Concrete:- Cement is the most expensive and most important component of concrete. Cement has cohesive and adhesive properties that enable it to bond materials. The cements of interest for concrete production have the property of setting and hardening under water through chemical reactions with it, which is why hydraulic cement is called Hydraulic cement consists mainly of silicate, sand aluminates, and lime, and can be roughly divided into natural cement. For e. Portland cement, high alumina cement, etc.
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CHEMICAL COMPOSITION OF CEMENT
Cement mainly consists of lime, sand, alumina, and iron oxide. The major compounds of cement are classified as follows:
|Tricalcium Silicate (C₃S)||50±5%|
|Dicalcium Silicate (C₂S)||30±5%|
|Tricalcium Aluminate (C₃A)||9±4%|
|Tetracalcium Aluminoferrite (C₄AF)||12±3%|
Different Types Of CEMENT
- Ordinary Portland cement
- Ordinary Portland cement 33 Grade- IS 269:1989
- Ordinary Portland Cement 43 Grade- IS 8112:1989
- Ordinary Portland Cement 53 Grade- IS 12269:1987
- Rapid Hardening Cement – IS 8041:1990
- Sulphate Resisting Cement –IS 12330:1998
- Quick setting Cement
- Low Heat Cement –IS 12600:1989
- Portland Pozzolana Cement – IS 1489 (Part-1) 1991 (Fly ash based)
- Air Entraining Cement
- Colored Cement – (White Cement IS 8042:1989)
- Expansive Cement
- High Alumina Cement- IS 6452:1989
Concrete is a composite of gravel or crushed stone (coarse aggregate), sand (fine aggregate), and hydrated cement (binder) and gives the mixture considerable hardness. The cement reacts chemically with the water and other constituents to form a hard matrix that binds all materials together into a durable, stone-like material with many uses. Sometimes additives like pozzolans or superplasticizers are included in the mix. Concrete is poured with reinforcement materials (such as rebars) embedded to provide tensile strength, thereby obtaining reinforced concrete.
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Properties Of Concrete
Compressive Strength:- Compressive Strength is defined as the maximum measured the strength of a concrete or mortar sample when axially loaded, generally expressed in PSI (pounds per square inch) at 28 days.
The compressive strength of concrete depends on many factors: – -Quality and proportion of the ingredients -Curing environment
The grades are designated with a letter M (for mixing) and a number from 10 to 80, which defines the compression strength curve (fck) in N / mm2.
According to IS 456 (Table 2), concrete has three groups as
(i) normal concrete (M 10 to M 20),
(ii) normal concrete (M 25 to M 55)
(iii) high-strength concrete (M 60.). up to M80).
Note: This type of grade of concrete is generally used in highway pavements and is M30 M35 M40 M45.
Tensile Strength:- Concrete is usually not resistant to direct stress, knowledge of tensile strength is used to estimate the stress under which cracking occurs due to its influence on cracking and its propagation on the tensile side of reinforced concrete flexures.
The tensile strength of concrete is relatively low. Flexural tensile strengths and breaking strengths are obtained as described in IS 516 and IS 5816.
However, the following expression gives an estimate of the flexural strength (fcr) of concrete from its characteristic compressive strength. .fcr = 0.7 fck in N / mm2
Elastic Deformation:- It can be seen that the initial tangent modulus is much higher than the deformation components Et (each inelastic tangent modulus). The initial tangential modulus Ec in N / mm2 is estimated from Ec = 5000 fck. The initial tangential modulus Ec is also referred to as the short-term static modulus of elasticity of concrete in N / mm2 and is used to calculate the elastic deflections.
Shrinkage:- Shrinkage is a time-dependent deformation, generally of a compressive nature. The concrete components, the component size, and the environmental conditions are the factors on which the total shrinkage of the concrete depends. However, the total shrinkage is more influenced by the total amount. the water present in the concrete at the time of mixing at a given humidity and temperature. The approximate value of total shrinkage elongation for the design is taken as 0.0003. accepted
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Additives & Admixture
Additives are chemical products that are added to the concrete during the mixing phase in order to change some of the properties of the mixture. The reasons for using additives in concrete are the following:
The reasons for using additives in concrete are the following:
- To improve durability,
- Reduce the proportion of water in the mixture without changing the workability.
- To produce high-strength concrete,
- accelerate strength development in the initial phase, Improve strength, crack control (shrinkage reduction),
- Improve permeability, Improve surface,
- Early resistance, and reduced permeability.
- Make a liquid filling that flows easily and levels itself.
- Reduce the overall cost of the materials used in concrete.
Type of Admixture
Plasticizers (water reducing agents): When concrete with high workability is required without the use of excess water, plasticizers are used. The main types of plasticizers are lignosulfonate, melamine sulfate, and naphthalene sulfate.
Superplasticizers (high-range water reducers): The use of plasticizers is practiced for the production of liquid, self-leveling, self-compacting, and for the production of high-strength and high-performance concrete. Superplasticizers are chemical compounds such as modified technical jargon sulfates (MLS), sulfonated melamine formaldehyde (SMF), sulfonated naphthalene formaldehyde (SNF), and other polycarboxylate-based materials.
Type of Admixture (contd)
Retarder: Used when a delay in setting time is required to ensure adequate placement, vibration, or compaction. Well-known retarders calcium sulfate, hydroxylated carboxylic acids, sugars, acids, or acid salts
Accelerators: Accelerators work by accelerating the hydration of cement, which leads to shorter setting times and higher strengths at a young age, especially at colder temperatures.
