What Is Setting And Hardening Of Portland Cement?

What Is Setting And Hardening Of Portland Cement
Cement when mixed with water forms a plastic mass called cement paste. During hydration reaction, gel and crystalline products are formed. The inter-locking of the crystals binds the inert particles of the aggregates into a compact rock like material. This process of solidification comprises of (i) setting and then (ii) hardening Setting is defined as stiffening of the original plastic mass due to initial gel formation.

Hardening is development of strength, due to crystallization. Due to the gradual progress of crystallization in the interior mass of cement, hardening starts after setting. The strength developed by cement paste at any time depends upon the amount of gel formed and the extent of crystallization. The setting and hardening of cement is due to the formation of inter locking crystals reinforced by rigid gels formed by the hydration and hydrolysis of the constitutional compounds.

Reactions involved in setting and hardening of cement:- When cement is mixed with water, the paste becomes rigid within a short time which is known as initial setting. This is due to the hydration of tricalcium aluminates and gel formation of tetra calcium alumina ferrite. Dicalcium silicate also hydrolyses to tobermonite gel which contributes to initial setting. Final setting and hardening of cement paste is due to the formation of tobermonite gel and crystallization of calcium hydroxide and hydrated tricalcium aluminate. During setting and hardening of cement, some amount of heat is liberated due to hydration and hydrolysis reactions. The quantity of heat evolved during Complete hydration of cement is 500 KJ/Kg. Function of gypsum in cement :- Tri calcium aluminate (C3A) combines with water very rapidly. After the initial setting, the paste becomes soft and the added gypsum retards the dissolution of C3A by forming insoluble calcium sulpho aluminate.

What happens during setting and hardening of cement?

Setting describes the stiffening of the fresh cement paste. Onset of rigidity occurs. Then hardening begins, which indicates that a useful and measurable strength is developing. Setting and hardening result from the continuing reaction between the cementitious material and water.

What is time setting of Portland cement?

2 The Setting Time – The setting time of cement includes the initial setting time and the final setting time. The initial time refers to the time that cement turns into paste by mixing with water and begins to lose its plasticity. And the time that cement completely loses its plasticity by mixing with water and begins to have a certain structural strength is known as the final setting time.

The national standards prescribe that the initial setting time of Portland cement should not be earlier than 45 min and the final setting time should not be later than 6.5 h. All the products off-grade at the initial setting time are spoiled products and those unqualified at the final setting time are sub-quality products.

The setting time of cement is measured by time determinator. The sample is the standard cement paste of which the temperature is 20 °C ± 3 °C and humidity is more than 90%. Various mineral components of the cement clinker are different in the water consumption of their normal consistency.

  • The finer the cement is ground, the more water the normal consistency will need.
  • The normal consistency of Portland cement is within 24% ~ 30%.
  • The setting time of cement is very important in the construction projects.
  • The initial setting time should not be too fast in order to ensure that there is enough time to complete every process, such as casting, before the initial setting time; and the final setting time should not be too late in order to enable the cement to complete its setting and hardening as soon as possible after pouring and tamping to make the next process occur earlier.

Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9781845699550500049

What you mean by setting of cement?

What is setting of cement? – When water is mixed with cement, a smooth paste is produced that remains plastic for a short time. During this period, the paste can be disturbed and remixed without injury. As the reaction between water and cement continues, the plasticity of the cement paste is lost. This early period in the hardening of cement is known as ‘Setting of Cement’. Prev Post What are the raw materials used in the manufacturers of Portland cement? Next Post Are there different types of Portland Cement?

What is the purpose of hardening?

Hardening is a metallurgical metalworking process used to increase the hardness of a metal. The hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain. A harder metal will have a higher resistance to plastic deformation than a less hard metal.

What is mean by setting time of cement?

FAQs – What is initial setting time of cement? The initial setting time of concrete is the time when cement paste starts hardening after adding water. It is the time period between the addition of water to cement till the time at 1 mm square section needle fails to penetrate the cement paste, placed in the Vicat’s mold 5mm to 7mm from the bottom of the mold.

