MATERIALS

components of cement paste components of mortar components of concrete

air, water and cement cement and fine aggregate fine and coarse aggregates, and admixtures

raw materials of portland cement

clay, shales, limestone, chalk, iron ore, gypsum

manufacture of portland cement

1. collect raw materials such as limestone, clay and shale 2. grind raw materials into fine powder 3. mix in predetermined proportions 4. burn in large rotary kiln at 1400 degree and partially fuses into clinker 5. clinker cool and grind to fine powder with gypsum added 6. resulting product is commercial portland cement

Weathering steel

1. combination of alloying elements selected to provide special type of oxide coating after prolonged exposure to atmosphere. 2. develop resistance to atmospheric corrosion from four to eight times than plain carbon steel 3. exposure to atmosphere: develop tight adhering oxide coating that acts as barrier to moisture and oxygen to prevent further corrosion. damaged coating will heal itself.

Factors affecting fracture type

1. nature and condition of material 2. type of stress applied 3. rate of stress application 4. temperature and environmental conditions 5. component geometry and surface condition 6. nature and size of internal flaws

Supplementary cementitious materials

1. particle size smaller/similar to cement 2. add as concrete ingredients for property modification of concrete 3. environmental and economic benefit 4. common scm: fly ash, silica fume, slag

Steel strengthening mechanisms - recrystallisation

1. process where new strain-free grains are nucleared and grow 2. strain-hardening: plastic deformation below recrystallisation temperature where resistance to further deformation increase with increase deformation and dislocations. 3. strain-hardened: decrease ductility and toughness 4. materials strengthened this way cannot be joined by welding without soft annealing material in weld vicinity

What makes concrete a suitable construction material?

1. production ease 2. mouldability 3. durable 4. fire resistance 5. tailorable properties

Properties of scm

1. reduce overall heat of hydration and thermal cracking 2. reduce porosity and permeability of concrete 3. increase ultimate strength 4. improve durability and workability

Growth defects

1. shakes: occur during growth and seasoning - three varieties: 1. cup shakes 2. star shakes 3. radial shakes 2. fissures and pockets: occur during growth 3. knots: result of distortion of grain at joints between trunk and branches - high stress raises occur around bending and tension 4. reaction wood: forms when tree tries to restore displaced stem or branch - hardwoods: tension wood - softwoods: compression wood

Asphalt concrete requirements

1. stiffness: load spreading ability 2. fatigue resistance: ability to bend repeatedly without cracking - thick layer: stiff - thin layer: flexible 3. deformation resistance: resistance to excessive deformation under load deformation form: - rutting from mix densification - lateral movement influenced by binder properties 4. durability: disintegration resistance - major considerations: air voids and moisture damage - requires dense gradation of moisture-resistant aggregate, high degree compaction, thick asphalt film 5. workability: ease of placement and compaction 6. skid resistance: ability to provide skid resistance under all environmental conditions - require smaller sized hard aggregate for wearing course, and sufficient air voids to avoid bleeding

Factors on selection of structural steel

1. tensile and yield strength required 2. toughness and ductility 3. availability and cost 4. arbitrary local conditions

Durability influencing factors

1. timber species 2. seasoned timber condition 3. service environment 4. treatment received to improve resistance to fungal and insect attack 5. regular maintenance

Asphalt behaviour

1. viscosity-temperature relationship: increase temperature, decrease viscosity 2. visco-elastic behaviour: - high temperature + sustained load = viscous - low temperature + rapid load = elastic - intermediate = elastic and non-elastic response 3. aging behaviour: - mix at high temperature - evaporation or oxidation of oils

Steel reinforcement for concrete

All structural concrete contains steel reinforcement in form of bars or welded mesh to compensate for low tensile strength of concrete. 0.2% carbon, 0.8% manganese and 0.15% silicon 'B': Bar '500': yield stress 'A, B, C': ductility class min. elongation at max force: A: 2.5% B: 5.0% C: 7.5%

Methods to improve steel performance

1. Alloying: grain refinement through precipitation hardening with addition of carbide or nitride forming elements 2. Strain-hardening: generation and concentration of dislocation at grain boundaries 3. Heat-treatment: achieve very fine-grained microstructure and additional grain boundaries

Iron-carbon alloy characteristics

1. Changes in composition and mechanical properties affected by changes in carbon content in annealed plain carbon steels 2. strengthening increase resistance to yielding or plastic deformation by changing microstructure that impede motion of dislocations 3. strengthened through mechanisms: (1) introduction of interstitial and substitutional atoms (alloying) (2) generation and concentration of dislocations (work/strain hardening) (3) formation of additional grain boundaries (heat treatment) alloying and heat treatment combine synergistically to produce tremendous variety of microstructures.

How do water contribute to cement?

