cement and concrete Flashcards
(38 cards)
Concrete as a prolific material
- Most widely used building material globally
- 2nd most-used substance after water
- 70% of the world’s population lives in a structure that contains concrete
Concrete vs. cement
Cement
* Binding agent
* The grey powder (mixed with water to create concrete)
* Comprised of calcium silicates and smaller amounts of iron oxide, aluminium oxide + gypsum
Concrete
* Building material (synthetic stone) with the structural characteristics of stone (strong in compression, weak in tension)
* Made by mixing cement, water + aggregates (e.g. sand/gravel)
Primary reasons for concrete’s popularity as a construction material (3)
- Durability
- Strength
- Low cost
General cement ingredients (4 + 1)
and role in cement’s key qualities
Calcium oxide(s)
* Made from limestone
* Gives cement its strength + binding qualities
Silica
* Hardening agent, increases durability against elements
Alumina / aluminum oxide
* Gives cement resistance to high temperatures and chemicals (like sulphides + acids)
Iron oxide
* Provides grey colour, adds strength
+ Heated in a kiln, mixed with gypsum
Cement types and abbreviations (5)
- Ordinary Portland Cement (OPC)
- Portland Pozzolana Cement (PPC)
- Portland Slag Cement (PSC)
- Sulphate-Resistant Cement
- White Cement
Ordinary Portland Cement (OPC)
- Most common
- Clinker + gypsum
- Strong + versatile - used for constructing buildings, bridges, roads + infrastructure
Portland Pozzolana Cement (PPC)
- A blend of OPC + pozzolanic materials (e.g. volcanic ash)
- More workable - ideal for hydraulic + marine structures as well as mass concrete work
Portland Slag Cement (PSC)
- Ground OPC added to granulated blast-furnace slag
- High resistance to chemicals - suitable for both general + marine construction
Sulphate-Resistant Cement
- Formulated to resist sulphate attacks
- Ideal for coastal regions / locations w sulphate-rich soil or effluents (waste water)
White Cement
- Lower in iron
- Distinctive white colour
- Decorative applications (precast features, architectural finishes, coloured concrete)
Concrete ingredients (4 + 2 optional)
and role in fabrication
Cement
* Primary binding agent
* Type gives concrete many of its properties
Water
* Mixing + hardening agent
* Must be free from contaminants
Air
* Improves pumpability + workability
* Prevents freeze-thaw damage (by creating air pockets that allow water to expand without cracking the material)
Aggregates
* Make up 60-80% of the mixture, provides stability + strength
* Coarse (gravel, crushed stone) / Fine (sand, always < 20mm approx.)
OPTIONAL
Additives
* Chemicals to change concrete’s properties
Supplementary Cementitious Materials (SCMs)
* Materials that improve strength +/ durability
* e.g. fly ash, slag
Examples of concrete additives (6)
- Platicisers (workability)
- Retarders (increases setting time)
- Accelerators (decreases setting time)
- Bonding Agents
- Colours
- Hardeners
Cement mix proportion
(of main 4 elements)
CEMENT - 1
SAND - 3
GRAVEL - 3
WATER - 1/2
Concrete types (main 3) (11)
and brief applications
Standard
* Used for most construction
High-strength
* Designed for heavy loads (e.g. high-rise foundations)
Lightweight
* Roof/precast elements
High-performance
* Hard conditions - superior durability and strength
**Reinforced **
* Contains steel rebar - improves strength
**Precast **
* Factory-made, assembled onsite, used for components like walls + beams
Decorative
* Coloured/textured for aesthetic purposes
Self-compacting
* Flows easily, fills complex forms eithout needing vibration
Shotcrete
* Sprayable - onto surfaces, used for tunnels/pools
Pervious
* Allows water drainage - stormwater management
Eco-friendly
* Contains recycled materials
Constraint: locality of concrete construction
- Concrete must be made near application
- Hardens in about 90 minutes
- Encourages the use of local materials (particularly aggregates like sand/gravel) to reduce transport costs
Constraint: material weight
Concrete needs to be very well supported due to its density and weight
Requires robust structural systems and design
Brief history of cement/concrete
3000 BC
* Ancient Egypt + Northern China
* Early cement use - pyramids, the Great Wall
600 BC
* Ancient Romans - form of concrete called “opus caementicium (lime + volcanic ash)
- 14AD
- Roman architectural advancements - Panthenon, aqueducts
Mid 19th century
* Reinforced concrete - Joseph Monier
1889
* First large-scale use of reinforced concrete in France - the Garabit Viaduct
1904
* Concrete blocks for construction purposes
1930s
* Precast concrete - mass production of concrete elements
1960s-1980s
* Advanced technologies - high-strength + lightweight
2025
* Continuing innovations - sustainable, ‘smart’ concrete technologies
Case - Pantheon, Rome
- Concrete dome built in 1280 - still existing
- 43w x 43h - largest dome built for centuries
- Decorative patterning hollows the roof - reducing weight
Case - Dom-ino
- Le Corbusier, 1914
- Famous for modular, open structure + floorplan
- Reinforced concrete was able to span larger spaces - less columns required to support - open-plan becomes bpossible
5 pts of architecture
(Le Corbusier)
- Pilotis (columns) - open circulation
- Flat-roof terrace - usable roofs, extend living spaces
- Open floor plans - removal of load-bearing walls
- Horizontal windows - increase daylight
- Free facades - exteriors able to be unrelated to the interior
Tadao Ando
- Contemporary architect focussed on the versatility + simplicity of concrete
- Highlighting the natural properties of concrete to emphasise texture and light filtration through form
Reinforced concrete,
purpose + pre/post-tensioned
Inclusion of rebar - very tensile
Compensates for concrete’s inability to withstand tension
Enables larger spans of concrete - absorbs tension
Pre-tensioned + post-tensioned concrete
Steel mesh/cables are tightened at each end of a concrete beam
Limitations of reinforced concrete
Steel must be suitably covered by concrete - fire and corrosion protection
Case - Twig House
- TCL Architects
- Free standing concrete walls - landscape design
- Free standing concrete stairs
