What is Concrete?

Concrete, a mixture of cement, water, and aggregates, is one of the most extensively used construction materials. There is no construction nowadays that is not made of concrete. Even if the structure is made entirely of other materials, at least a tiny piece of it is made of concrete.

History

The history of concrete dates back to 6500 BC.

The United Arab Emirates began using it in the early times. They’ve built structures out of concrete. Egypt and China employed it in construction in 3000 BC.

It was also observed in Rome in 600 BC. By 200 BC, Rome had begun to use it widely.

The figure below depicts a portion of the development in this area.

How do you make concrete?

There are four main elements. Cement, water, fine aggregate, and coarse aggregate are the four components. These ingredients are combined in the proportions determined by the mix design and confirmed by a trail mix.

Other additives, such as admixtures, are added to increase their performance in addition to the above basic additives.

Mixing can be done manually or automatically, which is the most used approach in the world. All of the components are placed in the mixing bin according to their mixing proportions in this procedure.

It was subsequently loaded into the truck mixture after mixing. The water-cement ratio is monitored based on the workability requirements and the needed strength. The slump test at the batching plant and on arrival at the job site are used to determine the concrete’s workability.

Cement

Let’s talk about the most crucial material that went into making everything in the concrete.

The cement reacts with the water to form the bond that holds the particles together.

Cement is a complex material made up of various components. Furthermore, because it includes chemistry, the reaction to generate it is a little more complicated for basic engineering design.

The reactions that follow can be used to observe the cement manufacturing process.

Ca2SiO4 (declaim silicate (C2S)) = 2CaO + SiO2

Ca3SiO5 (tricalcium silicate (C3S)) = 3CaO + SiO2

Ca3Al2O6 (dicalcium aluminate (C2A)) is formed by combining 3CaO with Al2O3.

Ca4Al2Fe2O10 (tetracalcium aluminoferrite(C4AF)) = 4CaO + Al2O3 + Fe2O3

C3S and C2S are the most essential compounds that contribute to the strength of these materials. The strength of C3S is initially developed in the first four weeks. As demonstrated in the accompanying picture, C2S increases strength primarily after the first four weeks.

Cement Quality

To ensure the quality of the cement, it must be tested. Typically, the following tests are performed.

Fineness
Compressive Strength
Heat of Hydration
Time for the initial and final settings
Soundness
Consistency

6 Different Cement Tests delves more into the testing processes as well as the applicable standards.

The Process of Cement Hydration

Hydration is the reaction of cement with water that results in the formation of concrete by forming the necessary bonding with other components. This reaction produces a very hard
and strong in compression. It is, nevertheless, relatively weakconcrete mix in tension.

The materials C2S, C3S, C2A, and C4AF are included as fundamental materials in the cement, as previously stated. In addition, the cement contains additional components such as gypsum (CSH2) and other elements.

As mentioned below, the interplay of these components with each other and with water transforms them into other forms.

Tricalcium aluminate + gypsum + water ® ettringite + heat : C3A + 3CSH2 + 26H ® C6AS3H32, D H = 207 cal/g

Tricalcium silicate + water ® calcium silicate hydrate + lime + heat : 2C3S + 6H ® C3S2H3 + 3CH, D H = 120 cal/g

After the gypsum has completely reacted according to the first equation, the ettringite becomes unstable and begins to react with the remaining C3A. Monosulfate aluminate hydrate crystals are formed as a result of the reaction.

Tricalcium aluminate + ettringite + water ® monosulfate aluminate hydrate
2C3A + 3 C6AS3H32 + 22H ® 3C4ASH18,

Dicalcium silicates + water ® calcium silicate hydrate + lime
C2S + 4H ® C3S2H3 + CH, D H = 62 cal/g

The reactions of ferrite with gypsum

First reaction : Ferrite + gypsum + water ® ettringite + ferric aluminum hydroxide + lime : C4AF + 3CSH2 + 3H ® C6(A,F)S3H32 + (A,F)H3 + CH

Second Reaction : Ferrite + ettringite + lime + water ® garnets : C4AF + C6(A,F)S3H32 + 2CH +23H ® 3C4(A,F)SH18 + (A,F)H3

Let’s talk about Hydration Products.

