Which Constituent Contribute Towards Unsoundness Of Cement?

Which Constituent Contribute Towards Unsoundness Of Cement
Unsoundness in portland cement – Q. What is unsoundness in portland cement, and how is it detected and avoided? A. Concrete that shows excessive expansion after setting is said to contain unsound cement. In former times, this was a serious problem for concrete.

  • In more recent times, better manufacturing, testing, and controls have almost completely eliminated unsound cement.
  • Unsoundness is caused by free lime and magnesia in the clinker in sufficient quantity so that, upon hydration, excessive expansion and damage to concrete can occur.
  • The presence of such is detected by the autoclave expansion test ASTM C 151.

Unsoundness can be avoided by minimizing these expansive constituents. References: SP-1(02) ; ACI 225R-19 ; E3-13 ; ASTM C150 ; ASTM C151 ; ASTM C595 ; ASTM C1157 Topics in Concrete: Cementitious Material ; Concrete Fundamentals

Which is responsible for unsoundness of cement?

Free CT 1: Current Affairs (Government Policies and Schemes) 10 Questions 10 Marks 10 Mins Explanation: The unsoundness in cement is due to the presence of an excess of free lime, magnesia and sulphur trioxide. Soundness Test: Expansion of cement is measured/computed by soundness test.

Soundness means the ability to resist volume expansion and it is indication durability. The soundness of cement may be determined by two methods, namely Le-Chatelier method and autoclave method. The Le-Chatelier test detects unsoundness due to free Lime only. This method of testing does not indicate the presence and after effect of the excess of magnesia.

As per Indian Standard specification, if the content of magnesia is greater than 3% in cement then Autoclave Test is performed which is sensitive to both Lime and Magnesia. Latest DFCCIL Junior Manager Updates Last updated on Sep 29, 2022 Dedicated Freight Corridor Corporation of India (DFCCIL) will soon release the official notification for the DFCCIL Junior Manager Recruitment 2022.

What are the factors that causes soundness in cement?

01. Excess Lime – Soundness of cement is affected by the presence of excess lime (CaO) in the cement. This excess lime hydrates very slowly and forms slaked lime that occupies a larger volume than the original free calcium oxide. The slow hydration process, therefore, affects the properties of hardened concrete.

Which other compound can cause unsoundness in Portland cement products?

Manufacture of Portland Cement – Portland cement is simply a mixture of limestone and clay heated in a kiln to 1400 to 1600 degrees centigrade (2550 to 2990 F). Due to the high temperatures and large amounts of materials being used, considerable attention is given to each stage of the production process.

  • Raw materials – High quality cements require adequate and uniform raw materials.
  • Location near sources of calcium and clay.
  • Plant chemists analyze the material at all stages of production to ensure quality control.
  • Preparation of materials – quality control during mixing will produce a uniform end product.

The exact procedure varies from plant to plant based on design. Some plants use wet grinding processes to better blend their mixtures, however this causes an increase in kiln cost. In a dry process the grinding and blending phase is more expensive but is offset by cheaper kiln costs.

Another procedure is called a semi-dry procedure which is a dry process with 12 to 14% water added before the burning phase. The burning process – Once the materials are ground and blended, they are ready for the kiln. The heat process is called “clinkering” or partial melting. Only about one-fourth of the material is liquid at any time.

In a wet process, the material is in the kiln for 2 to 3 hours. This is reduced to 1 to 2 hours for a dry process. Some new heat exchanges only require 20 minutes. Final processing – The hot porous material nodules leaving the kiln are known as “clinker”.

  • This clinker is ground in ball mills into a fine powder with small amounts of gypsum to avoid flash setting.
  • Without the gypsum, the material is ground clinker and not Portland cement.
  • In ordinary Portland cement, approximately three-fourths of the mixture is some form of calcium silicate.
  • This material is responsible for the cementing process.

The chemical composition is traditionally written in an oxide notation used in ceramic chemistry. In this notation, each oxide is abbreviated to a single capital letter. For example, lime written as CaO is denoted as C. In order to write carbonates and sulfates in shorthand a single capital letter is used with an overbar.

Determining the exact chemical composition of a cement would be a very complex procedure. However, simpler oxide analysis is generally available from most cement plants on request. With this information, the compound composition may be determined using the Bogue calculation. More sophisticated procedures have been developed, but the Bogue calculation is suitable for most purposes.

When Portland cement is mixed with water, it undergoes a chemical reaction which leads to the hardening of the material. This process is called hydration and the results are the hydration products. The hydration process can be quantified by two characteristics; (1) the rate of reaction, and (2) the heat of reaction.

  • Type I – most common, no special properties
  • Type II – good strength with lower heat of hydration
  • Type III – rapid setting; used in precast work or at low temperatures – possible tensile cracking due to thermal stress if sections are large
  • Type IV – Used in mass concrete applications-low heat of hydration
  • Type V – provides protection from damage due to exposure to sulfates (seawater, some groundwater supplies, and particularly wetting and drying processes).

*** The ASTM standards are really performance specifications. There are few limitations on compound composition. Generally only Types I and III are available throughout the United States, Types IV and V in areas where a market exists. Type II is common in western states because of available materials.

  1. Portland-Pozzolan Cements – blended with pozzolan (reactive silica); reduces both the heat of hydration and early strength, but provides resistance to sulfate attack and high ultimate strength.
  2. Slag Cements – Use blast-furnace slag, a by-product of the iron and steel industry. Slag is composed of lime, silica, and alumina. Requires an activator for hydration. Generally not popular in the United States.
  3. Supersulfated Cements – Slag cement activated with calcium sulfate; lower heat of hydration and better sulfate resistance than Portland blast-furnace cements. Used in Europe.

