What is Concrete?
Concrete is the second most widely used material on Earth after water! In fact, the world is inconceivable without concrete because modern urban development depends on this popular material. The reason for using concrete is not only its wide range of applications, but this composite material has unique properties. But what exactly is concrete, and why has it been a necessity Since the past? Join us for the answer.
The History of Concrete
Since the early 1300s, architects in the Middle East have known the importance of limestone. They knew that this substance, mixing with water, was turned into a hard mass. Around the same period, the ancient Greeks used a mixture of lime and pebbles to create structural members.
476 AD is known as the Concrete Revolution. From the dome of the Pantheon to the aqueduct of Pont de Gard, the most prominent tourist attractions were built with concrete. After the fall of the Roman Empire, concrete technology crept backwards, and it re-emerged in the eighteenth century. It was due to two significant innovations, the first of which was the work of John Smeaton, who rediscovered many techniques for making ancient Roman cement, and the second was the method of producing hydraulic lime.
Dome of the Pantheon in Rome, Italy
The discovery of Portland cement in 1824 changed the world! Then, with the creation of reinforced concrete, the applications of this material increased. Today, the use of concrete is an integral part of the civil industry and its related ones.
What is Concrete?
Concrete is a composite and synthetic material such as stone that is made of a binder (cement), water and aggregates. The ratio of ingredients, known as the “mixing scheme”, is directly related to the strength and quality of the final product.
The formula of concrete compounds is as follows:
Concrete = binder + fine and coarse aggregate + water + additives (optional)
We now find that the three main constituents of concrete are cement, water, and aggregates. Now, we take into account the role of each of these materials in more detail:
Cement: Cement is the essential constituent of concrete. When cement and water are mixed, they form a sticky paste that binds the aggregates in the mixing design.
Water: Water is vital to make cement paste. Chemically, water reacts with cement to make concrete. The amount of water used in the mixing design changes the ratio of water to cement. It, in turn, affects the strength and properties of this composite material.
Aggregates: Aggregates help to improve the properties of concrete. Aggregates include sand (coarse-grained) and sand (fine-grained). Sand properties such as rounded or sharp corners or roughness directly affect the final compressive strength of this composite material.
Picture of Concrete
How is concrete made?
Concrete is an integral and valuable material for construction work. When all the ingredients are combined in the specified proportions, the cement and water start the hydration reaction to turn the final product into a solid mass.
The process of making concrete begins with the mixing plan. But you should pay close attention to this step! A mixture that does not have enough cement paste to fill the space between the aggregates reduces the compressive strength of the concrete. Conversely, a compound with a lot of cement paste increases the likelihood that the final product will crack.
The cement paste should completely cover the aggregates and leave no gaps. On the other hand, the slump (efficiency and flow) should not be too high for the dough to loosen and guide the aggregate downwards. At this stage, by determining the ratio of water to cement and the percentage of each aggregate, making concrete begins.
In general, the effective parameters in the concrete mixing design include:
- Pushing resistance
- Type of cement
- Water to cement ratio
The mixture begins to harden through a chemical reaction known as hydration. Once the final product is properly mixed in the mixer, it is time to pour the concrete into the mould. Vibrating the mixture after pouring then helps to reduce air bubbles and create a homogeneous mixture.
The importance of using concrete
Wherever a structure is seen, there is concrete. The use of concrete in today’s constructions is important because structures derive their strength and stability from this composite material. Second, the material is cheap and can be moulded in various ways.
Concrete is produced using natural materials. Therefore, it is environmentally friendly and recyclable. Recycled concrete can be crushed and used as a dry aggregate to make a new product. As long as construction activities are ongoing globally, there will be a constant demand for concrete.
Advantages of Concrete
- It is more economical than steel.
- It has high compressive strength.
- The maintenance cost of concrete is practically zero.
- It may be used as a soundproofing agent.
- It is durable, and its resistance increases over time.
- It has many uses.
- It acts as a waterproof material.
- It is easily controllable and can be moulded in any shape.
- Concrete ingredients are always available.
- Its surface can withstand abrasion.
- It is not exposed to ants or termites.
- It has very high fire resistance.
- It can be pumped and used in difficult situations.
- It does not mould and does not rot.
Disadvantages of Concrete
- It has a low tensile strength (this problem can be solved with steel and the formation of reinforced concrete)
- It is necessary to prepare shrinkage joints to prevent shrinkage.
- They increase the weight of the structure so that it creeps.
- It takes time to reach the maximum resistance.
- It has little ductility.
- Its mixing design is complex and requires expertise and engineering knowledge.
- For alkaline and sulfated environments, special cement should be used because ordinary cement breaks down quickly.