Calcium Silicate Hydrate is a kind of calcium silicate. This is the primary source of strength. C-H-S is the designation for this product.

Calcium Hydroxide, abbreviated as CH, is a product of alite hydration.

Ettringite: They are rod-like crystals that form at the beginning or later stages of a process. Its reactivity creates concrete fissures, particularly when it reacts later.

Monosulfate is formed 1-2 days after the mixing process begins.

Monocarbonate is produced by the presence of fine limestone or limestone aggregate.

Concrete’s Properties

Designers need to know the properties in order to carry out the structural design. There are a number of critical criteria that have a direct impact on structural performance.

Concrete Elasticity

Different standards have defied the concrete’s modulus of elasticity in different ways. It is connected to compressive strength, according to the majority of rules (characteristic strength).

There are equations in BS 8110 Part 2 that can be used to compute the modulus of elasticity.

Furthermore, in BS 8110 Part 2, there is a table that can be used to calculate the elastic modulus.

Also, Eurocode 2 provides the values and formula for finding the elastic modulus based on the strength of the cylinder.

Table 3 of Eurocode 2 is shown here.

Poisons Ratio

The relationship between longitudinal and transverse stresses is represented by Poisson’s ratio.

For linear analysis, the poison’s ratio is 0.2, according to BS 8110 part 1.

It is 0.2 for uncracked concrete and 0 for cracked concrete, according to Eurocode 2.

Fire Resistance

The ability to withstand fire is measured by fire resistance. It’s stated in terms of hours.

It is, on typical, more fire-resistant than many other construction materials.

Fire resistance is measured in hours according to British Standards.

First, we determine how long it will take to survive the migration. We choose the cover for the reinforcement based on the time period.

In addition to the concrete, the main ingredient that bears the strength is reinforcement.

Reinforcement is extremely heat-sensitive, and it expands fast as the temperature rises. If the reinforcement is sufficiently covered, it protects the concrete to some extent and also reduces the temperature rise of the steel.

Temperature of the Concrete

In two scenarios, we consider the temperature.

It refers to the temperature at the time of pouring as well as the temperature that rises as a result of the hydration process.

When it pours, the temperature is limited to 300 degrees C, according to BS 5328. However, it goes on to say that this value could change depending on the project’s specifications.

The ultimate goal of temperature control is to keep the temperature from rising during the hydration process.

It causes severe concerns with strength and durability if it climbs by a substantial amount without any control.

According to the majority of the research, the rise in temperature to the region of 70-800 degrees C throughout the hydration process is crucial. It causes the creation of delayed ettringites, which cause internal expansions as a result of the material produced during the reaction.

Internal cracks develop, as a result, lowering the strength and endurance of the material.

By lowering the pouring temperature and utilizing a different additive that minimizes the heat of hydration, the temperature rise could be reduced. Fly ash is one such substance that is frequently used.

The article Ways of Limiting Concrete Temperature examines the various methods for limiting concrete temperature as well as its causes of it.

Furthermore, the concrete’s early age temperature should be kept under control to prevent immature concrete from cracking. It may have a negative impact on the durability of the material.

The durability after construction is the most significant aspect. More information on concrete durability can be found in the article Factors affecting concrete durability.

Compressive Strength

Concrete is used due to its compressive strength. The hydration process produces a product with rock-like strength.

The compressive strength of the concrete in the design is referred to as its characteristic strength.

Axial forces, shear forces, and bending moments affect the majority of structural elements. Each of these loadings is resisted by concrete.

Concrete has high compressive strength and dominates the axial compression aspects. The compression loads are influenced by the entire section. However, in some circumstances, such as bending, only a portion of the segment is useful.

As we all know, British standards only consider 0.45 times the depth to the neutral axis for the compression stress block in beams subjected to bending moment. With the other criteria, this figure may change slightly. However, the entire section does not contribute effectively to carrying the loads.

The compressive strength is referred to as the characteristic strength, as previously stated. This detailed value is employed in structural designs and is validated by testing during construction.