Portland cement concrete experiences high shrinkage during drying which can cause tensile cracking if restrained. Expansion during moist curing does not offset the contraction. Several cements with expansive properties have been developed. Steel reinforcement is used to control the expansion and convert it to a prestress force.

Some additional restraint may occur through subgrade friction or from formwork. Lack of restraint will cause the concrete to self-destruct. Expansion is controlled by adjusting the admixture material in the cement compound and by the amount of water available to the curing mixture. Physical properties of expansive cement is assumed to be that of Type I cement concretes.

Several areas of applications: parking structures, eliminating water damage to cars; pavements, elimination of shrinkage-control joints; structures where watertightness is important; and in tilt-up construction to help in the stress during lifting. Two special types of cement are regulated-set (jet cement) and VHE (very high early strength).

  1. Regulated-set cement – modified Portland cement where the tricalcium aluminate is replaced with calcium fluoroaluminate. The result is more reactive than with water. Care has to be taken to avoid flash setting. By controlling flash setting, the handling time can range from 2 to 40 minutes. Strength develops very rapidly. There is a balance between handling time and early strength development. High heat of hydration, more than Type II cement. Applications: lightweight insulation of roof decks, pavement and bridge deck repair, shotcreteing, and slip forming.
  2. VHE cement – Basically a dicalcium aluminate compound with a high percent of calcium sulfoaluminate, similar to a Type K expansive concrete. Handling time and early strength development is similar to regulated-set except VHE will develop higher strength than regulated-set cement concretes. Durable, with creep and shrinkage lower than with Type III cement.
  1. Other rapid-hardening cements – extra-rapid-hardening cement – a modified Type III, ultra-rapid-hardening – a very finely ground Portland cement, super-high-early-strength developed in Japan.
  2. White cement – An iron poor cement with a white surface color, popular with architects because of its ability to be colored by pigments.
  3. Masonry cement – Type I Portland cement with finely ground limestone; workable, plastic, minimal water loss.
  4. Oil-well cements – Slow hardening under high pressure and temperature and stable in corrosive conditions.
  5. Natural cements – produced from natural clayey limestones burn at low temperatures containing very little tricalcium aluminate. Rarely used today.
  1. High-alumina cement (HAC) – also known as calcium aluminate cement, was developed as a sulfate-resisting cement. A major problem is loss of strength due to adverse chemical reactions. Unlike Portland cement, HAC undergoes a complete fusion of the raw materials. Develops strength rapidly. About 75% of ultimate strength is developed in the first seven days. The major disadvantage of HAC is the potential conversion problems if the cement is exposed to hot, moist conditions. The temperature causes an increase in porosity and a disruption of the original microstructure. This leads to an extreme loss of strength. Strength loss is also severe at high water/cement ratios. Several structural failures in Europe have lead to its ban in structural use. Some structural applications are possible if the strength can be accurately predicted after conversion has taken place. However, it is now used in refractories. At high temperatures, the cement forms a ceramic bond stronger than the original hydraulic bond.
  2. Gypsum plaster – used as a surface finish on interior walls or in the production of drywall products. Quick-setting with rapid strength development, however very soluble in water. Also, leachates from the plaster are rich in sulfates, which can attack any surrounding concrete.

To maintain quality control on Portland cement, a set of ASTM specifications for both the chemical and physical requirements have been established. A series of “standard” tests have been developed to ensure that these specifications are met. However, since results from different tests for the same property can vary widely, direct comparison of these tests is difficult.