1. dissolution of cement grains 2. growing ionic concentration in water 3. compounds form in solution 4. compounds precipitate out as solids after reaching saturation [desirable] concentration 5. products form near surface of anhydrous [contains no water] cement

water used for cement paste

1. drinking water: suitable 2. recovered water: suitable but requirements 3. natural water/industrial process water: maybe but tested 4. seawater/brackish water [mixture of seawater and freshwater] : non-reinforced concrete 5. waste water: unsuitable

Natural durability of timber

1. durability: measure of resistance to attack by insects and fungi 2. fungal attack prevention: ensure below 20% moisture content 3. should be stored under protected conditions until being used 4. marine borers: all untreated timbers placed in saltwater attack by organisms 5. four main durability groups: - group 1: very durable (>10) - group 2: durable (5-10) - group 3: moderately durable (2-5) - group 4: not durable (up to 2)

major chemical compounds of ordinary portland cement

tri-calcium silicate di-calcium silicate tri-calcium aluminate tetra-calcium aluminoferrite

Roles of aggregates in concrete

1. economical filler: 60-80% by volume 2. responsible for ductility 3. provides dimensional stability

Rate of cooling

1. strength depends on nature, distribution and size of phases and/or grains present 2. Pearlite: - slow cooling = coarse pearlite structure - rapid cooling = fine pearlite with extremely thin alternate layers 3. tensile strength - Ferrite: 280-300N/mm^2 - coarse Pearlite: 700N/mm^2 - fine Pearlite: 1300N/mm^2 4. steel cool rapidly - Austenite changes into BCC with all carbon trapped in interstitial solid solution 5. Martensite: extremely hard and brittle compound - Ferrite structure is highly strained and distorted by large amount of carbon in enforced solution into body centred tetragonal form

Pros of steel

1. strength: ability to carry load 2. stiffness 3. ductility: ability to sustain permanent deformation without strength loss 4. toughness: ability to absorb damage without fraction -> evaluated by: (1) area under stress-strain diagram (2) impact test (Charpy V-notch test) (3) fracture mechanics approach 5. weldability: ability to transfer load

Factors affecting workability

1. water-cement ratio: higher proportion of cement means stronger concrete mix. With the right amount of cement paste, aggregate coating delivers better consolidation and finish. 2. Aggregate type and grading: size and shape affect workability. As aggregate surface area increases, more cement paste needed to cover entire surface of aggregates. Crushed aggregate with decent proportions bond best with cement and deliver decent workability. 3. Admixtures: improve strength and workability of concrete mix.

Water reducers

Affects fresh properties of concrete by reducing amount of water while maintaining certain level of consistency, measured by slump. Accelerate or retard initial setting time of concrete.

Weldability

Capacity of metal to join by welding into structure that can perform in satisfactory manner for intended service. Weldability covers: 1. sensitivity to weld cracking 2. toughness in weld and HAZ required by service conditions and temperatures decrease weldability, increase carbon and alloy content Carbon Equivalent (CE) formula: assess equivalent and evaluate effect of alloying elements on weldability CE should not exceed 0.45 -> to avoid embitterment risk and control welding procedure

Corrosion

Deterioration of materials by chemical interaction with their environment. Effective thickness of load-bearing structure decrease, level of stress within material increase, increase corrosion acceleration in localised area 2 corrosion types: 1. dry corrosion: direct reaction between surface metal and atmospheric oxygen 2. wet corrosion: series of electrochemical reactions in presence of aqueous electrolyte Steel corrosion in concrete: 1. concrete highly alkaline 2. protects steel from rusting by creating a passive layer 3. rusting causes internal expansive stresses 4. expansive stresses result in cracking and spalling of concrete covering steel and lead to collapse

Aggregate properties

Determine is aggregate is suitable and needed for concrete mix design 1. shape and texture 2. soundness [stability of volume change in setting and hardening process] and durability 3. hardness and abrasion resistance 4. absorption [measure amount of water that penetrates into concrete samples when submersed] 5. specific gravity 6. strength 7. gradation [particles size distribution of coarse aggregates] 8. cleanness and deleterious materials [prohibited material that affect concrete properties]

fineness of cement

Fineness controls hydration rate because smaller cement particles have more surface area to react with water.

Fatigue

When metal subject to repeated stresses, may eventually fail. maximum stress < fracture stress Fatigue failure: result of processes of crack nucleation and growth. For components which may contain cracks introduced during manufacture, growth only. Fatigue limit defined at 10^7 or 10^8 cycles. Material designed by limited fatigue life of 10^6 to 10^7 cycles. Low cycle fatigue: maximum stress in any given cycle is greater than yield strength but less than ultimate tensile strength. High cycle fatigue: maximum stress in any given cycle is less than yield strength.

Relaxation

a decrease in stress which occurs in a material when a constant deformation is present Decrease in stress in response to same amount of strain. Amount of relaxation takes place is a function of time, temperature and stress level.

Thermal properties

Thermal conductivity: measure rate of heat transferred in one dimension Heat capacity: amount of heat needed to increase temperature of certain mass by certain amount both increase linearly with temperature rate of conductivity increase smaller

Need for standard tests

To provide information on concrete quality. Variables affecting results: 1. specimen geometry 2. specimen preparation 3. moisture content 4. temperature 5. loading rate 6. testing machine type 6. loading fixture

Gypsum

To slow down hydration process of cement once mixed with water. When water added into cement, it starts reacting with C3A and hardens.

