The testing procedure for fly ash bricks – The three major tests that should be undertaken at the site are compressive strength test, water absorption test, and efflorescence test. The procedure is well described below: (a) Compressive Strength Test:

1. 1. Apparatus – A compression testing machine (having capacity preferably 500 kN/50 Tons or above) and duly calibrated at intervals of every 3 (three) months.
   2. Preconditioning of sample – Remove any unevenness observed in the bed faces to provide two smooth and parallel faces. If required, a grinder may be used for the same. Immerse in the water at room temperature for 24 hours. Remove the specimen and drain out any surplus moisture by leaving the specimen at room temperature for 3-4 minutes. Fill the frog (where provided) and all voids in the bed face flush with cement (1 part of cement; 2 parts of clean coarse of grade 3 mm and down). Store under damp jute bags for 24 hours followed by immersion in clean water for 3 days. Remove and wipe out traces of excess water prior to starting the test. However, in cases where immediate indicative test result is required to allow unloading of bricks at the site, the procedure of filling the ‘brick frog’ with cement mortar is substituted by placing sand and uniformly screeding the same to fill up the void. Excess sand particles are brushed away from the face of the brick to avoid ‘point load’ during testing.
   3. Testing Process – Place the specimen with flat faces horizontal and mortar/sand filled face facing upwards between two 3-ply plywood sheets each of 3 mm thickness and carefully centered between plates of the testing machine. Apply load axially at a uniform rate of 14N/mm 2 (140 kgf/cm 2 ) per minute till failure occurs and note the maximum load at failure. The load at failure shall be the maximum load at which the specimen fails to produce any further increase in the indicator reading on the testing machine.
   4. Report – The report shall be prepared as per the calculation method given below:

• Compressive Strength in N/mm 2 (kgf/cm 2 ) = Maximum Load at failure in N (kgf) Average area of the bed faces in mm 2 (cm 2 )
• Classes of Fly Ash Bricks approved by Bureau of Indian Standards
• (b) Water Absorption Test:

1. Apparatus – A sensitive balance capable of weighing within 0.1 percent of the mass of the specimen and ventilated oven along with accessories for handling hot material.
2. Preconditioning of sample – Dry the specimen in a ventilated oven at a temperature of 105 0 C to 115 0 C till it attains substantially constant mass. Cool the specimen to room temperature and obtain its weight (M 1 ). Specimen warm to touch shall not be used for the purpose.
3. Testing Process – Immerse completely dried specimen in clean water at a temperature of 27 0 C (+/-) 2 0 C for 24 hours. Remove the specimen and wipe out any traces of water with a damp cloth and weigh the specimen. Complete the weighing 3 minutes after the specimen has been removed from water (M 2 ).
4. Report – The report on water absorption, percent by mass, after 24-hour immersion in cold water shall be calculated in the method given below:

100 (c) Efflorescence Test:

1. Apparatus – A shallow, flat bottomed dish containing sufficient distilled water to completely saturate the specimens. The dish shall be made of glass, porcelain or glazed stoneware of size 180 mm x 180 mm x 40 mm depth (for square-shaped) and 200 mm dia x 40 mm depth (for cylindrical shaped),
2. Testing Process – Place the end of the bricks in the dish, the depth of immersion in water being 25 mm. Place the whole arrangement in a warm (i.e.20 0 C to 30 0 C) well-ventilated room until all the water in the dish is absorbed by the specimens and the surplus water evaporates. Cover the dish containing brick with a glass cylinder, so that excessive evaporation from the dish may not occur. When the water has been absorbed and bricks appear to be dry, place a similar quantity of water in the dish and allow it to evaporate as before. Examine the bricks for efflorescence after the second evaporation and report the results.
3. Report – The liability to efflorescence shall be reported as “nil”, “slight”, “moderate”, “heavy” or “serious” in accordance with the following definitions:

• NIL – When there is no perceptible deposit of efflorescence.
• SLIGHT – When not more than 10% of the exposed area of the brick is covered with a thin deposit of salts.
• MODERATE – When there is a heavier deposit than under ‘slight’ and covering up to 50% of the exposed area of the brick surface, but unaccompanied by powdering or flaking of the surface.
• HEAVY – When there is a heavy deposit of salts covering 50% or more of the exposed area of the brick surface, but unaccompanied by powdering or flaking of the surface.
• SERIOUS – When there is a heavy deposit of salts accompanied by powdering and/or flaking of the exposed surface.

are environment-friendly, more affordable and contribute to a greener future. Harden Bricks is one of the finest fly ash manufacturers in Kolkata. For more information, email us at – or simply visit our website – : Fly Ash Bricks in Kolkata, Ash Bricks

How do I test my fly ash?