C25/30 is a commonly used approach to specify it. The cylinder strength is the first number in this expression. The cube strength is the second number.

Compressive strength is influenced by a variety of elements. The water-to-cement ratio is the most important component. Other variables include mix proportions, void ratio, curing time, compaction, and so on.

Concrete Tensile Strength

Tensile strength is, as we all know, extremely low. Furthermore, save in a few cases, the tensile strength range is rarely used in structural designs.

The tensile strength is used to design the prestress concrete, based on the design class chosen.

The tensile strength can be calculated using a variety of formulas.

The tensile strength can be calculated using Table 3 from Eurocode 2 (seen above). A table for prestressing concrete works is also included in BS 8110 Part 1.

The concrete’s weakness is its inability to endure tensile stresses. Steel possesses both of these characteristics. As a result, when tensile stresses are present, we choose steel as an effective material.

Concrete’s Workability

The workability refers to how easy it is to handle the mixture after it has been mixed till the pouring has been done. Workability is defined in a variety of ways.

However, in layman’s words, it’s the ability to work with it while it’s being handled.
Slump tests or flow tests are used to determine workability.

When the slump is low, the slump test is used, and when the slump is high, the flow test is used.

Concrete Permeability

The permeability of material with voids is a measure of the rate at which fluids flow through it.

For structures that hold fluids, permeability is critical. It must be adequately addressed.

The permeability of the concrete has a significant impact on durability. As a result, effective control is essential.

Concrete’s durability is influenced by the following factors:

Water-cement ratio:

Permeability is reduced when the water-to-cement ratio is low. The hydration process improves and more reactions occur when the cement content is increased. As a result, permeability decreases.

Curing:

Curing is one of the most significant aspects of improving the surface zone’s condition. When concrete is properly cured, it minimizes porosity by increasing its reactivity. It helps the cement to react properly when there is enough moisture in the concrete.

Use of Admixture:

Waterproofing admixtures are a type of admixture that is used in concrete. They have a negative impact on permeability.

Concrete Compaction:

Concrete compaction influenced not just the permeability but also the strength of the concrete. More voids result from poor compaction, which leads to an increase in permeability.

Pore Structure:

For permeability, it is critical to have a well-connected pore structure. The greater the pore connection, the greater the permeability.

Concrete Age:

Permeability varies with the age of the concrete or the degree of hydration.
The permeability can be determined using one of two approaches. They really are.

Method of a Constant Head
Method of the Falling Head

The article Construction Material Testing Techniques has more information on these tests.

Concrete’s Impact Resistance

The impact loads can be carried by concrete. They are a type of sudden load imposed on structural parts as a point load, pressure load, or distributed load.

The structural elements are subjected to impact loads on a number of occasions. The following are a few of them.

Accidents Loads
Blast Loads
Loads of Progressive Collapse

It has a higher bearing capacity in the event of a sudden rise in loads. Furthermore, a higher rate of strain might improve the material’s strength.

When designing, a multiplication factor might be used to the characteristic strength.

According to the book Blast Effects on Buildings, factors 1.25 and 1.15 can be used in bending and compression, respectively.

Design strength enhancements article is a good page to go for further information on material strength upgrades.

Concrete Abrasion Resistance

Abrasion resistance is critical in surfaces that are subjected to wear.

It is critical to improving the surface condition, particularly in car park buildings where the surface is subjected to wear. Abrasion resistance may be affected by the following factors:

Concrete’s strength

The abrasion resistance can also be improved by increasing the cement content and reducing the water content.

The abrasion resistance of natural sand is improved by using well-graded sand.

Soft sandstone or soft limestone should not be present in coarse aggregate.

Various Types of Concrete

They are categorized differently based on their application.

Mass concrete

It is used without any additives such as reinforcement, fiber, or other materials to increase strength.

According to the ACI standards, mass concrete is defined as follows.

Any volume of concrete in which the boundary conditions, as well as the dimensions of the member being cast, might result in undesired thermal strains, cracking, harmful chemical reactions, or deterioration in long-term strength as a result of elevated concrete temperature caused by hydration heat.

