Materials Flashcards
Hardwoods 6
Long-lasting Angiosperms (seed vessel) Longer to grow Most hardwood species are tropical Need to be managed sustainably Deciduous trees
Softwood 4
Gymnosperm (naked see)
60-120 years relatively shorter growth
1/3 of worlds wood / 80% of UK
From Conifers
How many types of Timber
30,000
Wood Properties 3
Low thermal conductivity - good heat storage
High strength - 2/3 of all houses timber frame
Low weight
Anisotropic
Different properties when measured in different ways
Wood stronger across the grain
Wood Conversion
Cut logs into sections
Finished by planing or sanding
Tree Workings
Trunk gives structural strength
Bark prevents mechanical damage
Radical rays move food into sapwood for storage
Potential Wood Damage
Fungi - Metabolising organic material (Wet/dry rot)
Insects
Fire Damage
Fire Retardants
Reduce flaming of surface
Slows it down
Impregnation with leach-resistant chemicals
Surface coatings.
Preserving Timber
Fungicides/Insecticides
Impregnation modification - Chemicals to fill gaps
Properties of Steel (6)
High Strength Good Ductility High Stiffness Suitable for prefabrication Highly recyclable Worked by sawing, drilling, flame cutting, welding bolting
Steel
Alloy of Iron and Carbon
0.4% carbon 2x strength
1% carbon 3x strength
More carbon incr tensile (hard) not strength more brittle.
Iron
Element Heated to 900 Allotropic Hematite/Magnetite Extracted with coal and limestone
Cast Iron
Remelting Pig Iron w/ steel and cast iron scrap
Finished product has a high carbon content
Pig Iron
Used to make Cast and Wrought Iron
4-5% Carbon
Wrought Iron
Pig Iron heated with Iron oxide in a furnace
Carbon/impurities react with oxygen to form slag
Cast Iron Properties
3-4% Carbon Better than Wrought Corrosion resistant Brittle Suitable for casting Not suitable for Hot working
Wrought Iron Properties
Low 0.15% High 0.5-1.5% Good Resistance die to oxide layer Reasonable tensile strength, Malleable and tough Can be forged, complex work Cannot be cast, tempered or welded
Uses of Steel
Hot or cold rolled sections
Off site quality control
Rapid assembly
Iron/Steel Corrosion
Destructive attacks by external elements
Water vapour (rust)/electrolysis/oxygen
Abrasion of protective coatings expose metal
Temperature change expan/cont may fracture coatings
Humidity > 70% will initiate rusting but occurs > 50%
Pollutants help hold moisture on the surface of the metal
Protective Coating
Painting - rust and mill scale must first be removed
Vitreous enamel - molten enamel form corro-resis coating
Plastic coatings - coating PVC, acrylic
Steel needs a zinc pretreatment
Zinc is used to galvanise steel
Zinc Coating
Spraying or dipping in molten zinc
Barrier to the environment
Better surface for welding/painting
Durability depends on thickness
Steel Reinforcement in Concrete
Take the tensile stresses away from concrete
Carry proportion of the compressive stresses
Control fire
Fire Protection Steel
Steel incombustible, strength reduced by high temps
Load bearing strength reduces
Structural integrity lost at 550
Intumescent paint, expand 25-30 times, 2 hour protection
Concrete composition
Cement, Sand, Aggregate
Slump Test
Determines workability on site
Indication of correct consistency
Concrete Accelerators
Increases reaction between water and cement, set faster
Calcium Chloride
Concrete Retarders
Decreases rate of setting
Reduces 28 day strength
Phosphates/hydroxycarboxylic acids
Water-resisting admixtures
Hydrophobic
Stearates or Oleates
Air-entraining Admixtures
Improve workability
Reduce risk of segregation
Increase frost resistance
Decrease compressive strength
Foaming Concrete
Low density
Concrete Failure
Chemical attack Frost - Freeze Thaw Abrasion Fire Movement – heat & moisture, creep Cracking/spalling from corrosion of steel reinforcement
Concrete Chemical Attack
Leaching
Sulphate Attack
Alkali-Silica Reaction
Carbonation
External Sulphate Attack
Water containing penetrates concrete Seawater - Sea defences Acid Rain Extensive cracking Expansion Loss of bond between cement paste and aggregate Loss of strength
Internal Sulphate Attack
Sulphate included in concrete when mixed
Sulphate rich aggregates
Screening and testing should prevent this
DEF
Delayed formation of the mineral ettringite
High early temps prevents normal formation of ettringite.
