Concrete, in technical terms, is any product or mass created with the use of a cementing medium. Concrete is the most extensively used building material in the construction industry and is made up of a composite man-made materials. It’s made up of a well-balanced mix of binding materials like lime or cement, fine and coarse aggregates, water and admixtures.
This mixture is then poured into moulds or forms and left to cure for a particular amount of time or days, depending on the application. Concrete is significantly stronger in compression than it is in tension. As a result, it is reinforced with steel to withstand tensile stresses.
Properties of Concrete
Concrete in its hardened form and concrete in its plastic state have different properties. The properties that concrete should possess at both stages are listed below.
Properties in Hardened State
- Durability
- Shrinkage
- Strength
- Creep
- Impermeability
- Thermal Expansion
Properties in Plastic State
- Workability
- Harshness
- Segregation
- Bleeding
Classification of Concrete
The classification of concrete depends on many factors such as their grades, additives used, cementing material used, compressive strength etc. Some of the common types of concrete are mentioned below.
- Plain Cement Concrete
- Lime Concrete
- Pre-stressed Cement Concrete
- Reinforced Cement Concrete
- Light-Weight Concrete
- Heavy-weight Concrete
- Stamped Concrete
- Self-compacting Concrete
- Cellular Concrete
- Rapid-strength Concrete
- Low-strength Concrete
- High-strength Concrete
- Saw-dust Concrete
- Fiber-reinforced Concrete
- Polymer Concrete
- Vacuum Concrete
Different Grades of Concrete
Ordinary concrete, standard concrete and high strength concrete are the three major groups of concrete, with a total of 15 grades. The compressive strength of various concrete grades varies. The table below displays the various concrete grades, as well as their compressive strengths and mix ratios.
| Sr. no | Grade of Concrete | Mix Ratio | Compressive strength (MPa (N/mm²) |
| 1 | M5 | 1 : 5 : 10 | 5 MPa |
| 2 | M7.5 | 1 : 4 : 8 | 7.5 MPa |
| 3 | M10 | 1 : 3 : 6 | 10 MPa |
| 4 | M15 | 1 : 2 : 4 | 15 MPa |
| 5 | M20 | 1 : 1.5 : 3 | 20 MPa |
| 6 | M25 | 1 : 1 : 2 | 25 MPa |
| 7 | M30 | Design Mix | 30 MPa |
| 8 | M35 | Design Mix | 35 MPa |
| 9 | M40 | Design Mix | 40 MPa |
| 10 | M45 | Design Mix | 45 MPa |
| 11 | M50 | Design Mix | 50 MPa |
| 12 | M55 | Design Mix | 55 MPa |
| 13 | M60 | Design Mix | 60 MPa |
| 14 | M65 | Design Mix | 65 MPa |
| 15 | M70 | Design Mix | 70 MPa |
Concrete Proportioning
The primary goal of proportioning of concrete is to obtain the desired strength and workability, which necessitates careful selection of cement and aggregates in accordance with the specifications. The following are some of the things to keep in mind:
- The strength and impermeability of concrete improve with the density of the mix while the cement content, additives, and workability remain constant.
- Strength, impermeability, density, and workability are all enhanced by a high cement concentration.
- The mixture must be workable so that it may be easily laid and finished.
Different Steps of Concrete Production
Measurement of Materials: In this process, all the materials used in concrete are properly weighed for proper proportions and uniformity. This process is also called batching.
Mixing: In order to make uniform concrete, the process of mixing the materials should be carried out thoroughly. For minimal and small household maintenance work, the mixing of concrete is done manually by hand. Normally, the mixing process is carried out with the help of a mechanical concrete mixer.
Transporting: For small projects, the transportation of concrete from the site of mixing to the site of placing is mainly done using iron pans and wheel barrows or 2-wheel carts.
Placing: The most important thing while working with concrete is the placement. The concrete should be placed in the right position and at the right time within the initial setting time of cement. Below are a few precautions that one should take while working with concrete on a construction site.
- To avoid the segregation of concrete, it should not be poured from height more than 1 meter.
- During the monsoon season, the concrete placement should be immediately discontinued during rains.
- To avoid the production of irregular and ugly lines on the surface, the concrete should be laid in a continuous pattern.
Compaction: In order to eliminate air bubbles and make dense concrete, the compaction process is carried out. It is done by means of mechanical vibrators or by manual tamping.
Finishing: The finishing process of concrete is one of the most important processes in concrete work. This process involves various stages of work which are as follows:
- Screeding: to give a uniform concrete surface by removing humps and hollows.
- Floating: removing any left-over irregularities from the surface after screeding.
- Trowellling: generally performed where a smooth and dense surface is required.
Curing: Curing is the final process in which concrete is kept moist for a certain period in order to give concrete more strength by hardening. Generally, concrete gains 100% strength after 28 days of proper curing.