← Construction Materials · JKSSB Draftsman Civil

Chapter 1 of 6

Stone, Bricks & Lime

In the JKSSB Draftsman Civil syllabus under Construction Materials · 3 parts

Building Stones · Bricks, Tiles & Clay Products · Building Lime

CIVILGYAN TEST SERIES · civilgyantests.com — free study notes for civil engineering exams

📑 Contents (34 sections)

Part 1 of 3

Building Stones

Last reviewed 16 Sept 2026 · 9 min read

Classification of rocks

Geological classification

Type	Formation	Examples
Igneous rocks	Cooling and solidification of molten magma — intrusive (plutonic), coarse-grained (cooled slowly deep inside) or extrusive (volcanic), fine-grained (cooled quickly at the surface)	Granite (plutonic), basalt and trap (volcanic), dolerite (hypabyssal), syenite, diorite
Sedimentary rocks	Deposition and consolidation of sediments by water, wind or ice — usually stratified	Sandstone, limestone, shale, laterite, conglomerate, gypsum
Metamorphic rocks	Alteration of igneous or sedimentary rocks by heat and pressure	Marble (from limestone), quartzite (from sandstone), slate (from shale), gneiss (from granite), schist

Physical classification

Stratified rocks — in layers (sedimentary rocks such as sandstone, limestone); can be split along bedding planes.
Unstratified rocks — no layers; compact crystalline structure (igneous rocks such as granite, trap).
Foliated rocks — tend to split along a definite direction (metamorphic rocks such as slate, gneiss, schist).

Chemical classification

Class	Main constituent	Examples	Remarks
Siliceous	Silica (SiO₂)	Granite, quartzite, sandstone (silica-cemented)	Hard, durable, resist weathering
Argillaceous	Clay (alumina)	Slate, laterite, shale	Dense and compact or soft and brittle depending on type
Calcareous	Calcium carbonate	Limestone, marble	Affected by acids and polluted (industrial) atmospheres

Common building stones and uses

Stone	Characteristics	Uses
Granite	Igneous, hard, strong, durable, takes a good polish; high crushing strength; poor fire resistance (cracks on heating)	Bridge piers, docks, retaining walls, steps, kerbs, facing, flooring, road aggregate
Basalt and trap	Igneous, hard, tough, dark, difficult to dress	Road metal, rubble masonry, railway ballast, aggregates
Sandstone	Sedimentary, stratified, porous; strength depends on cementing material (siliceous best)	Walling, ashlar work, flooring, ornamental work
Limestone	Sedimentary, calcareous; varieties include compact and oolitic	Flooring, walling, manufacture of lime and cement, road metal (hard varieties)
Marble	Metamorphic, crystalline, takes a high polish, variety of colours	Flooring, facing, decorative and ornamental work, statues
Slate	Metamorphic, splits into thin non-absorbent sheets	Roofing, damp-proof courses, sills, cisterns
Quartzite	Metamorphic, very hard, durable, difficult to work	Rubble masonry, road metal, concrete aggregate
Gneiss	Metamorphic, banded, strong	Street paving, rough stone work
Laterite	Residual (weathered) rock rich in iron and aluminium oxides; soft when quarried, hardens on exposure	Building blocks in coastal areas (e.g. Kerala, Konkan), road metal
Kankar	Impure limestone nodules	Lime manufacture, road metal for low-traffic roads

Qualities of a good building stone

Crushing strength — adequate for loads; good structural stones commonly have high strength (e.g. granite and trap rank highest; many sandstones and limestones are lower).
Appearance — uniform colour and texture for face work; free from clay holes, spots and cracks.
Durability — resistance to weathering (rain, frost, wind, temperature changes, chemicals).
Hardness — resistance to abrasion (important for floors, pavements, steps); measured by Mohs' scale.
Toughness — resistance to impact (road metal).
Low porosity and water absorption — porous stones absorb water and deteriorate by frost and chemical action (water absorption for good stones is low, commonly below about 5%).
Specific gravity — heavier stones (specific gravity above about 2.7) are generally more compact and durable, suited to dams and retaining walls.
Fire resistance — stones with minerals of different expansion (e.g. granite with quartz) crack in fire; argillaceous stones resist fire better.
Workability and dressing — ease of cutting and dressing (economy).
Texture — fine, compact, crystalline structure is desirable.
Seasoning — freshly quarried stones contain quarry sap and should be seasoned (allowed to dry) before use, commonly for several months.
Availability and cost.

