Brick & Block – Comprehensive Study Notes

Learning Outcomes

• Upon completion of the lecture, students should be able to:

  • Explain the definition of brick and block.

  • Classify the various types of bricks and blocks.

  • Identify production / manufacturing methods for both bricks and blocks.

  • Describe key physical, mechanical, and durability‐related properties of bricks and blocks.

Introduction: What Is a Brick?

• Brick = Building material used for constructing walls, pavements, linings, partitions, foundations, and other masonry elements.

• Typical raw materials: clay, cement, fly ash.

• Core advantages in practice:

  • Durability (withstands weathering, mechanical wear).

  • Fire resistance (non-combustible, high melting point).

  • Cost effectiveness & availability (abundant raw materials, scalable production).

  • Thermal mass → moderates indoor temperature swings.

Fundamental Ingredients of a Standard Clay Brick

• “Trick” mnemonic SALIM summarises composition of a good brick:

  • S – Silica (sand) $\approx 50\text{–}60\%\,\text{by weight}$

  • Fills the matrix, improves workability, controls shrinkage.

  • A – Alumina (clay) $\approx 20\text{–}30\%$

  • Provides plasticity during moulding, key for bonding.

  • L – Lime $\approx 2\text{–}5\%$

  • Reacts with silica, promotes fusion. Excess ⇒ cracking / warpage.

  • I – Iron Oxide $\le 7\%$

  • Contributes reddish colour, enhances strength & weather resistance.

  • M – Magnesia <1\%

  • Adds yellow tint, reduces shrinkage, improves glaze finish.

Brick Dimensions & Terminology

• Actual size: Physical size of the unit excluding mortar.

• Nominal size: Actual size $+$ thickness of mortar joint (typically $10\,\text{mm}$).

• Modular brick: Sized so that multiples fit a design module, streamlining layout.

• Current common UK sizes (including $10\,\text{mm}$ mortar):

  • Work size $215 \times 102.5 \times 65\,\text{mm}$

  • Format size $225 \times 112.5 \times 75\,\text{mm}$

• Key faces / edges:

  • Arise – sharp edge from plane‐plane intersection.

  • Frog – depressed section on face, reduces weight & improves mortar bond.

  • Stretcher – long face seen in elevation $\left(190 \times 90\,\text{mm}\right)$.

  • Header – end face $\left(90 \times 90\,\text{mm}\right)$.

  • Bed – bottom face laid in mortar.

Classification of Bricks

• Burnt clay brick (traditional)

• Concrete brick / CMU

• Sand-lime (calcium silicate) brick

• Fly-ash brick

• Fire (refractory) brick

• Engineering brick

• Facing brick

1. Burnt Clay Brick

• Manufacturing: Clay moulded → dried $24\text{–}48\,\text{h}$ → fired in kiln $900\text{–}1200^{\circ}\text{C}$ for $48\text{–}72\,\text{h}$ → cooled, packaged.

• Properties:

  • Compressive strength $7\text{–}20\,\text{MPa}$

  • Water absorption <20\%

  • Good fire & weather resistance, moderate thermal insulation.

• Typical applications: Load-bearing & partition walls, pavements, selected foundations.

2. Concrete Brick (Concrete Masonry Unit – CMU)

• Composition: Portland cement $+$ aggregates $+$ water.

• Process: Mix → vibrate & compact into steel moulds → cure (steam / autoclave) instead of firing.

• Properties:

  • Compressive strength $7.5\text{–}15\,\text{MPa}$ (higher grades available).

  • Lower water absorption vs clay bricks.

  • Highly dimensionally accurate, variety of colours/textures.

• Uses: Foundations, load/non-load walls, pavements, retaining walls (reinforced).

3. Sand-Lime (Calcium-Silicate) Brick

• Ingredients: Sand $+$ lime $+$ water (+ pigments).

• Production: Mix → press into moulds → cure in autoclave (steam) for $6\,\text{h}$.

• Properties:

  • Compressive strength $7\text{–}15\,\text{MPa}$

  • Water absorption $\approx 15\text{–}20\%$

  • Very smooth finish, high dimensional accuracy, good sound/fire insulation.

• Applications: Load & non-load walls, facing units, partitions in multi-storey buildings.

4. Fly-Ash Brick

• Mix: Fly ash $50\text{–}70\%$ $+$ cement or lime $+$ gypsum/sand/water.

• Cured (not fired), often in autoclave.

• Properties:

  • Compressive strength $7.5\text{–}12\,\text{MPa}$ (premium >$12$).

  • Water absorption <10\text{–}15\%.

  • Lightweight (≈$20\text{–}30\%$ lighter than clay), good thermal & acoustic insulation.

• Uses: High-rise walls, partitions, foundations in non-aggressive soils.

5. Fire (Refractory) Brick

• Made from alumina-rich clay + silica; sometimes special oxides.

• Characteristics:

  • Heat resistance up to $1500^{\circ}\text{C}$; retains strength after thermal shock.

