Concrete

Unit 24

Carpentry and Building Construction

Concrete Ingredients• Cement

– Measured by the sack = 94 lbs. = 1 cu. Ft.

• Water• Fine Aggregate

– Sand or other suitable material up to ¼” Dia.

• Coarse Aggregate– Gravel– Crushed Stone– Material larger than ¼” Dia.

Admixtures

• Change the characteristics or workability of concrete

• Air-entraining admixtures

• Retarding admixtures

• Accelerating admixtures

• Water-reducing admixtures

• Superplasticizing admixtures

Testing the Mix

• Slump Test– Concrete is placed in a conical shape and

measured to see how much it loses its shape

Placing the Concrete

• Should be poured continuously when possible

• Keep level• Vibrate or spade the concrete to remove air

bubbles• Protect the concrete from rapid drying• Keep concrete above freezing temperatures

to cure

Reinforcing

• Welded-wire fabric

• Steel bars

• Reinforced Concrete has excellent compression strength

Estimating Concrete

• Sold by the cubic yard ( 3’ x 3’ x 3’ )

• To calculate, figure the volume needed. – T x W x L

• If volume calculated = cubic feet, divide by 27– I.e. 4” x 20’ x 40’ = 267 cubic feet– 267/27 = 10 cubic yards