PREPARED BY:MARCIA C. BELCHER

CONSTRUCTION ENGINEERING TECHNOLOGY

Concrete: Fundamentals

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

Type IA, IIA, IIIA, IVA

“A” implies that air entraining is added to the portland cement

Cement Type Vs. Strength Gain

Temperature Vs. Cement Type

Effects of Moist Curing On Strength

Effects of Environmental Temperature on Strength Gain

W/C vs. Strength