For construction, many grades are implemented. Low-grade materials are commonly employed in construction since the heat created during the hydration process is negligible. Because we are not providing reinforcing to reduce cracking, controlling the temperature is critical to preventing concrete thermal cracking.

Furthermore, massive volumes of concrete are typically poured into constructions made of mass concrete.

The majority of gravity constructions are made of mass concrete. It must always be in compression because it does not carry tensile loads. When loads are applied to a structure, designers must ensure that all of the structure’s surfaces are not subjected to tensile forces.

These constructions, as we all know, are subjected to lateral loads. They cause overturning moments, which create tension in the structure’s face. The weight of the structure should counteract these tensile forces. For all load conditions, the structure’s face is kept in compression during design.

Reinforced Concrete

ACI 318 defines reinforced concrete as structural concrete with at least the minimum amount of prestressing tendons or non prestressed reinforcement.

Reinforced concrete is simply the structural concrete that has been reinforced. This is a widely recognized fact in the world.

Roller Compacted Concrete (RCC)

RCC is similar to traditional concrete in that it contains cement, water, and aggregates.

The composition, however, is not the same as usual.

In addition, this concrete is compacted until it reaches the appropriate density.

The roller-compacted concrete construction has the following important characteristics:

The RCC is subjected to compaction, as the name implies. The moisture content of the mix must be carefully checked. Water should not be introduced during the compaction process since the ideal moisture content allows for greater compaction.

RCC concrete is compacted to a modified proctor of 98 percent.
The care of the construction joints is one of the most significant aspects of RCC construction. To attach to the new layer, the joints must be moist and fresh.

To produce the desired strength and durability, enough curing is required.

Roller compaction has numerous advantages. The following are a few of them:

It lowers the amount of cement content Good   strength of the concrete
There are no reinforcements required.
Less cost due to no reinforcement requirements
When it hardens, there’s less chance of it cracking.
RCC can be used in the construction of roads, dams, and other structures.

Self Compacting Concrete

 It’s flowable concrete that doesn’t need vibration to compact.

Normally, this sort of concrete is not used often in construction. They are only utilized in rare circumstances. The following are a few of them:

Sections that have been heavily reinforced.
Concreting of Piles Columns in difficult-to-vibrate environments or depending on the project type
Construction of a raft base
Construction of a drill shaft
Earth retaining structures
Work on retrofitting and repairs

Self-compacting has both pros and downsides. The following are a few of the advantageous features:

Construction time is reduced.

Excellent long-term durability

Compaction is very high.

The greater bond to the reinforcements.

Reduces the structure’s permeability.

Flowing through locations where reinforcements are congested.

The concrete is easy to handle

During the pouring, a smaller workforce is necessary.

The finishing of the concrete surface is good

Reduce the number of skilled workers

The following are some of the drawbacks of self-compacting:

The formwork must be built to endure higher pressures than typical construction.

To complete it, you’ll need more experience.

The material is carefully chosen.

Quality control should be strictly enforced.

There are numerous tests that self-compacting concrete undergoes to ensure its quality. The following are some of the tests carried out during construction.

Segregation Resistance Test

Filling Ability Test

Slump Flow Test

V-funnel at T5 minutes

T50cm Slump Flow

Passing Ability Test

J-Ring Test

L-Box Test

GTM Screen Stability Test

V-Funnel Test

Orimet

U-Box Test

Fill-Box Test

High Performance Concrete (HPC)

ACI defines high-performance concrete as concrete that meets unique performance and homogeneity requirements that aren’t always possible to fulfill using standard constituents and mixing, placing, and curing techniques.

It’s not the same as regular concrete. It provides more advantages to the user than ordinary concrete.

Furthermore, HPC is used when high performance is required.

High-performance concrete could have the following benefits:

Extremely strong

High early strength

Elasticity with a high modulus

High abrasion resistance

Highly Durable

High Ability to withstand harsh environments

Permeability is low.

Chemical resistance is very high.

Superior impact resistance

Stability of volume

Handle and place easily

No segregation during compaction

Prestressed Concrete

Because of the benefits it provides, prestressed concrete is frequently employed in the construction sector.

