CONCRETE MATERIALS Technology of Material II TKS 4012 Prepared by

Overview  What is concrete made of?  Why do we use concrete?  How do we use concrete?  Where is concrete used?  Why is concrete often reinforced?  Why do we use solid waste as an aggregate in concrete?

Constituent Materials  Cement  Water  Coarse aggregate  Fine aggregate  Admixtures

Cement Cement is a building material made by grinding calcined limestone and clay into a fine powder. When mixed with water, it will harden as it undergoes chemical changes.

Cement (cont’d) Portland Cement: limestone, shale, and clay. Chemical Composition:  CaO (lime)  Al 2 O 3 (Alumina)  SO 3 (Sulfite)

Water We all know what water is …! In general, consumable water can be used in concrete making.

Coarse aggregate This is an aggregate that is usually close to ¼ inch (5 mm) in diameter or larger.

Fine aggregate This is an aggregate that is usually very small/fine, such as sand (< 5 mm).

Admixtures ASTM C 494 Descriptions of Admixtures Types: A : water reducing admixtures B : retarding admixtures C : accelerating admixtures D : water reducing & retarding admixtures E : water reducing & accelerating admixtures F : water reducing, high range & accelerating admixtures G : water reducing, high range & retarding admixtures

Concrete A mixture of two components: Paste (25-40%) Aggregates (60-75%) and Air

Paste Comprises of: a binder (cement) Water Entrapped air or purposely entrained air

Mortar Comprises of: a binder (cement) Fine aggregate Water

The chemical reaction of paste: 2(3CaO.SiO 2 ) + 6H 2 O 3CaO.2SiO 2.3H 2 O + 3Ca(OH) 2 2(3CaO.SiO 2 ) + 6H 2 O 3CaO.2SiO 2.3H 2 O + 3Ca(OH) 2 Where: CaO.SiO 2 : calsium silicate H 2 0: water CaO.SiO 2.H 2 O: tobermorite (hard) Ca(OH) 2 : calsium hydroxide (free) Chemical reaction

Aggregates Comprises of : Sand (fine aggregates) Gravel or crushed stone (coarse aggregates)

Volume distribution Percentage volume distribution of materials in concrete:

Mixing The main concern is characteristic compressive strength based on specific design codes. Manual or Machine?

Placing Considering about the height of fall to avoid segregation (pumping and vertical bucket). Compacting by using a vibrator or manual? Internal or external?

Curing Over time concrete will cure, which is a hardening process. Concrete has a 28 day curing time, this is the amount of time it takes to be considered completely cured.

Forms A form is the mold for setting concrete into a desired shape.

Why is concrete used? Economics  Inexpensive, readily available Material Properties  Long Lasting  Molded into a desired shape  Great insulator  Hard  Great Compressive Strength

Waste aggregates Why is it important to use solid waste as an aggregate in concrete?

Environmental Preservation New Material Properties  Recycled tires (crumb rubber) Insensitive to water  Broken Bricks Fire resistant  Plastic Greater resistance to freeze-thaw cycles  Glass, PVC, Wood Chips and several others Waste aggregates (cont’d)

Fresh Concrete Properties of Fresh Concrete: Workability Hydration Setting time Hardening Segregation Bleeding

Workability

Hardened Concrete Properties of hardened concrete: Strength (compressive & tensile) Unit Weight Resistance to freezing and thawing Permeability and water tightness Abrasion Resistance Volume Stability (creep & shrinkage) Control of cracking

Compressive strength

Influence factors Influence factors on compressive strength of concrete: Age Density w/c ratio Amount of cement Type of cement Type of aggregate

Types of concrete Based on its compressive strength:  Plain Concrete (< 10MPa)  Ordinary/Normal Concrete (10 – 30MPa)  Prestressed Concrete(30 – 40MPa)  High Performance Concrete/HPC(40 – 80MPa)  Ultra High Performance Concrete/UHPC (> 80MPa)

Types of Concrete (cont’d) Based on its unit weight: 1. Ultra Lightweight Concrete(< kg/m 3 ) for non structural 2. Lightweight Concrete(1.000 – kg/m 3 ) for lightweight structure 3. Normal Concrete(2.000 – kg/m 3 ) for structural 4.Heavyweight Concrete(> kg/m 3 ) for radiation shield structure

Any Questions? Thanks for your kind attention!