Concrete is one of the most commonly produced construction materials and consists of cement, water and aggregates. Nowadays there is no building without concrete. At least a small proportion of buildings are made of concrete, even if they are made from alternative materials.

History of concrete

According to online sources, the history of this material dates back to 6,500 BC. B.C.

According to an article by GIATEC, the initiative came from the United Arab Emirates. Concrete structures were created there. As early as 3000 BC They were used in construction in Egypt and China in the 4th century BC.

Furthermore, it can be seen in 600 BC. Observe in Rome. Around 200 BC Rome began to use it widely in the 4th century BC.

The following figure from the GIATEC website shows the proportion of development in this area.

This is how concrete is made

There are mainly four additives: cement, water, fine aggregates and coarse aggregates. These materials are mixed according to mixing proportions selected from the mix composition and confirmed by a student mix.

In addition to the basic additives mentioned above, other additives such as: Additives etc. are added to improve performance.

Mixing can be done manually or using an automated method, which is the most used in the world. With this method, all materials are transferred to the mixing vessel according to their mixing proportions.

After mixing, the mixture is loaded directly into the truck. Depending on the workability requirements and based on the required strength, the water-cement ratio is controlled. The workability of concrete is measured through the slump test in the concrete batching plant and upon arrival at the construction site.

cement

Let's discuss the most important material from which all things are made.

The cement reacts with water and creates the bond between the aggregates.

Cement is a complicated material that consists of several materials. Furthermore, its formation reaction is somewhat complex for basic engineering projects because it involves chemistry.

The cement production process can be observed through the following reactions.

2CaO + SiO ₂ = Approx. ₂ SiO ₄ (Declaim silicate (C ₂ S))

3CaO + SiO ₂ = Approx. ₃ SiO ₅ (Tricalcium silicate (C ₃ S))

3CaO +Al ₂ Ó ₃ = Approx. ₃ Al ₂ Ó ₆ (Dicalcium Aluminate (C ₂ A))

4CaO +Al ₂ Ó ₃ + Faith ₂ Ó ₃ = Approx. ₄ Al ₂ Faith ₂ Ó ₁₀ (Tetracalcium aluminum ferrite (C ₄ AF))

Of these materials, C is ₃ S and C ₂ S are the most important compounds that contribute to strength. C ₃ S initially develops strength in the first four weeks. C ₂ S develops strength mainly after the first four weeks, as shown in the figure below.

You can find more information about cement in the article: Cement and cement additives . It also indicates the different classification of cement. Furthermore, the Classification of cement can be done based on compressive strength. The cement must be tested to confirm its quality. The following checks are normally carried out.

1. fineness
2. Compressive strength
3. Heat of hydration
4. Initial and final setup time
5. solidity
6. Normal consistency

The article, 6 Different Cement Tests offers more information about testing procedures and corresponding standards.

Cement hydration

The reaction of cement with water and the production of concrete through the necessary bonding with other additives is called hydration. This reaction creates a very hard material that is very resistant to pressure. However, it is very weak.

As discussed above, the materials are C ₂ SC ₃ SC ₂ A and C ₄ AF are contained as basic materials in cement. There are also other materials such as plaster (CSH ₂ ) etc. in cement.

The reaction of these materials with each other and with water converts them into the different forms explained below.

• tricalcium aluminate + gypsum + water ® Ettringite + heat: C ₃ A+3C S H ₂ + 26 hours ® C ₆ AS ₃ H ₃₂ , D H = 207 cal/g
• tricalcium silicate + water ® Hydrated calcium silicate + lime + heat: 2 °C ₃ S+6H ® C ₃ S ₂ H ₃ + 3 channels, D H = 120 cal/g

• After all the gypsum reacts according to the first equation, the ettringite becomes unstable and begins to react with the remaining C3A. The reaction forms hydrated aluminate monosulfate crystals.