calcium silicate hydrate

responsible for cement setting and early age strength

Asphalt concrete

- upper layer of flexible pavement - asphalt concrete = mineral aggregates + bituminous materials + air voids -bitumens: 1. dark-coloured cementitious substance 2. comprises high molecular hydrocarbons 3. excellent waterproofing property 4. thermoplastic - heated: liquidified and coat aggregate particles - cold: solidifies and binds aggregates - bituminous functions: 1. form thin surface film of binder on all particles 2. holds aggregate particles together 3. provides tensile strength and flexural properties to mix 4. enhance durability 5. acts as lubricant - hot mixes: produced, placed and compacted at elevated temperature - cold mixes: produced, placed and compacted with little or no heating Bitumen types asphalt: cementitious material, principally bitumens 1. Natural asphalt (no longer wide use) : asphalt residue 2. Rock asphalt: asphalt-impregnated rocks such as limestone and sandstone - used in localities when occur 3. Tar: produced from destructive distillation of coal or wood - high concentration -> health problem 4. Petroleum asphalt: distilled from crude oil - separated by vacuum distillation or solvent extraction - blended with other distillates to meet specifications - polymer or additives added to enhance properties

Steel

-> Alloy of iron, carbon and other elements in various proportions, and combinations to produce different types of steel. -> <2.14% carbon content -> chemical composition has significant effect on microstructure of material and its mechanical properties -> common alloying elements: manganese nickel chromium molybdenum boron titanium vanadium tungsten cobalt niobium

Understanding steel

1. As-rolled (+AR): delivery condition without special rolling or heat treatment 2. Normalizing rolling (+N): final deformation carried out in certain temperature range to achieve specified mechanical properties after normalizing 3. Thermo-mechanical rolling (+M): (1) combined controlled-rolling at certain temperature range (2) accelerated-cooling to achieve mechanical properties which cannot achieved by heat treatment 4. Quenched and Tempered (+Q): heat treatment by direct or repeated quenching and tempering process to achieve ultra high strength steel

types of voids in hardened cement paste

1. Entrapped air (>1mm): naturally entrapped in concrete. Entrapped air is unstable and can be lost during mixing. No effect on concrete performance. Decrease strength and increase permeability. 2. Entrained air (10um-1mm): microscopic bubbles caused by admixtures. Air pockets relieve internal pressure on concrete by providing tiny chambers for water to expand into when freezes. To increase durability especially in climates subject to freeze-thaw. To increase workability while in plastic state [wet concrete] in concrete. 3. Capillary voids (10nm-10um): Occupied by water when concrete was fresh. As concrete hydrates, water in pores is used in hydration of cement. As concrete matures, much of capillary space filled with hydration and reaction products. Decrease strength and increase permeability. Depends on initial water-cement ratio and degree of hydration. 4. Gel pores (0.5-10nm): pores within hydration product structure.

Tensile test

1. Failure by ductile yielding: limit maximum stress under service load to yield or proof strength divided by safety factor. 2. Failure by brittle fracture: internal cracks and other defects act as points of local stress concentration

Various Fe solutions and compounds

1. Ferrite: - structure of pure iron - BCC - soft and ductile - very little carbon 2. Austenite: - iron structure at high temperatures - formed when material cools from elevated temperature - FCC 3. Cementite: - compound of iron and carbon - hard and brittle - presence in steels (increase hardness, decreasae ductility and toughness) 4. Pearlite: - laminated structure formed of alternate layers of ferrite and cementite - combined hardness and strength of cementite with ductility of ferrite - laminar structure acts as barrier to crack movement as in composites (toughness) 5. Martensite: - very hard needle-like structure of iron and carbon - only formed by very rapid cooling - needs to be modified by tempering before acceptable properties reached 6. Bainite: - non-equilibrium microstructure consist of supersaturated ferrite and cementite - formed when austenite breaks down at cooling by combination of shear and diffusive processes

Corrosion types

1. General corrosion: numerous micro-corrosion cells activated at corroded area. - In atmospheric exposures, oxygen is oxidizing agent, and readily available water in form of rain, condensation or humidity. - Rust does not form effective barrier to further corrosion, yet permits reactants to penetrate and continue rusting. 2. Pitting corrosion: non-uniform, highly localized form of corrosion that occurs at distinct spots where deep pits form - source for corrosion pits: non-homogeneous metal and presence of inclusions of impurity may cause breaks in passive coating - film presence prevent corrosion spread to wider area - stainless steel susceptible with presence of chloride solutions 3. Galvanic corrosion: two metals of different electrochemical potential joined electrically in presence of moisture, where one act as anode and corrode. - solution: isolate different metals from each other 4. Stray current corrosion: electrical potential from stray current flow through paths other than intended circuit, caused by externally induced electrical current. 5. Stress corrosion: initiated from crack and propagates through material due to combined effects of stress and corrosive environment. - lead to brittle failure due to localized corrosion 6. Crevice corrosion: occurs when moisture and contaminants retained. - small volumes of stagnant corrosive caused by holes, surface deposits and joints

Types of iron

1. Iron: -> required less energy to extract from ore than other engineering materials -> pure state: very soft grey metal 2. Pig iron (raw iron): -> immediate product of smelting iron ore with coke and limestone in blast furnace -> very high carbon content of 4-5% -> very brittle and not very useful directly as material 3. Wrought iron: -> smelting of pig iron with iron oxide to remove carbon -> low carbon content (<0.08%) -> strong in tension and ductile -> welded and good corrosion resistance 4. Cast iron: -> re-smelting of pig iron with steel scrap -> high carbon content of 2-4% -> weak in tension, strong in compression -> cannot be welded -> heat treatment to improve structure

