Flashcards
Concrete is produced from
Portland Cement course and fine aggregates and water
The aggregates used in concrete are
Inert mineral ingredients that reduce the amount of cement that would otherwise be needed
Aggregate
Gravel stone sand or other inert material used in concrete these materials may be fine of course
Coarse aggregate
Gravel or stone
Fine aggregate
Sand
Aggregates make up a
Large percentage of the total volume of concrete
Concrete must be Cured in order to reach
It’s proper strength
Curing fresh concrete requires
Correct hydration and temperature control
Improper curing methods will negatively affect
The finished surface of the concrete as well as it’s strength
Hardening of concrete involves a chemical process known as
Hydration
As concrete hardens the gel gives of heat which is known as
Heat of hydration
Because hydration involves water proper curing requires
That the concrete be kept moist until it reaches its desired strength
Moist curing of concrete produces
A stronger concrete
Concrete can be kept moist by several techniques including
Sprinkling it with water, ponding, or covering it with a plastic film
In addition to maintaining proper moisture concrete that is curing must be maintained at the correct temperature ideally between
50-70 degrees F
Concrete that is cured at or above 100 degrees Fahrenheit will
Not reach its proper strength
Concrete cured near freezing temperatures will
Harden more slowly
In massive concrete structures the heat of hydration generated can
Adversely affect the final strength of the concrete
Concrete can be cooled using
Cold water during curing or using chilled water in the mixing process
During the curing process Concrete will
Shrink slightly
Theoretically properly cured concrete continues the to harden indefinitely at a gradual rate however normal design strength is reached
After 28 days
Different types of concrete Can be produced for specific purposes this is accomplished by varying the ingredients or adding chemicals to the concrete mixture these are generally known as
Admixtures
The density of concrete can be reduced by using a lighter weight aggregate such as
Shale or clinker
An admixture known as superplastizer can be used to produce
A mixture that flows more freely