Theory

Question 1

Copper and its alloys

Answer 1

High thermal and electrical conductivity
Easy weldable
Easy deformable
Easy castable
Corrosion resistant
Properties
- High electrical conductivity
- High thermal conductivity
- High corrosion resistance
- Good ductility
Application:
- Only second to silver for electrical conductance
+ Electronic products
+ Copper finish parts/ trolley wires

Question 2

Aluminium and its alloys

Answer 2

Low density
Low elastic modulus
Very high specific properties
High corrosion resistance
Ductility

Question 3

Tensile test

Answer 3

Determine different properties of the material
Usually the sample is deformed to fracture with a gradually increasing tensile load applied uniaxially along the axis of the specimen
During the test, the specimen undergoes an elongation at a constant rate; the instantaneous applied load and the elongation of the specimen are monitored using respectively a load cell and an extensometer

Question 4

Compressive test

Answer 4

Conducted in a manner similar to the tensile test, except that the force is compressive and the specimen contracts along the direction of the stress
By convention, a compressive force is taken to be negative, which yields a negative stress

Question 5

Elastic deformation

Answer 5

The degree to which a structure deforms or strains depends on the magnitude of an imposed stress.
Deformation in which stress and strain are proportional is called Elastic Deformation
The slope of the linear segment corresponds to the modulus of elasticity E
This modulus maybe thought as stiffness, or a material’s resistance to elastic deformation
The greater the modulus, the stiffer the material, or the smaller the elastic strain
Elastic deformation is non permanent, which means that when the applied load is released, the piece returns to its original shape

Question 6

Poisson ratio

Answer 6

The amount of reduction in the size respect to the pulling is so-called Poisson ratio
-> ratio between the deformation in terms of strength in x or y in respect to the deformation in the z direction where the stress is applied
(Reduction in size -> negative)

Question 7

Yield strength

Answer 7

The point in which the stress-strain curve goes from elastic to plastic area is called proportional limit
Beyond this point, yielding occurs
In some cases, the position of this point cannot be determined precisely so that we construct a parallel line to elastic portion of the cureve at 0,002 off set to the right
The stress corresponding to the intersection of this line and the stress-strain curve as it bend over in the plastic region is defined as the yield strength

Question 8

What is yield strength of ductile material? How is it measured? Howe is it evaluated?

Answer 8

*Draw the stress-strain curve of Ductile
Ductility is a measure of the degree of plastic deformation that has been sustained at fracture. A material that experience very little or no plastic deformation upon fracture is termed brittle
Ductility may be expressed quantitatively as either Percent Elongation or Percent reduction in area.
%EL = (Lf-Lo / Lo) x 100
%RA = (Ao-Af / Af) x 100

Question 9

What is the main constituents of concrete? Describe the role of each constituent in terms of the final mecanical resistance of hardened concrete

Answer 9

Concrete is a mixture of PORTLAND CEMENT, COARSE AGGREGATES, FINE AGGREGATES AND WATER. together with any ADMIXTURE which may be add to modify the placing and curing processes or ultimate mechanical properties
CEMENT
- important ingrdient since the concrete is in contact with soil that has lots of sulphite -> adding consideration to cement material
AGGREGATES:
- 80% weight of the cured mass
- strength of concrete depends on strength of aggregate particles and strength of hardened paste
- Compresssive strength: higher than concrete strength 40-120MPa
- Void: amount of air space between aggregate particles
- Moisture content: amount of water in aggregates
ADMIXTURE:
- Added to plastic concrete to change 1 or more properties of Fresh or Hardened concrete
- FRESH concrete: influence its workability, setting time and heat of hydration
- HARDENED concrete: influence its durability and strength
WATER:
- Determines the composition of a concrete mix, given the workability or ease of placement and compaction of the fluidmix

Question 10

Characteristic of ceramic materials

Answer 10

Compression resistance
Very low resistance to tensile and bending
Brittleness
High hardness
High resistance to heat
Good thermal and electrical insulation
Chemical inertness
Low thermal shock resistance

Question 11

Properties of wood as a construction material. Explain the anisotropy in the mechanical properties of wood and how they change with different percentage of moisture in wood

