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
