Construction Materials Notes for NEC License Preparation Nepal
Complete construction materials study material for Nepal Engineering Council license examination covering stone classification geological chemical physical, igneous rock sedimentary rock metamorphic rock, granite slate sandstone limestone marble quartzite, characteristics of good stones compressive strength hardness toughness water absorption, minerals and properties Mohs hardness scale, quarrying dressing seasoning of stone.
Lime manufacture calcination slaking, fat lime hydraulic lime poor lime, types of hydraulic lime feebly moderately eminently, setting of lime carbonation hydrolysis, lime mortar hydraulic lime mortar gouged mortar surkhi pozzolana mortar.
Cement manufacture raw materials dry process wet process, Bogue's compounds tricalcium silicate dicalcium silicate tricalcium aluminate tetracalcium alumino ferrite, special types of cement RHPC high alumina quick setting Portland pozzolana low heat sulphate resistance expansive blast furnace slag cement, tests on cement fineness consistency setting compressive strength tensile strength soundness, cement storage.
Wood and timber endogenous exogenous conifers deciduous, cross section of hardwood trunk pith heartwood sapwood cambium bark medullary rays, defects of timber shakes rind galls dry rot wet rot, seasoning of timber natural artificial air water kiln chemical electrical, preservation of timber tarring charring creosoting, forms of timber plywood.
Clay products brick manufacture SALIMA composition, moulding drying burning, classification of bricks first second third class jhama, tiles ceramic porcelain mosaic clay tiles testing.
Metals and alloys iron ores hematite magnetite limonite siderite, pig iron cast iron wrought iron, types of cast iron grey white mottled ductile malleable, steel manufacture cementation crucible Bessemer open hearth process, classification of steel plain carbon alloy stainless, alloys brass bronze solder invar monel metal.
Paint composition base vehicle coloring pigment thinner drier filler extender, types of paint oil aluminum asbestos cellulose cement emulsion enamel graphite distemper, defects of painting blistering crawling fading, varnish oil spirit turpentine.
Polymers polymerization addition co-polymerization condensation, plastic thermoplastic thermosetting, asphaltic materials bitumen asphalt tar, local construction materials Nepal straw bales rammed earth bamboo fly ash stabilized adobe traditional bricks mud, ceramics types manufacture.
Stone
Classification of Stone
A. Based on Formation / Geological Classification
1. Igneous Rock
Rocks formed by the cooling of Magma are called igneous rock. These rocks are stronger than other kinds of rocks and have a glossy and fused texture.
i. Intrusive Rock
If the cooling of magma occurs below the surface of earth then it is called intrusive rock. It is of two types:
- a) Plutonic rock: If magma cools at very great depths (3 to 8 km) below the surface of earth. e.g. granite, pegmatite. These rocks have a smooth appearance and are the strongest type.
- b) Hypabyssal rock: If rocks formed at only 2-3 km from the surface of earth. e.g. dolerite, porphyry, micro-granite and diorite.
ii. Extrusive Rock
If cooling of magma occurs at the surface then the rock is called extrusive rock. Also called volcanic rock. e.g. Basalt, trap, andesite, dacite, obsidian, pumice, rhyolite, scoria.
2. Sedimentary Rock
If igneous rocks are eroded by agents like wind, water etc. and gradually deposited in layers, then the kind of rock is called sedimentary rock. The process of formation is called petrifaction.
- These rocks show stratification i.e. formed of layers having slight difference in their characteristics
- e.g. Sandstone, Limestone, Gravel, magnesite, laterite etc.
- It occupies 90% of the area of earth's crust
3. Metamorphic Rock
If igneous or sedimentary rocks are subjected to high pressure and/or temperature, then the original crystals undergo recrystallization and metamorphosis to form a new kind of rock called metamorphic rock.
| Parent Rock | Metamorphic Rock |
|---|
| Granite | Gneiss |
| Limestone | Marble |
| Sandstone | Quartzite |
| Shale | Slate |
Metamorphic rock covers 12% of the surface of earth.
B. Chemical Classification
- i. Siliceous Rock: Silica as main constituent. e.g. Quartzite, Basalt, Trap, Gneiss, Granite
- ii. Argillaceous Rock: Alumina (Clay) as major constituent. e.g. Laterite, China clay, Slate
- iii. Calcareous Rock: Lime as major component. e.g. Marble, Limestone
C. Physical Classification
- i. Stratified: Rocks formed in distinct layers. e.g. Limestone
- ii. Unstratified: Rocks that cannot be split into thin layers. e.g. Pumice, Granite
- iii. Foliated: Rocks that can be split along a certain direction. e.g. Quartzite
MCQ – Classification of Stone
1. Igneous rock has
a) Crystalline glossy and fused texture ✓ b) Foliated structure c) Layers of different composition d) None
2. Laterite is chemically classified as
a) Argillaceous ✓ b) Silicious c) Metamorphic d) Calcareous
3. Gneiss is chemically classified as
a) Calcareous b) Argillaceous c) Silicious rock ✓ d) None
4. Marble is
a) Stratified ✓ b) Foliated c) Igneous d) Argillaceous
5. Rocks having tendency to split in definitive direction
a) Foliated ✓ b) Stratified c) Igneous d) Argillaceous
Q. If molten magma forces itself into an already existing rock and solidifies, the rock is called
a) Metamorphic b) Igneous c) Intrusive rock ✓ d) Extrusive
Some Important Stones
Granite