Answer 11

Properties of wood:
- Mechanical properties:
+ Compressive strength
+ Tensile strength
+ Wear resistance
+ Hardness
- Excellent thermal insulation
- High specific heat
- Anisotropic thermal coefficient
- Good electric/acoustic insulation
Anisotropy
- Stronger along the grain then across it
- The 12% humidity tensile strength different depends on parallel or perpendicular

Question 12

Describe the main characteristic of THERMOPLASTIC & THERMOSETTING polymers and underline the differences between them. Give at least 1 example of polymer and possible application in architecture for each of the two categories

Answer 12

THERMOPLASTIC
- Can be linear or cross-linked
- Made up by limited length macromolecules, linear or cross-linked, with secondary bondings between the chians
- Soften with heat and solidify when cooling in a reversible way, without structure alterations
- Exist in a solid state in amorphous form or in semicrystalline state, this later prvide a higher resistance to temperature and chemical agents
- They produce genereally big injection, at lower T than for other polymers, with high production rates
- Example: Polysterene, Plexiglass
THERMOSETTING
- cross-linked
- Have better chemical and mechanical characteristicss
- Primary bonds, covalent also between chians
- They can be worked only one, before cross-linking
- In case of further heatings, they decompose
- Higher mechanical strength than thermoplastic
- Two categories: elastomers (rubbers) and thermosets at high crosslinking rate
- Example: polisher

Question 13

How is it possible to classify a steel? How do properties change?

Answer 13

CLASSIFICATION OF STEELS
In terms of CHEMICAL COMPOSITION
- Carbon steels
- Low alloyed steels
- High alloyed steels
In terms of QUALITY REQUIREMENTS
- Standard steels
- Quality steels
- Special steels
In terms of APPLICATIONS
- General purposes construction steels
- Stainless steels
- Special construction steels
- Tool steels

PROPERTIES CHANGE
- Process during which the alleys undergo proper thermal treatmentss in order to provide the requested properties and mechanical characteristics
- Made up with
1. Heating up to T
2. Keeping at T
3. Cooling from T to room temperature
- Main thermal treatments of steels includew
1. Annealing
2. Normallizing
3. Quenching + (tempering)
4. Surface heating and quenching

Question 14

What is SELF-COMPACTING CONCRETE? What are the main characteristic?

Answer 14

Product with high fluidity: they can be put into work without any compaction applied
- No segregation
- Low W/C ratio, given the presence of super plasticizers
Passing ability through reduced areas such as those typical of metallic grids
High fluidity -> slump test is meaningless -> other testing method will be applied
Only my means of corrent propotion of mixture components, it is possible to achieve NO BEDDING also in a very fluidity condition:
- Reduce amount of coarse aggregate
- Reduce the maximum diameter of coarse aggregate
- High volume of fines
- Proper closing of water and super-plasticizers
- Addition of VISCOSITY MODYFYING AGENTS (VMA)
Using in high level of reinforcing.

Question 15

What is an Elastomer? Compare its mechanical behaviour with a typical polymer’s one on a stress-strain graph

Answer 15

Highly elastic polymer material
In the stress-strain curve, normally it’s a very low curve goes linear then grows at some point and breaks -> “rubber-like behavior”

Question 16

Material fracture

Answer 16

Simple fracture is the separation of a body into 2 or more pieces in response to an imposed stress and at a temperature thart are low relative to the melting temperature
1. Brittle fracture
- Take place in elastic area
- Typical of ceramics
- Take place rapidly and spontaneously
2. Ductile fracture:
- Exhibits sustaintial plastic deformation
- Typical of metals
- Slow propagation of the crack, with high plastic deformation
3. Fatigue
- Occurs as consequence of the repeated application of a load with limited intensity
- Usually occures for metals and plastics
4. Creep
- Occur as consequence of a plastic deformation determined by a constant load applied at a given temperature (metals)

Question 17

Heat capacity

Answer 17

• A material in its solid state, once heated, shows an increase in T: thermal energy absorption
• Heat capacity is the amount of energy necessary to increase the T of one mole of material of 1 degree
• Sometimes the specific heat (c) is used to represemt the heat capacity per mass unit
• Specific heat depends on the conditions with which the heat is transferred

Question 18

Thermal conductivity

Answer 18

The phenomenon by which heat is transported from high to low temperature regions of a substance
The property that characterized the ability of a material to transfer heat is the thermal conductivity
Heat is transported in solid materials by
- Lattice vibration wave (phonons)
- Free electrons