What is final setting time of cement? Final setting time is that time period between the time water is added to cement and the time at which 1 mm needle makes an impression on the paste in the mould but 5 mm attachment does not make any impression. What is the need for determining initial and final setting time of cement? Initial setting time is the time when the paste starts losing its plasticity.

The test is important for transportation, placing and compaction of cement concrete. Initial setting time duration is also required to delay the process of hydration or hardening. Final setting time is the time when the paste completely loses its plasticity.It is the time taken for the cement paste or cement concrete to harden sufficiently and attain the shape of the mould in which it is cast.

What is initial setting time?

1. objective – For convenience, initial setting time is regarded as the time elapsed between the moments that the water is added to the cement, to the time that the paste starts losing its plasticity. The final setting time is the time elapsed between the moment the water is added to the cement, and the time when the paste has completely lost its plasticity and has attained sufficient firmness to resist certain definite pressure.

What is the minimum setting time for cement?

2 The Setting Time – The setting time of cement includes the initial setting time and the final setting time, The initial time refers to the time that cement turns into paste by mixing with water and begins to lose its plasticity. And the time that cement completely loses its plasticity by mixing with water and begins to have a certain structural strength is known as the final setting time.

The national standards prescribe that the initial setting time of Portland cement should not be earlier than 45 min and the final setting time should not be later than 6.5 h. All the products off-grade at the initial setting time are spoiled products and those unqualified at the final setting time are sub-quality products.

The setting time of cement is measured by time determinator. The sample is the standard cement paste of which the temperature is 20 °C ± 3 °C and humidity is more than 90%. Various mineral components of the cement clinker are different in the water consumption of their normal consistency.

  1. The finer the cement is ground, the more water the normal consistency will need.
  2. The normal consistency of Portland cement is within 24% ~ 30%.
  3. The setting time of cement is very important in the construction projects.
  4. The initial setting time should not be too fast in order to ensure that there is enough time to complete every process, such as casting, before the initial setting time; and the final setting time should not be too late in order to enable the cement to complete its setting and hardening as soon as possible after pouring and tamping to make the next process occur earlier.

Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9781845699550500049

What is the process of hardening?

Metal Hardening – The use of this treatment will result in an improvement of the mechanical properties, as well as an increase in the level of hardness, producing a tougher, more durable item. Alloys are heated above the critical transformation temperature for the material, then cooled rapidly enough to cause the soft initial material to transform to a much harder, stronger structure.

  1. Alloys may be air cooled, or cooled by quenching in oil, water, or another liquid, depending upon the amount of alloying elements in the material.
  2. Hardened materials are usually tempered or stress relieved to improve their dimensional stability and toughness.
  3. Steel parts often require a heat treatment to obtain improved mechanical properties, such as increasing increase hardness or strength.
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The hardening process consists of heating the components above the critical (normalizing) temperature, holding at this temperature for one hour per inch of thickness cooling at a rate fast enough to allow the material to transform to a much harder, stronger structure, and then tempering.

What is the process of hardening concrete called?

What is in This Stuff? The importance of concrete in modern society cannot be overestimated. Look around you and you will find concrete structures everywhere such as buildings, roads, bridges, and dams. There is no escaping the impact concrete makes on your everyday life.

So what is it? Concrete is a composite material which is made up of a filler and a binder. The binder (cement paste) “glues” the filler together to form a synthetic conglomerate. The constituents used for the binder are cement and water, while the filler can be fine or coarse aggregate. The role of these constituents will be discussed in this section.

Cement, as it is commonly known, is a mixture of compounds made by burning limestone and clay together at very high temperatures ranging from 1400 to 1600 ]C. Although there are other cements for special purposes, this module will focus solely on portland cement and its properties.

