Concrete Mixture Classes and Requirements

Study Notes

Concrete Mixture Classes

Class AAA: Proportions of 1:1:2, often used for pre-stressed and post-tensioned structures.
Class AA: Proportions of 1:1.5:3, suitable for underwater retaining walls and shear walls.
Class A: Proportions of 1:2:4, used in footings, piers, columns, girders, beams, joists, and slabs.
Class B: Proportions of 1:2.5:5, appropriate for slabs on fill and non-load bearing walls.
Class C: Proportions of 1:3:6, commonly used for concrete plant boxes and parapet walls.
Class D: Proportions of 1:3.5:7, ideal for plant boxes, footpaths, and walkways.

Cement Bag Requirements

Class AA Concrete Mixture needs 12 bags of 40-kg cement or 9.5 bags of 50-kg cement.
Class A Concrete Mixture requires 9 bags of 40-kg cement or 7 bags of 50-kg cement.
Class B Concrete Mixture requires 7.5 bags of 40-kg cement or 6 bags of 50-kg cement.
Class C Concrete Mixture needs 6 bags of 40-kg cement or 5 bags of 50-kg cement.
Class D Concrete Mixture requires 5 bags of 40-kg cement or 4 bags of 50-kg cement.

Compressive Strength of Concrete

Class AA exhibits a strength of 4000 psi with a minimum compressive strength of 2400 psi for cylinders and 2800 psi for cubes.
Class A has a strength of 3500 psi with a minimum compressive strength of 2000 psi for cylinders and 2400 psi for cubes.
Class B has a strength of 3000 psi with a minimum compressive strength of 1600 psi for cylinders and 2000 psi for cubes.
Class C shows a strength of 2500 psi with a minimum of 1300 psi for cylinders and 1600 psi for cubes.
Class D has a strength of 2000 psi, with a minimum of 1000 psi for cylinders and 1200 psi for cubes.

Water Requirements

Class A Concrete requires 5 gallons of water per 40kg of cement.
Class B Concrete requires 5.75 gallons.
Class C Concrete uses 6.5 gallons.
Class D Concrete requires 7 gallons.

Cement Types and Characteristics

Portland Cement is a hydraulic cement made from clay and limestone, prized for its strength.
Types include:
- Type I (Normal): General construction.
- Type II (Moderate): Resistant to sulfates.
- Type III (High Early Strength): Cures faster, used in cold weather.
- Type IV (Low Heat): Generates less heat, ideal for massive structures.
- Type V (Sulfate Resisting): Reduced tricalcium aluminate content for sulfate resistance.

Cement Storage and Handling

Store cement at least 12 inches off the ground on a raised wooden floor.
Height of cement piles should not exceed 12 sacks.
Warehouse setting can cause lower layers to harden due to pressure.

Testing and Metrics

Slump test measures the consistency and workability of concrete.
Metal cone specifications for the slump test:
- 8" diameter bottom opening, 4" diameter top opening, 12" height.
Rod and compact concrete inside the cone 25 times during testing.
Minimum and maximum slumps vary by application:
- Reinforced foundation walls: 2"/5".
- Plain footings, caissons: 1"/4".
- Slabs and beams: 3"/6".
- Pavements and floors: 1"/3".

Composition of Portland Cement

Major components include Tricalcium Silicate, Dicalcium Silicate, and Tricalcium Aluminate, contributing to different strength and setting characteristics.

Additional Materials

Quicklime is calcium oxide, while hydraulic lime sets underwater.
Plaster of Paris is pure gypsum; hard wall plaster contains 39.5% impurities.
Masonry cement is a proprietary mix requiring only sand and water.

Historical Figures

Smeaton: Rediscovered hydraulic cement in 1756.
Aspdin: Invented Portland cement in 1824.

Description

This quiz covers the various classes of concrete mixtures, including their proportions and specific applications. It also details the cement bag requirements for each mixture class. Test your knowledge on concrete types and their uses in construction projects.