  • Chemical requirements – These specifications are not very strict since cements with different chemical compounds can have similar physical behavior.
  • Physical requirements – These specifications are more important than chemical requirements
    • Fineness – Grinding of the clinker is the last step in Portland cement production. The degree that the material is ground is the fineness.
      • Rate of hydration increases with fineness, leads to high strengths and heat generation.
      • Hydration takes place on the cement particle surface. Finer particles will be more completely hydrated.
      • Increasing fineness decreases the amount of bleeding but also requires more water for workability which can result in an increase in dry shrinkage.
      • High fineness reduces the durable to freeze-thaw cycles.
      • Increased fineness requires more gypsum to control setting.
        • ** The most important properties are: specific surface of the particles, and particle-size distribution. Fineness was originally measured using a sieve analysis, but this method is very awkward and really gives no information about the distribution of fine particles. In general, fineness is measured by a single parameter, specific surface area. This parameter is considered the most useful measure of cement fineness even though it does not measure particle distribution.
      • There are two ASTM tests for fineness:
        • Wagner Turbidimeter – measured specific surface area from a suspension of the cement in a tall glass container. The test is based on Stoke’s Law that states a sphere will obtain a constant velocity under the action of gravity.
        • Blaine air permeability apparatus – This test is based on the relationship between the surface area in a porous bed and the rate of fluid flow (air) through the bed. The test is compared to a standard sample determined by the U.S. Bureau of Standards.
      • ** The Blaine method is used more often in practice and is generally 1.8 times larger than the Wagner method. However, in cases of dispute, the Wagner method governs.
    • Test on Cement Paste
      • Two of the common physical requirements for cement 1) time of setting, and 2) soundness depend on the water content of the cement. This is measured in terms of normal consistency. A cement paste is said to be of normal consistency when a 300 gram, 10-mm-diameter Vicat needle penetrates 10 + 1 mm below the surface in 30 seconds. The plasticity of the cement is sensitive to environmental conditions.
      • Time of setting – Two arbitrary points of no real significance are used to develop general relationships between addition of water and strength gain. Used mainly for quality control.
        • Initial set – paste begins to stiffen (2-4 hours)
        • Final set – ability to withstand load (5-8 hours)
        • ** Time of setting by Vicat needle – Initial setting occurs when a 1-mm needle penetrates 25mm into cement paste. Final set occurs when there is no visible penetration,
        • ** Time of setting by Gillmore needle – Less common than Vicat needle test. Initial set occurs when a 113.4 gram Gillmore needle (2.12 mm in diameter) fails to penetrate. Final set occurs when a 453.6 gram Gillmore needle (1.06mm in diameter) fails to penetrate. Gillmore times tend to be longer than Vicat times.
      • Early stiffening – Two measures of early stiffening are:
        • False set – rapid rigidity without much heat generation, plasticity can be regained by further mixing with no additional water.
        • Flash set – rapid rigidity with considerable heat generation, plasticity cannot be regained.
        • A cement paste is mixed such that Vicat needle penetrates 32 +/- 4mm after 20 seconds. The final penetration is measured at 5 minutes. The result is a percentage of (final penetration/initial penetration) X 100%.
      • Unsoundness – is the characteristic of excessive volume change after setting. It may appear many months or years after setting. Therefore any test for unsoundness must detect the potential for this type of failure. Two standard tests are:
        • Le Chatelier test – Designed to test for expansion due to excessive lime. The device is filled with cement of normal consistency, covered with glass plates, and immersed in water at 20 + 1 degree C for 24 hours. The distance between the indicator points is measured and the device is returned to the water and brought to a boil in 25-30 minutes, and boiled for 1 hour. The device is cooled and the indicator points are measured again. The difference in the readings cannot exceed 10 mm.
        • Autoclave expansion – More severe test than Le Chatelier. A cement paste of normal consistency is molded and cured for 24 hours. Then it is measured and placed in an autoclave and the temperature is increased for 45-75 minutes until a pressure of 295 psi is achieved. It remains for 3 hours and then is cooled in the autoclave for 1 1/2 hours, then 15 minutes in water, and 15 minutes in the air and then its length is measured. The change in length must be less than 0.80% to be acceptable.
      • Heat of Hydration – Determined by the heat of solution method. The heat of solution of dry cement is compared to partially hydrated cement at 7 and 28 days. The heat of hydration is the difference between the dry and the partially hydrated cements.
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Mortar testing depends on the sand used for the test. Therefore, a standard ASTM sand is used, natural silica sand from Ottawa, Illinois. Mortar test provides a more reliable indication of quality than do neat pastes.

  • Mortar flow – Consistency of mortar is expressed as mortar flow. A mix of 2.75 parts Ottawa sand to 1 part cement (by weight) is compacted into a cone-shaped mold. The sample is placed on a flow table, a table whose top can be mechanically raised and lowered about 1/2 inch 25 times in 15 seconds. The flow is the increase in the base diameter as a percent of the original diameter.
  • Strength test
    • Compression is the most common measure of strength. A 2-in. mortar cube using a 2.75:1 sand/cement ratio with a water/cement ratio of 0.485 – 0.460 is tested. After a certain procedure is followed the specimens are failed.
    • Tensile strength is determined by a direct tensile test. The results are not of much value.
    • Flexural strength is determined by a flexural test of a small rectangular-shaped prism on simple supports with a center load. The flexural strength is directly calculated. This mortar strength does not necessary relate to concrete strength using the same cement; used for quality control.
  • Air Content of Mortar – Test for air content to determine the air entraining potential of a given cement.
  • Sulfate Expansion – Not a true measure of sulfate resistance, more of a measure of expansion. Useful for Type V cements.

What are the constituents of cement?

Visit ShapedbyConcrete.com to learn more about how cement and concrete shape the world around us. Portland cement is the basic ingredient of concrete. Concrete is formed when portland cement creates a paste with water that binds with sand and rock to harden.

Cement is manufactured through a closely controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients. Common materials used to manufacture cement include limestone, shells, and chalk or marl combined with shale, clay, slate, blast furnace slag, silica sand, and iron ore.

These ingredients, when heated at high temperatures form a rock-like substance that is ground into the fine powder that we commonly think of as cement. Bricklayer Joseph Aspdin of Leeds, England first made portland cement early in the 19th century by burning powdered limestone and clay in his kitchen stove.

With this crude method, he laid the foundation for an industry that annually processes literally mountains of limestone, clay, cement rock, and other materials into a powder so fine it will pass through a sieve capable of holding water. Cement plant laboratories check each step in the manufacture of portland cement by frequent chemical and physical tests.

The labs also analyze and test the finished product to ensure that it complies with all industry specifications. The most common way to manufacture portland cement is through a dry method. The first step is to quarry the principal raw materials, mainly limestone, clay, and other materials.

After quarrying the rock is crushed. This involves several stages. The first crushing reduces the rock to a maximum size of about 6 inches. The rock then goes to secondary crushers or hammer mills for reduction to about 3 inches or smaller. The crushed rock is combined with other ingredients such as iron ore or fly ash and ground, mixed, and fed to a cement kiln.

The cement kiln heats all the ingredients to about 2,700 degrees Fahrenheit in huge cylindrical steel rotary kilns lined with special firebrick. Kilns are frequently as much as 12 feet in diameter—large enough to accommodate an automobile and longer in many instances than the height of a 40-story building.

The large kilns are mounted with the axis inclined slightly from the horizontal. The finely ground raw material or the slurry is fed into the higher end. At the lower end is a roaring blast of flame, produced by precisely controlled burning of powdered coal, oil, alternative fuels, or gas under forced draft.

As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance called clinker. Clinker comes out of the kiln as grey balls, about the size of marbles. Clinker is discharged red-hot from the lower end of the kiln and generally is brought down to handling temperature in various types of coolers.