- Quartz, feldspar and mica (Main Composition)
- Igneous rock (primary)
- Grey, green, brown colour
- Compressive strength: 70 to 130 MN/m²
- Specific gravity: 2.64
Slate
- Composed of Alumina, quartz, muscovite and illite
- Argillaceous rock
- Dark blue colour
- Compressive strength: 60 to 70 MN/m²
- Specific gravity: 2.8
Sandstone
- Quartz, lime and silica (Main Composition)
- White, grey, pink, brown colour
- Compressive strength: 35 to 40 MN/m²
- Specific gravity: 2.65 to 2.95
MCQ – Important Stones
1. Sandstone contains mostly
a) Quartz & lime b) Quartz, lime and silica ✓ c) Silica, alumina & lime d) None
2. Granite is mainly composed of
a) Quartz and lime b) Quartz and silica c) Quartz, felspar and mica ✓ d) Quartz and mica
3. Granite contains primarily
a) Quartz b) Quartz & feldspar ✓ c) Mica d) Quartz & mica
4. The compressive strength of granite is
a) 50-70 MN/m² b) 70-130 MN/m² ✓ c) 130-170 MN/m² d) 170-200 MN/m²
5. The specific gravity of stone should not be less than
a) 2.2 b) 2.6 c) 2.9 d) 2.5 ✓
6. The specific gravity of majority of stones lie in the range of
a) 1-1.5 b) 1.5-2 c) 2.4-2.8 ✓ d) 3-4
Characteristics of Good Stones
(i) Compressive Strength and Crushing Strength
1. Crushing strength for most building stones should be more than
a) 500 kg/cm² b) 1000 kg/cm² ✓ c) 1500 kg/cm² d) 2000 kg/cm²
2. The minimum crushing strength of stones is
a) 100 kg/cm² ✓ b) 1000 kg/cm² c) 500 kg/cm² d) 2000 kg/cm²
3. Strength of stone in wet condition is reduced by
a) 20-30% b) 30-40% ✓ c) 40-50% d) 50-60%
4. Stone exhibiting highest compressive strength
a) Slate b) Gneiss c) Limestone d) Granite ✓
5. Highest crushing strength
a) Limestone b) Granite c) Gneiss ✓ d) Laterite
6. Lowest crushing strength
a) Slate b) Sandstone ✓ c) Laterite d) Granite
(ii) Hardness
Resistance to wear. Measured by Attrition test (Most common: LAA for indirect use)
(iii) Toughness
Resistance to impact. Measured by AIV (Aggregate Impact Value)
(iv) Water Absorption
Ratio of water absorbed to dry weight
1. Good quality stone must absorb water less than
a) 2.5% b) 5% ✓ c) 10% d) 20%
2. Stone is rejected if water absorption is more than
a) 15% b) 10% ✓ c) 22% d) 20%
(v) Other Tests
- Purity (Smith test): To find dirty material
- Frost Resistance (Brand test): For frost resistance
- Weather Resistance (Acid test): To check weather resistance
Minerals & Properties
Mineral → (Combine) → Rock → (Fragment) → Stone
Mineral Properties
- Streak: Color in powdered form
- Lustre: Appearance of surface
- Colour: Color in intact form
- Hardness: Abrasion resistance (Mohs scale)
- Cleavage: Property to split into one or more than one direction
Mohs Hardness Scale
| Mineral | Mohs Hardness | Observations |
|---|
| Talc | 1 | Very easily scratched by fingernail; greasy feel |
| Gypsum | 2 | Can be scratched by fingernail (~2.2) |
| Calcite | 3 | Scratched with knife and copper coin (~3.2) |
| Fluorite | 4 | Scratched with knife, not as easily as calcite |
| Apatite | 5 | Scratched with knife with difficulty (~5.1) |
| Orthoclase | 6 | ~6.5 steel needle |
| Quartz | 7 | Scratches glass easily (~7.0) |
| Topaz | 8 | Scratches glass very easily |
| Corundum | 9 | Cuts glass |
| Diamond | 10 | Used as a glass cutter |
1. Constituent responsible for strength of granite
a) Mica b) Feldspar c) Quartz ✓ d) All
2. Mica is composed of
a) Calcium carbonate b) Magnesium and calcium silicate c) Silica with oxygen d) Potassium and aluminum silicate ✓
3. Tendency of mineral to split along a direction is called
a) Cleavage ✓ b) Fracture c) Foliation d) Stratification
4. Minimum hardness number of marble
a) 3 ✓ b) 8 c) 5 d) 10
Quarrying, Dressing and Seasoning
Quarrying: The process of removing stone from its natural deposition. Can be done by excavating, wedging, heating, blasting.
Dressing: The process of bringing stones to desired shape and size. Done at quarry site just after quarrying.
Seasoning: Freshly quarried stone contains moisture called quarry sap. This decreases the strength and causes problems like efflorescence. Seasoning is the process of removal of quarry sap.
1. Quarrying by wedging is successful for
a) Sandstone b) Limestone c) Marble d) All ✓
2. For hard stone quarrying, which method?
a) Wedging b) Channeling machine c) By blasting ✓ d) All
3. To dry quarry sap, stones should be exposed to open air for
a) One month b) Four months c) Six to twelve months ✓ d) Two years
Selection of Stone
- Masonry = Hard stone
- Retaining wall = Heavy stone
- Sculpture = Soft / white stone
- Fire exposed = Compressed sandstone
Lime
Manufacture of Lime
Lime (CaO) is manufactured by burning lime sources to redness.
Calcination: CaCO₃ → CaO + CO₂ (Quick lime / Lump lime)
Slaking: CaO + H₂O → Ca(OH)₂ (Slaked lime / Hydrated lime)
Sources
- Limestone: Used for flooring, tracing, mortar for lime concrete
- Kankar: Used for substructure lime concrete as mortar, below water
- Animal Shell: Purest, used for ornamental purpose
Process of Manufacture
- Collecting of materials
- Burning
- Clamp burning: Limestone stacked in lumps with alternating layers of limestone and fuel, covered by dung soil and ignited. Produces impure lime.
- Kiln burning:
- Intermittent kiln: Mixture of limestone and coke ignited for 2 days, cooled for 3 days. Contains impurity.
- Continuous kiln: Hot air sent through bottom, limestone fed from top. Comparatively less impurity.
- Slaking of Lime: Adding water to quick lime. Purpose: reduce expansion, make lime plastic. Methods: Air slaking, Basket slaking, Platform slaking, Tank slaking.