- Conventional urban structures
- Parking lots
- Architectural and decorative applications
- Paving the streets
- Watersheds and sewers
- sea structures
Types of Concrete
Concrete is divided into the following types:
- Ordinary Concrete
- Lightweight Concrete
- Polymer concrete
- Reinforced Concrete
- Prestressed Concrete
- Precast Concrete
- Concrete glass
- Self-compacting Concrete
- Aerated Concrete
- Fibre concrete
- Smart Concrete
- Pumpable Concrete
- Sucked Concrete
- Sponge concrete
- And other types of concrete
Workability of the fresh concrete mix means pouring, pumping, spreading, filling, shaking without reducing the quality of concrete. Workability depends on water content, aggregate (shape and size distribution), amount of cement. It can be modified by adding chemical additives such as a superplasticizer.
Increasing the water content or adding chemical additives increases the performance of concrete. Excessive water leads to increased waterlogging or separation of aggregates (when cement and aggregates begin to separate), the resulting concrete also decreases in quality. Any combination of different factors may lead to a mixture that is too hard and not mentally sound. As a result, it will be challenging to finish the concreting work.
Efficiency can be measured by testing concrete slumps. Slump is usually calculated by filling a 30 cm high cone. The cone with the wide end is placed on a flat, non-absorbent surface. It is then filled in three layers of equal volume to integrate the layer.
When the cone is carefully removed, the enclosed material drops a certain amount due to gravity. A relatively dry sample sheds very little and has a slump value of one or two inches (25 or 50 mm) by one foot (305 mm). A relatively wet concrete sample may fall to eight inches.
Performance can be measured using the test table in the National Building Code. Slump can be increased by adding chemical additives such as emollients or superplasticizers without changing the ratio of water to cement. Some other additives, especially airborne additives, can increase the mix slump.
Concrete must be moistened during curing to achieve optimum strength and durability. During this process, hydration occurs and allows calcium silicate hydrate (C-S-H) to form. More than 90% of the final strength of the mixture is usually achieved within four weeks, and the remaining 10% will be completed over years or even decades.
The conversion of calcium hydroxide in concrete to calcium carbonate, due to the absorption of CO2 over several decades, further strengthens the concrete and makes it more resistant to damage. However, this carbonation reaction lowers the pH of the cement pore solution and can cause corrosion of the reinforcing bars.
The hydration and hardening of concrete in the first three days is critical. Rapid drying and abnormal shrinkage due to evaporation during placement may increase tensile stresses when the concrete is not yet strong enough, resulting in more cracking and shrinkage.
If the concrete is kept wet during the process, its initial strength can be increased. Minimizing pressure before treatment minimizes cracking. High-strength concrete is designed to hydrate faster and is often associated with increased cement use, which increases shrinkage and cracking.
Concrete strength increases up to three years. It depends on the elements and operating conditions of the structure. The addition of short-term polymer fibres can reduce the stresses caused by shrinkage during processing and increase the initial and final compressive strength.
Proper concrete curing leads to increased strength and less permeability and prevents cracking at the site of premature drying of the surface. Concrete should also be taken care of to prevent it from freezing or overheating. Improper processing can cause scaling, reduced strength, poor abrasion resistance and cracking.
Ready-mixed concrete is a type of concrete that is mixed in a factory according to the customer’s order and then delivered to the project site to be used immediately. The main difference between ready-mixed concrete and ordinary concrete is where it is mixed. The ready-mixed concrete is mixed off-site and delivered to the site with a mixer truck.
Ready-mixed concrete has several advantages:
- High-quality Concrete
- lower price
- saving time
Demolition of Concrete to create a suitable space for new structures creates a large amount of concrete waste. The most common way to dispose of this waste is to dump it in a landfill, which can pollute the air and water. It has led more countries to consider the importance of recycling concrete waste.
Concrete recycling is the use of debris from concrete structures that have been destroyed. Crushed concrete can be used for road sand, cavities, retaining walls, landscaping or coarse aggregate for new concrete.
The advantages of recycled concrete are:
- Contribute to the health of the environment
- Reduce transport pollution to landfills
- Reduce the cost of transporting materials and waste
- Save landfill space
- Return to the construction cycle
- Reduce the cost of producing coarse aggregates (sand)
Recycled concrete can be utilized in walls as building blocks. Smaller pieces will also be used as sand for new construction projects. Recycled concrete has application in road construction.
Concrete paving can be broken in place and used as a base layer for asphalt paving through debris removal. Crushed concrete can be used as a raw material (instead of sand) to make new concrete.
Recycled concrete with good grading and aesthetics can be used as landscaping stones and mulch. Wire gabions can be filled with crushed concrete and used as retaining walls (instead of fencing).
In A Nutshell
Concrete is a material that has a very high compressive strength and can be used in various industries. In addition, it is inexpensive and easily produced on site. This composite material allows fast and high-quality fabrication. Concrete structures are often operated for years with basic design and construction and withstand earthquakes, storms and environmental hazards. In the end, “Concrete is still an incredible material!”