CONCRETE MATERIALS Technology of Material II TKS 4012 Prepared by zacoeb@ub.ac.id 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? 1
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. 2
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. 3
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). 4
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 5
Paste Comprises of: a binder (cement) Water Entrapped air or purposely entrained air Mortar Comprises of: a binder (cement) Fine aggregate Water 6
Chemical reaction 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) Aggregates Comprises of : Sand (fine aggregates) Gravel or crushed stone (coarse aggregates) 7
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? 8
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. 9
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 10
Waste aggregates Why is it important to use solid waste as an aggregate in concrete? Waste aggregates (cont d) 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 11
Fresh Concrete Properties of Fresh Concrete: Workability Hydration Setting time Hardening Segregation Bleeding Workability 12
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 13
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: 1 Plain Concrete 2 Ordinary/Normal Concrete 3 Prestressed Concrete 4 High Performance Concrete/HPC 5 Ultra High Performance Concrete/UHPC (< 10MPa) (10 30MPa) (30 40MPa) (40 80MPa) (> 80MPa) 14
Types of Concrete (cont d) Based on its unit weight: 1. Ultra Lightweight Concrete (< 1.000 kg/m 3 ) for non structural 2. Lightweight Concrete (1.000 2.000 kg/m 3 ) for lightweight structure 3. Normal Concrete (2.000 3.000 kg/m 3 ) for structural 4. Heavyweight Concrete (> 3.000 kg/m 3 ) for radiation shield structure Any Questions? Thanks for your kind attention! 15