In this Post, we will discuss concrete and concrete tests.
Concrete and Concrete tests
Definition of Concrete:
Concrete is a building material made from a mixture of broken stone or gravel, sand, cement, and water, which can be spread or poured into moulds and forms a stone-like mass on hardening.
Concrete is made up of four main ingredients:
- fine aggregate (sand, usually between 0.005 and 0.25 inch in diameter)
- coarse aggregate (gravel, usually between 0.5 to 1.5 inch in diameter)
- Portland cement
Air also plays an important part.
To improve or modify the concrete’s properties, special additives (called admixtures) are also added.
Materials are mixed in specific proportions to obtain the required strength.
Grade of Concrete
The grade of Concrete is denoted as Strength of mix and is specified as M5, M10, M15, M20, M25, and M30 etc, where M denotes Mix and 5, 10, 15 etc. are their strength in kN/m2. In the United States, concrete strength is specified in PSI (Pounds per Square Inch.)
The mixed Proportion can be written as
The ratio of cement: The ratio of sand: The ratio of coarse aggregate
Based on the volume or weight of materials
Water-cement ratio plays an important role which influences various properties such as strength, durability, and workability. An adequate water-cement ratio is required for the production of workable concrete.
When water is mixed with the materials, the cement reacts with water and hydration reaction starts. This reaction helps ingredients to form a hard matrix that binds the materials together into a durable stone-like material.
Various structural members such as columns, beams, footings, lintels, slabs etc. are constructed with concrete.
Different types of admixtures are used to provide certain properties. Admixtures or additives are included in the mixture to improve the physical properties of the wet mix or the finished material.
Concrete mixes are of two types,
A nominal mix is used for normal construction works such as small residential buildings. Most popular nominal mix are in the proportion of 1:2:4.
Design mixed concrete are those for which mix proportions are finalized based on various lab tests for its compressive strength.
Mixing methods of Concrete
Two methods are used for mixing are Hand Mixing and Machine Mixing.
In the hand mixing, each ingredient is placed on a flat surface and water is added and mixed with hand tools.
In machine mixing, different types of machines are used. In the machine mixing, the ingredients are added in the required quantity to mix and produce fresh concrete.
Types of Concrete Construction
Concrete Construction is of two types
Plain concrete construction (PCC)
Reinforced concrete construction
The plane concrete construction (PCC) is poured and cast without the use of any reinforcement.
This is used when the structural member is subjected only to the compressive forces and not bending.
When a structural member is subjected to bending, reinforcement concrete construction is used. Reinforcements are required to withstand tension forces, structural member, as it is very weak in tension compared to compression. Generally, the strength of concrete in tension is only 10% of its strength in compression.
Steps of Concrete Construction
The steps in the Concrete Construction are as follows-
- Selecting quantities of materials for selected mix proportion
- Checking of workability
- Pouring in formwork for casting
- Vibrating for proper compaction
- Removal of formwork after a suitable time
- Curing member with suitable methods and required time
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