The heated air from the coolers is returned to the kilns, a process that saves fuel and increases burning efficiency. After the clinker is cooled, cement plants grind it and mix it with small amounts of gypsum and limestone. Cement is so fine that 1 pound of cement contains 150 billion grains. The cement is now ready for transport to ready-mix concrete companies to be used in a variety of construction projects.

Although the dry process is the most modern and popular way to manufacture cement, some kilns in the United States use a wet process. The two processes are essentially alike except in the wet process, the raw materials are ground with water before being fed into the kiln.

What is soundness and unsoundness of cement?

3 Soundness – The soundness of cement refers to the stability of the volume change in the process of setting and hardening. If the volume change is unstable after setting and hardening, the concrete structures will crack, which can affect the quality of buildings or even cause serious accidents, known as poor dimensional stability.

The cement product whose dimensional stability is poor will be disposed as spoiled product, not used in projects. The reasons for poor dimensional stability are: the free calcium oxide ( f -CaO) in the clinker is too much, or the free magnesium oxide in the clinker ( f -MgO) is quite a little, or the gypsum mixed in the clinker is excessive.

f -CaO and f -MgO in the clinker are all sintered, so their ageing speed is very slow. They start ageing slowly after the setting and hardening. CaO + H 2 O = Ca OH 2 MgO + H 2 O = Mg OH 2 In the ageing process, there is volume expansion which causes the cracking of cement.

The excessive amount of gypsum will react with the solid calcium aluminate hydrate to generate crystals of calcium sulfoaluminate hydrate. Thus, the volume will expand 1.5 times, which leads to the cracking of cement paste matrix. The national standards require: boiling method can be used to inspect the poor dimensional stability of the cement caused by the free CaO.

The so-called boiling method includes Pat test and Le Chatelier test. Pat test is to make the cement paste of normal consistency into cement cake, boil it for 3 h, and then observe it by naked eyes. If there is no crack and no bending by ruler inspection, it is called qualified soundness.

  1. Le Chatelier test is to measure the expansion value after the cement paste is boiled and get hardened on Le Chatelier needles.
  2. If the expansion value is within the required value, its stability is qualified.
  3. If there is contradictory between the results measured by Pat test and Le Chatelier test, Le Chaterlier test should prevail.

The hydration of free magnesium oxide is slower than that of free calcium oxide. Therefore, its harm can be inspected only by autoclave test. The harm of gypsum will be found by immersing in room-temperature water for a long time. Then the poor dimensional stability caused by magnesium dioxide and gypsum is inconvenient to be tested rapidly.

  • Thus, they should be controlled strictly in the production of cement.
  • The national standards require: the content of free magnesium oxide in cement should not be more than 5.0%, and the content of sulfur trioxide in slag cement should not be more than 4.0% and that in other kinds of cement should not exceed 3.5%.

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

Which oxide is responsible for soundness of cement?

Sulphur Trioxide – It is present in small quantities of about 1 – 2.0 % to make the cement sound. Excess of sulphur trioxide causes the cement to become unsound.

What are the effects of unsoundness of cement?

The change in volume is called ‘unsoundness’ which produces cracks, distortion and disintegration in the structure, thereby allowing water and atmospheric gases that may have injurious effect on concrete or the steel reinforcement. If expansion occurs after concrete has set, the structure will get damaged.

Which of the following oxides composition causes unsoundness on cement?

Functions of Chemical Compounds Present in Cement – Calcium Oxide CaO It controls the strength gain of cement It controls the soundness of cement Deficiency of CaO in cement reduces strength as well as the setting time of cement. Silica SiO 2 It provides strength to cement.

Excess of silica reduces the setting of cement. Aluminium Oxide Al 2 O 3 It is responsible for the quick setting of cement Excess of aluminium oxide reduces the strength of cement Ferrous Oxide Fe 2 O 3 It imparts the characteristic grey colour to the cement It also helps in the fusion of different materials Magnesium Oxide MgO It provides colour to the cement It also provides hardness to the cement Excess of magnesium oxide causes cracks in mortar and produces unsound concrete.

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Alkalis Na 2 O, K 2 O, P 2 O 5 Alkalis are present as residues in cement. Excess of alkalis causes efflorescence in concrete Excess of alkalis may also result in the cracking of the concrete Sulphur Trioxide SO 3 Sulphur trioxide provides soundness to the cement.

What will be the effect on structure of unsound cement is used?

If the unsound cement is used in structure where mass concreting is required, excessive heat may be accumulated due to slaking of lime and magnesia, this can cause thermal cracks and passage for water which may cause ultimate failure of structure.

Which chemical is used to destroy cement?

US3577349A – Composition for destroying hardened cementitious mixtures – Google Patents United States Patent 3,577,349 COMPOSITION FOR DESTROYING HARDENED CEMENTITIOUS MIXTURES Robert Glenn Haines, South Charleston, W. Va., assignor to Union Carbide Corporation, New York, N.Y.

No Drawing. Filed Jan.31, 1969, Ser. No.795,709 Int. Cl. C09d 9/00; Clld 7/05; 023g /02 US. Cl.252-170 8 Claims ABSTRACT OF THE DISCLOSURE A composition for destroying hardened cementitious mixtures comprising methyl acetoacetate and water. A method for destroying hardened cementitious mixtures utilizingsaid composition is also covered.

This invention relates to a novel composition for destroying hardened concrete and/ or cement mortars, and to a process for the removal of hardened concrete and/0r cement mortars from various substrates. l Concrete builds up on the bafiles and other inside surfaces of concrete ready-mix truck drums because of the inability or failure to remove all of the concrete from the ready-mix truck drums before the concrete begins to set-up.