  • The production of portland cement begins with the quarrying of limestone, CaCO 3,
  • Huge crushers break the blasted limestone into small pieces.
  • The crushed limestone is then mixed with clay (or shale), sand, and iron ore and ground together to form a homogeneous powder.
  • However, this powder is microscopically heterogeneous.

(See flowchart.) Figure 1: A flow diagram of Portland Cement production. The mixture is heated in kilns that are long rotating steel cylinders on an incline. The kilns may be up to 6 meters in diameter and 180 meters in length. The mixture of raw materials enters at the high end of the cylinder and slowly moves along the length of the kiln due to the constant rotation and inclination. Figure 2: Schematic diagram of rotary kiln. As the mixture moves down the cylinder, it progresses through four stages of transformation. Initially, any free water in the powder is lost by evaporation. Next, decomposition occurs from the loss of bound water and carbon dioxide.

  • This is called calcination,
  • The third stage is called clinkering.
  • During this stage, the calcium silicates are formed.
  • The final stage is the cooling stage.
  • The marble-sized pieces produced by the kiln are referred to as clinker,
  • Clinker is actually a mixture of four compounds which will be discussed later.

The clinker is cooled, ground, and mixed with a small amount of gypsum (which regulates setting) to produce the general-purpose portland cement. Water is the key ingredient, which when mixed with cement, forms a paste that binds the aggregate together.

The water causes the hardening of concrete through a process called hydration. Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydrates or hydration products. Details of the hydration process are explored in the next section. The water needs to be pure in order to prevent side reactions from occurring which may weaken the concrete or otherwise interfere with the hydration process.

The role of water is important because the water to cement ratio is the most critical factor in the production of “perfect” concrete. Too much water reduces concrete strength, while too little will make the concrete unworkable. Concrete needs to be workable so that it may be consolidated and shaped into different forms (i.e.

  1. Walls, domes, etc.).
  2. Because concrete must be both strong and workable, a careful balance of the cement to water ratio is required when making concrete.
  3. Aggregates are chemically inert, solid bodies held together by the cement.
  4. Aggregates come in various shapes, sizes, and materials ranging from fine particles of sand to large, coarse rocks.

Because cement is the most expensive ingredient in making concrete, it is desirable to minimize the amount of cement used.70 to 80% of the volume of concrete is aggregate keeping the cost of the concrete low. The selection of an aggregate is determined, in part, by the desired characteristics of the concrete.

For example, the density of concrete is determined by the density of the aggregate. Soft, porous aggregates can result in weak concrete with low wear resistance, while using hard aggregates can make strong concrete with a high resistance to abrasion. Aggregates should be clean, hard, and strong. The aggregate is usually washed to remove any dust, silt, clay, organic matter, or other impurities that would interfere with the bonding reaction with the cement paste.

It is then separated into various sizes by passing the material through a series of screens with different size openings. Refer to Demonstration 1 Table 1: Classes of Aggregates

class examples of aggregates used uses
ultra-lightweight vermiculite ceramic spheres perlite lightweight concrete which can be sawed or nailed, also for its insulating properties
lightweight expanded clay shale or slate crushed brick used primarily for making lightweight concrete for structures, also used for its insulating properties.
normal weight crushed limestone sand river gravel crushed recycled concrete used for normal concrete projects
heavyweight steel or iron shot steel or iron pellets used for making high density concrete for shielding against nuclear radiation

Refer to Demonstration 2 The choice of aggregate is determined by the proposed use of the concrete. Normally sand, gravel, and crushed stone are used as aggregates to make concrete. The aggregate should be well-graded to improve packing efficiency and minimize the amount of cement paste needed.

  1. Also, this makes the concrete more workable.
  2. Refer to Demonstration 3 Properties of Concrete Concrete has many properties that make it a popular construction material.
  3. The correct proportion of ingredients, placement, and curing are needed in order for these properties to be optimal.
  4. Good-quality concrete has many advantages that add to its popularity.

