Chp 6 Flashcards
(25 cards)
Define the following terms:
- Cement paste
- Mortar
- Concrete
Cement paste: Cement + water.
Mortar: Cement paste + sand
Concrete: Cement paste + Sand + aggregate
What are the 2 basic materials used in the production of cement?
- Calcareous: CaO such as limestone
- Argillaceous: Silica and alumina, can be obtained from shale, clay…
What are the types of Portland Cement?
There are 5 types of portland cement:
1- Normal cement
2- Moderate sulfate resistance
3- Early Strength
4-Low heat of hydration
5-High sulfate resistance
What is Soundness of Cement?
it refers to the ability of cement to retain its volume after setting.
How is Soudness measured?
It is measured using the autoclave test where it is exposed to heat and pressure. The increase in volume should not surpass 0.8% for the cement to be be acceptable.
What are the different types of voids?
- Interlayer hydration space: It is between CH gel. It does not effect the properties of strength and durability.
- Cappilary Voids
When w/c ratio is too high.
Esentially, this water will evaporate creating voids. The more water we add, the more the voids. This effects strength and durability.
-Trapped Voids
During mixing, air will get into concrete. We vibrate and compact the concrete to avoid this issue. - Entrained air
Microscopic bubbles causd by ad mixtures that improve the durability and helps in freeing conditions.
Why are ready mix trucks prohibted from disposing their waste anywhere?
Because their waste is highly alkaline, thus it would effect the ph of the soil.
Can sea water be used in cocnrete mix?
Yes it can be used if the cooncrete is not reinforced with steel rebars as sea water corrodes te steel rebards.
What are Addmixtures for concrete?
Add mixtures are subtances added to concrete to improve a specefic quality of concrete.
List all the Addmixtures:
- Air Entrainers
- Water reducers
- Accelerator
- Retarder
- Hydration controller
-Specialty add mixtures
Describe Air entrainers.
it is an add mixture that increases the durability of concrete. It creates voids that allow for the expansion of concrete in freezing conditions why avoiding creating internal stresses which reduce the durability of concrete. However, air entrainment reduces the strength of concrete. They also increase the workability of concrete.
Describe water reducer.
They are admixture that increases the workability of concrete without adding water to it.
What are the benefits of water reducers?
- increase strength
- reduce cost
- increase workability
What are Retarders?
It is an add-mixture that delays setting time. It is used generally in hot conditions as usually in hot conditions the concrete sets rapidly.
Define SCMs
They are materials used as partial replacement of portland cement to improve both fresh and hardened concrete properties.
What are the benefits of using water reducers?
There are 3 benefits:
- Increase the compressive strength of concrete by adding water reducer, using the same amount of cement, and decreasing the
amount of water.
- Increase the workability by adding water reducer, and using the same amounts of cement and water.
- Reduce cost by adding a water reducer, and decreasing the quantity of both water and cement to maintain the w/c ratio.
What are accelerators?
They are an add mixture used yo develop the early strength of concrete at a faster rate.
Why are accelerators used?
They are used to increase the rate of strength gain, reduce the operation time, reduce curing time.
What are hydration-control admixtures?
These admixtures can stop and reactivate the hydration process of concrete.
They consist of two parts: a stabilizer and an activator. Adding the stabilizer completely stops the hydration of the cementing materials for up to 72 hours,
while adding the activator to the stabilized concrete reestablishes normal hydration
and setting.
List all type of SCMs.
- fly ash
- slag cement
- silica fume
- natural pozzolans
what is silica fume and the effect of silica fume?
Silica fume is an SCM that is a by-product of the production of silicon metal. They increase strength and durability.
What is slag cement and what are its effects?
Cement Slag cement is made from iron blast furnace slag. They can increase the strength of concrete.
What are the effects of natural pozzolans?
- Increase workability
- Increase strength
- Increase durability
- decrease premability
What are the 2 Cement Production Processes ?
There are 2 processes, the wet and dry process.
The wet process is more water and energy consumptive. It is more expensive.
It also causes water pollution.