Since concrete adheres better to concrete than to smooth steel, concrete build-up in the ready-mix truck drums enhances more concrete build-up. Because of the angle of the baflles in conventional concrete ready-mix truck drums, rotation of the drum in one direction mixes the drum contents by continuously forcing the upper portion of the contents towards the back or larger closed end of the drum, whereas rotation of the drum in the opposite direction discharges the contents.

Any good attempt at washing a ready-mix truck drum by rotating the drum in the mixing direction, if done before the concrete sets-up, will clean the backside of the baflles in essentially all of the back, larger closed end of the drum. However, the front side of the baffle, and front, smaller end of the drum can only be cleaned by diligent and timely use of a high pressure water spray.

All ready-mix trucks have a high pressure water hose with a spray nozzle for this purpose, but when and how this water is used depends of course, on the individual operators of the truck. Depending on the slump of the concrete being hauled (low-slump concrete will form build-up in readymix truck drums faster than high-slump concrete), a poor truck operator will have one cubic yard of concrete build-up occur during a period of from 3 to 6 months.

A good truck operator, i.e., one who regularly and thoroughly cleans the ready-mix drums, may not have this much build-up in more than 3 years. It must be realized, of course, that this more thorough drum cleaning does require operator time which may well result in an average of one less truck-load per day of concrete delivered.

Once there is concrete build-up in the truck drum, there are various conventional ways in which ice it can be removed. Most ready-mix concrete firms use coarse aggregate and water with drum rotation and/or air hammers to remove the concrete build-up from their truck drums. Other firms, use shaped dynamite charges to destroy the concrete build-up.

Either of these two latter methods, however, can cause considerable damage to the drums not to mention the danger involved with these methods. There are other problem areas in the art wherein concrete build-up presents problems. For example, concrete build-up is very detrimental to construction equipment, such as to precast forms, form clamps, mortar boxes, laboratory forms and other tools.

  • The use of dy-namite charges and other physical means for removing this concrete build-up in construction equipment is obviously undesirable.
  • More recently, the art has relied heavily on chemical compounds and/or compositions which can be employed as concrete dissolvers.
  • Various organic and inorganic compounds have been found to be effective for this purpose.

The inorganic compounds which are useful as concrete dissolvers generally include inorganic acids such as hydrochloric, phosphoric, hypochlorous and carbonic acid. Salts of these acids and alkalies such as sodium-hydroxide, sodium bicarbonate and ammoniumsulfate are also eifective.

The organic chemicals which have been found to be effective as concrete dissolvers generally include organic acids such as oxalic, acetic, lactic, citric, tannic and humic acid as well as combinations of these acids and other organic compounds such as anhydrides or ethers of the above, the most widely used being hydrochloric or muriatic acid.

Use of acids whether organic or inorganic for dissolving and/or destroying cementitious mixtures of course, present safety hazards whereas other known compounds although somewhat effective for destroying concrete, unfortunately, also destroy or reduce the desirable properties of cementitious mixtures even when present in minute, residual concentrations.

It should be remembered that although a chemical compound may be effective for destroying concrete, inadvertent, residual concentrations of it should nevertheless be compatible with new batches of concrete or cementitious mixtures since there generally remain on the surface from which the concrete was removed, residual amounts of the chemical compound or dissolver.

Thus there is still a need in the art for a concrete destroyer which is easy to apply, safe to use, and which possess properties which do not harmfully affect the properties of new cementitious mixtures such as compressive strength, setting time and durability.

  • It is therefore an object of the present invention to provide a novel composition for destroying hardened cementitious mixtures such as concrete and/or cement mortars.
  • Another object is to provide a process for the removal of hardened concrete and/or cement mortars from various substrates.
  • Another object is to provide a novel composition for destroying hardened concrete inadvertently residual traces of which does not adversely alfect the properties of newly mixed concrete.

These and other objects will be apparent from the following description of the invention. As employed herein, the term cementitious mixtures is meant to include concrete, cement mortars, cinder blocks, masonary mortars, concrete lintels, concrete pipe, cementasbestos pipe, prestressed concrete and the like.

In an effort to provide a hardened cementitious destroyer such as a hardened concrete or mortar destroyer, which is easy to apply, safe to use, and residual traces of which does not affect the properties of new batches of freshly prepared cementitious mixtures I tried various compounds such as: ethylacetoacetate, alpha-chloroethylacetoacetate, ethyl levulinate, methyl levulinate, methyl pyruvate, methyl propionate and methyl chloroacetate.

None of these compounds however, were found to be effective in destroying hardened cementitious mixtures with the exception of ethylacetoacetate which was found to possess a degree of effectiveness on very young concrete, i.e., 8 hour old concrete. However, ethylacetoacetate had little or no effect on older concrete, i.e., 24 hour concrete.

During the course of this experimentation, I tried methyl acetoacetate, a compound closely chemically related to the above compounds, and found surprisingly, and contrary to normal expectations that the methyl acetoacetate was extremely effective in destroying hardened concrete and this destructive ability was maintained in treating young as well as old concrete.

Advantageously, it was found that in mixing new batches of concrete in equipment previously treated with methyl acetoacetate, that the new batches suffered little or no detrimental effects, and in fact there was actually an increase in the compressive strength of the new concrete which is attributed to the presence of the methyl acetoacetate or more correctly, to the reaction product of methyl acetoacetate and cement.

Broadly contemplated, the present invention provides a composition for destroying hardened cementitious mixtures which comprises methyl acetoacetate and water. More specifically, the composition for destroying hardened cementitious mixtures comprises from about 60% to 99% by Weight methyl acetoacetate, and from about 1 to 40% water.