1. Heating limestone to hot red in contact with air is termed as
a) Carbonation b) Oxidation c) Hydration d) Calcination ✓
2. Slaking of lime is affected by
a) Keeping exposed to air b) Immersing in water ✓ c) Crushing into lumps d) None
Types of Lime
Fat Lime
- Rich lime, high calcium lime
- Volume increases by 2.5 times on slaking
- Purest lime > 95% lime
- Made by burning pure limestone, animal shells
- Used for white washing, plastering
Hydraulic Lime
- Contains greater than 5% impurity in the form of clay which imparts hydraulicity (property to dry below water)
- With increase in clay amount, setting time under water is reduced while slaking time increases
| Type | Feebly Hydraulic | Moderately Hydraulic | Eminently Hydraulic |
|---|
| Clay Content | 5-10% | 11-20% | 21-30% |
| Drying Under Water | 21 days to 1 month | 7 days | 24 hours |
| Slaking Time | 5-10 min | 2 hours | 5 hours |
Poor Lime
Contains more than 5% impurity, low quality, not used for engineering work.
1. Lime suitable for making mortar
a) Quick lime b) Fat lime c) Hydraulic lime ✓ d) Pure lime
2. Lime containing high percentage of calcium oxide is
a) Fat lime b) Rich lime c) White lime d) All of above ✓
3. Commonly used lime for white washing
a) White lime b) Fat lime ✓ c) Hydraulic lime d) Quick lime
4. Setting time of hydraulic lime below water
a) 2-48 hr b) 7 days c) 21 days d) All of above ✓
Setting of Lime
The process of solidification of lime mortar or concrete. It can be through:
- Carbonation: Hardening occurs due to absorption of carbon
- Dehydration: Ca(OH)₂ → CaO + H₂O
- Carbonation: CaO + CO₂ → CaCO₃
- Hydrolysis: Occurs due to Ca(OH)₂ being altered by the action of silica in the presence of alumina
1. Initial setting time of hydraulic lime
a) 30 min b) 60 min c) 90 min d) 120 min ✓
2. Initial setting of lime pozzolana
a) 30 min b) 60 min c) 90 min d) 120 min ✓
3. Initial setting of gouged lime mortar
a) 30 min b) 60 min c) 90 min ✓ d) 120 min
Lime Mortar
- i) Hydraulic lime mortar: Lime:sand in 1:2 ratio. Used as mortar for concrete under water.
- ii) Gouged mortar: Made by adding small quantity of cement. Increases strength and decreases setting time.
- iii) Surkhi/Pozzolana mortar: Lime:surkhi 1:1 or lime:sand:surkhi 1:½:½. Pozzolana imparts hydraulicity, increases strength, reduces shrinkage.
1. Sand is used in lime mortar to
a) Help lime set by allowing CO₂ penetration b) Reduce cost c) Prevent shrinkage d) All ✓
2. Slump for lime concrete shall be
a) 25-50 mm b) 50-75 mm ✓ c) 75-100 mm d) 0-25 mm
3. Curing period for lime concrete
a) 1 day b) 3 days c) 7 days ✓ d) 10 days
4. Lime concrete is mostly used in
a) Foundation b) Roof slab c) Walls d) Under floor ✓
5. Advantage of adding pozzolana to lime
a) Reduced shrinkage b) Increased resistance to cracking c) Increased resistance to chemical attack d) All ✓
6. Pozzolana is used in lime to
a) Impart hydraulicity ✓ b) Prevent shrinkage c) Decrease setting time d) Decrease cost
Cement
Manufacture of Cement – Raw Materials
Cement is manufactured by mixing together and burning the mixture of calcareous and argillaceous material in standard composition:
| Compound | Percentage |
|---|
| Lime (CaO) | 60-66% |
| Silica (SiO₂) | 18-25% |
| Alumina (Al₂O₃) | 3-8% |
| Iron oxide (Fe₂O₃) | 1-5% |
| Magnesia (MgO) | 1-4% |
| Calcium sulphate (CaSO₄) | 3-5% |
| Sulphur trioxide (SO₃) | 1-2% |
| Alkali | 1-2% |
Role of Each Compound
- Lime: Most important compound. Reacts with other compounds for setting and hardening. Excess makes cement unsound; deficit makes it weak.
- Silica: Forms tricalcium silicate and dicalcium silicate responsible for setting and hardening. Excess causes slow setting.
- Alumina: Forms tricalcium aluminate responsible for setting. Excess causes flash set.
- Iron oxide: Imparts color and hardness. Excess makes cement weak.
- Magnesia: Imparts color and soundness. Excess makes cement unsound.
- Sulphur: Makes cement sound. Excess makes cement unsound.
- Alkalies: Causes problems like efflorescence, alkali-aggregate reaction.
- Calcium Sulphate (Gypsum): Added after burning to increase setting time.