Expansion and cracking
ASR
Alkali-Silica Reaction
React high alkaline cement + reactive silica in aggregate
Gel produces takes on water and leads to cracking
Over time
HAC
High Alumina Cement
Calcium aluminates rather than silicates
Rapid strength development
However mineralogical conversion reduced strength
Increased vulnerability to chemical attack.
Steel Carbonation
Increases susceptibility to chloride attacks
Concrete Creep/Shrinkage
Long term deformation under sustained loads
Shrinkage depends on aggregate size
Concrete Repair
Epoxy resin
How Glass is made
High melting/viscosity reduced by adding sodium oxide
Reduces it from 1700
Reduces energy and cost of manufacture
Float Glass
Thinner 6mm or 0.4mm/25mm Molten glass poured on molten tin Floats on tin, evenly spread Thickness controlled by pour speed Annealing (control cooling) exit as 'fire' polished product Virtually parallel surfaces Can be tinted
How Float Glass is made
Raw Material Feed Melting Furnace Float Bath Cooling Lehr Continuous ribbon of glass Cross Cutters Large plate lift-of devices Small plate lift-of devices
5 Main Glass Groups
Soda-Lime Glass - Bulbs/Containers Quartz Glass - High melting Borosilicate glass - Chem resistant Lead glass - Low Melting radiation shielding Alumino-silicate glass - Glass fibre
Glass Properties
Light transmission • Refractive index Thermal properties Strength Hardness - abrasion resistance Durability - weathering Fire resistance
Gas Filled Glass
Argon gas
Lasts 15-20 years
Recycled Glass
Landfill tax doubled in 2009
Fibreglass insulation
Remelting
Fine Aggregate
4 Material Considerations
Suitability
Durability
Reliability
Sustainability
Triple Bottom Line
Social
Economic
Environmental
Construction Stat
50% of all materials globally used in construction
UK 200m tons of waste in 2012
Building Cycle
Extract Raw Materials Primary/Secondary Manufacture Construction Building Use End of life Demolish
Waste Hierarchy
Landfill Recover energy Recycle/Compost Re-use Reduce
4 R’s + D
Reduce Re-use Recycle Recovery - (energy) Disposal
OSP
Off Site Construciton
Manufacture away from place of installation
Standardisation/Pre-Assembly
Occur all year round increase productivity
Rapid on site construction/improve time predictability
Quality control
Non-Volumetric Construction
Assembled within a factory
Don’t enclose usable space, flat/two- dimensional
Volumetric Construction
Pre-assembled Pods (Kitchen/bathroom)
3 Dimensional space
Closed/Open Systems
Closed - Combine w/ components from same manufactur
Open - More Flexibility, can combine with others
Need to be standard Sizes
Why Prefabrication
Quickly made water tight, early installation of services
Some modular systems have services incorporated
Factory better quality control and in theory zero defects
Factory Fabrication
Quickly address skill shortages Greater build cost accuracy Reduce on-site time/injury Waste minimised Less damage to components/no on site storage Enable integration of BIM with more ease
Prefabrication Problems
Factory specific on-site foundations specific
Walter Segal Method
Huf Haus
Timber primary design and modular
Standardised - no waste, cut/alter material, reduce cost
Reduce wet trades, concrete plastering and bricklaying
5 trained men in 6 days
EIA’s
BREEAM
Environmental Impact Assessment
Met environmental standards
Social/economic impact considered
Portland Cement
1824 - Joseph Aspdin
Heated mixture of clay & chalk gave hydraulic cement
Mix burnt limestone + clay more calcined until CO2 gone
Material ground into fine cement powder