Optionally, though desirably, there can be included in the composition a penetrating aid which has been found to increase the aggressiveness of the methyl acetoacetate water solution to the hardened cementitious mixture.v The methyl acetoacetate solution can be applied to the surface of the hardened cementitious mixture to be destroyed in any convenient manner known in the art.

  • When the hardened cementitious mixture is present on exposed accessible surfaces such as on tools, mortar boxes, clamps, precast forms, and the like, the methyl acetoacetate water solution can be applied directly to the surface such as by pouring, spraying, dipping and the like.
  • To reach inaccessible enclosed areas, such as the inner area of a drum of a ready-mix truck, the methyl acetoacetate solution is added to the enclosed area and the system agitated sufficiently to permit the solution to come in contact with any hardened cementitious mixture adhering to the drum including the bafiles of the drum.

The methyl acetoacetate-water solution apparently destroys the hardened cementitious mixture by reacting with the cement phase of the mixture. Application of the methyl acetoacetate to the hardened cementitious mixture produces a detectable heat of reaction and ultimately there results a low-density powder-like solid together with a yellow-orange liquid product.

As a result of the reaction, the chemical composition of the cement phase is changed (a portion of the cement phase is actually solubilized) and the hardened cementitious mixture is destroyed. The amount of methyl acetoacetate employed in the methyl acetoacetate-Water solution can be varied over a relatively wide range and depends in part, upon the age of the hardened cementitious mixture to be destroyed as well as the length of time available for destruction; Generally, in treating young hardened cementitious mixtures there can be employed as little as 25% methyl acetoacetate by weight, although higher concentrations such as 50% and 85% methyl acetoacetate by weight results in more destructive power in appreciably shorter periods of time.

Merely as illustrative an 85 weight percent solution of methyl acetoacetate destroyed a 12 hour old concrete specimen (prepared with limestone coarse aggregate) in about 3 minutes, whereas 50 and 25 weight percent solution of methyl acetoacetate required 5 minutes and 40 minutes, respectively, to dissolve similar concrete specimens.

  • Relatively similar results are achieved in treating older concrete, for example, in treating concrete which was about 17 hours old, with 85, 50 and 25 weight percent solutions of methyl acetoacetate, the time required to destroy the concrete was about 65, and 300 minutes respectively.
  • Thus, although some water is necessary for achieving maximum effectiveness in destroying concrete, too much water i.e., substantially more than 15 weight percent water merely dilutes and so decreases the rate of concrete dissolution.

Excellent results are obtained when the methyl acetoacetate in the methyl acetoacetate-water solution is in the range of about 80 to 90% preferably about by weight of the solution. Optionally, and desirably, there can be included in the composition, a penetrating aid, which as its name indicates, serves to facilitate contact of the destroyer solution with the hardened cementitious mixture.

Illustrative of the anionic type penetrating aids are the alkyl sulfates or ethoxy sulfates of secondary alcohols such as the sodium sulfate of tetradecanol; sodium sulfate of 2-methyl 7 ethyl undecanol-4 (Tergitol 4); sodium sulfate of 3,9 diethyl tridecan0l-6 (Tergitol 6) and the sodium ethoxysulfate of C to C linear, secondary alcohols (Tergitol 15-S-3S). Illustrative of the non-ionic type penetrating aids are the ethoxylates of branched secondary alcohols such as the ethoxylate of 2,6,8-trimethyl 4 nonanol (Tergitol 15-S-3) and the 9 mol ethoxylate of C to C linear, secondary alcohols,Tergitol 15-8-9). Illustrative of a cationic type penetrating aid is l-hydroxyethyl-Z-heptadecenyl glyoxalidine. The above penetrating aids may be obtained from Union Carbide Corporation under the trademark Tergitol.

The penetrating aid can be added to the composition in an amount of up to about 5 %E by weight preferably about 0.5% by weight based on the weight of the composition. The methyl acetoacetate to hardened cementitious mixture weight ratio can also be varied over a relatively wide range as from about 0.01 to 2 parts by weight methyl acetoacetate to 1 part by weight hardened cementitious mixture preferably 0.1 to 1 part by weight methyl acetoacetate to 1 part by weight hardened cementitious mixture.

  • The following examples will illustrate the present invention.
  • EXAMPLES 1 THROUGH 30 In these examples, the effect of concrete age and methyl acetoacetate solution concentration on destruction time is illustrated.
  • Static tests were performed on the specimen, i.e., weighed specimens were immersed in a vessel containing the methyl acetoacetate solution and the specimens were checked periodically for weight loss.
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In Examples 1 to 3, the concrete specimens ‘were broken concrete test cylinders and in Examples 4 to 30, the concrete specimens were 2″ x 2″ x 2 blocks. The concrete age, concentrations, course aggregate used, and results are summarized for convenience in Table I below.

TABLE I.-STATIC” TESTS WITH METHYL ACETOACETATE/WATER SOLUTIONS THE EFFECTS OF CON- CRETE AGE AND METHYL ACETOACETATE SOLUTION CONCENTRATION ON DESTRUCTION TIME Methyl aceto- Methyl acetoacetate conc. acetate to Coarse aggregate in solution, concrete wt. used in Example Concrete age wt. percent ratio Time required to destroy concrete concrete 85 1.1.0 hr Limestone.85 l.0 Do.85 1.0 Do.85 1.0 Do.50 0.

Do.25 0.25 Do.85 1.0 Ohio river gravel.50 0.5 D0.25 0.25 Do.85 1.0 Limestone.50 l).5 D0.25 0.25 Do.85 1.0 Ohio river gravel.50 0.5 D0.25 0.25 Do.85 1.0 37% dissolved in 31 hrs., specimen so Do.50 0.5 17% dissolved in 31 hrs.; specimen s0ft Do.25 0.25 7% dissolved in 31 hrs.; specimen so1id Do.85 1.0 3 mins Limestone.50 0.5 5 mins Do.25 0.25 40 mins Do.85 1.0 85% dissolved in 9 hours Ohio river gravel.50 0.5 22% dissolved in 9 hours Do.80 0.25 6% dissolved in 9 hours.