• Tricalcium aluminate + ettringite + water ® Monosulfate aluminate hydrate
  2C ₃ A + 3 C ₆ A S ₃ H ₃₂ + 22 hours ® 3C ₄ ASH ₁₈ ,
• Dicalcium silicates + water ® Hydrated calcium silicate + lime
• C ₂ S+4H ® C ₃ S ₂ H ₃ +CH, D H = 62 cal/g

The reactions of ferrite with gypsum

• First reaction: Ferrite + gypsum + water ® Ettringite + aluminum and iron (III) hydroxide + lime: C ₄ AF+3C S H ₂ + 3 hours ® C ₆ (A,F) S ₃ H ₃₂ + (A,F )H ₃ + CH
• Second reaction: Ferrite + Ettringite + Lime + Water ® Garnet: C ₄ AF+C ₆ (A,F) S ₃ H ₃₂ +2CH +23H ® 3C ₄ (A,F) S H ₁₈ + (A,F)H ₃

Let's discuss hydration products

1. Hydrated calcium silicate : This is the main source of energy. This product is known as CHS.
2. Calcium hydroxide : This is called CH and is formed from the hydration of alite.
3. Ettringite : These are rod-shaped crystals that form in the early stages of the reaction or some time later. Their reactivity causes cracks in the concrete, especially if they react later.
4. Monosulfate : Forms 1-2 days after mixing begins.
5. Monocarbonate : It is caused by the presence of fine limestone or calcareous aggregate.

Concrete properties

Knowledge of these properties is very important for designers when carrying out structural projects. There are very important parameters that directly affect structural performance.

Elasticity of concrete

The modulus of elasticity of concrete is defined differently in different standards. According to most guidelines it is linked to compressive strength (characteristic strength).

According to BS 8110 Part 2 there are equations that can be used to calculate the modulus of elasticity.

There is also a table in BS 8110 Part 2 which can also be used to determine the modulus of elasticity.

Eurocode 2 also provides the values ​​and formula for determining the modulus of elasticity based on cylinder thickness.

This is Table 3 of Eurocode 2.

Poison ratio

Poisson's ratio represents the relationship between longitudinal and transverse stresses.

According to BS 8110 Part 01, the toxic proportion in linear analysis is 0.2.

According to Eurocode 2, it is 0.2 for uncracked concrete and 0 for cracked concrete.

Fire resistance

Fire resistance is a measure of resistance to fire. It is given in hours.

In general, it is more fire resistant than many building materials.

According to British standards, fire resistance is measured in hours.

First, we determine how many hours it will take to withstand the evacuation. Depending on this period, we select coverage for reinforcement.

Along with concrete, reinforcement is the main material that guarantees resistance.

The reinforcement is very sensitive to heat and expands rapidly when the temperature increases. If the reinforcement is sufficiently encapsulated, it will protect the concrete to some extent and also minimize the temperature rise of the steel.

Concrete temperature

We talked twice about temperature. On the one hand, the pouring temperature and, on the other, the temperature that increases due to the hydration process.

According to BS 5328 the temperature is limited to 30°C. ⁰ C when it rains . However, it goes on to say that this value may vary depending on the project specification.

The ultimate goal of temperature limiting is to limit the increase in temperature during the hydration process.

If the value increases significantly uncontrollably, it may cause serious strength and durability problems.

As mainly reported in the literature, the temperature increase during hydration is 70-80 ⁰ C is very critical. It leads to the formation of delayed ettringites, resulting in internal expansions due to the material formed in the reaction.

This leads to internal cracks that reduce strength and durability.

The temperature increase can be minimized by reducing the pouring temperature and using another additive that reduces the heat of hydration. A material often used for this is fly ash.

Method for Limiting Concrete Temperature The article describes the available methods for limiting temperature and their causes.

Further and further Initial temperature of concrete should also be checked to avoid cracking of immature concrete. This can lead to durability issues.

The most important aspect is durability after construction. The article, Factors Affecting the Durability of Concrete provides more information about durability.

Compressive strength

We use concrete because of its compressive strength. The hydration process creates a rock-strong product.

Compressive strength is referred to as the characteristic strength class of concrete in design.

Most components are exposed to axial forces, shear forces and bending moments. Concrete offers resistance to each of these stresses.

Concrete is very resistant to compression and dominates axial compression elements. The entire cross section acts on compressive loads. However, in cases such as bending, only part of the cross section is effective.

As we know, for beams subjected to a bending moment, according to British Standards, we consider only 0.45 times the depth to the neutral axis for the compressive stress block. This value may change slightly depending on other policies. However, the entire section does not effectively contribute to supporting the load.

As explained above, compressive strength is given as characteristic strength. This specific value is used in structural designs and verified through tests during construction.

It is usually indicated as C25/30. The first number is the thickness of the cylinder. The second number is the matrix resistance.