1. Which in excess causes cement to set slowly?
a) Lime b) Silica ✓ c) Alumina d) Iron oxide
2. Which provides color to cement?
a) Lime b) Silica c) Alumina d) Iron oxide ✓
Manufacturing Process
A. Dry Process
- Treatment of Raw Materials: Crushing (Ball Mills), Fine Grinding (Tube Mills), Mixing and feeding to silo
- Fed to Rotary Kiln and Formation of Clinker: Dehydration → Dissociation (CaCO₃ → CaO + CO₂) → Compound Formation (clinker)
- Adding of Gypsum and Grinding: 3-5% gypsum added, clinker fine grinded
- Weighing, Packaging and Dispatch
B. Wet Process
- Treatment of Raw Materials: Calcareous materials broken, argillaceous washed and stored in silos
- Grinding and Mixing: Materials crushed, grinded, made into thin paste
- Feed to Rotary Kiln and Formation of Clinker
- Adding of Gypsum and Grinding: 3-5% gypsum added
- Weighing, Packaging and Dispatch
1. Materials in kiln, temperature raised upto
a) 1300-1600°C ✓ b) 1100-1500°C c) 1300-1500°C d) 1100-1600°C
2. Dry process, limestone burnt in rotary kiln at
a) 1100-1200°C b) 1200-1300°C c) 1300-1400°C d) 1400-1500°C ✓
3. In wet process, raw materials heated to about
a) 650-900°C b) 900-1300°C c) 1300-1450°C ✓ d) 900-1050°C
4. In wet process the kiln is
a) Horizontal b) Vertical c) Slightly inclined to vertical ✓ d) Slightly inclined to horizontal
5. Moisture content in slurry for wet process
a) 35-50% ✓ b) 12% c) 40-45% d) 100%
Bogue's Compounds
On burning raw materials they form clinker, mainly composed of the following end products (Bogue's compounds):
| Compound | Abbreviation | Properties |
|---|
| Tricalcium Silicate (Alite) | C₃S | Develops early strength, generates more heat |
| Dicalcium Silicate (Belite) | C₂S | Generates less heat, responsible for ultimate strength |
| Tricalcium Aluminate (Celite) | C₃A | Reacts very rapidly, generates high heat of hydration, responsible for initial setting, greater tendency of volume change |
| Tetracalcium Alumino Ferrite (Felite) | C₄AF | Less cement property, increases volume and reduces cost |
1. Early strength of cement is due to
a) C₃S ✓ b) C₂S c) C₃A d) C₄AF
2. Ultimate strength of cement is due to
a) C₃A b) C₂S ✓ c) C₃S d) C₄AF
3. Setting and hardening mainly due to
a) C₂S b) C₃S c) C₃S d) All ✓
4. Dicalcium silicate
a) Hydrates rapidly b) Generates less heat of hydration ✓ c) Hardens rapidly d) Bad ultimate strength
5. Initial setting caused by
a) C₂S b) C₃S c) C₃A ✓ d) C₄AF
6. C₃A property
a) Reacts fast b) Generates maximum heat of hydration ✓ c) Hardens rapidly d) Bad ultimate strength
7. Undesirable property of cement due to
a) C₂S b) C₃S c) C₃A ✓ d) C₄AF
8. Good quality cement has higher percentage of
a) C₃S ✓ b) C₂S c) C₃A d) C₄AF
Special Types of Cement
(i) Rapid Hardening Portland Cement (RHPC)
- Greater strength in early stage due to extra amount of lime and increased fineness
- Produces same strength in 1 day as OPC in 3 days
- Used in road construction; not used in mass concrete
(ii) Extra Rapid Hardening Cement
- Made by adding CaCl₂ (<2%) in RHPC
(iii) High Alumina Cement
- High alumina content, resists high temperature
- Used as refractory material in linings
- Develops highest early strength
(iv) Quick Setting Cement
- Obtained by adding Al₂SO₄ and CaCl₂ with OPC. Used for underground construction.
(v) Portland Pozzolana Cement
- Lower initial strength, higher final strength
- Increased workability, reduction in bleeding and shrinkage
- Reduction in chemical reaction with sulphur
(vi) Low Heat Cement
- Lower amount of C₃S and C₃A. Lower initial strength but final same as OPC.
- Uses: Abutments, retaining walls, Dams
(vii) Sulphate Resistance Cement
- OPC grinded with gypsum. Resistant to sulphate attack. Uses: Marine conditions, sulphate infected soil.
(viii) Expansive Cement
- Contains expansive agents. Used in repair works, crack filling, frost resistant concrete.
(ix) Blast Furnace Slag Cement
- Clinker + gypsum + ground granulated blast furnace slag. Low heat of hydration. Used for economy in mass concrete.
1. RHPC attains early strength due to
a) Larger proportion of lime grinded finer than OPC ✓ b) Smaller proportion c) Gypsum d) None
2. Cement for construction in sea water
a) Portland pozzolana cement ✓ b) Quick setting c) Low heat d) RHPC
3. Structure subjected to sea water action
a) RHPC b) Low heat c) High alumina d) Sulphate resisting cement ✓
4. Portland pozzolana cement possesses
a) Higher chemical resistance b) Lower heat of hydration c) Lower shrinkage d) Water tightness e) All ✓
5. Cement for formwork removed earlier
a) Rapid Hardening Cement ✓ b) Colored c) High Alumina d) Low Heat
6. Cement for water-retaining structures
a) Waterproof Portland cement ✓ b) Colored c) High Alumina d) Low Heat
7. Cement to create bond with old concrete
a) RHPC b) Expansive Cement ✓ c) Sulphate Resisting d) Low Heat
8. Cement for frost resistance concrete
a) RHPC b) Expansive Cement ✓ c) Sulphate Resisting d) Low Heat
9. Cement for sewage and water treatment plants
a) RHPC b) Low Heat c) Sulphate Resisting Cement ✓ d) Quick Setting
10. Cement where economic considerations predominant
a) Waterproof b) Colored c) High Alumina d) Blast Furnace Slag Cement ✓
Tests on Cement
(a) Fineness Test
- IS Sieve: Residue on IS sieve No. 9 shall be less than 10% for OPC and 5% for RHPC
- Air Permeability Method: Specific area = area per unit weight (cm²/gm). Min 2250 cm²/gm for OPC, 3000 cm²/gm for RHPC
(b) Consistency Test
- Done by Vicat's apparatus
- Plunger/Needle Diameter: 10 mm
- Water content corresponding to 30-35mm penetration = Normal consistency (denoted by P)
(c) Setting Test (Performed at 0.85P water)
- Initial Setting: Time when cement changes from plastic to semi-solid stage. Needle: 1mm² area. Penetration of 30-38mm = Initial setting time.