Do.80 1.0 mins Limestone.50 0.5 81% dissolved in 129 hours Do.0.25 14% dissolved in 129 hours Do.80 1.0 38 %dissolved in 71 hours. D0.50 0.5 18% dissolved in 71 hours Do.25 0.25 10% dissolved in 71 hours Do. TABLE II. ROLLING TESTS WITH METHYL ACETO- EXAMPLES 31 THROUGH 48 In these examples, the effect of concrete age and methyl acetoacetate solution concentration on destruction time utilizing a rolling test procedure is illustrated.

The hardened concrete was located in the interior of a baffied five gallon steel container into which was introduced the methyl acetoacetate solution. Three such baffles each measuring 2 /2 to 3 inches wide of /8 inch steel were welded at a slight angle from vertical to the side of the containers.

The concrete formed on and around the baffles. In the rolling test, the chemical solution was charged to the bafiled container which contained the concrete specimen, the container lid was clamped in place (the lid had a 1-inch diameter hole in the center of it) and the container placed on a laboratory roller and rotated continuously at 20 rpm.

Periodically, the rotation was stopped and the concrete specimen was examined for deterioration. These rolling tests were continued until the specimen was completely dissolved. The concrete age, concentration and results are indicated in Table II. ACETATE/WATER SOLUTIONS IN BAFFLED, FIVE- GALLON CONTAINERS The effect of concrete age and methyl acetoacetate solution concentration on destruction time 1 Apparently not enough methyl acetoacetate present.

EXAMPLES 49 THROUGH 52 These examples demonstrate the effect of a penetrating aid for the methyl acetoacetate solution in destroying concrete. In Example 50 the penetrating aid employed was Tergitol 7, an anionic detergent (sodium heptadecyl sulfate) available from Union Carbide Corporation. In Ex ample 51, the penerating aid employed was Terg-itol TMN a non-ionic detergent (trimethyl nonanol polyethylene glycol ether) available from Union Carbide Corporation and in Example 52, the penetrating aid was Terigtol amine 220, a cationic detergent (hydroxyalkyl alkenyl glyoxalidine).

For convenience the characteristics and results of.the tests are indicated in Table III. TABLE III.STATIC TESTS: THE EFFECTS OF VARIOUS TYPES OF DETERGENTS AS PENETRATING AIDS FOR METHYL ACETOACETATE IN DESTROYING CONCRETE Concrete specimens: 2″ x 2″ x 2″ concrete cubes.

  • Ohio river gravel coarse aggregate Contact time Ex.
  • Dissolver” solution 1 hour 23 hours 27 hours 49.- Methyl acetoacetate Cube 81% of original weight.
  • Cube 57% of original weight.
  • Reac- Cube 54% of original weight.
  • Tion product a heavy paste.50″.- Methyl acetoacetate plus 0.5 wt.
  • Percent Cube 75% of original weight.

Cube 17% of original weight Cube disintegrated. TE R GITOL 7 (anionic). I 51 Methyl acetoacetate plus 0.5 wt. percent Cube 01 original weight. Cube 16% of original weight Cube 13% of original weight. TERGITOL TMN (non-ionic). t 52 Methyl acetoacetate plus 0.5 wt.

Percent Cube 84% of original weight. Cube 42% of original welght Cube 41% of original weight. TE R GITO L AMIN E 220 (cationic).7 EXAMPLE 53 The example demonstrates the effectiveness of methyl acetoacetate and compares its effectiveness with inhibited hydrochloric acid (38 wt. percent). The hydrochloric acid was inhibited with alkyl pyridine HB.

The test characteristics and results are indicated in Table IV.85% by weight methyl acetoacetate, about 14.5% water by weight and about 0.5% penetrating aid.3. A composition according to claim 2 wherein said hardened cementitious mixture is concrete.4.

A process for destroying hardened cementitious mixtures which comprises contacting said hardened cementitious mixture, with a composition consisting essentially of TABLE IV I Contact Weight ratio, pH of time, Chemical W aterChem1cal-Specimens mixtures hours Remarks 4.0 Small pieces falling from specimen.5.0 golution ambyer colore,1 l 5.

peeimen 90 of angina weig 1t. Methyl acetoacetate 25 148 148 6.4 5 Specimen 76 72 or original weight.7 Specimen 57% of original weight.2(4). Notling left but paste and stones. Inhibited hydrochloric acid (36 wt. percent) 2.210 790 300 {8 25251323 ZZZ; 33351333153;- (10% H01) 1.

  1. O 21 Specimen 81% of original weight.
  2. As will be evident and from the above examples a methyl acetoacetate in an amount of about 60-99% by water solution of methyl acetoacetate is extremely effective as a concrete destroyer and the most effective concentration is an 85/15 weight percent methyl acetoacetate water solution.

The elfectiveness is even more pronounced when a penetrating aid is added to the solution. Although, a water solution of methyl acetoacetate is somewhat corrosive, corrosion tests on mild steel indicated that metal lost due to corrosion from the use of methyl acetoacetate to dissolve the concrete build-up that occurs in ready-mix concrete truck drums is not a significant factor in the useful life of the drums.

This is because the reaction product of methyl acetoacetate, water and concrete is less corrosive to mild steel than water solutions of methyl acetoacetate. Moreover, no permanent detrimental effects were obtained in 24 hour immersion (immersion in eighty-five weight percent methyl acetoacetate-water solutions) tests on neoprene, black rubber, black gum rubber, rubber latex, polyethylene or tygon tubing.