First, it is economical when ingredients are readily available. Concrete’s long life and relatively low maintenance requirements increase its economic benefits. Concrete is not as likely to rot, corrode, or decay as other building materials. Concrete has the ability to be molded or cast into almost any desired shape.

Building of the molds and casting can occur on the work-site which reduces costs. Concrete is a non-combustible material which makes it fire-safe and able withstand high temperatures. It is resistant to wind, water, rodents, and insects. Hence, concrete is often used for storm shelters. Concrete does have some limitations despite its numerous advantages.

Concrete has a relatively low tensile strength (compared to other building materials), low ductility, low strength-to-weight ratio, and is susceptible to cracking. Concrete remains the material of choice for many applications regardless of these limitations.

  • Hydration of Portland Cement Concrete is prepared by mixing cement, water, and aggregate together to make a workable paste.
  • It is molded or placed as desired, consolidated, and then left to harden.
  • Concrete does not need to dry out in order to harden as commonly thought.
  • The concrete (or specifically, the cement in it) needs moisture to hydrate and cure (harden).

When concrete dries, it actually stops getting stronger. Concrete with too little water may be dry but is not fully reacted. The properties of such a concrete would be less than that of a wet concrete. The reaction of water with the cement in concrete is extremely important to its properties and reactions may continue for many years.

Cement Compound Weight Percentage Chemical Formula
Tricalcium silicate 50 % Ca 3 SiO 5 or 3CaO, SiO 2
Dicalcium silicate 25 % Ca 2 SiO 4 or 2CaO, SiO 2
Tricalcium aluminate 10 % Ca 3 Al 2 O 6 or 3CaO, Al 2 O 3
Tetracalcium aluminoferrite 10 % Ca 4 Al 2 Fe 2 O 10 or 4CaO, Al 2 O 3, Fe 2 O 3
Gypsum 5 % CaSO 4,2H 2 O

Table 2: Composition of portland cement with chemical composition and weight percent. When water is added to cement, each of the compounds undergoes hydration and contributes to the final concrete product. Only the calcium silicates contribute to strength. Tricalcium silicate is responsible for most of the early strength (first 7 days). Dicalcium silicate, which reacts more slowly, contributes only to the strength at later times. Tricalcium silicate will be discussed in the greatest detail. The equation for the hydration of tricalcium silicate is given by: Tricalcium silicate + Water->Calcium silicate hydrate+Calcium hydroxide + heat 2 Ca 3 SiO 5 + 7 H 2 O -> 3 CaO,2SiO 2,4H 2 O + 3 Ca(OH) 2 + 173.6kJ Upon the addition of water, tricalcium silicate rapidly reacts to release calcium ions, hydroxide ions, and a large amount of heat. The pH quickly rises to over 12 because of the release of alkaline hydroxide (OH – ) ions. This initial hydrolysis slows down quickly after it starts resulting in a decrease in heat evolved. The reaction slowly continues producing calcium and hydroxide ions until the system becomes saturated. Once this occurs, the calcium hydroxide starts to crystallize. Simultaneously, calcium silicate hydrate begins to form. Ions precipitate out of solution accelerating the reaction of tricalcium silicate to calcium and hydroxide ions. (Le Chatlier’s principle). The evolution of heat is then dramatically increased. The formation of the calcium hydroxide and calcium silicate hydrate crystals provide “seeds” upon which more calcium silicate hydrate can form. The calcium silicate hydrate crystals grow thicker making it more difficult for water molecules to reach the unhydrated tricalcium silicate. The speed of the reaction is now controlled by the rate at which water molecules diffuse through the calcium silicate hydrate coating. This coating thickens over time causing the production of calcium silicate hydrate to become slower and slower. Figure 3: Schematic illustration of the pores in calcium silicate through different stages of hydration. The above diagrams represent the formation of pores as calcium silicate hydrate is formed. Note in diagram (a) that hydration has not yet occurred and the pores (empty spaces between grains) are filled with water. Diagram (b) represents the beginning of hydration. In diagram (c), the hydration continues. Although empty spaces still exist, they are filled with water and calcium hydroxide. Diagram (d) shows nearly hardened cement paste. Note that the majority of space is filled with calcium silicate hydrate. That which is not filled with the hardened hydrate is primarily calcium hydroxide solution. The hydration will continue as long as water is present and there are still unhydrated compounds in the cement paste. Dicalcium silicate also affects the strength of concrete through its hydration. Dicalcium silicate reacts with water in a similar manner compared to tricalcium silicate, but much more slowly. The heat released is less than that by the hydration of tricalcium silicate because the dicalcium silicate is much less reactive. The products from the hydration of dicalcium silicate are the same as those for tricalcium silicate: Dicalcium silicate + Water->Calcium silicate hydrate + Calcium hydroxide +heat 2 Ca 2 SiO 4 + 5 H 2 O-> 3 CaO,2SiO 2,4H 2 O + Ca(OH) 2 + 58.6 kJ The other major components of portland cement, tricalcium aluminate and tetracalcium aluminoferrite also react with water. Their hydration chemistry is more complicated as they involve reactions with the gypsum as well. Because these reactions do not contribute significantly to strength, they will be neglected in this discussion. Although we have treated the hydration of each cement compound independently, this is not completely accurate. The rate of hydration of a compound may be affected by varying the concentration of another. In general, the rates of hydration during the first few days ranked from fastest to slowest are: tricalcium aluminate > tricalcium silicate > tetracalcium aluminoferrite > dicalcium silicate. Refer to Demonstration 4 Heat is evolved with cement hydration. This is due to the breaking and making of chemical bonds during hydration. The heat generated is shown below as a function of time. Figure 4: Rate of heat evolution during the hydration of portland cement The stage I hydrolysis of the cement compounds occurs rapidly with a temperature increase of several degrees. Stage II is known as the dormancy period. The evolution of heat slows dramatically in this stage.