Types of steel products

1. Plain carbon steels: up to 2% compositions by weight of carbon 2. Low carbon steels: -> up to 0.3% carbon -> use in normalised, cold worked -> weldable 3. Medium carbon steels: -> contain 0.3-0.6% carbon -> hardened and tempered 4. High carbon steels: -> contain more than 0.6% carbon -> hardened and tempered condition

Workability tests

1. Slump test (for medium-high workability) : measure of wetness of compacted inverted cone of concrete under action of gravity. Procedures: 1. fill three layers of equal volume in inverted cone 2. rod each layer 25 times 3. scrape off surface and lift cone vertically 4. slump measurement 2. Compacting factor test (for medium-low workability) : measures degree of compaction resulting from application of standard amount of work. Compacting factor: ratio of weight of partially compacted concrete to weight of fully compacted concrete. Procedures: 1. fill upper hopper with concrete 2. release concrete into lower hopper by opening bottom door of upper hopper 3. release concrete into cylinder by opening bottom door of lower hopper 4. excess concrete is cut and net weight in known volume determined. 3. Vebe test (very low workability) : measures remolding ability of concrete under vibration. Vebe seconds: assumed energy required for compaction. Procedures: 1. slump cone placed and filled in center of cylinder 2. set glass plate atop fresh concrete after remove slump cone 3. record time for concrete to remold

Flexible pavement components

1. Subgrade: soil underlying subbase - weak subgrade: capping layer of inferior type of subbase materials - upper subgrade: stabilise 2. formation: level upon subbase - constitute pavement 3. Subbase: with subgrade and capping form foundation - main structure of pavement laid - good drainage 4. Base: main structural layer - sufficient strength to withstand deterioration to itself 5. Surfacing: binder course joint with wearing course - strongest structural layer - maintains adequate skid resistance - resists crack propagation

Factors affecting fatigue strength

1. Surface condition: scratches or notches provide stress-raising features for initiation of fatigue cracks. 2. Component design: sectional changes with small fillet radii, keyways and oil holes in shafts are all stress-concentration features. 3. Nature of environment: corrosion or fatigue life very greatly reduced, rate of corrosion increased. combined effect is corrosion fatigue

Asphalt physical properties

1. Temperature susceptibility: indicate by kinematic viscosity (135 degree), absolute viscosity (60 degree) and penetration (25 degree). - viscosity changes with temperature and aging effects - hot climate: rutting problems - cold weather: cracking problems 2. Durability: ability to maintain original properties when exposed to weathering and aging processes - considerations: 1. moisture damage: - stripping: loss of adhesion between asphalt and aggregate due to water - softening: loss of cohesion results in loss of strength and stiffness 2. age hardening: evaporation and oxidation 3. Adhesion: ability to adhere to aggregate surface - depends on aggregate and asphalt characteristics 4. Cohesion: ability to retain shape - indicate by ductility test at low temperature

Mortar

1. To bind individual brick or block 2. mix of sand and opc 3. provide lower strength mortar than masonry units, smaller cracking will occur 4. 1 : 1 : 6 [cement : lime : sand] - decrease strength - increase workability and bond properties

Curing approaches

1. Water curing: maintain water presence 2. Sealed curing: seal surface so mix water cannot escape 3. Heat and additional moisture Considerations: 1. curing materials availability 2. structure shape and size 3. production facilities (in-place/precast) 4. economics

Factors affecting steel reinforcement for concrete

1. bendability 2. fatigue properties 3. bond to concrete 4. weldability 5. corrosion resistance

roles of cement paste

1. bind aggregate particles by coating and filling spaces between aggregate particles 2. provide strength and stiffness 3. responsible for shrinkage and creep

ingredients for concrete making

1. binder materials (6-16%) 2. aggregates: fine (20-30%) and coarse (40-55%) 3. water (12-20%) 4. air content (1-8%) 5. admixtures

Steel strengthening mechanisms - Heat treatment

1. formation of very fine microstructures and additional grain boundaries 2. to achieve ultra high strength through control of very fine microstructure by phase transformation through rapid cooling. Quenching: 1. consists of heating to 815-900 degree then suddenly cool in water, brine, oil or molten lead 2. rapid cooling cause formation of fine grained structures with certain material properties 3. cooling rate influences residual stresses and distortion -> potential formation of quench cracks Tempering: refine microstructures and partially relieve residual stresses 1. reheating steel to 370-650 degree and cool in air 2. internal stresses are partially relieved. ductility and toughness improved without great reduction in strength Annealing: 1. heat steel to temperature higher than tempering 2. after maintain specific temperature for sufficient time, cool steel very slowly in furnace 3. improve ductility 4. decrease residual stresses, yield strength, tensile strength and hardness Normalizing: refine grains deformed through cold work 1. heat ferrous alloy to suitable temperature above transformation temperature range and cool in air 2. small grains are formed, lead to tough metal with normal strength. but not as ductile as steel achieved by annealing.

disadvantages of concrete

1. low tensile strength 2. low ductility 3. volume instability 4. low specific strength

Corrosion consequences

1. metal thickness reduction lead to loss of mechanical strength and structural failure 2. hazards arise from structural failure 3. reduced value due to deterioration of appearance 4. contamination of surroundings due to corrosion of vessels and pipes 5. added complexity and expense for maintenance

