Concrete and Non-Portland Cement Flashcards
What are the components of cement paste?
cement + water
What are the components of mortar?
cement + fine aggregates (<5 mm) + water
What are the components of concrete?
cement + fine aggregates + coarse aggregates + water
What are aggregates?
Inert additives which can be bound together with cement to make concrete
What are the three main roles of adding aggregates to a cement?
-Can increase strength
-Can reduce weight
-Higher integrity
How do aggregates change a concretes strength?
-A concrete cannot be stronger than the aggregate, because it fails at its weakest point
-Need good quality, clean, strong aggregates
-Clay contamination tends to have bad effects
How do aggregates change a concretes weight?
Lightweight aggregates for lightweight concretes
How do aggregates change a concretes integrity?
Reduces thermal cracking (dilution of cement)
Why is water important in concrete?
-Required to make cement hydration reactions
-Makes concrete flow (increased slump)
What happens if too much water is added to a concrete?
-Delays setting/hardening
-Forms extra pores, which reduces durability and strength
Describe the flow of concrete?
Shear-thinning, which means it flows more readily when a force is applied, this is why mixing trucks are kept rotating.
Self-compacting concrete flows like a liquid with no vibration, this is achieved by adding chemicals.
What causes the shear-thinning nature of cement?
Needle shape of ettringite crystals
What causes plastic shrinkage cracking?
-Rapid evaporation from the surface makes the paste shrink
-Evaporation also causes drying shrinkage cracks
How can shrinkage and cracking be reduced?
Aggregate particles stay in place and prevent shrinkage that causes cracking/crazing
What causes plastic settlement?
Solid aggregate particles can sink through the paste, leaving water pockets under aggregates and reinforcing bars and cracks on the surface
What is an expected water/cement mass ratio for a regular concrete?
0.3-0.7
Name the main 6 non-Portland cements.
-Calcium aluminate cement (CAC)
-Calcium sulpho-aluminate cement (CSA)
-Magnesium oxychloride cement
-Magnesium phosphate cement
-Alkali-activated (geopolymer) cement
-Bitumen/Tar
What are the physical properties of Magnesium oxychloride cement?
-Very high early strength (>70 MPa after 3-7 days)
-Sensitive to water
-Useful for indoor floors, tiles, artificial ivory and billboard balls
What are the main physical properties of Alkali-activated (geopolymer) cement?
-Can use blast furnace slag or pozzolans
-60-90% less carbon emissions than Portland cement
-Need an alkaline solution
What is Bitumen?
A mixture of heavy organic molecules, solid at room temperature
What are the main physical properties of Bitumen?
-Used to bind stones/gravel together into solid hardened material
-Is technically a binder not a cement
-Use heat to soften and make flowable
