate
- mixing water and porosity
- curing method
https://ibb.co/hHFXYt1
bagan untuk CONCRETE STRENGTH
- strength of component phases
- moisture state
- rate of stress
- degree of consolidation
- curing time, temp, humidity
Explain water/cement ratio
- 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
how to lower w/c ratio
- proper mixing proportioning
- use of superplasticizer
- use of pozzolans material
just explain this graph of w/c ratio vs age and strength vs strain
https://ibb.co/zSvLf17
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
Explain aggregate to strength
- rough surface has better bonding strength
- irregular shape is not good for the workability
Explain mixing water and porosity to strength
- too much mixing water -> more pores -> more bleeding -> less compressive strength, durability, and water tightness
Explain curing to strength
- 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
Compressive Strength of Concrete (what is the test, general characteristic, factors)
- 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
Explain the size effect to compressive strength
bigger size -> bigger deficiencies (void and crack)
Explain tensile strength (general, function, methods)
- 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
https://ibb.co/nfGqQCB
- direct tensile test
- splitting test
- flexure test
Explain pure tension or direct tensile test
- waktu lab yg pake mesin
- the shape of stress-strain curve, elastic modulus, poisson’s ratio unixaial tension = uniaxial compression
Explain the splitting tension test
- 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)
Explain flexure test
- 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
