Term
| Moisture Content in Concrete Mix? |
|
Definition
Water is required to provide sufficient workability and react with cement to provided strength.
More water is required to lubricate aggregates with angular shapes than rounded smooth particles
SSD is the ideal moisture content of mix constituents as no moisture is added or removed during mixing. |
|
|
Term
| How do impurities in water affect the concrete mix? |
|
Definition
Chlorides can cause deterioration of steel bars
Other impurities can also accelerate or decelerate the setting time.
Lowers the strength of the concrete |
|
|
Term
| What are the five stages in manufacturing cement? |
|
Definition
1) Quarrying- quarried then crushed
2) Drying the Grinding - storage hall, rawmill, rawmeal silos
3) Kiln Burning & Cooling - Suspension preheaters, rotary kiln, clinker cooler silos
4) Finish Grinding - Gypsum added, cement mill, cement silos
5) Packing - packed or sold in bulk |
|
|
Term
| How does the presence of gypsum affect the hydration reaction |
|
Definition
| In the presence of gypsum C3A reacts to form ettingite, which coats C3A grains and prevents rapid reaction. |
|
|
Term
|
Definition
| stiffness or sloppines of mix influenced the fluidity of the cement phase (slump) |
|
|
Term
|
Definition
| The amount of energy required to place and compact |
|
|
Term
| Water demand should be kept as low as possible too... |
|
Definition
1) Reduce Cost - more water means more cement
2) Minimise Shrinkage and Creap
3) Control Bleeding and Segregation |
|
|
Term
| What is bleeding? What are it's positive and negative effects |
|
Definition
Water rises, solids settle on the bottom.
lenses - trapped water under aggregate
channels - formed by water rising
Positive Effects:
Removes excess water, improves surface finish, Indicates when setting occurs, prevent plastic shrinkage cracking.
Negative Effects:
lenses under aggregate or steel bars reduce bond strength, top bar effect, segregation of mix. |
|
|
Term
| What are some ways to prevent plastic shrinkage cracking? |
|
Definition
Pre-wet surfaces
Protect from rapid drying
Avoid extreme weather conditions
Ensure reasonable bleed |
|
|
Term
| Effect of Temperature on Concrete Strength Development |
|
Definition
Increased temperature
Increased Rate of Hydration
Increases Strength of Early Age
Decreases Long term Strength |
|
|
Term
| How can we decrease the permeability of porous material? |
|
Definition
1) Decrease Total Porosity
2) Decrease Connectivity
3) Decrease Pore Size
4) Increase Tortuosity (crookedness of pores)
This can be done by
1) Reduce the quantity of paste by
- decrease water and cement content
- improve aggregate grading
2) Improve the quality of the paste
- Reduce W/C ratio
- Use SCM |
|
|
Term
| How does air-entrainment help? |
|
Definition
| Air bubbles provide spaces for water and freezing advances, relieving pressure in the concrete |
|
|
