020301c Concret Mix Design Flashcards
The tensile strength of concrete is approximately 10% of the compressive strength. T or F
T
The concrete used in most construction projects is between ___ and ____
14 mPa to 35 mPa
A chemical reaction known as ____ occurs between the cement and water.
Hydration
Hydration is what causes the solidification of the plastic concrete into a stone-like mass. T or F
T
The cement paste, aggregate and reinforcing steel in reinforced concrete all have similar thermal expansion rates. T or F
T
Why does rebar have lugs or deformations?
For the concrete to bond to the steel
Why might cast in place concrete be more expensive than precast?
Because forms must be erected and stripped for each pour.
Is case-in-place quality harder to maintain than precast concrete?
Yes. It is often cast in an uncontrolled environment.
How is pre-stressed concrete achieved?
Post-tensioning or pre-tensioning.
Pre-stressed concrete allows members to have long, clear spans with a smaller cross-sectional area than that of traditional reinforced concrete. T or F
T
Does pre-stressed concrete reduce the weight of the building and the cost of construction. T or F
T
____ is concrete that had the consistency of plaster.
Shotcrete
Self-levelling gypsum concrete is used as a fire separation on floors of multi-storey wood frames residential structures and reduces the transition of sound between floors. T or F
T
Portland cement accounts for 7% to 15% of the volume of concrete. T or F
T
All Portland cements are _____ cements which set and harden through _______.
Hydraulic, hydration
Portland cement is a finely ground powder manufactured from a variety of raw materials. These materials can be?
Limestone, iron, silica, alumina, gypsum
Portland cement is a brand name. T or F
F
Portland cement is a fine grey powder made with ____ _____ and limestone.
Calcium silicate
______ _____ is a dry powder that, when mixed with water, forms the paste that binds aggregates together to form concrete.
Portland cement
Property had high compressive strength, is durable, permeable or watertight. T or F
T
Does Concrete has fire resistant and sound resistant qualities?
Yes
Concrete can withstand harsh elements and resist corrosive chemicals, decay and abrasives. T or F
T
A chemical reaction known as ______ occurs between the cement and water. This causes the solidification of the plastic concrete into s stone-like mass.
Hydration
Aggregates are usually gravel and sand that are graduated so that the voids between the particles are filled with smaller particles. T or F
T
To be at the most sound, cement must entirely cover the surface of each aggregate particle and fill any voids between the aggregates. T or F
T
The strength of concrete depends on the ratio of water to Portland cement. T or F
T
What is the normal range for concrete used in most construction projects?
14 MPa to 35 MPa (2300 psi and 5000 psi)
Cement is strong in compression but weak in ______.
Tension
What helps concrete resist tensile forces?
Reinforced steel such as rebar.
Why does concrete have lugs or deformations?
Increases the bond between steel and concrete.
What allow cement paste, aggregate and reinforcing steel in reinforced concrete to work together?
They have similar thermal expansion rates.
A chemical action takes place during hydration that may clean small amounts of rust and corrosion from the surface of the steel. T or F
T
Cast-in-place concrete tends to be more expensive and quality control is harder to maintain. T or F
T
How are architectural concrete finishes created?
Different colours and surface textures, ranging from urged to a smooth, ceramic-like finish.
What is the benefits of Pre-Stressed concrete?
Allows members to have long, clear spans with a smaller cross-sectional area than that of traditional reinforced concrete. This reduces the weight of the building and the cost of construction.
What are 3 reasons concrete is a good paving material?
- Can be used for architectural surfaces for sidewalks and patios and for non-slip surfaces.
- Durable surfaces that resists the grinding action of traffic.
- Withstand freeze-thaw cycles and de-icers.
For patterned concrete the face of the concrete form or casting bed is lined with plastic or rubber form liners. T or F
T
To achieve an exposed concrete surface the face form or surface of the concrete can be treated with a _____ that prevents the surface concrete from setting. After the base concrete sets, the surface is _____ washed leaving the aggregate exposed.
Retarder, pressure washed
What are some ways to achieve an exposed aggregate surface?
Sandblast, high pressure water jet to wash the mortar away from the aggregate before the concrete is completely set, grind the surface of the hardened concrete to expose the aggregates.
How does one attain a smooth terrazzo-like floor surface?
Grind the surface of hardened concrete to expose the aggregates.
What are the most common methods to colour concrete?
Dry shake colour gardeners, colour admixtures, pigments, chemical stains, and white and coloured cements.
Dry shakes are designed for colouring and hardening the surface of new concrete. T or F
T
_____ _____ is a powder material that is spread on the surface of the concrete at a predetermined rate.
Dry shake.
Dry shake colour hardeners are mixed into the fresh concrete paste at the surface and a colour sealed is sprayed onto the surface after the concrete has been given its final troweling. T or F
T
Colouring agents (synthetic pigment admixture) increases the strength, improves workability and disperses the pigment uniformly throughout the concrete mix. T or F
T
What is a one benefit and one detractor for using colouring agents opposed to dry shake colouring?
Colouring agents cost increases proportionately to the desired concrete thickness but if the surface is damaged the colour is not lost. This is not the case when using a dry shake, since only a thin layer of the concrete surface is coloured.