Question 19

Visual light? Visual appearance of insulators, metals, and semiconductors

Answer 19

Light that can be detected by the human eye has wavelengths in the range 450nm to 650nm is called visible light
The human’s eyes can detect light of many different colors where each color is detected with different efficiency
A material’s appearance and color depend on the interaction between light with the electron configuration of the material
Normally
- High resistivity material (insulators) are transparent
- High conductivity materials (metals) are “metallic luster” and are opaque
- Semiconductors can be opaque or transparent
- This and their color depend on the material band gap

Question 20

Inorganic binders

Answer 20

They are constituted by the blend of inorganic oxides obtained by firing natural rocks and usually in form of fine powders
After being mixed with water, they produced a plastic mass (“fresh paste”) that can easily to work with mold
After setting and hardening reactions, the paste transformed in a stone like material (hardened paste)
- SETTING: phase transformation during which the paste progressively loose its ability to be molded. Its duration from few minus to ten hours (depends on binder)
-HARDENING: phase transformation after setting during which the paste assume its definitive mechanical properties as a stone-like material duration is indefinite
Inorganic binders are classified into 2 groups
- NON hydraulic (or “air”) binder: contact with air is necessary for hardening
- HYDRAULIC binders: hardening occurs without the contact with air
Binders are used to produce:
- Binder paste: water + binder
- Mortar: water + binder + fine aggregate as a finishing or joining material for bricks on tiles
- Concrete: water + binder + fine aggregate + coarse aggregate for construction

Question 21

What is Plaster? How it is manufacturing? Types of Plaster

Answer 21

Plastering, based on LIME
Originally used to strengthen and seal surfaces, in case of combustible material, to afford some fire protection
Manufacturing:
- Rock gypsum is mined, crushed into fine powder
- Natural mineral may be white or discolored pale pink, grey or brown due to small quantities of impurities, which do not affect the product
- On heating to temperature in the range 130-170 degree, water is driven off the hydrated gypsum; the type of plaster produced in largely dependent upon the extent of this dehydration process
Two types of Plaster
- Plaster of Paris
- Retarded hemi-hydrate gypsum plaster

Question 22

Additives in traditional gypsum plaster

Answer 22

The admixture used in traditional gypsum plasters were setting retarders, hardeners, and traditional setting retarders and hardeners. They are using to add characteristics to the paste.
The admixtures can be classified as:
- Dispersant: to facilitate the dispersion of products in the liquid phase
- Wetting: to favor the enveloping of solid constituents by decreasing the stress between solid and liquid phase
- Thickeners: to increase the consistency of the products in the paste
- Fungicides and anti-moulds: to stop the attack of fungi or moulds
- Anti-sedimentation: to prevent sedimentation of the solid constituents during stocking
- Antifoam: to prevent formation of foam during application
- Anti-skin: to prevent the formation of skins on the surface
- Drying: to shorten the drying time

Question 23

Plasterboard and Special Plaster

Answer 23

Plasterboard consists of aa gypsum core banded to strong paper liners. Most wallboard have one light surface for direct decorative or plaster skin and one grey surface
The decorative surface may be either tapered or square
The standard board sizes are 1200 and 900mm wide to coordinate with timber or metal stud partitioning system
Special plaster:
- RENOVATING plaster: use where walls have been stripped of existing plaster during the sucessful installation of a new damp-proof course. Should not use in permanently damp location.
- PROJECTION plaster: spray onto the background from a projection machine as a continouos ribbon. Should be build up with required thickness, flattened surface, NOT under freezing, or dry conditions
- ACOUSTIC plaster: has a higher sound absorption than standard ones. Alluminium is added to create bubbles of hydrogen gas
- X-RAY plaster: retarded hemi-hydrated plaster used as an undercoating plaster in hospitals where the protection from X-ray is required
- VOC plaster

Question 24

Lime

Answer 24

Building lime
- Air or non-hydraulic lime
+ Calcium Lime CL
. Quicklime Q
. Hydrated lime S
+ Dolomitic Lime DL
. Quicklime Q
. Completely hydrated lime S2
. Semi-hydrated lime S1
- Hydraulic lime
+ Formulated lime FL
+ Natural hydraulic lime NHL
+ Hydraulic lime HL

Question 25

Hydraulic lime

Answer 25

Manufactured from chalk or limestone containing various proportion of clay impurities
The materials produced have some of the properties of Portland cement, and partially harden through hydration process
Hydraulic limes rich in clay impurities are more hydraulic and set more rapidly than those with only a low silica and alumina content
Natural hydraulic lime NHL are traditionally categorized as freebly, moderately or eminently hydraulic depending on their clay content
Hydraulic lime HL is produced by blending lime with other constituents such as cement, blas furnance slag for fly ash
Hydraulic lime may be used for interior lime washes, and also for fixing glass bricks where a flexble binding agent with minimum shrinkage is required.