- Final Setting: Time when cement changes to hardened stage. Tested using annular needle.
| Cement Type | Initial Setting | Final Setting |
|---|
| OPC | 30 min | 600 min |
| Quick Setting | 5 min | 30 min |
(d) Compressive Strength
- Test on cubes of cement:sand mortar in 1:3 ratio, 7.06 cm side cube
- Dried at 90% humidity for 24 hours, then cured in water
- Minimum: 115 kg/cm² for 3 days, 175 kg/cm² for 7 days
(e) Tensile Strength
- By pulling briquette. Minimum: 20 kg/cm² (3 days), 25 kg/cm² (7 days)
(f) Loss of Ignition
- Loss in weight after heating at 900°C. Shall not exceed 4%.
(g) Soundness Test
- Property to resist cracking on freezing or thawing
- Measured by Le-Chatelier's apparatus. Maximum expansion < 10 mm
1. Loss of ignition, insoluble residue, and residue on IS sieve No. 9
a) 4%, 1.5%, 10% ✓ b) 1.5%, 4%, 10% c) 4%, 10%, 1.5% d) 10%, 1.5%, 4%
2. In loss of ignition test, cement heated to
a) 100°C b) 200°C c) 500°C d) 1000°C ✓
3. For Normal consistency, penetration of Vicat's apparatus
a) 20-30 mm b) 30-35 mm ✓ c) 35-38 mm d) >40 mm
4. Normal consistency of OPC
a) 10% b) 15% c) 20% d) 25% ✓
5. Water percentage for normal consistency
a) 5-15% b) 10-25% c) 15-25% ✓ d) 20-30%
Storage of Cement
- Store in dry, leak-proof, moisture-proof building with minimum windows
- Stack bags 150-200 mm above floor on wooden planks
- Space of 300 mm between exterior walls and stacks
- Maximum stack height: 12 bags; width: 4 bags or 3 meters
- Use old cement first (FIFO)
| Months of Storage | % Decrease in Strength |
|---|
| 2 | 20% |
| 6 | 30% |
| 12 | 40% |
| 24 | 50% |
Wood and Timber
Wood: The hard fibrous material that forms the main substance of the trunk or branches of a tree or shrub.
Timber: Wood suitable for building, carpentry or various engineering works. It is a renewable source of energy with satisfactory engineering properties and is easily workable.
Tree Classification
| Endogenous | Exogenous |
|---|
| Grows by adding cells only at end portion; slender, thin, knotted. e.g. Bamboo, banana, cane | Grows by adding cells in lateral and longitudinal direction; thick and solid |
Exogenous trees are further classified as:
| Conifers | Deciduous |
|---|
| Grow in high altitude; leaves fall and new ones grow continuously; light colored resinous soft wood. e.g. Chir, pine, uttis, Deodar | Leaves fall in winter and grow in spring; heavy durable dark colored wood; age judged from annular rings. e.g. Walnut, kail, Teak, Sal |
1. Does not belong to endogenous tree
a) Palm b) Bamboo c) Teak ✓ d) Cane
2. Does not belong to exogenous tree
a) Coconut ✓ b) Teak c) Sisham d) Sal
3. Not a soft wood
a) Deodar b) Walnut c) Sisham ✓ d) Kail
4. Maximum resistance to white ants
a) Chir b) Sisham c) Sal d) Teak ✓
5. Not hard wood
a) Deodar ✓ b) Sal c) Teak d) Oak
Cross Section of Hardwood Trunk
- Pith: Innermost core of tree
- Heart wood: Dark colored wood surrounding the pith; dead and inactive, does not participate in growth
- Sapwood: Part between heartwood and cambium; active part. Adds a ring at end of each winter (annular ring)
- Cambium: Layers of fresh sap not yet converted to sapwood
- Bark: Outermost covering
- Medullary rays: Rays extending from pith to periphery
Defects of Timber
a) Natural Defects
- Shakes: Partial or complete separation along the grain
- Star shake: Crack from bark to pith
- Cup shake: Annual ring separation at some point
- Ring shake: Annual ring separation
- Heart shake: Cracks from heartwood to periphery
- Rind galls: Swollen mass on surface due to improper growth
- Wind crack: Crack due to wind but prevents honeycombing
- Droxiness: White spot due to attack of fungus
- Foxiness: Reddish yellow stains due to over maturity or improper storage
- Dry rot: Fungus converts wood to powder
- Wet rot: Alternative wetting and drying causes wood to become powder
- Check: Small cracks
b) Defects during Felling (Artificial/Man-made Defects)
- Warp: Twisted out of shape
- Case hardening: External surface evaporates causing cracks
- Honeycombing: Over drying causes radial and circumferential cracks
- Split: Crack from one end to another
1. Defect caused by improper seasoning
a) Wet rot b) Dry rot c) Honeycombing ✓ d) Cup shake
2. When timber is reduced to dry powder
a) Wet rot b) Dry rot ✓ c) Droxiness d) Foxiness
3. Defect caused by over maturity or improper storage
a) Knot b) Ring gall c) Foxiness ✓ d) Heart shake
Seasoning of Timber
Timber contains about 100% moisture (wrt dry weight). In seasoning, moisture is removed to make timber strong and attack resistant.