  • The dormancy period can last from one to three hours.
  • During this period, the concrete is in a plastic state which allows the concrete to be transported and placed without any major difficulty.
  • This is particularly important for the construction trade who must transport concrete to the job site.
  • It is at the end of this stage that initial setting begins.
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In stages III and IV, the concrete starts to harden and the heat evolution increases due primarily to the hydration of tricalcium silicate. Stage V is reached after 36 hours. The slow formation of hydrate products occurs and continues as long as water and unhydrated silicates are present.

  • Refer to Demonstration 5 Strength of Concrete The strength of concrete is very much dependent upon the hydration reaction just discussed.
  • Water plays a critical role, particularly the amount used.
  • The strength of concrete increases when less water is used to make concrete.
  • The hydration reaction itself consumes a specific amount of water.

Concrete is actually mixed with more water than is needed for the hydration reactions. This extra water is added to give concrete sufficient workability. Flowing concrete is desired to achieve proper filling and composition of the forms, The water not consumed in the hydration reaction will remain in the microstructure pore space. Figure 5: Schematic drawings to demonstrate the relationship between the water/cement ratio and porosity. The empty space (porosity) is determined by the water to cement ratio. The relationship between the water to cement ratio and strength is shown in the graph that follows. Figure 6: A plot of concrete strength as a function of the water to cement ratio. Low water to cement ratio leads to high strength but low workability. High water to cement ratio leads to low strength, but good workability. The physical characteristics of aggregates are shape, texture, and size.

  1. These can indirectly affect strength because they affect the workability of the concrete.
  2. If the aggregate makes the concrete unworkable, the contractor is likely to add more water which will weaken the concrete by increasing the water to cement mass ratio.
  3. Time is also an important factor in determining concrete strength.

Concrete hardens as time passes. Why? Remember the hydration reactions get slower and slower as the tricalcium silicate hydrate forms. It takes a great deal of time (even years!) for all of the bonds to form which determine concrete’s strength. It is common to use a 28-day test to determine the relative strength of concrete.