Question 26

Portland cement, Setting and hardening

Answer 26

Was named after the Isle of Portland, in the English channel where it first produced in 1800s
Since then, a number of developments were made
3 ways to process, depending on raw material used and their water content at extraction
All involve the decarbonisation of calcium carbonate, sintering at the point of incipient fusion, the resuting calcium oxide with the clay and iron oxide
- Semi wet process
- Semi dry process
- Dry process
When mixed with water, Portland cement form a paste which sets and hardens as a result of various chemical reaction between the cementitous compounds and water
The setting and hardening process enhance when excess moisture is present
Portland cement hardens under water, only a small amount of of added water is required for the chemical hydration to hydrated calcium cilicate
The additional water is needed to ensure the workability of the mix
It is necessary to control the amount of water content in the mix since if it is not enough, the evaporation will leave the capillary pores to the concrete and mortar products
Increasing 1% of void means reducing 6% of strength.

Question 27

Different types of cements

Answer 27

WHITE PORTLAND CEMENT
- Virtually free of iron oxide and other impurities, which impact to the grey color
- China clay and limestone are used and the kiln is fired with natural gas
- Up to 5% of white titanium oxide pigment may be added to enhance the whiteness
- Twice the price compare to the equivalent grey product
- Typical applications: rendering, cast stone, precase

SULPHATE-RESISTING PORTLAND CEMENT
- Suitable for concrete and mortar in contact with soils and ground water

VERY LOW-HEAT SPECIAL CEMENT
- Appropriate to use in mass concrete, where rapid internal evolution of heat may cause cracking
- Contain higher amount of dicalcium silicate -> hardens and evolves heat more slowly
- Typical application: massive constructiono but not for bridges and buildings

MASONRY CEMENTS
- Alternative to Portland cement plus hydrated lime or plasticizer
- Weaker mortars, contain water-retaining mineral constituents
- Typical application: rendering, inorganic pigment

PORTLAND SLAG AND BLAST FURNANCE CEMENTS
- By product of iron making in steel industry
- Combination between Portland cement and appropriate aggregates makes a durable concrete
- Sulphate attake is reduced by decreasing in tricalcium alumnae content

Question 28

Reinforce concrete

Answer 28

• Strong in compression, with crushing strengths typically range 20-40 MPa, and up to 100 MPa for high-strength concretes
• Tensile strength of concrete is usually only 10% of the compressive strength
  Stell is universally accepted reinforcing material, as it is strong in tension, forms a good bond and has a similar coefficient of thermal expansion to concrete
• Concrete: no useful tensile strength
• Reinforcing steel: tensile strength
• Theory of steel location: “place reinforcing steel where the concrete is in tension”

Question 29

Different between Concret and Mortars

Answer 29

CONCRETE: Cement + fine aggregates + coarse aggregates
- Self-compacting
- Light
- High performance
MORTARS: Cement + fine aggregates + sand
- Joining also referred to as bedding mortars
- For plastering
- For repointing also referred to as restoration mortars

Question 30

Mortars

Answer 30

For finishing purposes (plaster)
- With protection purposes -> hygeinic functions, easthetic and environmental prodection
- For outdoor:
. Resistant to aggression derivving from atmospheric agent
. Mortars use only air lime -> it is possible to have very dry atmospher condition in the first month after setting
- For outdoor:
. Good workability, easy smoothening and no cracking
Bedding bricks and masonry blocks
- High workability
- Capable of absorbing dimensional variation
- Easy brick placing
- Good adhesion to bricks and masonry
- Good resistance to water and environment
For restoration
FRESH MORTARS
- Workability
- Time setting for place in work
- Air content
HARDENED MORTARS
- Bending and compression resistance
- Adhesion to substrate
- Dimensional stability
- Water absorption due to capillary
- Permeability to water and vapor
- Thermal conductivity
FOR RESTORATION
- Alcalinity
- Resistance to aggressive agents