1. Natural Seasoning
- Air seasoning: Wood arranged in spaced stacks, dried naturally for 60-80 days
- Water seasoning: Logs submerged in stream with wider end toward flow; sap washed out
2. Artificial Seasoning
- Kiln seasoning: Stacks dried in kiln
- Chemical seasoning: Immersed in NaNO₃, Na₂SO₄, urea solution then dried
- Electrical seasoning: Electricity passed through logs (costly, not commonly used)
1. Time for water seasoning
a) 1-2 months b) 2-4 months c) 4-6 months ✓ d) None
2. Time for air seasoning of soft wood
a) 15-30 days b) 30-60 days c) 60-90 days ✓ d) 90-120 days
3. Time for kiln seasoning
a) 2-5 days b) 5-10 days c) 10-20 days ✓ d) 20-40 days
4. Seasoning is done to
a) Reduce shrinkage b) Reduce weight c) Increase strength and durability d) All ✓
5. Based on dry weight, freshly felled tree may contain
a) 25% b) 50% c) 75% d) 100% ✓
6. Well-seasoned timber moisture content
a) 20-25% b) 15-20% c) 10-12% ✓ d) 5-7%
7. According to IS 399-1963, weight of timber specified at
a) 8% b) 10% c) 12% moisture ✓ d) 14%
8. Moisture content for timber in framework should not exceed
a) 5% b) 10% c) 15% ✓ d) 20%
Preservation of Timber
- Tarring: Coating with tar; parts embedded below ground; protects from ants
- Charring: Ends burnt to 15 mm depth; protects against dry rot and insects
- Creosoting: Surface coated with creosote oil; makes timber resistant to ants
- ASCU treatment: Coat with ASCU; makes timber resistant to ants
Fire Proofing: Impregnation, Hot and cold dipping, Sir Abel's process
1. Creosote oil preserves wood from
a) Rot and ant ✓ b) Fire hazard c) Cracking d) None
2. Timber can be made fire resistant by
a) Soaking in ammonium sulphate ✓ b) Tar paint c) Creosote oil d) None
3. Impregnating is done to increase
a) Fire resistance ✓ b) Moisture content c) Weight d) None
Clay Products – Brick
Nepal Standard size: 224 × 108 × 57 mm
India Standard: 19 × 9 × 9 cm (Standard Size) | 20 × 10 × 10 cm (Nominal Size)
Composition of Good Brick Earth (SALIMA)
| Component | Percentage | Role |
|---|
| Silica | 50-60% | Main ingredient; retains shape, imports durability. Excess: brittle & weak |
| Alumina | 20-30% | Renders clay plastic. Excess: cracking and warping on drying |
| Lime | ~10% | Reduces shrinkage, causes silica to melt. Excess: over melting |
| Iron Oxide | <7% | Imports color, reduces shrinkage. Excess: dark blue color |
| Magnesia | <1% | Reduces warping. Excess: yellow color |
| Alkali | <1% | Causes efflorescence |
1. Clay and silt content in good brick earth must be at least
a) 40% b) 30% c) 50% ✓ d) 60%
2. Excess of silica in clay causes
a) Loss of cohesion ✓ b) Cracking and warping c) Yellow color d) Impermeability
3. Excess of alumina causes
a) Loss of cohesion b) Impermeable c) Cracking and warping on drying ✓ d) Brittleness
4. Soil good for making brick is
a) Clay soil ✓ b) Alluvial c) Silty d) Sandy
Manufacture of Bricks
- Unsoiling: Top soil up to 20 cm depth removed
- Weathering: Soil dug and formed into lumps, allowed to weather in open
- Blending: Mixing of appropriate constituents to improve quality
- Kneading/Tempering/Pugging: Kneading of appropriate soil mixture. Done in pug mills or by cattle feet
- Moulding: Bringing brick to desired shape (hand or machine)
- Drying: Reduction in moisture before burning (3-8 days in air, not in direct sunlight)
- Burning: In pajhwas or kilns (700-1000°C for 24 hours). Bulls Trench Kiln (semi-continuous), Hoffman's Kiln (continuous), Intermittent Kiln
1. Process of mixing clay, water and ingredients
a) Moulding b) Tempering ✓ c) Pugging d) Blending
2. Process of mixing sand with powdered soil
a) Moulding b) Tempering c) Pugging d) Blending ✓
3. Pug mill is used for
a) Clay preparation ✓ b) Clay moulding c) Drying d) Burning
4. Bricks should be dried in
a) Hot air b) Direct sunlight c) Air for 3-8 days not in sun ✓ d) Air for 1-3 days
5. Bricks are burnt at
a) 300-500°C b) 500-700°C c) 700-1000°C ✓ d) 1000-1200°C
6. Burning completed in hours
a) 12 b) 24 ✓ c) 48 d) 96
7. Bricks after burning require ___ days to cool
a) 4 b) 8 c) 10 d) 12 ✓
Classification of Bricks (Based on Quality)
1st Class Bricks
- Well defined edges, even surface with uniform color, dense
- Max water absorption: 15% (NS), 20% (IS)
- Min compressive strength: 10.5 N/mm²
2nd Class Brick
- Not well defined edges, rough surface with uniform color
- Max water absorption: 20% (NS), 22% (IS)
- Min compressive strength: 7.0 N/mm²
3rd Class Brick
- Not well defined edges, rough surface, non-uniform color
- Water absorption > 25%
- Crushing strength: 3.5 to 7 N/mm²
Jhama Bricks
- Overburnt, no definite shape, brittle
- Crushing strength > 15 N/mm²
Defects of Bricks
- Bloating: Swollen mass due to excess gas forming carbonaceous matter
- Chuffs: Deformation caused by rain on hot bricks
- Lamination: Formation of thin lamina due to entrapped air
Special Bricks
1. Brick used for lining of furnace
a) Under-burnt b) Over burnt c) Refractory ✓ d) All
2. Fire bricks are used to
a) Reflect heat b) Increase heat flow c) Decrease heat flow ✓ d) All
3. Hollow bricks are used for
a) Ornamental design b) Thermal insulation ✓ c) Cost reduction d) Earthquake resistance
Metals and Alloys
Iron Ores
| Ore | Iron Content | Chemical Formula |
|---|
| Hematite | 70-75% | Fe₂O₃ |
| Limonite | 60% | 2Fe₂O₂ |
| Magnetite | 70-72% | Fe₃O₄ |
| Siderite | 42-44% | FeS₃ |
| Pyrite | 45-47% | FeCO₃ |
| Black band | 40-42% | - |
Types of Iron
A. Pig Iron
- Crude and impure form made in blast furnace
- Composition: Iron 92-95%, Carbon 2-4%, Silicon 0.5-2%, Sulphur 0.01-0.005%, Phosphorus 0.1-0.0005%, Manganese 0.5-0.6%
- Manufacturing: Dressing → Calcination/Roasting → Smelting (blast furnace)
Types of pig iron:
- Bessemer Pig: Free from sulphur/phosphorus; made from hematite; for Bessemer steel process
- Grey/Foundry Pig: Slow cooling; suitable for foundry work
- White/Forge Pig: Rapid cooling; to make wrought iron
- Mottled Pig: Intermediate cooling and properties
B. Cast Iron
Manufactured by refining pig iron. Contains 2-4% carbon.