  • Low thermal conductivity (insulating grades) or high density (dense grades) depending on purpose.

  • Chemically inert to slag, gases.

• Applications: Linings of kilns, furnaces, fireplaces, pizza ovens, stoves.

• Limitations: High cost, specialised mortar & installation.

6. Engineering Brick

• High-performance clay/shale units fired at higher temp; two common British classes:

  • Class A: $\ge 125\,\text{MPa}$ strength, water absorption <4.5\%.

  • Class B: $\ge 75\,\text{MPa}$ strength, water absorption <7\%.

• Properties: Very low porosity, excellent acid/frost/abrasion resistance.

• Uses: Damp-proof courses, bridges, tunnels, retaining walls, manholes.

• Downsides: Expensive, hard to cut, limited aesthetic range.

7. Facing Brick

• Purpose: Provide aesthetically pleasing, weather-resistant façade. May or may not be structural.

• Typical properties: Moderate-high strength, low-moderate absorption, fade-resistant colours.

• Finishes: Antique, rock face, cobble, sand blast, smooth, etc.

• Advantages: Boosts curb appeal, low maintenance, suits modern & traditional styles.

Brick Manufacturing Methods (Recap Table)

• Clay route: Mix → extrude or mould → dry → fire in kiln $\approx 1100^{\circ}\text{C}$ (≈$3\,\text{days}$ cycle).

• Concrete route: Mix cement + aggregates → vibrate/compact → cure $28\,\text{days}$ (accelerated steam optional).

• Calcium-silicate route: Mix lime/cement + silica → press → autoclave $6\,\text{h}$.

Brick vs. Block: Modular Relationship

• Dimensional convention:

  • Standard brick: $215 \times 102 \times 65\,\text{mm}$ (nominal).

  • Standard block: $440 \times 215 \times 100\,\text{mm}$.

• One standard block ≈ $6$ bricks (two bricks long, three bricks high).

• Implications:

  • Blocks cover more area faster → labour savings.

  • Different thermal & structural performance trade-offs.

Block Types & Characteristics

• Material families:

  • Concrete blocks (dominant in modern construction).

  • Clay blocks (less common; mainly hollow terra-cotta in some regions).

Concrete Blocks – General Manufacturing

1. Combine Portland cement, sand, fine gravel (for high density) + water.

2. Compact mixture into mould box.

3. De-mould, then cure (ambient or steam) to achieve design strength.

Concrete Block Properties & Advantages

• Typical size: $450 \times 225 \times 100\,\text{mm}$ (may vary by code).

• Mass: $17.2\text{–}19.5\,\text{kg}$ (lightweight aerated variants lighter).

• Roles: Load-bearing & non-load walls; excellent substrate for rendering.

• Advantages vs bricks:

  • Larger unit ⇒ fewer joints ⇒ quicker construction & reduced mortar.

  • Better thermal insulation (especially aerated blocks; entrained air pockets).

  • Easier to saw, nail, drill.

Block Categories by Void Configuration

• Solid block: No formed voids → highest density & strength.

• Cellular block: One or more un-penetrating voids (do not pass through).

• Hollow block: Voids extend fully through unit; lighter, allows reinforcing & grouting.

Practical / Ethical / Sustainability Notes

• Fly-ash bricks divert industrial waste (fly ash) from landfills, lowering carbon footprint.

• Autoclaved sand-lime bricks use lower firing temps than traditional kilns ⇒ reduced energy.

• Concrete CMUs can incorporate recycled aggregates (glass, slag).

• Fire & engineering bricks enhance safety (fire resistance, chemical durability) in critical infrastructure.

Connections to Foundational Principles

• Masonry design relies on compressive strength: $\sigma_c = \frac{F}{A}$; values quoted for each brick/block inform allowable loads.

• Thermal insulation performance relates to thermal conductivity k; hollow or aerated units reduce $k$ via entrapped air.

• Dimensional coordination aligns with modular grid systems in architectural design, minimising on-site cutting and waste.

Quick Reference – Typical Strength & Absorption Ranges

• Burnt clay: \sigmac = 7\text{–}20\,\text{MPa},\; w{abs}<20\%

• Concrete: $\sigma<em>c = 7.5\text{–}15\,\text{MPa},\; w</em>{abs}\downarrow$

• Sand-lime: $\sigma<em>c = 7\text{–}15\,\text{MPa},\; w</em>{abs}=15\text{–}20\%$

• Fly-ash: \sigmac = 7.5\text{–}12\,\text{MPa},\; w{abs}<10\text{–}15\%

• Engineering: $\sigma<em>c = 75\text{–}125\,\text{MPa},\; w</em>{abs}\ll$

• Fire brick: Heat endurance $\le 1500^{\circ}\text{C}$

End‐of-Lecture Checklist

• Know SALIM composition.

• Memorise standard brick & block sizes.

• Distinguish manufacturing methods (fired vs cured vs autoclaved).

• Match each brick type to core properties & applications.

• Understand advantages / disadvantages of blocks vs bricks in real projects.