There are several factors that affect compressive strength . The most important factor is the water-cement ratio. There are also other factors such as mixing proportions, number of pores, curing time, compaction, etc.

Tensile strength of concrete

As we all know, tensile strength is very low. Furthermore, tensile strength range is not commonly used in structural design except in a few cases.

When sizing prestressed concrete, we take into account the tensile strength depending on the selected design class.

There are different formulas for calculating tensile strength.

Eurocode 2 Table 3 shown above can be used to determine tensile strength. A table for prestressed concrete work is also included in BS 8110 Part 1.

The weakness of concrete is that it cannot withstand tensile forces. Steel, on the other hand, has both properties. Therefore, we use steel as an effective material for tensile stresses.

Concrete workability

Processability indicates how easy it is to handle after mixing until casting is complete. There are different definitions of workability.

However, to put it simply, it is the ability to be editable when handled.

Workability is measured using a slump test or soil test.

If the slump is low, it is measured by the Slump Test and a high slump is measured by the flow test.

Concrete permeability

Permeability is a measure of the rate at which liquids flow through a solid with voids.

For structures that retain fluids, permeability is very important. It must be checked accordingly.

Durability is strongly influenced by permeability. Therefore, it is necessary to control them properly.

The following factors affect the durability of concrete

1. Water-cement ratio: A low water-cement ratio reduces permeability. If we increase the cement content, the hydration process improves and more reactions occur. This reduces permeability.
2. Curing: Curing is one of the most important factors in improving the conditions of the superficial zone. When sufficiently cured, porosity is reduced improving the reactivity of the concrete. If the concrete is wet enough, this will help the cement react sufficiently.
3. Use of additives: There are special additives, called impregnating agents. They reduce permeability.
4. Concrete Compaction: Proper compaction affects not only permeability but also strength. Poor compaction leads to more voids and therefore an increase in permeability.
5. Pore ​​structure: A well-connected pore structure is very important for permeability. The more interconnected the pores are, the greater the permeability.
6. Age of Concrete: Permeability varies with age or degree of hydration.

There are two main methods by which permeability can be tested. They are

1. Constant pressure method
2. Suspended head method

For more information about these tests, see the article Testing Techniques for Building Materials .

Impact resistance of concrete

Concrete is capable of withstanding shock loads. These are sudden loads that act on structural elements in the form of point, compressive or distributed loads.

There are several cases where shock loads act on structural elements. Some of them are as follows.

• explosive charges
• Accident loads
• Progressive collapse loads

It has a greater load capacity under sudden load increases. Furthermore, the strength of the material can also be improved by a higher strain rate.

A multiplication factor can be applied to the characteristic resistance during construction.

According to the book “Blast Effects on Buildings”, bending and compression can use factors of 1.25 and 1.15, respectively.

For more information about improving material strength, see the Structural Strength Improvements article.

Abrasion resistance of concrete

For surfaces exposed to intense use, abrasion resistance is very important.

The surface is particularly exposed to wear in parking garages. Therefore, it is very important to improve the surface condition. The following factors may affect abrasion resistance.

• Concrete strength
• Furthermore, increasing cement content and decreasing water content improves abrasion resistance.
• The use of well-selected natural sand improves abrasion
• Coarse aggregate must be free of soft sandstone or soft limestone

Different types of concrete

Depending on the application, they can be categorized as described below.

mass concrete

Pure concrete is used for construction, without using any type of additives such as reinforcement, fibers, etc.

Mass concrete is defined in ACI standards as follows.

Any volume of concrete where a combination of the dimensions of the element to be cast and the boundary conditions may result in undesirable thermal stresses, cracking, harmful chemical reactions, or a reduction in long-term strength due to an increase in the temperature of the concrete due to the heat of hydration. .

Different quality classes are used for construction. Most of the time, lower grades are used because the heat generated in the hydration process is minimal. Since we have not demonstrated reinforcement to minimize cracking, limiting temperature is critical to thermal cracking in concrete .

Furthermore, large quantities are often poured into structures cast in solid concrete.

Gravity structures are generally constructed of solid concrete. As it does not absorb any tensile stress, it must always be under pressure. Designers must ensure that the entire surface of the structure is not subject to tensile stresses when loads are applied to it.