Paving petroleum asphalt types

3 types: 1. Asphalt cement: distilled from crude oil - graded by: 1. penetration: measures hardness at 25 degree. - higher values = softer asphalts 2. viscosity: absolute viscosity tested at 60 degree - higher values = harder asphalts 3. performance: based on high and low temperatures - high temperature (46-82 degree): average max air temperature for seven consecutive days. Reflect pavement temperature at 20mm deep of layer being designed - low temperature (-10--46 degree): average min temperature at surface layer - 3 types of hydrocarbons: 1. asphaltenes: provides strength and stiffness 2. resins: provides ductility and adhesiveness 3. oils: contributes viscosity and fluidity 2. Cutback asphalt 3. Asphalt emulsion

Accelerators

Accelerate setting, hardening and development of early strength of concrete. Use to reduce curing time and increase rate of strength gain. Calcium chloride is commonly use as accelerator. But use in reinforced concrete can promote corrosion activity of steel reinforcement.

Aggregate shape and texture

Affects properties of fresh concrete more than hardened concrete. Concrete is more workable with smooth and rounded aggregate. Angular and elongated aggregates have higher surface-to-volume ratio for better bond, but require more paste to produce workable mixture. Smooth surface improve workability. Rough surface generates stronger bond and higher strength. 1. Rounded: good packing but less interlocking between particles 2. Angular: loose packing but good interlocking between particles 3. Flaky and elongated: thin and long. Bad concrete durability due to easy breakage and compacting difficulty.

Durability

Biological decay: due to fungi and insects - naturally durable due to extractives content which provides protection -> decay resistance Fungi: feed on cell wall polymers lead to loss of properties Non-destructive fungi: 1. mould type: feeds on free sugars in timbeer surface 2. staining type: feeds on starch in sapwood cells Destructive fungi: 1. soft rots: waterlogged timber - rots remain within cell walls where they consume celluloses causing surface to soften and darken 2. brown rots: consume cellulose and slightly attack lignin - rotted wood crumbles under pressure 3. white rots: consume both celluloses and lignin - leave fibrous mass that does not crumble under pressure Growth of fungi: obtain nutrients from dead organic matter - growth conditions: 1. food (wood) 2. suitable temperature 3. oxygen 4. adequate moisture - eliminate all moisture sources supporting rot. then cut out and replace affected timber Timber preservatives: 1. Tar oil: - cheap and effective - staining, unpleasant odour, flammable, unsuitable for internal use 2. Water soluble: - odourless, non-staining, non-flammable - internal and external - require redry after application 3. organic solvent: - good penetration - non-corrosive - flammable

Silica fume

By-product from manufacture of silicon and alloys. Super pozzolan with high fineness and silica content. Challenge on handling and dispersion.

Fly ash

By-product of coal combustion. Fly ash is pozzolan, substance containing aluminous and siliceous material that forms cement in presence of water. Improves strength and segregation. Two class: (1) Class C: resistant to expansion from chemical attack. High calcium oxide percentage. Used for structural concrete. (2) Class F: contain particles covered in melted glass. Reduce expansion risk due to sulfate attack. Occur in fertilized soils or near coastal areas. Benefits: good workability, reduce permeability and heat of hydration. Disadvantages: slower strength gain, increase need for air-entraining admixtures

tri-calcium aluminate (C3A) tetra-calcium aluminoferrite (C4AF)

C3A: - 8-12% - low early and ultimate strength - fast reacting with water. lead to immediate stiffening of paste known as flash set. - Provides weak resistance against sulphate attack. Not much contribution to strength development. C4AF: - 6-10% - low early and ultimate strength - Hydrates rapidly but contribute little strength

tri-calcium silicate (C3S) di-calcium silicate (C2S)

C3S: - 30-50% - good early and ultimate strength - hydrates and hardens rapidly. responsible for initial set and early strength gain. - release 3 times of calcium hydroxide chemical reaction as c2s. C2S: - 20-45% - good ultimate strength - hydrates and hardens slowly. strength gain beyond seven days of age - greater resistance to chemical attack

what is cement?

Cement is a hydraulic binder. When mixed with water, forms a paste that sets and hardens by hydration reactions. After hardening, retains strength and stability even under water.

Bricks

Characteristics: 1. made from clay containing sand and alumina 2. strong in compression 3. weak in tension and toughness Types: 1. common: non-load bearing brick 2. engineering brick: high strength required 3. facing brick: use when no plaster on wall Manufacture: 1. collect raw materials 2. grind and mix with water 3. fill into moulds to compact 4. demould and fire to 900-1500 degree - heating: clay fuses and bonds particles - cooling: brick absorbs moisture and swells Problems: 1. rain penetration - measures: (1) increase wall thickness (2) apply water resistant plaster outside 2. efflorescence: clay contains soluble salts that migrate to surface with moisture to form white crystals on surface 3. sulphate attack: sulphate salts from brick interact with cement in plaster or mortar used for bonding, causing local expansion, leading to cracks - measure: use bricks with low sulphate content