Tests on stones

Test	Purpose / procedure
Crushing strength test	Cube specimens tested in a compression testing machine; strength = failure load ÷ area
Water absorption test	Dry specimen immersed in water (24 hours or boiling); absorption $= \frac{W _{2} - W _{1}}{W _{1}} \times 100$
Specific gravity	$G = \frac{W _{1}}{W _{1} - W _{3}}$ ( $W_{1}$ dry weight, $W_{3}$ weight in water) — heavier stones more compact
Hardness test (Mohs' scale)	Scratching with minerals of known hardness; also Dorry's abrasion test
Impact (toughness) test	Resistance to repeated blows of a hammer (as in aggregate impact tests)
Attrition (Deval) test	Rate of wear of stone pieces rotated in a cylinder — for road stones
Acid test	Stone immersed in dilute hydrochloric (or sulphuric) acid — sharp edges and firm grains indicate resistance to acidic atmospheres; calcareous stones effervesce
Crystalline test	Microscopic examination of crystals
Freezing and thawing (frost) test	Repeated cycles in a freezing mixture — weathering resistance; Brard's test uses sodium sulphate crystallisation
Smith's test	Stone chips shaken in water — clear water indicates absence of soluble or earthy matter

Mohs' scale of hardness

Hardness	Mineral	Hardness	Mineral
1	Talc	6	Orthoclase (feldspar)
2	Gypsum	7	Quartz
3	Calcite	8	Topaz
4	Fluorite	9	Corundum
5	Apatite	10	Diamond

Part 2 of 3

Bricks, Tiles & Clay Products

Last reviewed 16 Sept 2026 · 10 min read

Brick earth

Composition of good brick earth

Constituent	Proportion (approx.)	Role
Alumina (clay)	20–30%	Gives plasticity for moulding; excess causes shrinkage, warping and cracking on drying and burning
Silica	50–60%	Prevents cracking, shrinkage and warping; gives uniform shape and durability; excess makes bricks brittle
Lime	Less than about 5%	In fine powder, reduces shrinkage and helps silica to fuse slightly (binding); excess causes melting and loss of shape; lumps of lime cause splitting
Magnesia	Less than about 1%	Gives a yellow tint; reduces shrinkage; excess causes decay
Iron oxide	About 5–6%	Gives red colour and helps fusion; improves strength and impermeability

Harmful ingredients

Lime lumps — expand on slaking after burning, causing bricks to split (lime bursting).
Iron pyrites — cause crystallisation, discolouration and splitting.
Alkalis (salts of sodium, potassium) — cause efflorescence (white patches) and melting.
Pebbles and gravel — prevent uniform mixing and weaken bricks.
Organic matter and vegetation — leave pores after burning, making bricks porous.

Manufacture of bricks

1. Preparation of clay

Unsoiling (removal of top soil), digging, cleaning (removing stones, roots), weathering (exposure to atmosphere to soften and mature the clay), blending (mixing ingredients) and tempering (mixing with water and kneading — in a pug mill for large-scale production) to obtain a homogeneous plastic mass.

2. Moulding

Method	Description
Hand moulding — ground moulding	Moulds filled on levelled ground; bricks left on the ground
Hand moulding — table moulding	Moulding on a table; bricks carried to drying area
Slop moulding	Mould dipped in water before filling — smooth surface
Sand moulding	Mould sprinkled with sand — prevents sticking
Machine moulding — plastic clay (wire-cut) method	Clay extruded as a column and cut by wires — uniform, many bricks
Machine moulding — dry press method	Nearly dry clay pressed in moulds under high pressure — dense, accurate bricks

A frog — a shallow depression on one face of a hand-moulded brick — provides a key for mortar, reduces weight and may carry the manufacturer's mark. Bricks with frogs are laid frog upward.

3. Drying

Green bricks are dried (naturally in the shade/open air, or artificially in drying chambers) to reduce moisture before burning, preventing cracks and distortion. Natural drying commonly takes one to two weeks depending on weather.

4. Burning

Burning gives strength, hardness and durability through dehydration and partial vitrification of clay; bricks are commonly burnt at around 900–1100 °C.

Kiln / clamp	Type	Features
Clamp	Intermittent, temporary	Bricks and fuel stacked in alternate layers and burnt; cheap, but uneven burning, many under- and over-burnt bricks
Intermittent kilns (e.g. Scotch kiln)	Loaded, fired, cooled and unloaded batch by batch	Better control than clamps; fuel waste in reheating
Bull's trench kiln (BTK)	Continuous, trench in ground (circular or oval); fire moves round the trench	Widely used in India; large output; traditional fixed-chimney kilns cause air pollution
Zigzag kiln	Continuous, air flows in a zigzag path through the bricks	Better fuel efficiency and lower emissions — promoted as an improvement over conventional BTKs
Hoffman's kiln	Continuous, permanent (circular, with chambers and roof)	Burning even in rain; good-quality bricks; high initial cost
Tunnel kiln	Continuous; bricks on cars move through a tunnel with fixed preheating, firing and cooling zones	High quality and output; mechanised factories

Sizes of bricks

Brick	Size (mm)
Modular (IS) brick	190 × 90 × 90 (nominal with 10 mm mortar joint: 200 × 100 × 100)
Modular brick (thinner variant)	190 × 90 × 40
Conventional (traditional) brick	About 230 × 110 × 70 (9″ × 4½″ × 3″)

For modular bricks, about 500 bricks make one cubic metre of masonry (including mortar joints).