As we know, these structures are subject to lateral loads. They create tilting moments that create stresses on the structural surface. These traction forces must be balanced by the weight of the structure. During construction, the structural surface is held under pressure in all load cases.

For more information, see the mass concrete article for more information.

Reinforced concrete

Reinforced concrete is defined as structural concrete reinforced with at least the minimum amount of reinforcement or non-prestressed reinforcement in accordance with ACI 318.

Simply put, structural concrete that has reinforcement is called reinforced concrete. This is widely known throughout the world.

The reinforced concrete article This topic will be discussed further below.

Laminated concrete (RCC)

RCC is the same as traditional concrete and consists of cement, water and aggregates.

However, the mixture differs from the traditional one.

And also this specific is compacted until the desired density is reached .

The following essential aspects must be taken into consideration when rolling concrete construction:

• As the name suggests, RCC undergoes some compression. The moisture content of the mixture must be monitored carefully. No water should be added during compaction as the ideal moisture content allows for better compaction.
• RCC concrete is compacted to achieve 98% modified Proctor
• One of the most important factors in reinforced concrete construction is the treatment of construction joints. The joints must be damp and cool so that the new layer can adhere.
• To achieve the expected strength and durability, sufficient curing must occur.

Roller compaction offers many advantages. Some of them are as follows.

• Reduces cement content
• Has good strength
• No reinforcements needed
• Lower cost for reinforcements
• Reduced risk of cracking during curing
• RCC can be used in road construction, dam construction, etc.

The Laminated Concrete article may be helpful if you need more information on this topic.

Self-compacting concrete

The name itself suggests it: it is fluid and does not require vibration to compact.

This type of concrete is not normally used. They are used on special occasions. Some of them are as follows.

• Heavily reinforced sections
• Concreting piles
• Construction of columns where vibration is difficult or depending on the type of project
• Slab foundation construction
• Drill shaft construction
• Construction of earth support systems
• Conversions and repair work

There are advantages and disadvantages to self-compacting concrete . Some of the useful benefits are as follows.

• Faster build time
• Excellent durability
• Very high compression
• Friction connection to reinforcement
• Reduces the permeability of the structure
• Flow through areas crowded with reinforcements
• Easy to deal with
• Less work is required for casting
• The concreting work is well completed
• Shortage of qualified workers

Disadvantages of self-compression include, but are not limited to, the following.

• The formwork must be designed to withstand higher pressures than normal
• More experience is required for manufacturing
• Material selection is strict
• Quality control must be strict

There are several tests on self-compacting concrete to ensure its quality. Some of the tests carried out during construction are as follows.

Fill test	Passing the skills test	Segregation resistance test
Soil Drop Test	J ring test	V funnel in T 5 protocol
T 50cm drop	L-box test	GTM Screen Stability Test
V funnel test	U-Box Test
Orimet	Stuffing Box Test

High Performance Concrete (HPC)

ACI defines high-performance concrete as Concrete that meets specific combinations of performance and uniformity requirements that cannot always be routinely achieved using conventional components and normal mixing, placing and curing procedures.

It is different from traditional concrete and offers users more benefits than regular concrete.

Furthermore, HPC is used when we need high performance.

The following advantages can be achieved with high-performance concrete:

• High strength
• High initial strength
• High modulus of elasticity
• High abrasion resistance
• High durability
• High durability in aggressive environments
• Low permeability
• High resistance to chemical attacks
• High impact resistance
• Volume stability
• Easy to handle and place
• Proper compression without segregation

prestressed concrete

Due to its structural advantages, prestressed concrete is widely used in the construction industry.

Prestressing design is often used to construct and simplify cable when carried out on a small scale. However, as the scale increases, heavy equipment is required for construction.

Prestressing is very useful for supporting large spans where it is not effective in normal construction. Furthermore, slabs can also be built with these systems.

The article is written as Bridge construction to BS 5400 provides information on tension girder construction.

In addition, there are other advantages of preload, as described in the article Advantages of prestressed concrete .

Fiber reinforced concrete

According to the ACI, fiber-reinforced concrete is defined as Concrete with dispersed and randomly oriented fibers .

Fibers are added to concrete and serve as reinforcement. They improve strength. Furthermore, they serve as tensile reinforcement in case of tensile stresses.

There are different types of fibers.