  1. Concrete’s strength may also be affected by the addition of admixtures.
  2. Admixtures are substances other than the key ingredients or reinforcements which are added during the mixing process.
  3. Some admixtures add fluidity to concrete while requiring less water to be used.
  4. An example of an admixture which affects strength is superplasticizer.

This makes concrete more workable or fluid without adding excess water. A list of some other admixtures and their functions is given below. Note that not all admixtures increase concrete strength. The selection and use of an admixture are based on the need of the concrete user.

TYPE FUNCTION
AIR ENTRAINING improves durability, workability, reduces bleeding, reduces freezing/thawing problems (e.g. special detergents)
SUPERPLASTICIZERS increase strength by decreasing water needed for workable concrete (e.g. special polymers)
RETARDING delays setting time, more long term strength, offsets adverse high temp. weather (e.g. sugar )
ACCELERATING speeds setting time, more early strength, offsets adverse low temp. weather (e.g. calcium chloride)
MINERAL ADMIXTURES improves workability, plasticity, strength (e.g. fly ash)
PIGMENT adds color (e.g. metal oxides)

Table 3: A table of admixtures and their functions. Durability is a very important concern in using concrete for a given application. Concrete provides good performance through the service life of the structure when concrete is mixed properly and care is taken in curing it.

  1. Good concrete can have an infinite life span under the right conditions.
  2. Water, although important for concrete hydration and hardening, can also play a role in decreased durability once the structure is built.
  3. This is because water can transport harmful chemicals to the interior of the concrete leading to various forms of deterioration.

Such deterioration ultimately adds costs due to maintenance and repair of the concrete structure. The contractor should be able to account for environmental factors and produce a durable concrete structure if these factors are considered when building concrete structures.

What is the difference in meaning of the two words setting and hardening?

01. Definition / Description – Setting of Cement / Mortar / Concrete

The term ‘ Setting ‘ is used to define the stiffening of the cement paste as well as concrete or mortar. The setting of cement refers to transformation from liquid to plastic state and further plastic to a solid state. In the setting process, the surface of cement or mortar or concrete becomes sufficiently rigid to withstand a certain amount of pressure but still contains some moisture within the mixture. Hence, during setting, cement/mortar/concrete does not gain considerable strength.In other words, the setting of cement/mortar/concrete is a stage in which it achieves stiffness to retain its shape in accordance with the support inside in which it is moulded.There are two stages of setting: Initial setting and final setting.

01. Initial Setting is when the cement or mortar or concrete starts to lose its plasticity.02. Final Setting is when the cement/mortar/concrete completely loses its plasticity. Hardening of Cement / Mortar / Concrete

The term ‘ Hardening ‘ is defined as the strength gain of a set cement or mortar or concrete., Even during the hardening the cement/mortar/concrete continue to acquire some strength, however, hardening happens after the setting state.In other words, hardening of cement as well as mortar or concrete is the stage when the mixture gains strength or the development of the strength, only after which, it can carry the intended loads.In the process of hardening, a useful and measurable strength gets developed.

What Is Setting And Hardening Of Portland Cement

What is called hardening?

From Wikipedia, the free encyclopedia Jump to navigation Jump to search Look up hardening or harden in Wiktionary, the free dictionary. Hardening is the process by which something becomes harder or is made harder. Hardening may refer to:

Hardening (metallurgy), a process used to increase the hardness of a metal Hardening (botany) or cold hardening, a process in which a plant undergoes physiological changes to mitigate damage from cold temperatures Hardening (computing), the process of securing a system against attack Target hardening, strengthening of the security of a building or installation to protect it from attack Sclerotization, a biochemical process forming cuticle in arthropods

What are the 3 hardening process?

Types of Metal Hardening Processes Updated November 26, 2018 By Rachelle Dragani Metal is known for being a tough substance that can stand up to a lot of wear and tear, but it might not have started out that way. Many types of metals have gone through the process of metal hardening in order to make them better suited for the job they need to do.