Crystal structure

Considers how atoms in a crystal are packed together. Move between different structures depending on temperature. Depends on interatomic bonds and relative sizes of atoms. Common crystal structures: 1. Face Centred Cubic (FCC) - 4 atoms: crystal structure has many slip planes where displacements can slide High temperature crystalline structure of cobalt. Stabilise with addition of nickel for lower temperatures to demonstrate high level of tensile resistance and creep behavior 2. Hexagonal Close Packed (HCP) - 6 atoms: fewer slip planes thus less easily plastically deformed 3. Body Centred Cubic (BCC) - 2 atoms: temperature reduced 900 degree changes from FCC to BCC Iron-carbon alloy system, phase transformation takes place. Exact temperature determined by amount of carbon and other alloying elements in metal. Iron transform from FCC - Austenite at high temperature to BCC structure - Ferrite at lower temperature. The transformation marked by distinct increase in length as metal cools below critical temperature because BCC is less compact than FCC. High temperature Austenite allows enough space for carbon to squeeze in between iron atoms. Iron atoms maintain their place on lattice and carbon atoms become interstitials. In low temperature Ferrite, there is no room for carbon atoms. During slow cooling of low-carbon steel, transformation begins at metal reach 1555 farenheit. Metal transform to Ferrite and expels interstitial carbon into remaining regions of Austenite. As metal cools further, more iron transform into Ferrite, leaving less Austenite and more regions rich in expelled interstitial carbon. At 1350 farenheit, remaining Austenite transform into two different elements. The carbon bonds with iron atoms form Cementite, and precipitates out as discrete structure. Remaining Austenite transforms to Ferrite. Final transformation structure is lamination consisting of alternating layers of Ferrite and Cementite. Large islands of pure Ferrite remain. Laminated structure formed at last moment is Pearlite. Combined structure of Ferrite and Pearlite is soft and ductile - steel in its lowest-strength condition. When ferrous alloy are cooled rapidly or quenched, expelled carbon atoms do not have time to move away from iron as it transforms to Ferrite. Steel undergone this transformation is Martensitic. Martensite is in unequilibrium state, owing much of its high strength and hardness to its distorted stressed lattice structure. Heat-treatment cycles alter steel structure. When Martensite is tempered, some internal stresses are relieved, so resulting structure has more ductility. Other heat treatments alter grains size or structure patterns, providing improved strength or toughness.

Bleeding

Create poor bond between cement paste and large aggregate particles. Causes: lack of fines, high free water content, water reducing admixture overdose. Measures: increase fineness, increase hydration rate, and reduce free water content. Process where free water in mix is pushed upward to surface due to settlement of heavier solid particles. High w/c ratio lead to excessive bleeding. Cement type and fine aggregates determine bleed rate. Fewer fines, more bleeding. Types of bleeding: 1. Normal bleeding: uniform seepage of water over entire surface of structure 2. Channel bleeding: water rising through particular paths Not all bleed water reach surface, some may rise and trapped under aggregates and reinforcing. Results in bond weakening. Ways to reduce bleeding in concrete: - reduce water content - use finer cements - increase amount of fines in sand - use scm or air entraining admixtures

Gradation types

Determines paste requirement for workable concrete. Paste control cost as cement is the most expensive component. Desirable to minimize amount of paste consistent with concrete production while providing necessary strength and durability. Required amount of paste is dependent upon amount of void space must be filled and total surface area must be covered. When range of sizes used in void spaces are filled, paste requirement is lowered. The more voids filled, less workable. 1. continuous (well-graded, dense): good mix of all particles sizes 2. one-size gradation (uniform): all same size - vertical curve 3. gap-graded: missing some sizes - horizontal curve 4. open-graded: missing small aggregates to fill holes

Linear defects - dislocations

Dislocations: areas where atoms are out of position in crystal structure Movement of dislocations when stress is applied allows slip-plastic deformation to occur.

Welding

Effective way to join steel components together with join strength higher than strength of both components. Gas welding: 1. use fuel gas and oxygen to create flame 2. maintenance and repair 3. advantage for carbon and low alloy stress 4. weld area preheated and posy heated with flame to reduce cooling rate 5. filler rod coated with layer of flux. flux melts and dissolve surface oxides, form protective layer over weld Arc welding: 1. to melt filling material 2. bare electrode wire/ welding rods/ coated electrodes 3. electrode coating formulated to: - form fusible slags - stabilise arc - generate inert gas shield Temperature gradient establish, varies from fusion temperature at weld metal to room temperature at some point of parent metal away from weld. Heat-affected zone (HAZ): changes from metallurgical condition and properties of parent metal in vicinity of weld. Changes depend on: - parent metal composition - original condition - cooling rate after weld

Workability

Effort required to manipulate concrete mix with minimum segregation.

Moisture in wood

Equilibrium moisture content (EMC): combination of relative humidity and temperature - no inward or outward diffusion of water vapour Causes: 1. changes in dimension 2. fungi attack 3. lower strength and stiffness Fibre saturation point: dropped in moisture content graph - no free water in cell cavitites - walls hold max amount of bound water

factors affecting quantity of heat in cement hydration

Heat of hydration is heat generated when water and cement react. Heat of hydration is most influenced by proportion of calcium silicate and calcium aluminate. Also influenced by water-cement ratio, fineness and curing temperature. As each of these factors increase, heat of hydration increases.

hydration of cement

Hydration is a chemical reaction where major compounds of cement form chemical bonds with water molecules and become hydrates. Rate of reaction affected by composition and fineness of cement. Rate of reaction increase with temperature increase. Rate of reaction decrease with time increase, and decrease moisture content. Water mixed with cement forms paste that binds aggregate together. Water causes hardening of concrete through hydration. Water needs to be pure to prevent side reactions that weaken concrete. w/c ratio affect workability of concrete. Too much water reduces concrete strength, while too little make concrete unworkable. Strength of concrete increase when less water is used to make concrete. Hydration consumes specific amount of water so concrete mix need more water than required. Extra water give concrete sufficient workability, ensuring proper filling. Water remained will stay in microstructure pore space, making concrete weaker due to lack of strength-forming calcium silicate hydrate bonds.