• Glass fibers
• Polypropylene and nylon fibers
• steel fibers

Steel fibers are often used in construction work involving the casting of fiber-reinforced concrete elements. They can be used with or without reinforcement. Furthermore, they improve structural resistance.

The construction of industrial floors is made of fiber-reinforced concrete. Reinforcement is not normally used in this type of construction. There are guidelines such as Technical Report 34, Industrial Concrete Ground Floors, a design and construction guide published by the Concrete Society.

There are also other standards that can be used for planning and construction.

• EN 14889-1:2006
• EN 14845-1:2007
• ASTM A820-16
• ASTM C1018-97

Concrete qualities

The quality of concrete is an indicator of the characteristic strength. According to British standards, the grades are C20, C25, C30, C40 etc.

The characteristic resistance considered in the design is determined based on the probability of the test result of a given class. The definition is given in BS 5328 Part 1 and the article Characteristic strength of Concrete discusses this topic in more detail.

According to Eurocode, a different definition is used. There, the cylinder resistance is used to represent the characteristic resistance.

Resistance ratios C25/30, C30/37, C35/40, etc. are used.

Concrete Project

Variations in stresses and strains are taken into account during construction planning. Based on most guidelines, the ultimate elongation of concrete is 0.0035.

By British standards concrete fails when its elongation reaches 0.0035 . Therefore, the possibility of preventing the concrete from reaching this elongation during its ultimate load was considered.

Additionally, serious problems can arise if concrete fails sooner than steel because there is no advance warning. Therefore, it is considered to prevent earlier failure of concrete than steel.

As shown in the figure above, Steel begins to yield at an elongation of 0.002 . Thus, the deformation diagram becomes an equilibrium point when the concrete and steel deformations reach 0.0035 and 0.002, respectively.

The corresponding x/d ratio for the steady state is 0.64 .

Consider British standards x/d = 0.5 which is less than in the balanced state. This could have several reasons, e.g. B. that the sections react to additional forces due to moment distributions, etc.

Furthermore, considering a lower x/d ratio reduces concrete discoloration at the ultimate limit state .

When x/d = 0.5, both strains (steel and concrete) are 0.002, which is good in terms of concrete failure.

In summary, the ultimate goal of limiting the x/d ratio is to prevent ductile failures.

Concrete Creep

Concrete is subject to creep deformation under long-term loading.

It causes deformations of the structure, such as: B. long-term deflections. However, it generally does not cause structural failure.

The following affect fluency:

• Aggregates
• Mixing proportions
• Age

Concrete additives

Various additives are used as fillers, as cement substitutes and as additives to reduce the heat of hydration.

Additionally, they increase surface area because materials like silica fume have a larger surface area.

Fly ash is widely used in construction to replace cement or reduce cement content. Particularly in thick concrete, where greater heat of hydration is generated, fly ash is added to reduce the heat.

Another commonly used material is ground blast furnace slag.

The article Cement and Cement Additives Each of these additives will be discussed in more detail.

Additions

Most concrete poured today is made with additives. In the future, additive-free concrete may no longer be available.

The industry has developed a lot and offers many advantages to traditional concrete. Different types of additives offer a series of benefits to the industry.

The following advantages can be highlighted:

• Maintains concrete workability until installation
• They can be used to increase setting time or to shorten setting time
• Reduce construction costs

According to BS EN 934-2-2001 the following types of additives can be identified.

• Water reducing/plasticizing additives
• High quality reducing/superplasticizing additives
• Water Storage Additives
• Air entraining agent
• Define accelerator additives
• Additives that accelerate hardening
• Setting the retarder
• Water repellent additives
• Setting retardant/water reducing/plasticizer additives
• Highly effective retardant/water reducer/superplasticizer additives
• Accelerator/water reducing/plasticizer additives.

The article Concrete additives For more information and additive testing, please contact us.

Concrete Mix Design

When everything is ready to start construction, mixing projects will be created. The designer specifies the required strength of the concrete. It is the contractor's responsibility to produce the same quality.

Based on available materials and resources, mix designs are prepared for each class and submitted to the engineer for approval.

The water-cement ratio and the mixing proportions of cement, water, sand and coarse aggregate are determined in the composition of the mixture.

Furthermore, the composition of the mixture also indicates the dosages of all additives, if used.

After approval by the engineer, the composition of the mixture is checked. Trial mixing is performed for each mix composition to ensure that the specified mix achieves the desired strength.

