Concrete Flashcards
1
Q
Concrete production
A
Uses rotary kiln
2
Q
Usage in high rises
A
- Lower stories to support the rest of the building
- Lightweight concrete used for higher stories
- Need strong soils in the area
3
Q
Concrete makeup
A
- Air
- Cement (15%)
- Water (8%)
- Fine aggregate (sand) (34%)
- Coarse aggregate (gravel) (43%)
4
Q
Where does the strenght come from?
A
Reaction between the cement and water that produces a heat - hydration
5
Q
Curing
A
- Develops strength and durability
- Reduce heat by adding water
6
Q
Fresh concrete
A
- Between mixing and setting
- Can measure workability through slump test
7
Q
Hardened concrete
A
- After setting
- Can measure tensile and compressive strength
8
Q
Strength and Durability
(One is long term, one is short)
A
Strength = short
Durability = long
9
Q
Water:Cement ratio
A
- Most important factor in strength and durability
- Can alter to obtain desired results
10
Q
Aggregates
A
- 75% of concrete makeup
- Help the strength and durability
11
Q
Classified by:
A
- Production method
- Petrological characterisitc - rock mechanics (geology)
- Particle size
- Unit weight
12
Q
Production method
A
- Natural (sand/gravel from land or sea)
- Crushed (large rocks crushed to size, sharp surfaces help them to bond and increase strength)
13
Q
Particle size
A
- Sieve analysis
- Coarse (gravel) - 4.75mm
- Fine aggregate (sand) - 0.075mm
- Silt - 0.002-0.075mm
- Clay - smaller than 0.002mm
14
Q
What affects workability?
A
- Shape
- Texture
- Porosity
- Grading (particle size distribution)
15
Q
What affects strength?
A
- Individual strength
- Deformation
- Toughness
- Hardness
- Density
16
Q
What affects durability?
A
- Toughness
- Hardness
- Volume
- Stability
- Chemical compatibility
17
Q
Aggregate shapes
A
- Round
- Irregular - natural or partly shaped by attrition, rounder edges
- Flaky - fairly thin
- Angular
- Elongated
- Flaky and elongated
18
Q
Mechanical properties of aggregate
A
- Bond - interlocking of aggregate/paste
- Strength - crushing value test
- Toughness - resistance to failure by impact
- Hardness - resistance to wear
19
Q
Concrete Stability
A
- Ability to resist segregation
- Gravity causes denser materials to sink/water to rise (bleeding)
20
Q
Compaction Problems
A
- Workability must be high enough to allow it
- If compacted poorly, mould wont be filled and cause steel exposure - corrosision
21
Q
Plastic settlement
A
- Occours before setting due to bleeding/segregation
- To prevent: reduce water and recompact concrete after cracks develop
22
Q
Plastic shrinkage
A
- Happens before setting due to water loss
- More bleeding = less cracking (as still present even if on the surface)
- Prevent by good curing, covering concrete and fibre reinforcement
23
Q
Workability
A
- Resistance to flow
- Determined by particle friction - affected by proportion of materials and particle shapes/sides
24
Q
Stability
A
- Ability to resist segregation
- Bleeding = water rising to the surface
25
Q
Concrete stength factors
A
- W:C ratio
- Cement type
- Aggregate properties
- Age
- Curing
- Humidity
- Temperature
- Heat of hydration
26
Q
W:C Ratio
A
- Higher the ratio, increased chance of segregation and bleeding
- Ideally 0.4-0.6
