Chapter 10 Flashcards
Aggregates make up
A large percentage of the total volume of concrete
3 types of admixtures and their purposes
Shale or clinker- reduce the density of the concrete
Superplasticizer- produce a mixture that flows more freely
Coloring- Added for aesthetic or after reasons
4 Primary advantages of concrete
Produced from locally available and low cost raw materials
Fundamentally non combustible
Performs well under mild to moderate fire conditions
Good insulating properties
concrete has good compression strength however has poor ______ strength and is reinforced when that stress is applied
Tensile
Reinforced concrete unltimate compressive strength can range from
2,500 to 6,000 PSI
Ordinary reinforcing uses
Steel bars placed in the formwork then wet concrete placed in the formwork around the bars
Most commonly used size rebar
5 -0.625 inches
vertical reinforcing bars are know as _______ and are provided to resit the diagonal tension
Prestressing technique is
Preloads the reinforcing steel adding compressive stress to the surrounding concrete
Two Common methods of prestressing are
Pretensioning
Posttensioning
Pretensions reinforcement uses
Steel strands stretched between anchors producing a tensile force the the steel, concrete is then placed around the steel strands and allowed to harden. Once harden the strands are released causing a compression force
Postentensioning reinforcement uses
Steel cables that are not tensioned untill after the concrete has hardened.
cutting through reinforcing steel with saw or torch is particular dangerous in posttension concrete because
the steel is not bonded to the concrete the stell strands are stretcher like giant rubber bands
The systems use reinforcing cables and rods can yield temperatures as low as
752 F
Concretes normal design strength is reached
After 28 days
the single most important factor in determining the ultimate strength of concretes is
Water to cement ration
Hardening of concrete involves a chemical process is know as
Hydration
during the hardening of concrete heat is given off by the chemical process
Heat of hydration
The Process of curing must be maintained at the correct temperature
Ideally between 50 and 70F
Slump test
Uses a standard sized cone shape mold and a sample of wet concrete to check the moisture content of a batch
separate test that uses small test cylinders of a concrete batch to determine the compression strength of that batch is know as
Compression testing
Concrete structural systems can have fire resistance ratings from
1 to 4 hours
the fire resistance of a concrete assembly is affect by 5 Variables which are
concrete density
concrete thickness
concrete quality
supported load
depth of concrete cover over the reinforcing bars
Slab concrete ranges in thickness from
6 to 12 inches