  • There are different types of hardening that, through complex processes of heating and cooling, help to make metals tough, durable and easy to work with.
  • Each metal hardening process includes three main steps: heating, soaking and cooling the metal.
  • Some common types of hardening include strain hardening, solid solution strengthening, precipitation hardening, and quenching and tempering.

While engineers and metal workers have come up with several different types of hardening depending on the type of metal and the results they want to see, each type involves three basic parts: heating the metal, soaking it and then cooling it. During the first step, heat treatment, metal workers heat the material, often at extremely hot temperatures.

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Sometimes, they do this to change the the physical or chemical composition of the metal, often to make it easier to manipulate and work with. For instance, when some metals are exposed to temperatures higher than 1,000 degrees Fahrenheit, their internal structure changes. This can be temporary, so that metal workers can change its shape and then have it go back to its original state.

In other metals, the change is permanent. Sometimes, that internal structure becomes stronger and tougher, making it a better material to be used in something that requires strength, like the construction of a skyscraper. Other times, heat treatment is used to increase the ductility of a metal.

  1. Metals with high levels of ductility are able to withstand forces pulling at them from either end.
  2. This is an important quality for metals like copper, which need to be pulled into thin strips of copper wire, or gold, which is often pulled into thin strands to make jewelry.
  3. The second part of the process is soaking the metal.

Although the word “soaking” might make you think of the way you would soak a dog in a bath after a run through a muddy backyard, soaking in the metal-hardening process is a little different. A metal isn’t soaked in a tub full of a liquid substance. Instead, soaking in this instance refers to making sure that once the metal has hit the desired temperature during the heating process, it “soaks” in that heat.

  • The timing is different for all the different types of hardening, but in general, a metal worker has to make sure that all of the pieces of metal reach the right temperatures for a specific amount of time.
  • The third and final step in the hardening process is cooling.
  • After metal has been heated and allowed to soak in that heat, the metal must be cooled.

Sometimes, metals revert back to their original chemical or physical structure after this process. Other times, metal workers make sure that the metals are altered for good. There are several different types of processes for hardening metal, depending on the type of metal that workers start with and the material they want to turn it into.

One of the most common is Martensitic transformation, also known as quenching and tempering. It is a complex process to harden steel, and metal workers have to be careful to carry out each step correctly. First, they must heat the steel to an extreme temperature. Then, the crystal structure inside the steel changes to allow more carbon to be dissolved.

At that point, the metal has to be quenched, or cooled, quickly enough so the carbon doesn’t have time to form other unwanted materials in the metal. The quick cooling makes it stay in a hardened state, making it a stronger material better suited to withstand a lot of wear and tear.

The different states it goes through during the process are called austenite and martensite, and an austempering and martempering resource can give you more information about the process. Other types of hardening processes include case hardening, annealing and precipitation hardening. Each works in different ways to make metals more durable, ductile, tough or malleable in order to help engineers use them in a variety of ways.

There are all kinds of metals in the world around you, and chances are, a metal worker used a hardening process to get them into the state they are in today. : Types of Metal Hardening Processes

What is the most important factor in hardening?

Factors That Affect Hardenability Steel is a mixture of iron, carbon from 0.0 to 1.2 percent, and alloying elements. Carbon provides the hardness, and the alloying elements provide how deep this hardness will occur. This concept is called “hardenability.” Hardenability should not be confused with the maximum hardness after quenching, which is only dependent on the amount of carbon present and the percentage of martensite.

What happens during hardening?

Metal Hardening – The use of this treatment will result in an improvement of the mechanical properties, as well as an increase in the level of hardness, producing a tougher, more durable item. Alloys are heated above the critical transformation temperature for the material, then cooled rapidly enough to cause the soft initial material to transform to a much harder, stronger structure.