- Grey cast iron: Carbon as graphite; high compressive strength; used in automobile parts
- White cast iron: Carbon as carbide; high tensile strength; used in balls, rings
- Mottled/Malleable cast iron: White cast iron heat treated; used for thin sheets
- Ductile cast iron: Magnesium added to grey cast iron; used for wires
C. Wrought Iron
- Purest form of iron; made in puddling furnace
- Process: Refining → Puddling → Shingling → Rolling
1. Process of removing clay impurities from iron
a) Dressing ✓ b) Calcination c) Roasting d) Smelting
2. Pig iron for wrought iron manufacture
a) Bessemer b) Foundry c) Forge pig ✓ d) Mottled
3. Brittleness of cold due to excess of
a) Sulphur b) Carbon c) Silicon d) Phosphorus ✓
4. Red short (cracking of iron) due to
a) Sulphur ✓ b) Carbon c) Phosphorus d) Silicon
5. Process of making wrought iron from pig iron
a) Rolling b) Puddling ✓ c) Shingling d) Refining
6. Cast iron is used for
a) Beams b) Water pipes c) Column strut ✓ d) None
7. Wrought iron is used for
a) Beams b) Small size water pipes ✓ c) Column strut d) None
Alloys & Alloying Elements
| Element | Property Imparted |
|---|
| Nickel | Toughness, tensile strength, yield strength |
| Chromium | Tensile strength, heat resistance, impact resistance |
| Manganese | Abrasion resistance |
| Silicon | Elasticity, magnetic property |
| Vanadium | Tensile, ductility, fatigue yield |
| Titanium | Hardness |
Important Alloys
| Alloy | Composition |
|---|
| Brass | Copper 60-70% + Zinc 30-40% |
| Solder | Lead:Tin = 1:2 |
| Invar | Steel 64% + Nickel 36% |
| Monel metal | Copper 60% + Nickel 40% |
| Brazing solder | Copper:Zinc:Tin = 4:3:1 |
| Bronze | Copper:Tin = 3:1 |
Steel – Manufacture
- (a) Cementation process: Iron heated with coke; weight gained as carbon; produces blister steel
- (b) Crucible process: Wrought iron heated with molten metals rich in carbon; produces cast steel
- (c) Bessemer process: Air blown through molten Bessemer pig iron; produces soft steel
- (d) Open hearth process: Steel manufactured in open hearth furnace; does not involve complete decarbonization
Classification of Steel
- Plain Carbon Steel: Dead steel (<0.15%), Mild steel (0.15-0.3%), Medium carbon (0.3-0.8%), High carbon (0.8-1.5%)
- Alloy Steel: Silicon steel, High speed tool steel (drills), Heat resistant steel (furnace), Spring steel, Stainless steel (utensils), Invar steel (staff)
1. Stainless steel contains
a) 18% chromium, 8% nickel ✓ b) 12% Cr, 6% Ni c) 18% Ni, 8% Cr d) 12% Ni, 6% Cr
2. Steel used for manufacture of rails
a) Bessemer steel ✓ b) Mild c) Cast d) Stainless
3. Stainless steel resists corrosion due to
a) Chromium ✓ b) Carbon c) Nickel d) Sulphur
4. Soft variety of steel manufactured by
a) Cementation b) Crucible c) Bessemer ✓ d) Open hearth
5. Blister steel is manufactured by
a) Cementation process ✓ b) Crucible c) Bessemer d) Open hearth
Miscellaneous Materials – Paint, Varnish, Polymers, Bitumen
Paint – Composition
- (a) Base: Main component forming protective covering (metal oxides like red lead, white lead)
- (b) Vehicle: Medium supporting base for uniform spreading (Linseed oil most used)
- (c) Coloring Pigment: Imparts color (White=zinc white, Blue=cobalt blue, Green=chrome green, Yellow=chrome yellow, Brown=umber)
- (d) Thinner: Volatile substance making paint thin and applicable (Turpentine most used)
- (e) Drier: Helps mix elements, dries rapidly
- (f) Filler: Increases volume, makes paint durable
- (g) Extender: Used for easy spreading
Types of Paint
- Oil paints: Linseed oil vehicle, turpentine thinner
- Aluminum/Bronze paint: Heat resistant; used for hot water pipes, radiators
- Asbestos paint: Fire resistant; used for DPC, leaked roofs
- Cellulose paint (DUCO): Used in airplanes
- Cement paint: Pigment (5-10%) added to white cement
- Emulsion paint: Pigment in emulsion carrier
- Enamel paint: Acid resistant, less affected by cold water
- Graphite paint: Used for sea structures
- Distemper: Powdered chalk + pigment + water
Defects of Painting
- Blistering: Bubbles due to moisture
- Crawling: Too thick paint becomes uneven (vertical=Sagging, horizontal=Wrinkling)
- Fading: Loss of color
- Flashing: Shining surface in cheap paints
- Grinning: Background exposure due to low quality
- Running: Exposure due to too much thinner
- Chalking: Formation of powder
- Flaking: Flakes from too thick paint
- Checking/Crazing/Crocodiling: Superficial cracks
- Alligatoring: One layer slides over another
- Cracking: Deep cracks
1. Commonly used thinner in oil paints
a) Olive oil b) Naphtha c) Turpentine ✓ d) Creosote oil
2. Commonly used thinner in distemper
a) Naphtha b) Olive oil c) Turpentine d) Water ✓
3. Best primer for structural steel
a) Zinc oxide b) Red lead ✓ c) White lead d) Iron oxide
4. Paint highly resistant to fire
a) Enamel b) Asbestos paint ✓ c) Aluminum d) Cement paint
5. DUCO paint is
a) Plastic b) Cellulose paint ✓ c) Emulsion d) Bituminous
6. Radiator is painted with
a) Asbestos b) Plastic c) Oil paint d) Bronze paint ✓
Varnish
Liquid made by dissolving resin in spirit or oil, used for giving finish to wood.