Question 31

Sulphate attacks

Answer 31

Most active at the temperature below 15 degree. It occurs in damp conditions in the presence of ground water sulphat and limestone within the aggregate, causing decomposition of the concrete into a soft friable material
It can be “external” or “internal”
- EXTERNAL: due to penetration of sulphate in solution, in groundwater for ex into the concrete from outsite
- INTERNAL: a soluble source being incorporated into the concrete at the time of mixing, gypsum in the aggregate, for ex
Sulphate are frequently presence in soils but the rate of sulphate attack is depending on the content of ground water
The presence of sodium or magnesium sulphate in solution is more critical than that of calcium sulphate, which is relatively insoluble
This material occes a greater volume than the original ticalcium allumnae, therefore, expansion causes cracking, loss of strength and increased vulnerability for sulphate attake
The use of SULPHATE RESISTING Portland cement or combinations of Portland cement and fly ash or granulated blast furnance slag resuce the risk of attack.
Sources that cause sulphate attack:
- Sea water
- Oxifation of sulfide minerals in clay
- Bacterial action in sewers
- In masonry, sulphate present in bricks and can gradually released over a long period of time especially where sulphates are concentrated due to moisture movement.

Question 32

Alkali-silica reaction

Answer 32

May occur between cements containing sodium or potassium alkalis and any active silica within the aggregate.
In reverse cases, expansion of the gel produced by chemical reaction causes map cracking of the concrete, which is characterized by a random network of very fine cracks bounded by a few larger ones.
Aggregates are defined as having low, normal or high reactivity.
The risk of alkali-silica reaction when using normal ractivity aggregates can be controlled by restricting the alkali content of the Portland cement to maximum of 0,5%.
Alkali-silica reaction can occur in the presence of some moisture

Question 33

Acid attack

Answer 33

Gas pollution, typically deriving from combustion processes
- CO2, NP2, SO2
In presence of water create acid substances which can attack hardened concrete
- Typical case -> CO2 acid attack
CARBONATION
- Carbon dioxide from the atmosphere is slowly absorbed into moist concrete and reacts with the calcium hydroxide content to form calcium carbonate
- The process occurs mainly at the surface and only penetrates very slowly into the bulk material. The rate of penetration is dependent upon the porosity of the concrete, the temperature and humidity.
- It becomes problematic only when concrete surrounding steel reinforcement is affected
- Carbonation turns strong alkaline hydrated clement into an almost neutral medium in which steel reinforcement will corrode rapidly if subjected to moisture.
- Good-quality dense concrete may only show carbonation to a depth of 5-10mm after 50 years
- Low-strength permeable concrete may carbonate to a depth of 25mm within 10 years.

Question 34

Corrosion of reinforcement and stell

Answer 34

REINFORCEMENT
- Carbonation -> pH reduction -> deprivation of the reinforcements
- Chloride attacks
+ Marine environment, dicing salts: NaCl, CaCl2
+ Deterioration of passivating layer on the top of steel -> corrosion
- Deterioration from carbonation -> all over
- Deterioration from chlorides -> both all over and localized
- Two phases in the corrosion of reinforcements: INITIATION and PROPAGATION
Worst possible condition:
- De-passivation of reinforces
- Availability of oxygen
- Humid environment
Formation of rust
- Pull out of concrete layer -> volume of the products of corrosion in the range of 2-6 times > volume of concrete

STEEL
- Structural consequences:
+ Reduction of the bearing area of streel reinforces
-> decrease in rupture strength, fatigue resistance, deformation
- Cracking in the concrete
-> Danger of de-anchoring of steel reinforces
-> Increase in the corrosion rate
-> Concrete pull out

Question 35

Rocks types

Answer 35

All rocks are classified into 3 groups according to the natural processes by which they were produced within or non the Earth’s surface
Place of origin should be detailed as much as possible including location of quarry, it’s nearest town and the region, country

IGNEOUS ROCKS
- The oldest, form by the solidification of the molten core of the Earth or magma
- Denpends on solidification occured slowly within the Earth’s crust or rapidly at the surface.
- They are defined as: plutonic (sloow cooling from the molten state allowed large crystal to grow) and volcanic (fine-grained)
- High-silica-content magma produce acid rocks (Granite)
- Low-silica content forms basic rocks (Bassalt)