When working on a small scale, prestress building is highly popular since it is easy to manage. When the scale is expanded, however, substantial construction equipment is necessary.

Prestressing is highly useful for supporting big spans where conventional construction is ineffective. Furthermore, similar technologies can be used to manufacture floor slabs.

The article, titled Bridge Design to BS 5400, explains how to design a post-tension beam.

Fiber Reinforced Concrete

Concrete with fiber reinforcement
Fiber-reinforced concrete is defined by the ACI as concrete with distributed, randomly oriented fibers.

Fibers are included in the concrete as reinforcements. They help to increase strength. They also serve as tensile reinforcement in areas where tensile stresses exist.

Fibers come in a variety of forms:

Glass Fibers

Steel Fibers

Nylon and polypropylene fibers

Steel fibers are commonly employed in building projects including fiber reinforced concrete parts. It’s possible to utilize them with or without reinforcements. They also add to the structural integrity of the building.

Fiber-reinforced concrete is used to construct industrial flooring. In most cases, no reinforcements are employed in this style of structure. Technical Report 34, Concrete Industrial Ground Floors, a design and construction guide produced by The Concrete Society, is one example.

There are several additional design and construction standards that could be applied.

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

Grades of Concrete

The strength of concrete is determined by its grade. Grades are designated as C20, C25, C30, C40, and so on, according to British standards.

The characteristic strength used in structural design is calculated by the probability of a certain grade’s test result. BS 5328 Part 1 contains the definition, and the article Characteristic Strength of Concrete delves more into the topic.

A separate definition is applied according to the Eurocode. The characteristic strength is represented by the cylinder strength.

C25/30, C30/37, C35/40, and other strength relationships are utilized.

Design of Concrete

The structural designs take into account variations in stress and strain. The limiting strain of concrete, according to most guidelines, is 0.0035.

Concrete fails when the strain hits 0.0035, according to British standards. As a result, it suggested avoiding this strain during the concrete’s ultimate limit stage loading.

Furthermore, the collapse of the concrete before the steel causes serious problems because there are no prior warnings. As a result, it is thought to be preferable to steel in terms of avoiding concrete failure.

Steel begins to yield at strain 0.002, as shown in the diagram above. As a result, the strain diagram’s balancing consideration emerges when the concrete and steel strains reach 0.0035 and 0.002, respectively.

For the balance condition, the equivalent x/d ratio is 0.64.

According to British standards, x/d = 0.5 is less than the balanced condition. It could be due to a variety of factors, including sections reacting to additional stresses caused by moment distributions, and so on.

Furthermore, taking into account a lower x/d ratio minimizes the staining of concrete at the ultimate limit condition.

Both strains (steel and concrete) become 0.002 when x/d = 0.5, which is favorable in terms of concrete failure.

In conclusion, the ultimate purpose of reducing the x/d ratio is to ensure that ductile failures do not occur.

Concrete Creep

When concrete is subjected to a long-term load, it undergoes creep deformation.

It produces structural deflections such as long-term deflections. It is not, however, causing structural breakdowns in general.

The creep is influenced by the following factors.

Mix proportions
Aggregates
Concrete Additives

As a filler to replace the cement and as an additive to lower the heat of hydration, a variety of additives are utilized.

They also enhance the surface area because a material with a large surface area, such as silica fume, has a large surface area.

Fly ash is commonly used in construction to replace or reduce the cement component. Fly ash is added to thick concretes to lower the heat of hydration, which is especially important in thick concretes.

Ground granulated blast furnace slag is another commonly used substance.

The article Cement and Cement Additives went into greater detail about each of these additives.

Admixtures

Today, admixtures are used in the vast majority of concrete pours. Concrete without admixtures may become obsolete in the future.

The construction industry has grown significantly, and it now offers several benefits over traditional concrete. Various types of admixtures offer a variety of benefits to the industry.

The benefits listed below should be underlined:

Maintains the concrete’s workability until it is placed.

They can be used to either lengthen or shorten the setting time.

