Concrete Flashcards
Prestressing beams
Supplementary cementitious materials
Added to concrete as a substitute for some portion of the Portland cement to acheive a range of benefits
Classified as either pozzolans or hydraulic cements
Enhances the sustainability of concrete by reducing reliance on energy-intensive Portland cement
Pozzolans
Materials that react with the calcium hydroxide in wet cement to form cementing compounds
Includes:
Fly ash
Silica fume
Natural pozzolans
High-reactivity metakaolin
Fly ash
A fine powder that is a waste product from coal-fired power plants
Increases concrete strength, sulfate resistance
Decreases permeability
Reduces temperature rise during curing, the amount of mixing water needed, and concrete drying shrinkage
Improves pump ability and workability of concrete
Silica fume / micro silica
A powder that is approximately 100 times finer than Portland cement, consisting mostly of silicon dioxide. Byproduct of electronic semiconductor chip manufacturing
Produces extremely high-strength concrete that also has very low permeability
Natural pozzolans
Derived from shales or clays
Reduces the internal temperature of curing concrete, the reactivity of concrete with aggregates containing sulfates
Improved the workability of concrete
High-reactivity metakaolin
White-colored pozzolan that enhances the brilliance of white or colored concrete
Improves tha materials workability, strength, and density
Well suited for exposed architectural concrete applications where appearance and finish quality are critical
Blast furnace slag / slag cement
A hydraulic cement; reacts directly with water to form a cementitious compound
Byproduct of iron manufacture
Improve workability
Increase strength
Reduce permeability, temperature rise during curing
Improve sulfate resistance
Air-entraining admixtures
Increase the workability of the wet concrete, reduce freeze-thaw damage in hardened concrete, and, when used in large amounts, create a very light-weight no structural concrete with thermal insulating properties
Water-reducing admixtures
Allow a reduction in the amount of mixing water while retaining he same workability, which results in higher-strength concrete
High-range water-reducing admixtures / superplasticizers
Organic compounds that transform still concrete mix into one that flows freely into the forms. Not used with to facilitate placement of concrete under difficult circumstances or to reduce the water content of a concrete mix so as to increase its strength
Accelerating admixtures
Cause concrete to cure more rapidly
Restarting admixtures
Slow its curing to allow more time for working with the wet concrete
Workability agents
Improve the plasticity of wet concrete to make it easier to place in forms and finish
Includes possolans and air-entraining admixtures, along with certina fly ashes and organic compounds
Shrinkage-reducing admixtures
Reduce drying shrinkage and the cracking that results therefrom
Corrosion inhibitors
Used to reduce rusting or reinforcing steel in structures that are exposed to road deciding salts or other corrosion-causing chemicals
Freeze protection admixtures
Allow concrete to cure satisfactorily at temperatures as low as 20 degrees F
Extended set-control admixtures
May be used t delay the curing reaction in concrete for any period up to several days
Includes 2 opponents:
The stabilizer, added at the time of ignition mixing, defers the onset of curing indefinitely
The activator, added when desired, reinitiates the curing process
Lower water-cement ratios make concrete
That is denser and stronger and that shrinks less during curing
Reinforcing steel in concrete
The concrete is in compression on the top half, the bottom has to force, the steel is resisting the tension
The combined action of concrete and steel in reinforced concrete elements is such that the reinforcing steel is usually loaded acidly in tension or compression, and occasionally in shear, but never in bending
In a continuous concrete beam
The bottom of the beam is in tension at the midspace, and the top of the beams is in tension at points of support (girders, columns, or walls)
Vertical bars / columns bars
Share the compressive loads with the concrete, resist tensile stresses that may occur in columns, and impart ductility to the column
Column ties
Small steel bars wrapped around the vertical bars to prevent them from buckling under load: inward buckling is prevented by the concrete core of the column, outward buckling by the ties
Precast concrete formwork
Wood and fiberglass forms can be used up to 50 times
Concrete and steel forms can be used hundreds or thousands of times
