Reinforced concrete – grade and prices

1. Sand and other constituents of concrete

Unlike wood, glass or metal, concrete is an artificial composite material. It consists of a binder (most often, cement), aggregates such as sand, gravel or crushed stone, and water. Chemical or mineral admixtures and various fibres can be added to these basic components to alter and improve certain characteristics of the concrete, i.e. to obtain concrete that is a certain quality, strength, and resistance.

Aggregate is the main component in concrete, with its proportion accounting for up to 75% of the mix. Cement paste, i.e. the mixture of cement and water, makes up the remaining 25%. Any other additives are used in significantly smaller quantities compared to the primary mix. These additives, whether chemical or mineral, even in very small quantities greatly improve the quality of concrete.

Mineral aggregate increases the cohesiveness of the concrete, lowers the hydration temperature, and prevents shrinkage. The characteristics of concrete are also influenced by the fraction of the aggregate, i.e. the size of the particles; aggregate size is different for different types of structures. Generally, aggregate sizes of 16 to 32 mm are used. The cement paste also has a major impact on the concrete with the moisture in it binding the mineral aggregate and filling the voids in the mix.

1.1. Price of sand for concrete

How much does sand cost? The price depends mostly on its granulation, i.e. the grain size. For the type of plain concrete required when laying screed or a levelling course, sand with a granulation of between 0-8 mm is used. For slabs, foundations or retaining walls, a coarser concrete is required and hence a larger grain is used – up to 16 mm. Sand used in foundations can even be up to 32 mm in diameter. The price depends on both the supplier and the distance to the construction site. On average, it costs NGN75000 per trip.

2. Concrete grade and other characteristics

Types of concrete also differ according to various other characteristics, of which the most significant are density, grade, elasticity, and resistance to water, wear, and the like. If the concrete structure is to last, the concrete must have suitable properties.

2.1. Concrete density

The basic division of concrete is mainly based on its specific weight, so there are lightweight, ordinary, and heavyweight concretes. Depending on their purpose, there are concretes for construction, hydraulic concrete, special concrete, and so on.

2.2. Drying and strength

One thing that affects the quality of concrete is the speed it hardens at and the environment in which this process takes place. For concrete to cure successfully, the relative humidity needs to be above 80% and the temperature high enough, too. If conditions are not suitable, the concrete is wetted as needed. How does this process work in real time? Concrete can be walked on after 24 hours, but the projected strength is only reached after 28 days. Any formwork must remain in place during this time.

2.3. Concrete grade

The most significant classification of concrete is according to the grade. Concrete grade can be denoted by the letter M, which stands for Mix. The number after M stands for the characteristic compressive strength of the concrete at 28 days when checked with a 15x15x15 cm cube in a direct compression test - in other words, how resistant to pressure it is. The higher the grade, the higher the quality of the concrete and the greater the load it can withstand. Standard concrete has a grade between M20 and M30. The grade can also be denoted by the letter C, which stands for ‘Concrete Strength class’ and refers to the characteristic compressive strength of concrete at 28 days when tested with a 15 cm diameter and 30 cm height cylinder in a direct compression test. Standard concrete, which is mainly used for construction, has a grade of C25/30.

3. Reinforcing mesh and reinforced concrete

The tensile strength of concrete can be increased by using reinforcement. The first thing one thinks of when they hear reinforcement is iron bars; however, other types exist. There are smooth, mild steel bars and also deformed, ribbed ones, which bond more easily to the concrete. There is also reinforcing mesh and PC strand, or prestressed concrete steel strand, which is a twisted steel cable composed of 2 or more high-strength steel wires.

Today, the strength of concrete can be increased dramatically in many ways; one of them is with the addition of organic fibres or fibres made from steel or some other metal or glass. In doing so, the fibres act as the reinforcement.

4. Concrete plants

The quality of concrete certainly depends a lot on whether it is prepared properly. You can mix it yourself, although for larger quantities it is always better to order it ready mixed from a concrete plant. Concrete plants make all types of concrete, so suitable concrete can be found whatever the design requirements. You can order concrete made with any aggregate and in any amount from 0.2 m3 to 100 m3 and more. Concrete plants generally offer expert help, too.

5. Concrete - prices

How much does concrete cost? The price of a cubic metre depends on its quality, i.e. the grade. C25/30 concrete with standard characteristics costs between NGN75000 - NGN90000/m3. When reinforcement and labour costs are included,  the price will increase.