Construction costs are decreasing.

The following types of admixtures can be identified according to BS EN 934-2-2001:

High range water reducing/ superplasticizer admixtures
Water reducing/plasticizing admixtures
Air entraining admixtures
Water retaining admixtures
Set acceleration admixtures
Hardening accelerating admixtures
Water resisting admixtures
Set retarding admixtures
Set retarding/high range water reducing/superplasticizer admixtures
Set retarding/water reducing/plasticizing admixtures
Set accelerating/water reducing/plasticizing admixtures.

For more information and testing of admixtures, please refer to the article Concrete Admixtures.

Design of Concrete Mix

The concrete’s required strength is specified by the designer. It is the contractor’s job to create the same grade.

Mix designs for each grade are created based on the available materials and resources, and they are then submitted to the engineer for approval.

The mix design specifies the water-cement ratio, as well as the proportions of cement, water, sand, and coarse aggregate in the mix.

Furthermore, if any admixtures are employed, the doses will be specified in the mix design.

Verification of the mix design is completed after receiving the engineer’s approval. For each mix design, trial mixtures are made to ensure that the stated mix will attain the desired strength.

The mix design specifies the target strength, which must be met by concrete made from trial mixes.

Target strength=fck + 1.65x =

Where,

fck – Concrete Characteristic Strength

1.65 – a factor that could be changed depending on the standard

σ- Standard deviation, which could be chosen based on the concrete type.

It is safe to proceed with the construction once the concrete has reached the desired strength.

Pouring Concrete

Most individuals overlook the relevance of concrete pouring while considering other components of quality control.

As a result, it’s critical to understand the most important aspects of concrete pouring. When concrete is poured, the following critical issues linked to quality control should be considered.

Concrete Setting Time: The initial and final setting times must be considered. Before beginning the concrete pouring, they must be tested. It could be done once the trial mixes have been completed. As mentioned in the article, there are six distinct cement tests that can be used to determine the setting time. In addition, admixtures can be used to change the setting time.

Cold Joints Must Be Avoided: Cold joints must be avoided when concrete is poured over concrete that has already begun to set.

Pouring Sequence: Alternatively, the construction process must be planned before the concrete pouring begins. It will be planned in accordance with the type of project and resources available.

Concrete Compaction: To attain the desired quality and strength, the concrete must be compacted properly.

Free Fall Height: To avoid segregation, free fall height is usually limited to 3 to 5 feet.

Temperature Control: It is necessary to control the rising of the concrete in order to avoid cracking and to reduce the impact on the concrete’s durability.

In a separate post, we go through how to keep the temperature of concrete from becoming too high.
In addition, the piece published on the subject of concrete pouring is recommended reading.

Concrete Compaction

It must be ensured that the concrete is sufficiently compacted. Many challenges arise as a result of poor compaction, including durability.

In addition, poor compaction diminishes strength while increasing permeability.

Due to insufficient compaction, the following concerns may arise such as:

Concrete low strength

Increase in the porosity

Effect on the durability

Honeycombs formation

The following compactions method is extensively used.

Manual compaction entails compacting the material by hand. Rods or other similar tools could be utilized.

Vibration compaction methods include the use of a poker vibrator, a formwork vibrator, a table vibrator, a flatform vibrator, and a vibratory roller, among others.

Other techniques include applying pressure, jolting, and spinning.

The curing of concrete is one of the most critical factors that must be attended to after it has been poured. It has several advantages for the structure.

It increases strength.
Permeability should be reduced.
Plastic shrinkage cracks are avoided.
Increase the resistance to abrasion.
Increase the durability of the concrete.
Increase the durability of the concrete.

Curing is influenced by a variety of things. These difficulties are discussed in the article Factors Affecting Concrete Curing Time.

There are numerous methods for curing listed below.

Curing with water
Formwork Curing 
Membrane Curing 
Sheet Curing 
Wet Covering
Heat Absorption Curing
Method of hot mixing
Electrical Curing 
Infrared Curing 
Cover made of sand, sawdust, soil, and other materials

Each approach has been thoroughly covered in the article concrete curing processes.

