Concrete is a fixture in urban infrastructure, from interstate highways to towering city skyscrapers. Concrete can be spotted anywhere to no surprise as it is the most commonly used manmade material in the world. In the United States alone, approximately 10 billion tons of concrete are produced annually.
Concrete is an exceptionally versatile building material with malleable or solid properties, depending on its stage of curing. It consists of aggregates and rocks mixed with fluid cement. After a certain amount of time, concrete hardens into a rock-like mass due to a chemical reaction known as hydration. Once hardened, it becomes exceptionally strong and durable at a strength of 3000–20,000 psi—enough to hold up bridges, skyscrapers, and dams.
Concrete is produced at a plant or on a job site. Equipment can vary from hand tools to large industrial machinery. Whatever the scale of production, concrete components must be thoroughly mixed, molded, and shaped within specific time constraints. Any disruptions can affect the integrity and appearance of the final product.
Large-scale concrete production
Large-scale concrete production takes place in two types of concrete plants: ready-mix plants and central mix plants. Ready-mix plants mix all concrete components except for water. Central mix plants mix all concrete components including water and are best for accurate control. Typically, concrete is a viscous fluid that is poured into molds to give a desired shape. However, concrete can also be in non-fluid form. This dryer version is preferred for manufacturing precast concrete products.
Small-scale concrete production
Smaller amounts of concrete are made at a job site using a volumetric mixer or mobile batch mixer. These mixers serve as mini concrete plants, capable of producing various types of concrete. They are perfect for sites that only require minimal concrete for installing smaller applications. For example, an installer uses a volumetric mixer to make concrete for embedding bike racks, or for installing bollards and steel pipes as traffic safety devices.
Types of concrete
There are dozens of concrete types available on the market for construction and building needs. Listed below are a few common types of concrete used in modern infrastructure.
Ordinary concrete is one of the most popular forms of concrete. A typical mix includes cement, sand, and coarse aggregates mixed with specific quantities of water. It has a setting time of approximately 30–90 minutes with strength values of 1450–5800 psi. At 28 days of curing, 75–80% of total strength is achieved, and after 90 days, 95% is achieved.
High-performance concrete has higher strength, workability, and durability compared to ordinary concrete. It has long-term mechanical properties and early age strength. It can withstand harsh environments and is resistant to creep and shrinkage which minimizes cracking. Strength ranges from 10000–15000 psi.
Reinforced concrete uses various forms of steel as reinforcement. The combination of concrete (with its high compressive strength) and steel (with its high tensile strength) gives reinforced concrete its unique strength properties. Reinforced concrete has the capacity to endure many forms of stress in any type of construction.
Precast concrete casts concrete into molds in a controlled environment. Once completely set and hardened, they are transported to the construction site. The curing stage happens under controlled conditions where temperature and humidity are monitored. Steam curing is sometimes used to produce precast products with high strength with less curing time.
Lightweight concrete is any concrete with a density less than 240 kg/m³. It includes lightweight aggregate concrete, foamed concrete, and autoclaved aerated concrete. Lightweight concrete typically improves thermal abilities and fire resistance. However, it is more susceptible to creep and shrinkage.
Pervious concrete allows air or water to circulate through a series of holes or voids created within the concrete. Water can drain naturally, allowing for the drainage of surface water and replenishment of groundwater. It is a low-impact development material that protects water quality and used in sustainable construction.
Before starting on any concrete application, the appropriate concrete type must first be determined. For example, reinforced concrete is suitable for building materials requiring high tensile strength, such as columns and beams. Lightweight concrete is best for building light concrete blocks for home construction.
Concrete is a versatile material and its applications are plentiful. Concrete’s malleable, yet tough characteristics make it ideal base materials for constructing buildings, urban infrastructure, and various precast products.