Chapter 5- Clay and Clay Products

Page 1: Course Overview

  • Compiled By: Zerihun M.

  • Title: Lecture Notes on Clay & Clay Products

  • Institution: Adama Science and Technology University

  • School: Civil Engineering and Architecture

  • Course Name: Construction Materials

  • Course Code: CEng- 2205

  • Instructor: Zerihun M.

  • Level: 2nd Year Students

  • Chapter: Clay and Clay Products

  • Year: 2024 GC

  • Location: Adama, Ethiopia

Page 2: Introduction to Clay Products

  • Purpose: Discuss the application of clay products in civil engineering.

  • Clay Definition: Finely grained soils resulting from rock decay, categorized as residual or sedimentary based on their formation and transport.

  • Chemical Constituents of Clay:

    • Hydrate of alumina silicate: A12O3.2SiO2.2H2O

    • Key chemicals in clay:

      • Silica (SiO2)

      • Ferric Oxide (Fe2O3)

      • Lime (CaO)

      • Magnesia (MgO)

      • Carbon Dioxide (CO2)

      • Alkalies (K2O, Na2O)

      • Water

  • Impurities: Clays often contain impurities that influence their properties.

Page 3: Manufacturing Process of Clay Products

  1. Mining: Extracting clay from earth via open-pit or underground mining.

  2. Processing: Removing impurities, possibly through washing with water or chemical treatments.

  3. Blending: Mixing different clays to achieve desired properties (e.g., kaolin, ball clay).

  4. Forming: Shaping clay using methods like extrusion or pressing.

  5. Drying: Reducing moisture content through air-drying or kiln drying.

  6. Firing: High-temperature treatment to harden and strengthen the clay.

Types of Clay Products

  • Bricks: Commonly used as artificial stones in construction; available in various types, including mud, refractory, silica, and fire bricks.

Page 4: Raw Materials for Brick Production

  • Components: Brick-making clays consist of key chemical elements like:

    • Alumina (Al2O3)

    • Silica (SiO2)

    • Ferric Oxide (Fe2O3)

    • Lime (CaO)

    • Magnesia (MgO)

    • Carbon Dioxide (CO2)

    • Sulphur Trioxide (SO3)

    • Alkalies (K2O, Na2O)

    • Water (H2O)

  • Quality Requirements for Clay: A suitable clay for brick-making should be capable of molding and firing without cracking or changing shape.

    • Recommended Composition:

      • Clay: 20-40%

      • Sand: 30-50%

      • Others (lime, silt, loam): 20-35%

Page 5: Functions of Constituent Materials

  • Alumina: Enhances plasticity, moldability, and strength after firing, but risks shrinkage and cracking.

  • Silica: Reduces shrinkage; contributes to hardness and durability (high content in firebricks).

  • Lime: Acts as a flux, lowers fusion temperatures, and enhances binding. Excess can lead to melting issues.

  • Iron Oxide: Affects fusion point and color of bricks; can cause cracking if present in pyritic form.

  • Manufacturing Stages: Overview of interdependent operations in brick manufacturing.

Page 6: Clay Preparation and Molding Techniques

Clay Preparation

  • Breaking Down Raw Clay: Involves crushing, grinding, and mixing while adding tempering water to enhance plasticity.

Molding Techniques

  • Soft-Mud Process: Utilizes high moisture clay; mechanically forced into molds.

  • Stiff-Mud Process: Extrudes clay through dies to cut bricks into predetermined shapes.

  • Dry-Pressed Bricks: Made from non-plastic clays compacted into molds.

Page 7: Drying and Firing Processes

  • Drying: Reduces moisture before kiln firing; can take several days or weeks.

  • Firing Stages:

    • 100°C: Evaporation of water

    • 400°C: Carbon combustion

    • 700°C: Dehydration

    • 900°C: Oxidation

    • 900-1000°C: Sintering

  • Importance of Firing Control: Proper temperature management is key to achieving quality bricks.

Page 8: Types of Bricks

  • Common Bricks: Basic, inexpensive bricks with no aesthetic finish.

  • Facing Bricks: Designed for appearance; free from defects and suitable for external use.

  • Engineering Bricks: High strength, durability, and density; used in demanding applications.

Ethiopian Standards for Clay Bricks

  • Solid Clay Bricks:

    • Types based on holes or depressions: Type TS, TH, TD.

    • Standard dimensions of solid bricks.

  • Hollow Clay Bricks:

    • Types based on design (e.g., keyed for plastering).

    • Standard dimensions for hollow bricks.

Page 9: Functions of Indentations in Bricks

  • Structural Contribution: Facilitates bonding and reduces firing time while conserving material.

Page 10: Tests and Classification of Bricks

Field Tests

  • Includes appearance, hammer tests, and hardness assessments.

Laboratory Tests

  • Quality Assessment: Includes dimensional verification, strength, water absorption, and efflorescence tests.

  • Classifications based on compressive strength and water absorption limits.

Page 11: Efflorescence and Expansion

  • Efflorescence: Formation of white deposits due to dissolved salts; assessed through saturation tests.

  • Expansion on Wetting: Increase in volume due to moisture absorption; requires movement joints in construction.

Page 12: Thermal Expansion and Tiles

Thermal Expansion

  • Coefficient: Approx. 7x10^-6 per °C; typically not a significant issue in brickwork.

Types of Tiles

  • Definitions: Thin slabs of burnt bricks, categorized into common and encaustic tiles.

Page 13: Ceramics Overview

  • Ceramics Definition: Inorganic, non-metallic materials with significant historical applications; essential in understanding technological advances.

Properties Comparison

  • Ceramic vs. Metals vs. Polymers: Showing differences in density, hardness, ductility, wear resistance, and corrosion resistance.

Page 14: Classification of Ceramic Materials

  • Common classifications based on composition and applications.

Types of Ceramics

  1. Silicate Ceramics: Include alumosilicates and magnesium silicates; differences in water absorption depend on type.

  2. Oxide Ceramics: Non-metallic materials characterized by high melting points; example: aluminum oxide.

  3. Non-Oxide Ceramics: Offer solutions for high-wear and high-temperature applications.

  4. Glass-Ceramics: Share features of both glasses and ceramics; used for specific properties like biocompatibility.

Page 15: Earthenware and Stoneware

Earthenware

  • Details on production, glazing properties, and applications (e.g., drainage pipes, conduits).

Stoneware

  • Characteristics of stoneware, applications in sanitary ware, durability, and resistance to corrosion.

Page 16: Porcelain Production

  • Definition: Fine, delicate ware made from high-quality clay; widely used in decorative and functional items.