Let’s take a detailed look at the five most commonly used building materials!

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Let’s take a detailed look at the five most commonly used building materials! The main building materials include cement, steel bars, wood, ordinary concrete, clay bricks, etc. 1. Cement (1) Common types of cement: there are five types, namely portland cement, ordinary portland cement, slag portland cement, pozzolanic portland cement, and fly ash portland cement. (2) Cement grade: The cement grade indicates the compressive strength of the cement after it has hardened. Common cement grades include, for example: 325, 425, 525, 625, etc. (3) Technical properties of common cement: Setting time: The setting time of cement is divided into initial setting and final setting. Initial setting is the time when cement mixed with water turns into a paste that loses its plasticity. Final setting is the time from when mixing of the cement paste begins until the cement loses all its plasticity and starts to develop strength. Volume stability: refers to the property of whether the volume change of cement is uniform during the hardening process. Uneven volume changes that occur after cement hardens result in poor volume stability, rendering it unusable. Hydrothermal reactivity: The hydration reaction of cement is an exothermic reaction. As the hydration process progresses, the continuous release of heat is known as hydrothermalization. The amount of heat released during its hydrothermal reaction, as well as the rate at which this heat is released, are primarily determined by the cement grade, mineral composition, and fineness. Fineness: Refers to the degree of coarseness or fineness of cement particles. The finer the particles, the higher the early strength. However, the finer the particles, the higher the production cost, and they are prone to becoming damp and losing their functionality. Standard consistency water requirement: refers to the amount of water required for the cement mortar to reach standard consistency. Standard consistency is the consistency specified by standards for testing the soundness and setting time of cement. 2. Rebar (1) Types of construction rebar: Rebar is produced by hot-rolling steel ingots; hence it is also known as hot-rolled rebar. It is the most widely used type of steel in construction projects. Based on their shape, they can be divided into plain round bars and ribbed bars. According to the type of steel, they can be divided into carbon steel rebar and ordinary low-alloy steel rebar. Based on strength, it can be divided into four grades: I, II, III, and IV. Among them, grade I steel bars are low-carbon steel bars, while grades II, III, and IV are low-alloy steel bars. (2) Application of steel bars in construction: Grade I steel bars are hot-rolled plain bars with relatively low strength, but good plasticity and weldability. It is widely used in parts of ordinary reinforced concrete structures that are subject to less stress. Reinforcing bars of grades II and III among deformed steel bars exhibit good comprehensive performance parameters such as strength, plasticity, and weldability; they are the most widely used type of reinforcing bar in ordinary reinforced concrete structures. They can also be used as prestressed bars after cold drawing. Cold-worked steel bars: Steel bars that have been cold-drawn exhibit an increased yield strength, but reduced plasticity. Cold-drawn Grade I steel bars are suitable for load-bearing parts in ordinary reinforced concrete, while cold-drawn Grade II, III, and IV steel bars can all be used as prestressed bars. Cold-drawn low-carbon steel bars: They possess high tensile strength and are the primary prestressing materials for small structural elements. 3. Timber (1) Types of timber: It is divided into two categories – coniferous trees and broad-leaved trees. Among them, coniferous trees have tall and straight trunks with straight grain; their wood is relatively soft and easy to work with, making them the primary materials used in construction projects. Broadleaf tree wood is relatively hard and is referred to as hardwood; it is mainly used in construction projects. (2) Properties and uses of construction timber: Red pine: It has a soft texture with straight grain, is resistant to warping and cracking, contains plenty of resin, is resistant to decay, and is easy to work with; it is mainly used for making doors and windows, roof trusses, purlins, formwork, etc. Fish-scale spruce: also known as white pine. It has a light weight, straight texture, fine structure, dries easily, and is easy to process; it is mainly used for making doors, windows, formwork, floors, etc. Masson pine: It has a moderately hard texture, with straight to irregular grain patterns; its structure is medium to coarse. It is not resistant to decay, has a strong resinous odor, and is very durable in water. It is mainly used for making formwork, doors and windows, rafters, and wooden columns. Larch: Its wood is hard and brittle, it contains a lot of resin, is resistant to decay, dries slowly, and is prone to cracking during drying. It is mainly used for purlins, floors, wooden