The target strength is determined in the mix composition and must be achieved by concrete made from test mixes.

Target force = f _ck + 1.65 xσ

Where,

F _ck – Characteristic resistance of concrete

1.65 – a factor may vary with different patterns

σ – standard deviation, can be selected depending on the type of concrete

When the concrete reaches the desired strength, construction can continue.

For more information, see the relevant article Factors Affecting Concrete Mixing .

Concrete

Most people are unaware of the importance of concreting, but consider other aspects of quality control.

Therefore, it is important to know the main factors when pouring concrete. Regarding quality control, the following key factors should be highlighted that must be taken into account when concreting.

• Concrete setting time : Pay attention to the initial and final setting times. They must be tested before concreting. This can be done when the test mixes are ready. Setting time can be tested as described in the article. 6 different cement tests Additionally, the setting time can be changed by adding additives.
• Formation of cold joints : The formation of cold joints that occur when concreting already hardened concrete must be avoided.
• Casting pattern : Or the construction process must be planned before concreting. It must be planned project by project and based on available resources.
• Concrete compaction : To achieve the required quality and strength, sufficient compaction is required.
• Free fall height : Generally, free fall height is limited to 3 to 5 feet to prevent segregation.
• Temperature control : Controlled lifting of concrete must be carried out in such a way as to avoid cracking and minimize the impact on the durability of the concrete. Methods of limiting the temperature rise of concrete are discussed in a separate article.

The article on this topic Concrete could be used as additional information.

Concrete Compaction

Care must be taken to ensure that the concrete is sufficiently compacted. Poor compaction can lead to problems such as durability.

Furthermore, poor compaction reduces strength and increases permeability.

The following issues may occur due to improper compression.

• Low resistance
• Increase porosity
• Honeycomb formation
• Effects on durability

The following compression method is commonly used.

1. Manual compaction : Compact manually. Poles or similar devices may be used.
2. Mechanical compaction through vibration The following methods are used for compaction: internal vibrator, formwork vibrator, table vibrator, flat-form vibrator, vibratory roller, etc.
3. Other processes such as printing, stirring and centrifugal processes are also used.

The following figure makes it clear how important compression is.

If compaction creates more voids, this will have a direct impact on strength. Therefore, great care is required during the concreting work.

Concrete hardening

One of the most important aspects to consider after concreting is curing. Offers greater benefits to the structure.

• Increases strength
• Reduce permeability
• Prevents cracks due to plastic shrinkage
• Increase abrasion resistance
• Improve durability

There are many factors that affect healing. The article Factors Affecting Concrete Curing Time Discuss these issues.

Depending on the type of work, a suitable post-treatment method must be chosen. The methods used for thinner concrete are not applicable to thicker concrete.

There are many healing methods. 11 methods are shown below.

1. Water hardening
2. Wet cover
3. Formwork hardening
4. Membrane hardening
5. Plate hardening
6. Heat absorption hardening
7. Hot mixing process
8. Electric curing
9. Infrared healing
10. Cover with sand or sawdust, earth, etc.
11. Natural post-treatment (exposed concrete)

Each of the methods has been discussed in detail in the article Methods for Curing Concrete .

durability

All structures are designed for a certain service life and the structure is classified accordingly. Different Structure Class used in design to determine service life.

Projects are created based on initially determined parameters. Failure to meet durability requirements may lead to the following problems.

• Reinforcement corrosion
• deterioration
• Structural errors
• Concrete cracking and spalling
• Regular maintenance and costs

Therefore, it is very important to pay attention to durability during construction planning until the structures are completed.

The article was written as Durability requirements for reinforced concrete projects to have more relevant technical information on this topic.

The main factors that affect durability are listed in the article Factors that affect the durability of concrete are listed below.

1. High humidity and rain
2. UV resistance
3. Chemical resistance
4. Exposure to sea water
5. Chloride and corrosion resistance of steel
6. Sulfate resistance
7. Alkali-silica reaction resistance (AKR)
8. Carbonation
9. Abrasion resistance
10. Moderate to Heavy Load Conditions for Concrete
11. Frost and thaw resistance
12. Cement content
13. Quality of aggregates
14. Water quality
15. Concrete Compaction
16. Installation time after filling and cold joint formation
17. Healing time
18. permeability
19. temperature
20. Construction defects (honeycombs, cracks, etc.)

