Building Materials Chapter 1

Materials Composition and Structure

• Materials composition includes chemical composition and mineral composition, which are key factors for the properties of materials.
• Chemical composition refers to the chemical constituents, and varying chemical compositions result in different properties.
• For example, increasing carbon content in carbon steel changes its strength, hardness, and toughness, making it prone to rust, which can be addressed by adding chromium, nickel, and other chemical components to create stainless steel.

Mineral Composition

• Many inorganic materials consist of various mineral compositions, which are key factors for the properties of some building materials (e.g., natural stone, inorganic gel, and other materials).
• Cement exhibits different characteristics due to different clinkers.

Structure of Materials

• The structures of materials can be divided into macro-structure, meso-structure, and micro-structure, which are key factors related to the properties of materials.

Macro-structure

• Macro-structure refers to the thick structure above millimeter that can be identified with a magnifying glass or naked eyes.
• At the engineering level, the total material is considered, and it is normally taken as continuous and homogeneous, with average properties assumed throughout the whole volume of the material body.
• The minimum scale that must be considered is governed by the size of the representative cell, which varies from 10^(-3) m for metals to 0.1 m for concrete and 1 m for masonry.

Meso-structure

• Meso-structure refers to the micro-level structure that can be observed by optical microscope.
• It includes the size, shape, and interface of grains and particles, and the size, shape, and distribution of pores and micro-cracks.
• The material is considered as a composite of different phases, which interact to realize the behavior of the total material.

Microstructure

• Microstructure refers to the atomic and molecular structures of materials that can be studied by electron microscopy, X-ray diffractometer, and other means.
• Atoms consist of a nucleus surrounded by a cloud of orbiting electrons, and the nucleus consists of positively charged protons and neutral neutrons.

Bonding of Atoms

• Atoms tend to arrange themselves in the most stable patterns possible, which means they have a tendency to complete or fill their outermost electron orbits.
• Ionic bonding involves a transfer of an electron, resulting in high strength, hardness, and melting point, but also volatility and medium density.
• Covalent bonding involves the sharing of electrons between two atoms, resulting in strong bonding force, high strength, hardness, melting point, and density.
• Metallic bonding involves sharing electrons, resulting in volatile strength and hardness, high density, and good thermal and electrical conductivity.