Thus, the methyl acetoacetate solution can be employed with tools or equipment fabricated from these materials. What is claimed is: 1. A composition for destroying hardened cementitious mixtures consisting of methyl acetoacetate in an amount of about 60-99% by weight, water in an amount of about 140% by weight and a penetrating aid selected from the group consisting of anionic, nonionic or cationic detergents in an amount of about 0.5-5% by Weight.2.

A composition according to claim 1 containing about weight and water in an amount of about 140% by weight for a time sufiicient to destroy said hardened cementitious mixture.5. A process according to claim 4 wherein said composition is employed in an amount of about 0.1 to 1% by weight based on the weight of the hardened cementitious mixture.6.

A process according to claim 4 wherein said composition also includes a penetrating aid selected from the group consisting of anionic, nonionic or cationic detergents.7. A process according to claim 6 wherein said methyl acetoacetate, said water and said penetrating aid are employed in an amount of about 14.5% and 0.5% by weight respectively.8.

What is the most constituent of cement?

Portland cement consists essentially of compounds of lime (calcium oxide, CaO) mixed with silica (silicon dioxide, SiO2) and alumina (aluminium oxide, Al2O3). The lime is obtained from a calcareous (lime-containing) raw material, and the other oxides are derived from an argillaceous (clayey) material.

Which constituent is the best cementing material?

Which of the following is the first one to participate in hy Option 3 : Tricalcium aluminate Free 150 Questions 150 Marks 90 Mins Concept-

Component Estimated Reaction Time
3 CaO.SiO 2 Fast Relative to 2 CaO.SiO 2
2 CaO.SiO 2 Slow compared to 3 CaO.SiO 2
3 CaO.Al 2 O 3 Fastest but the addition of gypsum retards the time
4 CaO.Al 2 O 3,Fe 2 O 3 Relatively slow
CaSO 4,2 H 2 O (Gypsum) Retardant

Tri-calcium silicate –

It is supposed to be the best cementing material and is well-burnt cement. It is about 25-50% (normally about 40 percent) of cement. It renders the clinker easier to grind, increases resistance to freezing and thawing, hydrates rapidly generating high heat, and develops an early hardness and strength. However, raising C 3 S content beyond the specified limits increases the heat of hydration and solubility of cement in water. The hydrolysis of C 3 S is mainly responsible for 7-day strength and hardness.

Di-calcium silicate-

It is about 25-40% (normally about 32 percent) of cement. It hydrates and hardens slowly and takes a long time to add to the strength (after a year or more). It imparts resistance to chemical attacks. Raising of C 2 S content renders clinker harder to grind, reduces early strength, and decreases resistance to freezing and thawing at early ages, and decreases heat of hydration. The hydrolysis of C 2 S proceeds slowly.

Tri-calcium aluminate – ( 3 CaO.Al 2 O 3 )

It is about 5-11% (normally about 10.5 percent) of cement. It rapidly reacts with water and is responsible for the flash set of finely grounded clinker. The rapidity of action is regulated by the addition of 2-3% of gypsum at the time of grinding cement. Tricalcium aluminate is responsible for the initial set, high heat of hydration, and has a greater tendency to volume changes causing cracking.

Tetra calcium aluminoferrite –

It is about 8 –14% (normally about 9 percent) of cement. It is responsible for the flash setting but generates less heat. It has the poorest cementing value. Raising the C 4 AF content reduces the strength slightly. The heat of hydration is 420 J/g.

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Which of the following is not a constituent of cement concrete?

So mortar will not be a constituent of cement concrete.

What effect does calcium sulphate have on cement?

Retarders – Calcium sulphate, usually as gypsum, is universally added to ground cement to control the otherwise rapid ‘flash set’. Many other compounds have a retarding effect and these have been put on a systematic basis by Forsen, according to their effect on the solubility of alumina.

Following his categorization, retarders may be divided into four sets depending on their actions as a function of concentration. Typical examples from each group as (i) CaSO 4 ∙2H 2 O, (ii) CaCl 2, (iii) Na 2 CO 3, (iv) Na 3 PO 4, Type (iv) retarders may hold up setting and hardening indefinitely if used in sufficient quantity, but they are not all harmful and some, such as the calcium lignosulphonates, are used as water-reducing agents.

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Which of the following test determines unsoundness of cement due to an excess of calcium sulphate?

The soundness of cement is determined either by Le-chatelier’s method or by means of an Autoclave test.

Is code for soundness of cement?


What is sodium sulphate soundness test?

Sodium-sulphate soundness test A method of testing the weathering resistance, particularly to frost action, of building materials. A sample is soaked in saturated sodium-sulphate solution, drained, and dried. This is repeated and the sample examined for cracks. The method simulates the stresses due to frost action.

Which oxide is responsible for soundness of cement?

Sulphur Trioxide – It is present in small quantities of about 1 – 2.0 % to make the cement sound. Excess of sulphur trioxide causes the cement to become unsound.

What are the effects of unsoundness of cement?

The change in volume is called ‘unsoundness’ which produces cracks, distortion and disintegration in the structure, thereby allowing water and atmospheric gases that may have injurious effect on concrete or the steel reinforcement. If expansion occurs after concrete has set, the structure will get damaged.

What should be soundness of cement?

This must not exceed 10 mm for ordinary, rapid hardening and low heat Portland cements. If in case the expansion is more than 10 mm as tested above, the cement is said to be unsound. Soundness/expansion of cement = L1-L2 L1=Measurement taken after 24 hours of immersion in water at a temp.