Protective coatings

Isolate metal from its environment, prevent attack as long as coating is intact. Cathodic protection: 1. use for structures below ground or immersed in water 2. control magnitude and direction of current flow to reduce or eliminate corrosion 3. reverse-current flow: electrically connect steel structure to higher electromotive energy metal 4. steelwork protected with proper reverse current flow maintain Galvanic protection: 1. process where adherent, protective coating of zinc or zinc-iron compounds develop on surfaces of iron and steel

Structure

Macro-structure: 1. outer bark: - rough-textured dense layer - protect living tree from physical damage and rigours of climate 2. inner bark: - softer and moister than outer bark - conduct sap produced in leaves to all areas of active growth or into storage until required 3. cambium: - cellular plant tissue which divide cells tangentially and radially for tree growth 4. pith: - trunk centre - relatively sott - decay-prone original tissue of tree stem 5. sapwood: - outermost growth layers - conduct moisture absorbed by roots to crown - store sap from crown until required for growth 6. heartwood: - tree bulk - provide necessary structural rigidity 7. growth rings - width varies with ring age and external conditions - composed of earlywood and latewood - strength determined by relative share of latewood Micro-structure: - composed of cellular tissue of different functions: 1. moisture conduction 2. mechanical conduction 3. sap storage or conversion - cells aligned parallel or perpendicular to tree axis Ultrasurface and chemistry: three main structural polymers: 1. cellulose 2. hemicelluloses 3. lignin

Blocks

Made from concrete and lightweight aggregates bigger in size have fewer joints, faster to construct than brick masonry three basic forms: 1. solid 2. cellular 3. hollow

Stainless steel

Martensitic: 1. low carbon steel with 12-14% chromium 2. heat treatable and made very hard 3. retain keen cutting edge 4. not corrosion resistant Ferritic: 1. 10.5-27% chromium with very low carbon and little nickel 2. not heat treatable 3. reasonably ductile, medium strength Austenitic: 1. max 0.15% carbon, 18% chromium, and 8/10% nickel 2. not heat treatable 3. reasonably ductile, good strength Duplex stainless steel: 1. 28% chromium and 6% nickel 2. contain Austenite and Ferrite 3. use when corrosion resistance and strength are equally important

Masonry

Masonry structure: formed by combining masonry units with mortar Terminology: 1. masonry: combination of small building units set in mortat 2. units: brick assembled to make masonry 3. mortar: compound from binder and filler 4. binder: finely ground material which reacts chemically when mix with water. Hardens and binds aggregates into solid masses

Solutions and compounds

Most metals are alloyed with other elements to obtain better mechanical properties. 1. Alloy: homogeneous mixture of two or more elements, at least one is a metal. 2. Solid solution: alloying elements are fully dissolvable in base metal (completely miscible system) 3. Intermediate compound: alloying elements are partially dissolvable in base metal (partially miscible system)

Highway pavement

Multi-layered structure of selected or processed material, while protecting underlying weak substrata from deformation. Flexible pavement: load distributed over wide area with depth at top layer, with increase lower stress with depth Rigid pavement: load distributed uniformly over slab

Prestressed concrete

Prestressing was adopted to overcome tensile forces. Prestressing puts beam in compression, prevents cracks. Tension from bottom vertical load reduces overall compression from prestressing. Characteristics: 1. tension applied by single wires, strands or bars 2. made from carbon-chrome alloy steel 3. all sizes have ultimate tensile strength of 1030MPa and 0.1% proof stress of 835MPa 4. corrosion-resistant bars made from martensitic nickel-chrome alloy steel 5. prestressing should not be welded

Curing concrete

Procedure that maintains proper moisture and temperature to ensure continuous hydration. Increase maturity and strength, decrease capillary porosity. Seven days of curing attain 70% of compressive strength. 70% strength reached quicker when cures at higher temperatures. More time needed for curing when concrete temperatures are lower. 20 degree consider ideal curing temperature. Proper curing techniques will prevent in-situ concrete from drying, shrinking, and/or cracking, affecting performance. Curing should occur as soon as it has been placed. Essential for continuous monitoring concrete curing conditions for seven days. If water evaporates from concrete before attaining maximum strength, there will not be enough water remaining in concrete to fully hydrate cement and achieve maximum compressive strength. Methods to retain moisture at early ages: 1. Maintain presence of water in concrete during early hardening period 2. reduce loss of water from concrete surface 3. accelerate concrete strength gain by supplying heat and additional moisture

Steel strengthening mechanism - Alloying

Process of two or more metal elements melted together in precise combination to form alloy. 1. increase resistance to yielding -> change microstructure that impede motion of dislocations 2. strengthening through mechanisms: - interstitial atoms: smaller atoms than host atom. Extra atom inserted into lattice structure of normally unoccupied position. - substitutional atoms: similar in size to host atom. Replaced by different type of atom.

