what is concrete? concrete grade, prestressed concrete, mass concrete
what is concrete? concrete grade, Prestressed concrete, mass concrete
Concrete is a mixture of Portland cement, water, and coarse and fine aggregates. It consolidates into a hard mas because of a chemical reaction called hydration between cement and water. Proportioning a concrete mix for a given purpose is thus the art of obtaining a suitable ratio of the various ingredients of concrete with the required properties at the lowest cost.
Table of contant
Table of contant
Concrete is generally graded according to its compressive strength. In the designation of concrete mix, the letter M refers to the mix and the number is the specified characteristic strength of 150 mm work cubes at 28 days, expressed in MPa (N/mm²).
Concrete is a construction material composed of cement, fine aggregates (sand) and coarse aggregates mixed with water which hardens with time. Portland cement is the commonly used type of cement for the production of concrete. Concrete technology deals with the study of properties of concrete and its practical applications.
In building construction, concrete is used for the construction of foundations, columns, beams, slabs and other load-bearing elements.
There are different types of the binding material is used other than cement such as lime for lime concrete and bitumen for asphalt concrete which is used for road construction.
Various types of cement are used for concrete works which have different properties and applications. Some of the types of cement are Portland Pozzolana Cement (PPC), rapid hardening cement, Sulphate resistant cement, etc.
Types of grade
Materials are mixed in specific proportions to obtain the required strength. The strength of mix is specified as M5, M10, M15, M20, M25, M30, etc, where M signifies Mix and 5, 10, 15, etc. as their strength in kN/m2. In the United States, concrete strength is specified in PSI which is Pounds per Square Inch.
Water-cement ratio plays an important role which influences various properties such as workability, strength, and durability. The adequate water-cement ratio is required for the production of workable concrete.
Water-cement ratio plays an important role which influences various properties such as workability, strength, and durability. The adequate water-cement ratio is required for the production of workable concrete.
When water is mixed with materials, 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.
Concrete can be cast in any shape. Since it is a plastic material in the fresh state, various shapes and sizes of forms or formworks are used to provide different shapes such as rectangular, circular, etc.
Various structural members such as beams, slabs, footings, columns, lintels, etc. are constructed with concrete.
ACI 318 Building code requirements for structural concrete and ACI 301 Specifications for Structural Concrete are used in the United States as a standard code of practice for concrete construction.
a minimum grade of concrete for RCC
There are different types of admixtures which use to provide certain properties. Admixtures or additives such as pozzolans or superplasticizers are included in the mixture to improve the physical properties of the wet mix or the finished material.
Various types of concrete manufacture these days for construction of buildings and structures. These have special properties and features which improve quality of construction as per requirement.
Components of Concrete
Components of concrete are cement, sand, aggregates, and water. A mixture of Portland cement and water call paste. So, concrete can call a mixture of paste, sand, and aggregates. Sometimes rocks use instead of aggregates.
The cement paste coats the surface of the fine and coarse aggregates when mixed thoroughly and binds them. Soon after mixing the components, hydration reaction starts which provides strength and a rock-solid concrete obtained.
What is Grade of Concrete?
A grade of concrete denotes its strength required for construction. For example, M30 grade signifies that compressive strength require for construction is 30MPa. The first letter in grade “M” is the mix and 30 is the required strength in MPa.
Based on various lab tests, the grade of concrete presence in Mix Proportions. For example, for M30 grade, the mix proportion can be 1:1:2, where 1 is the ratio of cement, 1 is the ratio of sand and 2 is the ratio of coarse aggregate based on volume or weight of materials.
The strength measure with concrete cube or cylinders by civil engineers at the construction site. Cube or cylinders make during casting of the structural member and after hardening, its cure for 28 days. Then the compressive strength test conducted to find the strength.
Regular grades of concrete are M15, M20, M25, etc. For plain cement concrete works, generally, M15 uses. For reinforced concrete construction minimum M20 grade of concrete uses.
Grade of concrete table
| Concrete Grade | Mix Ratio | Compressive Strength MPa( N/mm²) | PSI |
|---|---|---|---|
| Normal Grade of Concrete | |||
| M5 | 1:5:10 | 05 MPa | 725 psi |
| M7.5 | 1 : 4 : 8 | 7.5 MPa | 1087 psi |
| M10 | 1 : 3 : 6 | 10 MPa | 1450 psi |
| M15 | 1:2:4 | 15 MPa | 2175 psi |
| M20 | 1:1.5:3 | 20 MPa | 2900 psi |
| Standard Grade of Concrete | |||
| M25 | 1:1:2 | 25 MPa | 3625 psi |
| M30 | Design Mix | 30 MPa | 4350 psi |
| M35 | Design Mix | 35 MPa | 5075 psi |
| M40 | Design Mix | 40 MPa | 5800 psi |
| M45 | Design Mix | 45 MPa | 6525 psi |
| High Strength Concrete Grades | |||
| M50 | Design Mix | 50 MPa | 7250 psi |
| M55 | Design Mix | 55 MPa | 7975 psi |
| M60 | Design Mix | 60 MPa | 8700 psi |
| M65 | Design Mix | 65 MPa | 9425 psi |
| M70 | Design Mix | 70 MPa | 10150 psi |
How to Make Concrete?
Concrete is manufactured or mixed in proportions w.r.t. cement quantity. There are two types of concrete mixes, i.e. nominal mix and design mix. The nominal mix uses for normal construction works such as small residential buildings. The most popular nominal mix is in the proportion of 1:2:4.
Design mixed concrete are those for which mix proportions finalize based on various lab tests on cylinder or cube for its compressive strength. This process is also called as mix design. These tests conduct to find a suitable mix based on locally available material to obtain strength required as per structural design. A design mixed offers economy on use of ingredients.
Once suitable mix proportions are known, then its ingredients are mixed in the ratio as selected. Two methods used for mixing, i.e. Hand Mixing or Machine Mixing.
Based on the quantity and quality required, the suitable method of mixing is select. In the hand mixing, each ingredient places on a flat surface and water add and mix with hand tools. On machine mixing, different types of machines use. In this case, the ingredients add to the required quantity to mix and produce fresh concrete.
Once its mixes adequately its transports to casting location and poured in formworks. Various types of formworks are available which as selected based on usage.
Poured concrete allows setting in formworks for a specified time based on the type of structural member to gain sufficient strength.
After removal of formwork, curing is done by various methods to make up the moisture loss due to evaporation. Hydration reaction requires moisture which is responsible for setting and strength gain. So, curing generally continues for a minimum 7 days after removal of formwork.
Types of Concrete Construction
Concrete generally use in two types of construction, i.e. plain concrete construction and reinforced concrete construction. In PCC, its pours and cast without the use of any reinforcement. This uses when the structural member subjects only to the compressive forces and not bending.
When a structural member is subjected to bending, 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.
Its uses as a construction material for almost all types of structures such as residential concrete buildings, industrial structures, dams, roads, tunnels, multi-story buildings, skyscrapers, bridges, sidewalks, and superhighways, etc.
Example of famous and large structures made with concrete are Hoover Dam, Panama Canal, and Roman Pantheon. It is the largest human-made building materials used for construction.
Prestressed concrete
Pre Stressed concrete is basically cocnrete in which internal stresses or a suitable magnitude and distribution are introduced so that the pre-compressive stress in concrete will balance the tensile stress produced in concrete due to external loads. Due to this, the whole of the concrete can participate in resisting the external forces. In reinforced cocnrete members, the prestress is commonly introduced by tensioning the steel reinforcement.
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