CONCRETE TECHNOLOGY Flashcards
Concrete?
- Corse Aggregate
- Fine Aggregate
- Cement
- Water
+Optional Admixers
Can be described as stone, sand, cement and water
Advantages of Concrete
- Low Cost
- Strong compressive strenght
- Flexible in Application
- Variety of Finishes
- Reinforcable
Cement Process
To produce fine powder
- Clay/Shale + Chalk/Limestone
- Mixed in a kiln
- Gypsum added (prevents flash setting)
Types of Portland Cement
6
- Low Heat
- Rapid Hardening
- Sulphate Resistant
- Blast Furnace
- Plverised Fuel Ash
- White Portland Cement
High Alumna Cement
Not A Portland
- Limestone and bauxite
- Very rapid hardening
- Acheives required strenght in 24 hours
Low Heat PC
Mass concrete structures
Rapid Hardening PC
Sets faster than OPC
Sulphate Resistant PC
Sulphate bearing soils
Blast Furnace Cement
OPC + Blast furnace slag
Plverised Fuel Ash Cement
Coal power stations
White Portland Cement
White china clay
Concrete Performance Requirements
Workability
Compressive Strength
Durability
Waiting days for Concrete Hardening?
28 Days
Advantages of Using Aggregate
- Reduces costs
- Reduces shrinkage
- Can be used as decorative
- Improves fire resistance
- Versatile density qualities
- Produces palstic properties
Aggregate Sizes
5mm - Screeds bellow 50mm
10mm - Thin sections
20mm - General concrete work
40mm - Mass road construction
(C, M, F) Grading
Workability
PCF
Ability of concrete to be placed, compressed and finished
Tests for workability Include: Slump Test, Vebe Test, Compacting Factor Test, Cube Test
Admixers
Materials other than cement, water, aggregates added to modify properties of the mix
Types of Admixers
4
- Water reducing agents
- Superplasticizers
- Air- Entraining agents
- Accelerators
Effects of Admixers
- Improve pumpability
- Increases strength
- Reduce permeability
- Improves durability
- Increase workability without changing the water content
- Reduce water content without changing the workability
Causes of concrete deterioration
- Frost attack
- Sulphate attack
- Crystallisation damage
- Map cracking (concrete cancer)
- Corrosion of steel reinforcement
Slump Test
- Concrete placed in 3 layers
- Tamped 25 times
- Usual results at 50mm - 75mm
Steel Slump Cone, Tamping Rod, Tamping Stick
Results: True, Shear, Collapsed
Compacting Factor Test
Finds Compacting Factor
- Concrete is gently loaded into hopper and allowed to vertically fall into lower hopper
- Falls into cylinder
- Concrete in cylinder is struck off and weighed
- Cylinder is tipped empty, refilled then re-weighed with fully compacted concrete
Result: M. of partially compacted concrete/M. of fully compacted concrete
Vebe Test
