Civil Engineering Building Materials

Materials Composition and Structure

• The composition of materials includes chemical composition and mineral composition, which are key factors for the properties of materials.
• Chemical composition refers to the chemical constituents, and various chemical compositions result in different properties.
• For example, the increase of carbon content in carbon steel changes its strength, hardness, and toughness.
• Mineral composition is the key factor for the properties of some building materials, such as natural stone, inorganic gel, and cement.

Structure of Materials

• The structure 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 refers to the thick structure above millimeter that can be identified with a magnifying glass or naked eyes, and is considered at the engineering level.
• Macro-structure is normally taken as continuous and homogeneous, and average properties are 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, and is also known as sub-microstructure.
• This level is a step up in size from the molecular level, and the material is considered as a composite of different phases that interact to realize the behavior of the total material.
• The size, shape, and interface of grains and particles, and the size, shape, and distribution of pores and micro-cracks are mainly studied in this structure.

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, the building block of elements, consist of a nucleus surrounded by a cloud of orbiting electrons.
• The bonding of atoms is essential to form materials, and there are three types of bonds: ionic bond, covalent bond, and metallic bond.

Atomic Bonds

• Ionic bond involves a transfer of an electron, resulting in a high strength, hardness, and melting point, but with a volatile and medium density.
• Covalent bond involves the sharing of electrons between two atoms, resulting in a strong bonding force, high strength, hardness, and melting point, and high density.
• Metallic bond involves sharing electrons, resulting in a volatile strength and hardness, high density, and good thermal and electrical conductivity.