Portland Cement Properties
Excellent strength
Stronger than Roman cement
5x stronger than hydraulic lime
Portland Cement Development
Rotary Kilns
Addition of gypsum control setting
Use of ball mills to grind clinker and raw materials
Hydraulic Lime
Non Hydraulic Lime
Limestone with reactive clay, hydration similar properties Portland cement
Higher Clay stronger and less permeable 18-25%
No clay non hydraulic
5 Types of Cement
Portland Cement Portland-composite Cement Blast furnace Cement Pozzolanic Cement Composite Cement
Sustainability in Concrete
Reduce amount
Low embodied C - Heat eff, diff fuels, Clinker substitution
Use of recycled materials
Carbon capture and storage
Thermosetting
Thermoplastics
Elastomers
Synthetic polymers can be:
Thermosetting - harden on heat and do not re-melt
Thermoplastics - soften and melt on heating
Elastomers - Rubber retain original shape
4 Mineral Constitutions of Cement
Alite
Belite
Aluminate
Ferrite
Cement Clinker
Clinker a nodular materials
Large rotating drum containing steel balls
Gypsum ground in to control setting properties
Clinker Process
- Clinker cools, liquid crystal = aluminate, ferrite low belite
- Fast cool good - lots hydraulic react silicates + small, intergrown, aluminate and ferrite crystals.
- Slow cool less hydraulic react silicates + coarse crystals of aluminate and ferrite - over-large aluminate crystals can lead to errattic seeng of cement.
- Very slow cool, alite decomposes to belite + free lime.
Thermoplastic Example
PTFE
ETFE
Thermosetting Example
Phenolic Resins
Amino Acids
Polyester Resins
Epoxy Resin
Thermoset Adhesive Good electrical insulator Hard / brittle unless reinforced Resists chemicals well
Polyester Resin
Thermoset Stiff / hard / brittle unless laminated Good electrical insulator Resists chemicals well Casting and encapsulation Bonding of other materials
PTFE
Thermoplastic Resistant to chemical attack Light in weight Not brittle Inexpensive Adaptable Cause minimal tissue reaction
ETFE
Thermoplastic High corrosion resistance Strength over a wide temperature range High melting temperature, Excellent chemical / electrical / high-energy radiation resis
Elastomeric
Undergo large deformations / high elasticity
Large chain molecules twisted/coiled random manner
Rubber
Additives
Added to improve desired properties
Plasticisers - increase flexibility
Fillers - Reduce cost, improve fire resistance, chalk/sand
Pigments - Dyes/pigments added
Stabilisers - Reduce degradation by absorbing UV light
Flame retardants
Heat Stabilisers - work same under increased heat
Admixture
Modify setting/hardening properties of cement Accelerators Air-entraining - lightweight blocks Retarding Water reducing - plasticisers
Clay and Clinker
From clay reactants in the kiln of Lime, Silica, Alumina and iron produce the four mineral
Glass additions
Soda - reduce melting temp of silica
Flurospa and soldium sulphate - reduce bubbles
Calcium/magnesium - stronger glass
Paint component
Pigment - colour
Binder - bind to surface
Solvent - control properties of paint for application
Extender - go further
Plastic Sustainability
Un recyclable plastics
Reduce different types, easier to recycle
Unfired Brick
Air dried Reduces shrinkage Improves strength Low embodied energy Easier to recycle No moisture resistance more sustainable
Stone
Igneous - Granite
Metamorphic - Marble (limestone)/slate (clay)
Sedimentary - Limestone/clay
Brick Creating
Press, wire cut, moulded Dried Kiln 3 different temperatures 100 water, 400 burning carbon matter, 900 sintering