SEDIMENTARY ROCKS
- Produced by the weathering and erosion of older rocks.
- Weathering action by water, ice and wind breaks the rocks down into small fragments which are then carried by river and sorted into size and nature by water action
- Limestone rocks -> limestone (organic sandstone, crystallized limestone, dolomitic limestones), dolomite
+ siliceous -> sandstone (calcareous sandstone, siliceous sandstone, ferruginous sandstone, dolomitic sandstone)
+ sulphate -> gypsum
+ admixture -> clay, tuff
- The natural bedding places associated with the formation of the deposits may be thick or thin but are potentially weak

METAMORPHIC ROCKS
- Formed by recrystallisation of older rocks, when subjected to intense heat or pressure or both, within the Earth’s crust
- Clay is metamorphosed to slate, limestone to marble and sandstone to quartzite
- Processes occuring at high T: 300-800 degree and pressure -> recrystallization -> very often oriented crystals -> schistosity
+ Slate
+ Marble
+ Quartzite

Question 36

Properties of stones

Answer 36

POROSITY
- Variable according to the material taken into account
- Ranging from 1% vol to 10% vol
- Porosity related to: water absorption -> degradation -> density -> thermal insulation
DENSITY
- From 2,5 g/cm3 to 1g/cm3
MECHANICAL PROPERTIES
- Compressive strength, bending strength, wearing resistance
- Usually brittle, for higher impact resistance -> igneous effusive rocksk
- Water resistance -> floow -> hardness and surface finishing
THERMAL PROPERTIES
- Low thermal conductivity
- High porosity -> higher thermal insulation
DURABILITY AND DETERIORATION
Main agents causing deterioration:
- Soluble salt action
- Atmospheric pollution
- Frost
- Corrosion of metal components
- Poor ddesign or workmanship

Question 37

Characteristic of ceramic materials

Answer 37

• Compression resistance
• Very low resistance to tensile and bending
• Brittleness
• High hardness
• High resistance to heat
• Good thermal and electrical insulation
• Chemical inertness
• Low thermal shock resistance

Question 38

Classification of ceramics

Answer 38

TRADITIONAL: bricks, tiles gypsum and cements refractories
- Tiles
- Sanitary fixtures
- Tableware
- Bricks
- Refractories

ADVANCED:
- Bio ceramics
- Electrical and technical porcelain
- Ceramics for electronics
- Catalyzes
- Special refractories

Question 39

Clay (keranos)

Answer 39

The term “ceramic” comes from the Greek meaning “burn stuff”, indicating the desirable properties of these materials are normally achieved through a high-temperature heat treatment process called FIRING (or sintering)
Natural clay is made up of
- Aluminosilicate hydrated
- Oxides and hydro-oxides of Fe, K, Al, Si
- Carbonates of Ca, Mg, Fe
Clay produced by weathering igneous rocks, typically granite, which is composed mainly of feldspar, an alumino-silicate mineral
- PRIMARY CLAYS: produced within the vicinity of the parent rock, pure material, less plastic and more vulnerable to distortion and craking on firing. KAOLIN is the purest clay
- SECONDARY CLAYS: transported by water, have higher degree of plasticity, and fire to buff or brown color depending on the nature content of incorporated oxides. Characterized by a narrower size distribution and more oriented particulate strudcture
Most common clay minerals used in manufacture of building materials: keolin, illite
Clay crystals are generally hexagonal in form, and in pure kaolin, the crystals are built up of alternating layers of alumina and silica
Admired with water: providing plastic behavior which is easy to be mold
Clays are:
- Aboundant and rather cheap
- Hydrplastic
Typical composition of clay products:
- 50% Clay + 25% Quartz (filling material: cheap, hard, intert, high T melting) + 25% Feldsphate (melting agent: low melting point)

Question 40

Durability of ceramic materials

Answer 40

Residual porosity -> penetration of water
Porous ceramics: open and interconnected porosity
- Freezing-thawing degradation
- Transportation of salts and/or solubilization
- Presece of free lime -> swell cracking
- Surface abrasion -> walking surfaces
- Biological degradation
- Corrosion deriving from metallic inserts

