What is concrete? An overview of this versatile building material

Concrete is one of the most widely used building materials in the world. It can be found everywhere: in buildings, bridges, roads, and even works of art. But what exactly is concrete, and why is it so important to the construction industry? In this article, you'll learn what concrete is made of, how it's produced, and why it's essential to our modern world.

The history of concrete

Concrete is not a new building material—its history dates back to ancient times. Over 2,000 years ago, the Romans used a precursor to today's concrete, known as "Opus Caementitium." "Roman concrete" was a mixture of lime, water, sand, and stone. The Romans used this concrete to build some of the world's most impressive structures, such as the Pantheon in Rome. The dome of this building remains the largest self-supporting concrete dome in the world.

The components of concrete

Until the development of modern concrete, concrete was known as a “3-material mixture”:

• cement
• Aggregates (sand/gravel)
• Water

Since the mid-20th century, admixtures and additives have been added to concrete to positively influence certain fresh and hardened concrete properties. Since then, this has been referred to as the "5-component mixture":

• cement
• Aggregates (sand/gravel)
• Water
• Additives (flow agents, stabilizers, defoamers, etc.)
• Additives (silica dust, rock flour, trass, etc.)

Cement: Cement is a so-called "hydraulic" binder. This means that it fully hardens even under water or in the absence of air. Cement consists of limestone and clay (marl), which is fired at 1450°C (until sintering) and then finely ground together with other major and minor components. As soon as cement comes into contact with water, a chemical reaction known as hydration begins. This reaction causes the cement to harden and firmly bind the rock particles together. To ensure that the cement remains workable once it comes into contact with water, up to 5% gypsum (a minor component - less than 5%) is added at the factory. Important! Gypsum may only be added at the factory! Never by the user!

Aggregates: Aggregates include sand, gravel, or chippings from various rock types; granite is frequently used. Only "suitable" aggregates may be used. Many factors play a role in determining "suitability," including:

• Compressive strength
• Acid resistance
• Frost and de-icing salt resistance
• Abrasion resistance
• Chloride content

They form the "framework" of concrete and make up the majority of its volume. Mixing different grain sizes creates a dense structure, which is crucial for concrete strength.

Water: Without water, there is no concrete. Water is necessary to activate hydration and make the mix workable. Cements require approximately 40% of their own weight to fully complete the hydration process. If more water is added than the cement can absorb (so-called "excess water"), this improves the workability of the concrete but also reduces its strength. This is because the "excess water" evaporates from the hardened concrete and leaves capillary pores in the concrete structure, which negatively impacts the hardened concrete properties in almost every respect.

Admixtures and additives: Admixtures are chemical substances that are added to concrete in small quantities to improve certain fresh or hardened concrete properties, such as consistency, density, setting rate, air void content, etc.

Admixtures are substances that are often added in such large quantities that they must be taken into account in the volumetric calculation. Their primary purpose is to positively influence the consistency of fresh concrete as well as the strength and density of hardened concrete.

From fresh to hardened concrete

Fresh concrete is the term for concrete before it has hardened. In this state, it is still workable and can be poured into any desired shape. Once the concrete has hardened, it is referred to as hardened concrete. Cement paste -> cement gel -> cement stone.

The strength of concrete depends on several factors, including the mixing ratio of water to cement (the so-called "water-cement ratio"), the type of aggregate used, and the grading curve. Concrete typically needs to cure for about 28 days to reach its full strength.

Different types of concrete

Depending on the application, there are different types of concrete:

Regular concrete: The most common form of concrete used for many construction projects. It consists of the main components listed above and is used in buildings, bridges, and roads.

Lightweight concrete: Lightweight concrete is often used in residential construction where good thermal insulation or low weight for transport, assembly, and use is required. Lighter aggregates such as pumice or expanded clay are used.

Heavy-duty concrete: This concrete is particularly dense and heavy and is primarily used for radiation protection in hospitals or nuclear power plants. Ballast weights in ships or counterweights for cranes and bridge abutments are other applications. Steel scrap is often used as an aggregate.

Environmental compatibility and sustainability

Concrete has a reputation as an environmentally friendly building material when used correctly. Recycled materials are used in concrete production, and the use of so-called secondary raw materials can reduce the consumption of natural resources. Concrete also offers the possibility of constructing structures that can be used for many decades, thus conserving resources in the long term.

However, it's important to note that the production of cement—a key component of concrete—is energy-intensive and generates CO2 emissions. Therefore, research is underway to develop alternative binders that are more environmentally friendly.

The importance of concrete in the modern world

Concrete has become an integral part of our modern world. It can be found everywhere – in the streets we drive on, the bridges we cross, and the buildings we live and work in. Concrete's versatility makes it an indispensable building material for many different construction projects.

Concrete can be cast into almost any shape, giving architects and engineers great design freedom. It is also highly durable and can withstand extreme weather conditions. These properties make concrete one of the most important building materials of our time.

Conclusion

Concrete is a fascinating building material with a very long history and a bright future. Its versatility, strength, and durability make it an indispensable material for the construction industry. With the continued development of more environmentally friendly manufacturing methods, concrete will continue to play a central role in the design of our infrastructure and architecture.