Types of concrete used in pavement construction
- High strength concrete
- High-performance concrete
- Stamped concrete
- Fibre-reinforced concrete
- Self Compacting concrete
High strength concrete
High-strength concrete has a compressive strength greater than 40 MPa (6800 psi). Recently, this strength has increased from 50 to 60 MPa and its use in the construction of high-rise buildings and long-span bridges has increased. Decrease the a / c ratio to 0.35 or less.
To prevent the formation of free calcium hydroxide crystals in the cement matrix, silica is often added, which reduces the strength of the cement-aggregate connection.
Silica fumes make concrete less workable, which is particularly likely to work in high-strength concrete applications where dense reinforcement cages are likely to be used. To compensate for the reduced workability, superplasticizers are typically added to high-strength mixtures.
HPC is widely used in road construction because of the potential economic benefits of HPC’s early strength gains, reduced permeability, increased water or abrasion resistance of steel studded tires, and improved freeze-thaw cycle durability.
It is considered for pavement repairs for early traffic openings, bridge coatings, etc.
A durable concrete called Fast Track Concrete is designed to provide high strength at a very early stage without the use of special materials or techniques. ) the technology can be used for complete roadway renovation, partial replacement by an insert of at least one roadway, reinforcement of existing bituminous or concreted roadways with a concrete layer, fast maintenance, and renovation processes as well as airport fortifications. Shorten construction time, open the roadway to traffic at an early stage and minimize the use of expansion concrete. Paving.
Punched concrete is architectural concrete with excellent surface quality.
After a concrete floor is laid, soil hardeners are impregnated into the surface (can be pigmented) and a shape is punched that can be textured to recreate a stone/brick or even wood. Once sufficiently hardened, the surface is cleaned and usually for protection sealed.
The wear resistance of stamped concrete is generally excellent and is therefore used in applications such as parking lots, sidewalks, sidewalks, etc.
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Fiber-reinforced concrete (FRC) is concrete that contains fibrous material that increases its structural integrity.
Fibers include steel fibers, glass fibers, synthetic fibers, and natural fibers, each of which gives concrete different properties. a concrete mix ranges from 0.1 to 3%.
Fiber concrete is used more and more because of the advantages of higher static and dynamic tensile strength, energy-absorbing property, and better fatigue resistance.
Self Compacting Concrete
Self-compacting or self-compacting concrete (SCC) is characterized by a low elastic limit, high deformability, and moderate viscosity, which is necessary to ensure a uniform suspension of solid particles during transport, installation (without external compaction) and then until the concrete sets guarantee.
This concrete can be used to pour heavily reinforced sections, in places where vibrators are inaccessible for compaction, and in complex formwork shapes that otherwise could not be poured, and provides a far better surface finish than conventional concrete. that a total sand content of approx. 50% of the total surcharge is favorable when designing SCC.
Dry Lean Concrete (For Sub-Base)
Dry lean cement concrete (DLC) is used as a substrate for concrete construction.
It is a simple concrete with a higher aggregate to cement ratio than conventional concrete.
If the temperature rises above 30 ° C, you should stop working and in this case, ice water can be applied. DLC can be hardened by spraying on liquid hardeners or by covering the surface with moistened jute sacks.
Disadvantages of using more water and Advantages of using less water
|Disadvantages of using more water||Advantages of using less water|
|Creates a diluted paste.||Increased strength|
|Excess water bleeds out onto the surface.||Lower permeability|
|This affects the compressive and tensile strengths.||Increased resistance to weathering|
|Loss of cohesiveness and homogeneity.||The better bond between concrete and reinforcement|
|Harmful to strength and durability||Reduced shrinkage and cracking|
|Less volume change from wetting and drying|
|FINE AGGREGATE||COARSE AGGREGATE|
|Size less than 4.75mm||Size more than 4.75mm|
|Includes natural sand or crushed stone with most particles passing through a sieve||Includes gravels and crushed stones|
|Obtained from pits, lake, river or sea-shore||Obtained by crushing various types of granites, hard limestones, and sandstones.|
|Thoroughly washed before use||Harsh concrete|
Reinforced concrete is a composite material in which the relatively low tensile strength and ductility of concrete is counteracted by the inclusion of reinforcements with higher tensile strength and / or ductility. the final structure under workload. In the United States, the most common methods of doing this are known as pre-tensioning and retensioning.
Properties Of Reinforced Concrete
For a strong, ductile and durable structure, the reinforcement must have at least the following properties:
- High relative strength
- High tensile stress tolerance
- Good adhesion to concrete, regardless of pH value, moisture and similar factors
- Thermal compatibility does not cause any inadmissible stresses as a reaction to temperature changes
- Durability in the concrete environment, regardless of corrosion or permanent load.
Characteristics Of Reinforced Concrete
Two physical properties give reinforced concrete its special properties:
The coefficient of thermal expansion of concrete is similar to that of steel, which eliminates large internal stresses due to different thermal expansion or contraction.
As the cement paste hardens in the concrete, it adapts to the details of the steel surface and enables an efficient transfer of stresses between the different materials. Typically, steel rods are roughened or corrugated to further improve the bond or cohesion between concrete and steel.