Question 41

Bricks

Answer 41

• Generally made in clay (but also in concrete_
• Common, facing or engineering
  COMMON BRICKS
• No visual finish, usually used for general building work where brickwork will be rendered, plastered or unseen from the finished one
  ENGINEERING BRICKS
• Dense and vitreous, with specific load-bearing characteristics and low water absorption
• Used to support heavy loads, also in positions where the effects of impact damage, water absorption or chemical attack need to be minimized
• Normally reds or blues and more expensive than other machine made facing bricks because of their higher firing temperature
  FACING BRICKS
• Manufactured and selected to give an attractive finish. The particular color, which may be uniform or multicolored, results from the blend of clay used as the firing conditions
• Surface may be smooth, textures or sand faced as required
• The most visual brick where it is pleasing and durable finish is required

Question 42

Main properties of glasses

Answer 42

• Transparent
• Fragile
• Recyclable
• Low tensile resistance
• Low impact resistance
• Cheap

Question 43

Amorphous

Answer 43

Amourphous or glassy material: obtained through a progressive increase in the viscosity of liquid, which has not been able to crystalline during cooling
Amorphous structures are thermodynamically metastable: they tend to transform to crystals if the thermodynamic and cynetic conditions are favorable
The phase transitions solid-liquid does not exist: the bongs in amorphous solid do not break all at the same T and there is no precise melting T
The main difference between amorphous solid and liquid: liquid show a bigger atomic and higher free volume
Amorphous structure is characterized by the absence of order at a long distance and by the absence of melting T
In amorphous structures, there is an ordered structure at a very short rage
The amorphous state is not stable
If it is heated up to a proper temperature, it will become crystalline
To get the amorphous structure, it is necessary to cool down the liquid with high cooling rates
It is needed to know the viscosity as function of T

Question 44

Amorphous material types

Answer 44

General definition of glass: any material which in proper condition generates an amorphous state
1. Ceramics: in organic oxides -> “traditional glasses”
- Inorganic fluorides -> fluoride glasses
- Tellurium oxide -> tellurium glasses
2. Metals: “metalic glasses”
3. Organic compounds: glycerin, glucose (caramel)
4. Polymers: polymers very often show amorphous areas (PET, Plexiglas,..)
5. …etc..: sulfur, selenium, phosphorus

Question 45

Reinforced glasses

Answer 45

TEMPERED GLASS
- Up to 4 or 5 times stronger than standard annealed glass of the same thickness
- Produced by subjecting pre-heated annealed glass at 650 degree gto rapid surface cooling
- Cannot be cut or work, all the necessary action must be completed in advanced of the toughening process
- If broken, it shatters into small granules which are not causeing serious injuries

LAMINATED GLASS
- Produce by bonding 2 or more layers of glass together with plastic sheet interlayer.
- The low-viscosity resin is more versatile, as it allows for the manufacture of curve laminates or in corporation of patterned glass
- If the glass is cracked, they do not splintering or disintergration since they are helded with interlayer
- May be defined as safety glass
- The resistant impact may be increased by increasing the number of glass layer
- To prevent spalling, the rear flace of bullet-resistant glass may be seated with a scratch-resistant polyester film and for fire protection

FIRE RESISTANT GLASS
- The ability to confrom to the criteria of integrity and insulation within a fire is measured as fire resistance. To ensure the performance in fire, it is depending on the whole glazing system and not a glass only

Question 46

What is polymer and how is there structure?

Answer 46

Polymer are defined as organic compounds formed by a set of molecules of big dimensions and high molecular weight
Each of ther macromolecules is made by the repetition of structural entities called repeat units, bonded with covalent bands: such entities are called monomers
- MONOMER: substance whose molecules, relatively simple, can react in order to form chains linked with covalent primary bongs so to form macromolecules
Natural polymers: ruber, resins, etc

STRUCTURE
Macromolecules: linear or cross-linked chains of units repeated for n times (n= degree of polymerization)
Chemical bonds in polymers can be of two different types
- Bonds inside the chain (INTRA-molecular): primary, strong
- Bond among the chains (INTER-molecular)
+ secondary, weak, as
. Van der Waals for Thermoplastics
. Hydrogen for Thermoplastics
+ covalent, strong for Thermosetting

Question 47

Polymers additives

Answer 47

PLASTICIZERS
- Polymeric materials which are added in order to improve some characteristics and decrease the costs
- They improve flexibility, decreasing the attractive forces between the chains. Must be neither volatile, dissolve in solvents or instable at light or hear

REINFORCING AGENTS
- They improve the tensile strength, bending, wear, the impact and T resistance.
- They are made up particles, long or short fibers, homogenerously dispersed or concentrated in mostly stressed areas

FILLERS
- They reduce the cose and may also increase the thermal resistance, dimensional stability, abrasion resistance

LUBRICANTS
- Improve workability by improving flowability in the mold

PIGMENT AND COLORANTS
- Added for aesthetic purposes

SWELLING AGENTS
STABILIZERS
HARDENING AGENTS OR INHIBITORS

Question 48

Properties of construction steel and what s COR-TEN steel?

