Concrete

FEBRUARY 6, 2015 (FRIDAY) TOPIC: CONCRETE

3. Drying/ shrinkage- water evaporates from concrete (concrete shrinks slightly)

History 8th century BC -Romans discovered concrete Pozzolana- from Pozzouli (town in southern Italy)

1. lime

Sources: a. limestone b. marble c. marl d. seashells

1824 -Joseph Aspidin patented Portland cement after English Portland limestone 1850’s -reinforced concrete was developed -Thaddeus Hyatt made and tested reinforced concrete beams

2. iron 3. silica 4. alumina Sources of 2-4: a. clay b. shale

Process of Making Concrete

1867 -Joseph Monier patented concrete flower pots 1920’s -Eugene Freyssinet established scientific design of pre-stressed concrete

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Concrete

Aggregates

1. 2. 3. 4. 5.

Crushing, grinding, proportioning, grinding Rotating kiln (1400-1600 0C Clinker Cooling Pulverizing

Types of Cement

Composition of Concrete:

Cement - fine gray powder

Composition of Cement

Water

Fine Aggregates -sand Coarse Aggregates - gravel or crushed stone

Process of Curing (28 days) 1. Hydration- cement and water combine, forming crystals 2. Heat of hydration- heat is produced

A. Type 1 - most widely used - 28 days - normal - used for most practices f construction B. Type 2 - combines type 4 and 5 - moderate resistance to sulfate attack C. Type 3 - cures before 28 days - ideal for cold weather - high early strength (used in precast elements and where high early strength is required) D. Type 4 - low heat of hydration used in massive structures such as dams, where heat is emitted may raise temperature E. Type 5 - used when concrete will be in contact with water that has high concentration of sulfates.

Note: Cement particle size affects performance. The finer the particle, the shorter the curing process is.

Approximate slump values: Walls and columns: 4”-5” Beams: 4”-5” Slabs: 3”-4”

Hardened Concrete Properties Aggregates - 65%-80% volume of concrete - must be well graded 1. Dusty, muddy aggregates - contaminate cement paste with particles that weaken strength 2. Chemicals - corrosion of steel - retardation of curing process - weakening of concrete

Aggregate Sizing Aggregates should be no larger than ¾” of clear spacing between bars or 1/3” the depth of a slab. Fine aggregates (sand) - passes through No. 4 sieve (1/4” in center) Coarse aggregates - ¾” Thick walls: 1.5” Dam: up to 6”

Properties of Concrete 1. Fresh (plastic state) concrete properties 2. Hardened concrete properties

Fresh (plastic state) concrete properties 1. Workability - able to retain homogeneity (nonsegregation of particles) - ease with which concrete can be placed and compacted in the form with the minimum loss of consistency and homogeneity. Slump Test - test concrete workability - acceptable slump: 2”– 6”

1. Durability - test: cast test cylinders 2. Strength

Determining Quality of Concrete Required Function Columns, beams, slabs Paving and floor slabs Paving, exterior concrete walls Tanks, dams, walls

Compressiv Flatness, su High degree Watertightn

Cement- Water Ratio: 0.45- 0.60 by weight

Concret e Class AA A B C D

Ratio of Concrete Components 1: 1: 1: 1: 1:

½: 3 2: 4 2 ½: 5 3: 6 3 ½: 7

Strength in PSI (after 28 days) 4000300020001000 50

50 25-50 10-25

Pipe Diameter (mm)

Gallons of Water

13 20 25 32 38 50

20 38 80 110 170 223