  • Alloys may be air cooled, or cooled by quenching in oil, water, or another liquid, depending upon the amount of alloying elements in the material.
  • Hardened materials are usually tempered or stress relieved to improve their dimensional stability and toughness.
  • Steel parts often require a heat treatment to obtain improved mechanical properties, such as increasing increase hardness or strength.

The hardening process consists of heating the components above the critical (normalizing) temperature, holding at this temperature for one hour per inch of thickness cooling at a rate fast enough to allow the material to transform to a much harder, stronger structure, and then tempering.

What happens in hardening process?

Grading is the ‘process by which a teacher assesses student learning through classroom tests and assignments, the context in which good teachers establish that process, and the dialogue that surrounds grades and defines their meaning to various audiences’ (1).

What is the process of concrete setting?

The setting is defined by ASTM C125 as ‘ the process, due to chemical reactions, occurring after the addition of mixing water, that results in a gradual development of rigidity of a cementitious mixture.’ In other words, it is the process a concrete mixture goes through, from being a liquid mixture to gaining certain

What is the process of hardening the concrete mixes?

Concrete Technology Questions and Answers – Curing of Hardened Concrete This set of Concrete Technology Problems focuses on “Curing of Hardened Concrete”.1. The slump would not exceed 50 mm when compacting concrete with vibrators. a) True b) False View Answer Answer: a Explanation: Segregation means concrete cement slurry & fine aggregates &coarse aggregate collapsed & have no slump & after hardening no strength but workability is the checking the concrete how much time used after mixing.

2. When vibrators are used for compaction, the consistency of concrete depends upon the _ a) Type of mix b) Efficiency of vibrator c) Placing conditions d) Type of mix, efficiency of vibrator, pacing conditions View Answer

Answer: d Explanation: When vibrators are used for compaction, the consistency of concrete depends upon the Type of mix, efficiency of vibrator, pacing conditions.3. Which of the following statement is correct while compacting concrete with vibrators? a) The vibrator should be inserted horizontally b) The vibrator should not be immersed through a full depth of freshly laid concrete c) The vibrator should not touch the form surface d) The vibrator should touch the form surface View Answer Answer: c Explanation: If there is a considerable amount of time lapse between the placements of subsequent lifts, it may be necessary to re vibrate the previous lift prior to placing additional concrete to minimize the potential for pour lines and cold joints.4.

The levelling operation that removes humps and hollows and give a true, uniform concrete surface is called _ a) Screeding b) Floating c) Troweling d) Compacting View Answer Answer: a Explanation: The levelling operation that removes humps and hollows and give a true, uniform concrete surface is called Screeding.5.

The final operation of finishing the concrete surface is called _ a) Screeding b) Floating c) Troweling d) Compacting View Answer Answer: c Explanation: The final operation of finishing the concrete surface is called Troweling. Participate in of the Month Now! 6.

The process of removing the irregularities from the surface of concrete left after screeding is called floating. a) True b) False View Answer Answer: a Explanation: The process of removing the irregularities from the surface of concrete left after screeding is called floating.7. The process of hardening the concrete mixes by keeping its surface moist for a certain period is called _ a) Curing b) Floating c) Troweling d) Compacting View Answer Answer: a Explanation: The process of hardening the concrete mixes by keeping its surface moist for a certain period is called curing.8.

After the curing of 28 days, the concrete gains strength upto _ a) 40% b) 60% c) 80% d) 100% View Answer Answer: d Explanation: After the curing of 28 days, the concrete gains strength upto 100 percentage.9. The construction joints in cement concrete _ a) Should be located where bending moment is large b) Should be located where shear force is large c) Should not be provided at the corners d) Should be spaced at a distance of 3 m apart in case of huge structures View Answer Answer: c Explanation: The construction joints in cement concrete should not be provided at the corners.10.

For compacting large sections of mass concrete in structures, the type of vibrator used is _ a) Internal vibrator b) External vibrator c) Screed vibrator d) Internal and Screed vibrator View Answer Answer: a Explanation: For compacting large sections of mass concrete in structures, the type of vibrator used is internal vibrator.

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