Answer 48

PROPERTIES
- Yield strength
- Ductility
- Weldability
- Tendency to plastic deformation

COR-TEN steels
- CORrosion resistance TENsile strength
- Low allyed steel
- Formation of a passivating layer, occuring only in particular conditions:
+ exposure at atmosphere
+ alternated wet-dry cycles
+ absence of water stagnation and of permanent contact with water
- Behaves as a standard Carbon steel

Question 49

Stainless steeels

Answer 49

As chromium is added to steels, the corrosion resistance increases progressively due to the formation of a thin protective film so called passive layer.
With an addition of 12% Cr, steels have good resistant to atmospheric corrosion
How ever, of all steel types, the stainless grades are the most diverse and complex in terms of composition, microstructure and mechanical properties
Different possible structures:
- Martensitic
- Ferrific
- Austenitic
- Precipication hardening
- Duplex
- Superduplex

Question 50

Properties of aluminium bronzes

Answer 50

High strength, resistance to wear and fatigue
Self-healing surface film of aluminium oxide, excellent corrosion resistance
Tensile strength increases with increased belta phase while ductility drops off
Increasing Al content -> increased tensile strength

Question 51

Corrosion and its defininf the environment

Answer 51

Corrosion can lead to failures in plant infrastructure and machines which are usually costly to repair, costly in terms of last or contaminated product, environmental damage and human safety
Some infrastructure requires maintenance in schedules, some just regular repainting and occasional inspection of electrical and plumbing lines
Environment rules:
1. Moist air is more corrosive than dry air
2. Hot air is more corrosive than cold air
3. Hot water is more corrosive than cold water
4. Polluted air is more corrosive than clean air
5. Acids are more corrosive than bases to steels
6. Salts water is more corrosive than fresh water
7. Stainless steel will outlast ordinary steel
8. No corrosion will occur in vacuum even at very high tempurature

Question 52

What is composites?

Answer 52

A composite is usually defined as a multiphase material that is artficially made, as opposed to one that occurs or forms naturally
The constituent phases must be chemically dissimilar and separeated by a distinct interface
Many composite materials are composed of just 2 phases; one is termed the matrix, which is continuous and the dispersed phase, surrounds the other phase
Man-made composite materials: 2 (at least) components
- Matrix
- Reinforcement
Three different froups of matrix:
- Polymer
- Metal
- Ceramic
Combination
- Polymer-polymer fiber-reinforced plastic
- Polymer-ceramic fiberglass
- Polymer-metal
- Metal-metal iron, aluminium
- Metal-ceramic aluminum
- Metal-polymer
- Ceramic-ceramic concrete

Question 53

Matrix and reinforcement of composite

Answer 53

MATRIX
Made from metal, polymer or ceramic
Continuous phase
Some ductility is desirable
Functions:
- Binds the reinforcements together
- Mechanically supporting the reinforcements
- Load transfer to the reinforcements
- Protect the reinforcements from surface damage due to abrasion or chemical attacks
- High bonding strength between fiber and matrix is important

REINFORCEMENT
Fiber
- Generally circular in cross-section, but can also be in form of tubular, rectangle and hexagonal
- Fibers used can either continuous (long length) or discontinuous (short length)

Particles and flacks
. Particles
- an important material form for metals and ceramics range in size from microscopic to macroscopic
- occurs in cemented carbides
. Flakes
- two-dimensional particles

Carbon
- a combination of graphite- has a tensile strength 3-5 times stronger than stell and has density = 1/4 steel

Boron
- Very high elastic modulus, but its high cost limits it application to aerospace components

Ceramics
- SiC and Al2O3 are the main fiber material among ceramics
- Both have high elastic modulus and can be used to strengthen low-density, low-modulus metals

Metals
- Steel filaments, used as reinforcing fiber in plastics