Classification of bricks

Traditional (field) classification

Class	Description	Use
First-class bricks	Table-moulded, well burnt in kilns, uniform red colour, sharp edges, metallic ringing sound, no scratch with finger nail, low water absorption	Exposed masonry, important structures
Second-class bricks	Ground-moulded, kiln burnt, slightly irregular shape or colour, fine cracks	Plastered masonry
Third-class bricks	Ground-moulded, burnt in clamps, soft, light-red, dull sound	Temporary structures, sheltered areas
Fourth-class (over-burnt) bricks — jhama	Over-burnt, distorted, very hard, dark	Broken as aggregate (brick ballast) for foundations, floors, lime concrete
Under-burnt bricks	Soft, yellowish, absorbent	Not used for masonry

IS classification (IS 1077)

Common burnt clay bricks are classified by average compressive strength into classes (designations in N/mm²) such as 35, 30, 25, 20, 17.5, 15, 12.5, 10, 7.5, 5 and 3.5 — the class designation is the minimum average compressive strength.

Tests on bricks

Laboratory tests (IS 3495)

Test	Procedure / requirement
Compressive strength	Frog filled with mortar, specimens immersed in water, capped and tested; strength = load ÷ bed area
Water absorption	Dry bricks immersed in cold water for 24 hours (or boiled for 5 hours); absorption = (wet − dry)/dry × 100; for common bricks it should generally not exceed about 20% by weight for lower classes (lower limits for higher classes)
Efflorescence	Bricks placed on end in distilled water in a dish until water is absorbed and evaporated; deposit of white salts rated as nil, slight (up to about 10% of exposed area covered by a thin deposit), moderate (about 10–50%), heavy (more than 50%) and serious (heavy deposit with powdering/flaking)
Dimensional tolerance	Twenty bricks placed in contact in a row along length, width and height; total dimensions must be within specified limits
Warpage	Measurement of distortion of faces

Field tests

Sound test — two bricks struck together should give a clear metallic ringing sound.
Hardness test — no impression when scratched with a finger nail.
Soundness/strength test — a good brick should not break when dropped flat on hard ground from a height of about 1 m.
Shape, size and colour — uniform, with sharp straight edges and uniform colour.
Structure — a broken brick shows a homogeneous, compact structure without holes or lumps.

Part 3 of 3

Building Lime

Last reviewed 16 Sept 2026 · 8 min read

Lime in construction

Lime was the principal binding material before Portland cement and remains useful in mortars, plasters, whitewash, soil stabilisation and restoration of heritage buildings.

Sources: limestone, chalk, kankar (impure nodular limestone), shells (sea shells), dolomite (for magnesian lime).

Terms

Term	Meaning
Calcination	Heating limestone to a high temperature (around 900 °C) to drive off CO₂
Quicklime (caustic lime)	Calcium oxide (CaO) obtained by calcination — white, amorphous, very reactive with water
Slaking	Chemical combination of quicklime with water, with heat, hissing and swelling
Slaked lime (hydrated lime)	Calcium hydroxide Ca(OH)₂ — a fine white powder
Milk of lime	Thin suspension of slaked lime in water — used for whitewash
Lime putty	Thick paste of slaked lime and water — for plaster and mortar
Setting	Hardening of lime — by carbonation (fat lime) or by hydration of silicates and aluminates (hydraulic lime)

Chemistry of lime

FormulaReactions

Calcination:

C a C O_{3} \approx 900 ° C C a O + C O_{2}

Slaking (exothermic, volume increases):

C a O + H_{2} O \to C a (O H)_{2} + heat

Setting by carbonation (slow; needs air):

C a (O H)_{2} + C O_{2} \to C a C O_{3} + H_{2} O

Hydraulic set: clay (silica and alumina) in limestone forms calcium silicates and aluminates on burning, which hydrate and harden like cement, even under water.

Molecular weights: CaCO₃ = 100, CaO = 56, CO₂ = 44, H₂O = 18, Ca(OH)₂ = 74.

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