piles, etc. Chinese fir: It has a straight and even grain, a medium to coarse structure, dries easily, and is highly durable. It is mainly used to manufacture roof trusses, purlins, doors and windows, scaffolding poles, etc. Cypress: It has a dense texture, with straight or slanted grain; its structure is fine, and it tends to crack when dried, yet it is tough and durable. It is mainly used for making templates and wood inlay decorations, etc. Spruce: There are two types, with fine bark and thick bark. Fine-pored surfaces are delicate, resistant to deformation, easy to process, and suitable for high-standard decoration ； The rough-skinned version has a looser structure, but it is sturdy with minimal deformation and shrinkage, making it suitable for decorations with modest requirements. (3) Categories of timber: For rational use of timber, it is classified into logs, cedar logs, square timbers, etc., based on differences in processing and application. Log refers to wood that has been felled, pruned, and cut into a certain length. There are logs for direct use and logs for processing. Sugihara jo refers to cedar wood that has only been pruned and peeled, without being processed into finished timber; it is at least 5 meters in length and has a diameter at the tip of at least 60 mm. Plate and square timber refers to plates and squares that are processed to specific dimensions. A slab refers to one whose cross-sectional width is three times or more of its thickness ； Square timber refers to those whose cross-sectional width is less than three times their thickness. 4. Ordinary concrete (1) Concept of ordinary concrete: It is primarily a type of concrete made from cement, ordinary crushed stone, sand, and water. Among them, stones and sand serve as a framework, and are known as aggregates. Gravel serves as the coarse aggregate, while sand serves as the fine aggregate. When water is added to cement, it forms cement paste that coats the surface of the aggregates and fills the gaps between them. This paste acts as a lubricant between the aggregates, giving the concrete mixture the workability necessary for construction. Once the cement hydrates and hardens, it binds the aggregates together to form a solid structure. (2) Properties of concrete: Workability of concrete: This refers to whether concrete is easy to handle during construction, and whether it has the ability to ensure that the quality of the poured components is uniform and their formation is dense. Strength of concrete: Compressive strength is the main indicator of concrete strength; it is much higher than other types of strength associated with concrete. In engineering applications, it is this compressive strength that is utilized, and it also serves as the primary basis for structural design. Durability of concrete: The ability of concrete to resist degradation caused by various natural environments is known as durability. In addition to having sufficient strength to safely bear loads, concrete must also possess durability, such as resistance to water penetration, freezing, wear, and weathering. 5. Clay bricks: Clay bricks are made from clay as the main raw material; this clay is first mixed to achieve plasticity, and then shaped through mechanical pressing. The extruded soil clumps are called brick blanks; after air-drying, they are sent into a kiln where they are burned at high temperatures of 900–1000°C to become bricks. (1) Types of clay bricks: Standard bricks: Standard bricks are the most commonly used bricks in construction projects. They are widely employed in load-bearing brick walls as well as in non-load-bearing filler walls. The dimensions of the clay brick are: 240mm×115 mm×53 mm. Each brick weighs about 2.5 Kg when dry, and about 3 Kg after absorbing water. Hollow bricks and porous bricks: The dimensions of hollow bricks are 190 mm×190 mm×90 mm, with a weight of approximately 1100 Kg per cubic meter. The specifications of the perforated brick are 240 mm×115 mm×90 mm, with a weight of approximately 1400 Kg per cubic meter. (2) Strength of clay bricks: Clay bricks are characterized by high compressive strength, allowing them to withstand significant external forces. The ability of brick to withstand external forces is called strength ； The degree that reflects the intensity is called the strength grade. Which strength grade of bricks should be used for a building shall be determined by the design unit through calculations. (3) Water absorption rate of clay bricks: Clay bricks all have a certain degree of water absorption capability, allowing them to absorb a specific amount of moisture; the extent of this water absorption can be expressed by the water absorption rate. The water absorption rate is generally allowed to be within the range of 8%–10%. (4) Frost resistance of clay bricks: refers to the ability of the bricks to resist frost damage. Freeze resistance is determined through experiments. (5) Appearance quality of clay bricks: Ordinary clay bricks should have a smooth and regular shape. The appearance shows no obvious defects such as bending, missing edges, chipped corners, or cracks; it produces a clear metallic sound when tapped, and its color is uniform.