- Oil Varnish: Most protective; used on external surfaces
- Spirit Varnish (Lacquer/French polish): Most attractive; used for decorative work
- Turpentine Varnish: Most resistant to moisture; used in moist/damp conditions
Polymers and Polymerization
Polymerization: Combination of small molecules to form a large molecule (polymer).
- Addition Polymerization: Molecules combine to form chain with exact form. e.g. polythene, polyethylene
- Co-Polymerization: Two or more different molecules form polymer. e.g. styrene-butadiene
- Condensation Polymerization: Formation of polymer with elimination of HCl, H₂O etc.
Plastic
- Thermoplastic: Softens on heating, solidifies on cooling, can be remoulded. e.g. Polythene, polystyrene
- Thermosetting Plastic: Does not soften on heating, once moulded is permanent, brittle. e.g. Bakelite, Polyester, Epoxy resin
Asphaltic Materials (Bitumen, Asphalt, Tar)
Bitumen
Chemical compound of carbon and hydrogen obtained by natural or artificial means.
- Natural bitumen: Natural lake asphalt, Native rock asphalt
- Artificial bitumen: Obtained by petroleum fractional distillation → Straight run bitumen, Liquid bitumen (Cutback bitumen, Bitumen emulsion)
Asphalt
Mixture of bitumen and inert mineral material.
- Natural Asphalt: Found in rock or lake
- Mastic Asphalt: Mixture of bitumen, fine aggregate and filler. Forms void-less mass. Used in road, bridge, DPC, waterproofing
- Asphalt Cement: Oxidizing asphalt at high temperature; used for waterproofing
Tar
Viscous material made by destructive distillation of wood or charcoal in absence of oil. Process: Carbonization → Refining → Diluting.
1. Asphalt is a mixture of
a) Bitumen and inert material ✓ b) Bitumen and asbestos c) Bitumen and cement d) Tar and asbestos
2. Mastic asphalt is mainly used for
a) Sound proofing b) Water proofing ✓ c) Fire proofing d) None
3. Plastic bitumen is used for
a) Road pavements b) Expansion joint c) Crack filling ✓ d) None
Local Construction Materials
Construction materials that can be made at local level without sophisticated methodologies and machines.
Straw Bales
Used for walls and roofing. Naturally provides high insulation. Affordable and sustainable. Life can be enhanced by treating with copper sulphates; fire resistance increased with phosphorylated CNBC.
Rammed Earth
Walls created from dirt tamped down tightly in wooden forms. Technology used for thousands of years. Can be made safer with rebar or bamboo.
Bamboo
Combination of tensile strength, light weight, and fast-growing renewable nature. Used for framing buildings and shelters; alternative to concrete and rebar in difficult areas.
Fly Ash
Silica rich pozzolanic materials from coal burning industries. Used as admixture for concrete; provides impermeability, light weight, thermal insulation.
Stabilized Adobe
Improvement over traditional adobe. Mud mixed with cement, lime, or cut dry grass as reinforcing media. Appropriate in dry climates.
Traditional Bricks
- Dachi appa (teliya ita): Veneer bricks fired at very high temperature, darker red, glossy finish. 8" × 4" × 2"
- Ma appa: Structural bricks. 8" × 5" × 1¾"
Mud
Used for plastering to protect from water penetration and give aesthetic character. Traditional inner wall coating: red clay + cow dung + husk (damp-proof and insecticidal).
1. Traditional mud-plaster consists of
a) Soil b) Janta Emulsion c) Cowdung d) Soil, Husk and Cowdung ✓
2. In old times, superstructure construction used
a) Rubber b) Bamboo c) Mud d) Timber ✓
3. Building roofing shall normally be
a) Mud roof b) Tile roof ✓ c) Wooden roof d) Bamboo roof
4. Roofing material for low cost buildings in plain areas
a) Mud b) Straw ✓ c) Clay d) Bamboo
Ceramics
Ceramics are inorganic, nonmetallic materials consisting of metallic and nonmetallic elements bonded by ionic or covalent bonds.
Properties of Ceramics
- Hard, wear-resistant, brittle, refractory
- Thermal and electrical insulators
- Nonmagnetic, chemically stable
- Prone to thermal shock
Types of Ceramics
- White ware: Porcelain
- Clay construction products: Bricks, clay pipe, building tile
- Refractory ceramics: High temperature applications (furnace walls)
- Glass: Bottles, lenses, window panes
- Glass fibers: Thermal insulating wool, fiber optics
- Abrasives: Aluminum oxide, silicon carbide, diamond, corundum
- Cutting tools: Tungsten carbide, aluminum oxide, cubic boron nitride
- Bio ceramics: Artificial teeth and bones
Manufacture of Ceramics
- a) Powder pressing: Pressing and extrusion with binder for higher density
- b) Vitrification (Gluing): Adding additives to produce lower melting point secondary phases
- c) Sintering: Initial heating (up to 250°C) volatilizes binders; then fired with shrinkage
1. Property of ceramics
a) Low strength b) Low melting point c) Resistant to corrosion ✓ d) Bad insulation
2. Porcelain is a type of ___ ceramic
a) White ware ✓ b) Stone c) Abrasive d) Cement
3. Diamond and corundum are examples of ___ ceramics
a) Glass b) Stone c) Refractories d) Abrasives ✓
4. Carbide used for cutting tools
a) Silicon carbide b) Tungsten carbide ✓ c) Vanadium carbide d) Chromium carbide