prepared by: marcia c. belcher construction engineering technology concrete: fundamentals
TRANSCRIPT
Common Uses
Slabs (roadways, bridges, airstrips)Beams & ColumnsParapets (highways)Piers (structures, bridges)Pipe Foundations (large and small)Retaining Structures (dams)
Special Needs of Concrete
Exposure & use conditions require attention in mix design.
Marine environment De-icing salt exposure Freeze-thaw Hi sulfate exposure Early use of structure (bridge decks) Very thick pours (homogenous pours like earth
dams & parapets) Very slender elements (pipe)
What Can We Do To Modify Concrete Design
Add plasticizers to increase workability
Use larger aggregates to increase strength
Reduce W/C ratio to increase strength
Use air entrainment to improve durability
Use pozzolans to improve chloride resistance
Use “accelerators” increase cure rate for hi early strength
Use set retarders or fly ash to decrease internal temperature & reduce shrinkage cracking
Portland Cement Types
The ingredients in the Portland cement can be modified to produce various properties.
These are called “Types”
Portland Cement Types – Type I
General Purpose
Most commonly used
No special curing, setting or resistance characteristics
Suitable where no special properties are required
Type II
Type II cement contains no more than 8% tricalcium aluminate (C3A) for moderate sulfate resistance.
Increases resistance to sulfate attack over Type I
Lower heat of hydration
Used for mass pours such as bridge piers
Used where ground water contains high sulfate levels
Type III – High Early Strength
Similar to Type I cements except it is ground finer
This increased hydration rate.
Results in rapid curing & higher early strengths.
Results in higher heat of hydration
Used in cold weather concreting
Used when early strength is required
Type IV
Hi levels of dicalcium silicate and tetracalcium aluminoferrite
Used in massive concrete structures where heat generated from hydration must be minimized.
Low heat of hydration = slow strength development
Used for mass pours such as dams where shrinkage problems may occur