10- Building Construction- Concrete Construction Flashcards
_____ is the hardened form of cement produced from portland cement, coarse and fine aggregates, and water.
Concrete
Like masonry, concrete is strong in compression but weaker in tension. The ultimate compressive strength can range from ____ to ____ psi.
2,500 to 6,000 psi
Concrete beams are typically cast in the shape of a __. The wider area at the top permits the concrete to support a greater load.
Tee
Vertical reinforcing bars in concrete are known as _____ and are provided to resist the diagonal tension.
Stirrups
The technique of ______ is a more efficient use of concrete than ordinary reinforcing. This technique tightens the reinforcing steel, adding compressive stresses to the surrounding concrete. The compressive stresses counteract the tensile stresses from the applied load.
Prestressing
Two common methods of prestressing concrete are ______ and ______.
Pretensioning and Posttensioning
_______ Reinforcement (concrete) uses steel strands (cables) stretched between anchors producing a tensile force in the steel. Concrete is then placed around the steel strands and allowed to harden. After the concrete has hardened sufficiently, the force applied to the steel strands is released.
Pretensioning
_______ Reinforcement (concrete) uses reinforcing steel cables that are not tensioned until after the concrete has hardened to a certain strength. The forces that are produced in the process remain locked in the steel for the life of the assembly.
Posttensioning
Prestressed concrete systems may be more vulnerable to failure than ordinary reinforced concrete. The systems use reinforcing cables and rods made of high-strength steels that can yield at temperatures as low as ___F.
752*F
One differentiation in concrete applications is where it is cast and used.
_____ concrete is placed in forms and cured at a plant away from the job site.
_____ concrete is placed into forms at the building site as a wet mass and hardens in prepared forms.
Precast Concrete
Cast-in-place Concrete
Theoretically, properly cured concrete continues to harden indefinitely at a gradual rate; normal design strength is reached after __ days.
28
“28 day concrete”
The single most important factor in determining the ultimate strength of concrete is the ______ ratio.
Water-to-Cement
Hardening of concrete involves a chemical process known as ______, in which water combines with the particles of cement to form a microscopic gel. As the concrete hardens, this gel releases heat of hydration.
Hydration
In addition to maintaining proper moisture, concrete in the process of curing must be maintained at the correct temperature, ideally between __ and __F. Concrete cured at or above 100*F will not reach its proper strength. Concrete cured near freezing temperatures will harden more slowly.
Between 50 and 70 *F
The ____ Test uses a standard-sized cone-shaped mold and a sample of wet concrete. Its purpose is to check the moisture content of a batch of concrete.
Slump