Each of the above points is discussed in detail in the article Factors Affecting the Durability of Concrete .

Concrete Test

The test serves as quality control and to verify that the required resistance has been achieved. Furthermore, it must be ensured that the project achieves the values ​​assumed in the project.

Furthermore, tests are carried out if there are doubts about the test results or if the strength of the concrete identified as defective needs to be checked.

Quality Control Tests

These tests are carried out in the initial phase. The main objective of these tests is to ensure that the poured concrete has reached the required or specified strength.

In addition to proving resistance, workability, slump, temperature tests, etc. are also carried out. to ensure the quality of the concrete.

Drop Test and Flow Test

These tests are carried out to check workability.

The construction level specified in the composition of the mixture must be achieved upon arrival at the construction site.

Before concreting begins, a slump test is carried out. Samples taken from each truck mix are tested.

There is an acceptable range for recession. For example, if the design slump is 150 and the allowable range is ±25, the local slump must be between 125 and 175. If the concrete does not reach this value, the truck may be rejected.

The allowable range varies depending on the rebate class, etc. Therefore, the specified limits on the mixture composition must be respected or the relevant specifications must be consulted.

Cube and cylinder test

The most widespread and frequently used method for testing strength is testing with test cubes or cylinders.

Depending on the type of project or the standards cited, cubes or cylinders are tested.

In British Standards, cube strength is used for structural design. However, in Eurocode 2 the cylinder strength is used for structural design.

The test cubes molded during concreting are immersed in the baths. Test cubes are sampled according to respective design specifications.

Normally tests are carried out for 7 or 28 days.

Checking construction defects

If there are problems with the design, testing will be carried out to ensure it is stable enough. Furthermore, these tests are particularly necessary when test results are not available.

Furthermore, failure of concrete cubes to achieve the specified strength also leads to these tests being carried out.

There are basically two types of tests that differ in the way they are carried out.

1. Non-destructive testing
2. Destructive testing

Non-destructive testing

The name itself implies the testing method. With this testing method, no damage is caused to the concrete during testing.

These tests are performed without damaging the concrete.

However, there are always doubts about the test results. It is not practical to assume they are 100% accurate.

Destructive testing provides accurate results because we test the actual samples.

There are many non-destructive testing methods, as described in the article Non-Destructive Testing of Concrete . They are listed below.

1. Visual inspection
2. Half-cell electronic potential method
3. Rebound Hammer Test
4. Test to measure depth of carbonation
5. Permeability test
6. Penetration resistance or Windsor probe test
7. Checking the coverage meter
8. X-ray exams
9. Ultrasonic Pulse Speed ​​Test
10. Tomographic modeling
11. Effects of the eco-test
12. Ground Radar or Pulse Radar Test
13. Infrared thermography

Destructive testing

With this test method, concrete samples are collected or tested on site with the corresponding material.

The following tests are commonly used in the construction industry, as explained in the article destructive testing of concrete .

1. Concrete Core Cutting
2. Extract verification

A core sample is taken by cutting and tested for strength. If the tested sample reaches the required strength, it may be acceptable. Additionally, these test results are correlated with non-destructive testing results for better understanding.

Environmental impact of concrete

Concrete is not an environmentally friendly material. It has serious impacts on the environment.

As a material, it has higher energy content. Greenhouse gas emissions are very high during concrete production.

Various materials are added to concrete. Of these materials, cement production causes very high greenhouse gas emissions. Cement production is very high across the world and the production rate is also increasing in emerging countries.

The image above from the internet gives a clear impression of the impact of the construction industry on the environment. As these effects are not irreversible, they should receive maximum attention.

To protect the environment, alternative materials must be used, the embodied energy of a structure must be reduced, etc.

The world is currently thinking about switching to green technologies that have less impact on the environment.

Recycling and reuse

It is recycled to reduce environmental impact. There are a few steps to consider when recycling.

• First, large pieces are crushed using special industrial equipment.
• Then the broken particles are sieved to remove dirt or contaminating particles. Additional processes and equipment, such as water flotation, separators, and magnets, are used to remove other contaminants.
• Concrete is separated into coarse and fine aggregates.

Furthermore, concrete is reused if there is a place to pour or set it. Especially at the end of the works, a significant amount of debris must be removed. These materials can be used to fill other construction sites. A similar arrangement can be made for reused materials.