Pros and cons of wood

Pros: 1. specific stiffness and tensile strength 2. low thermal conductivity 3. carbon sink potential Cons: 1. large variability in structure and defects 2. dimensionally unstable 3. subject to biological decay 4. burns 5. available in limited range of shapes and sizes

Water to cement ratio

Ratio between the weight of water and weight of cement used in concrete mix. Lower ratio leads to higher strength and durability. Water to cement ratio (w/c) expended to water to cementitious material ratio (w/cm) when supplementary cementitious materials are used to strengthen concrete.

Slag hydration

Reacts slowly with water due to presence of impervious coatings of amorphous silica and alumina that form around slag particles in hydration process. Activated by alkaline compounds.

Slag

Recovered from industrial by-product of furnace. Molten slag rapidly chilled, producing glassy granules that yield desired reactive cementitious characteristics when ground into suitable cement fineness, and used to replace portion of portland cement.

Factors affecting modulus of elasticity

Reflects the ability of concrete to deflect elastically. Modulus of elastically is sensitive to aggregate and mixture proportions of concrete. Increase modulus: increase age, concrete strength, aggregate modulus Decrease w/c ratio

Interfacial Transition Zone

Region of cement past around aggregate particles, which is perturbed [unsettled] by aggregate. Due to inability of cement particles to pack efficiently around aggregates, there is increase in local w/c ratio and localized bleeding [process where free water in mix is pushed upward to surface due to settlement of heavier solid particles].

Retarders

Retard initial set by slowing down early hydration reaction and early strength. Careful usage of retarder is required to avoid excessive retardation, rapid slump loss, and excessive plastic shrinkage. Use for long haul concrete delivery and to maintain slump.

Segregation

Separation of cement paste and aggregates of concrete from each other during handling and placement. Segregation also occurs due to over-vibration or compaction of concrete, where cement paste comes to the top and aggregates settles at the bottom. Segregation affects strength and durability. In good concrete, all aggregates are evenly coated with sand and cement paste. Prevention: Depth of more than 1.5m should be placed through temporary inclined chutes. Inclination angle kept between 1:3 and 1:2 so that concrete from chute top travels smoothly to bottom. Use of small quantity of free water from top at intervals help lubricate path flow of concrete to bottom smoothly. Delivery end of chute should be as close to point of deposit.

Setting of portland cement

Setting is to stiffen of cement paste from fluid to rigid stage. 1. initial set (2-4hrs): paste begin to stiffen and no longer be molded. 2. final set (5-8hrs): hardened paste can already sustain load.

Classification

Softwood: 1. general structural purposes 2. easier to work 3. cheap Hardwood: 1. density and durability 2. long term exposed structural work 3. expensive due to slow growth speed

Hardened concrete properties

Strengths: 1. compressive 2. tensile: plain concrete weak in tensile strength. Reinforcement introduced into concrete to get strong concrete in compression and tension. 4. shear: 20% of compressive strength 5. impact: resistance to sudden shock or load 6. fatigue: concrete strength against repeated loading Deformations: 1. moisture induced (shrinkage/swelling) 2. load induced (elastic/creep) 3. temperature induced (expansion/contraction) Shrinkage: volume changes accompany moisture loss by evaporation or hydration -> drying shrinkage (hardened concrete): water withdrawal from concrete stored in unsaturated air -> plastic shrinkage (fresh concrete): loss of water while in plastic state Elasticity: strains appear and disappear immediately on application and removal of stress. Creep: time dependent deformation under certain applied load shrinkage/creep increase with: increase aggregate volume friction, modulus of elasticity, w/c ratio decrease relative humidity Durability: 1. physical 2. chemical

Admixtures

Use as concrete ingredients before or during mixing. Use to modify concrete properties and ensure quality. Three types: 1. air-entraining agents: entrain small air bubbles in concrete. Air bubbles improve workability and effective in freeze-thaw cycles as they provide cushioning effect on expanding water at cold climate. 2. chemical admixtures 3. mineral admixtures

Indicate effects of each factor on workability of fresh concrete. Provide corresponding explanation.

Use type III cement: reduced The finer the cement, the greater the water demand. With the same water content, less water is used to lubricate surface, leading to decrease in workability. Use fly ash to replace cement: increased Fly ash is one of the principal admixtures affecting improvement in workability of concrete required by water content for same degree of workability. Spherical shaped particles of fly ash act as miniature ball bearings within concrete mix, thus providing lubricant effect. Use ice to replace water: increased Use of ice accomplish purpose of cooling mix in hot weather, more effective than cold water. Determine how much ice to use so concrete temperature can be reduce one degree for each two percent of total water replaced by ice. Use river gravel instead of crushed stone: increased Rounded aggregates result minimum percentage of voids hence more workability. They require lesser amount of w/c ratio.

Structural steel

minimum yield strength values vary with sectional thickness. higher for thinner sections. comparison: 1. most structural steels used in normalised condition of heat treatment 2. during normalising, thin sections cool through critical temperature range more rapidly than thick sections 3. thin sections possess finer grain structure -> higher strength than thick sections