Durability

All structures are built to last a particular amount of time, and the classification of the structure is based on that. To specify the design’s life duration, different structural classes are used.

The designs are carried out based on the parameters that were first identified. Failure to meet durability criteria may result in the following problems.

Corrosion of reinforcements
Deterioration
Failures of the structure
Concrete spalling and cracking
Maintenance on a regular basis and the cost
As a result, it is critical to consider durability from the beginning of the structural design process until the constructions are completed.

More relevant technical information on this subject can be found in the article durability requirements in reinforced concrete design.

Testing of Concrete

Testing is done as a quality control measure and to see if it has reached the desired strength. It’s also necessary to check if the values assumed in the design are met by the construction.

Testing is also done if there are any uncertainties about the test results or if it is necessary to check the strength of the concrete that has been identified as unsatisfactory.

Quality Control Testing

These tests are carried out at the start of the process. The main goal of these tests is to ensure that the poured concrete meets the needed or stipulated strength.

Workability, slump, temperature, and other factors were examined in addition to strength to ensure the concrete’s quality.

Slump and Flow Testing

In these tests, the workability of the concrete is tested.

The required design slump in the mix design must be reached at the time of delivery to the job site.

A slump test is performed on the concrete before it is poured. The samples taken from each truck mixture are tested.

The slump can be within a certain allowable range. If the design slump is 150 and the permissible variation is +-25, the site slump should be between 125 and 175 degrees. If the concrete fails to do this, the truck may be rejected.

The variation will vary depending on the slump classes and other factors. As a result, the mix design’s limits must be observed or appropriate requirements must be followed.

Concrete Cube and Cylinder Test

Testing cubes or cylinders are the most generally used method for determining strength.

Depending on the type of project or the referred standards either testing of cubes or cylinders is implemented.

For structural design purposes, British standards used cube strength. However, the structural design under Eurocode 2 was based on cylinder strength.

The test cubes cast during concrete pouring are submerged in the water. The test cubes will be sampled in accordance with the project’s applicable specifications.

Testing usually is done for 7 days and 28 days.

Testing for Concrete Construction Defects

When there are problems with the concrete construction, testing is done to ensure that the strength is met. Furthermore, these tests are particularly necessary when no test results are available.

Additionally, failure of the concrete cubes to meet the necessary strength results in doing the required test.

There are primarily two sorts of tests that are classified based on how they are conducted.

  • Destructive tests
  • Non-destructive tests

Non-Destructive Tests for Concrete

The method of testing is implied by the name. When using this test procedure, no harm to the concrete is done throughout the testing process.

These tests are carried out without causing any damage to the concrete.

However, there is always some skepticism about the outcomes of the tests. It’s unrealistic to expect 100 percent accuracy from these.

As we evaluate the genuine samples, the destructive test delivers reliable results.

As described in the article Nondestructive testing, there are numerous non-destructive testing procedures.

Non-destructive testing of concrete is listed as follows:

  • Visual examination/inspection
  • Method of half-cell electoral potential
  • Test with a rebounding hammer
  • Test to determine the depth of carbonation
  • Test for permeability
  • Windsor probe test or penetration resistance
  • Testing of cover meters
  • Radiographic examination
  • Pulse velocity testing with ultrasonic waves
  • Modeling with tomography
  • Impact eco testing
  • Testing with ground-penetrating radar or impulse radar
  • Thermography using infrared light

Destructive Tests for Concrete

Concrete samples are taken or the material is tested on the spot in this test procedure.

As mentioned in the article Destructive Testing of Concrete, the following tests are frequently employed in the construction business.

  • Cutting concrete cores
  • Pull-out Testing

Cutting a core sample is used to assess the strength of the concrete. It may be acceptable if the tested sample reaches the required strength. Furthermore, for a better understanding, these test results are correlated with the non-destructive test results.

Concrete vs Grout

Concrete and grout are usually roughly the same strength except for High-Performance Concrete, which is new to the market and 10 times stronger than ordinary concrete or grout. The compression strength of this concrete is larger than that of grout (7,500 vs. 5,000 psi, respectively).