The fineness of fly ash can be determined by wet sieving (Section 7.2), dry sieving (Section 7.3) or with the Blaine air permeability apparatus (Section 7.4). This test method describes the determination of fly ash fineness by wet sieving on a 45/. ~m sieve (ISO 565).

Which fly ash is good for bricks?

Fly ash brick – Wikipedia

This article needs additional citations for, Please help by, Unsourced material may be challenged and removed. Find sources: – · · · · ( July 2015 ) ( )

Fly ash bricks Fly ash brick ( FAB ) is a, specifically units, containing class C or class F and water. Compressed at 28 MPa (272 atm) and cured for 24 hours in a 66 °C steam bath, then toughened with an air entrainment agent, the bricks can last for more than 100 freeze-thaw cycles.

Is specification for fly ash bricks?

2- Raw material required are fly ash shall conform to Grade 1 or Grade 2 of IS 3812 (60-65%), Bottom ash used as replacement of shall not have more than 12 percent loss on ignition when tested according IS 1727, lime shall conform to class C hydrated lime of IS 712(8-12%), gypsum (5%), locally available sand/stone dust

What is the problem with flyash brick?

Let’s Summarise – Smaller builders and housing contractors may not be very familiar with fly ash products, that can have different properties depending on where and how the fly ash was obtained. Also, fly ash applications can face resistance from traditional builders who are well aware of its tendency to effloresce along with the concerns about thaw/freeze performance.

Slower strength gain Seasonal limitation Increased need for air-entraining admixtures Increase of salt scaling produced by higher proportions of fly ash

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The large size of the blocks promotes savings in mortar consumption since one Porotherm 8″ block is equivalent in area to 9 small bricks. Another spectacular feature of Porotherm is the precision in design. The blocks are highly dimensionally tolerant making Porotherm a one-of-a-kind wall solution in the market.

Also, Porotherm blocks are 60% light in weight than any other conventional walling block thus aiding in faster construction. Apart from all these, Porotherm blocks also have the lowest water absorption because of which possibility of superficial or shrinkage cracks on plaster is noneno wonder they are called POROTHERM SMART BRICKS! Read more at www.wienerberger.com, i want to buy Clomiphene online uk Recommended Videos: suturally Like this story? Or have something to share? Write to us: gos[email protected] or connect with us on Facebook and Twitter,

Which class of fly ash is better?

User Guidelines for Waste and Byproduct Materials in Pavement Construction

COAL FLY ASH	User Guideline
	Portland Cement Concrete

INTRODUCTION Coal fly ash has been successfully used in Portland cement concrete (PCC) as a mineral admixture, and more recently as a component of blended cement, for nearly 60 years. As an admixture, fly ash functions as either a partial replacement for, or an addition to, Portland cement and is added directly into ready-mix concrete at the batch plant.

Fly ash can also be interground with cement clinker or blended with Portland cement to produce blended cements. ASTM C595 (1) defines two blended cement products in which fly ash has been added: 1) Portland-pozzolan cement (Type IP), containing 15 to 40 percent pozzolan, or 2) Pozzolan modified Portland cement (Type I-PM), containing less than 15 percent pozzolan.

ASTM C618 defines two classes of fly ash for use in concrete: 1) Class F, usually derived from the burning of anthracite or bituminous coal, and 2) Class C, usually derived from the burning of lignite or subbituminous coal. (2) ASTM C618 also delineates requirements for the physical, chemical, and mechanical properties for these two classes of fly ash.

1. Class F fly ash is pozzolanic, with little or no cementing value alone.
2. Class C fly ash has self-cementing properties as well as pozzolanic properties.
3. PERFORMANCE RECORD A 1992 survey of all 50 state transportation agencies indicated that 40 states have had experience in the use of fly ash as a mineral admixture in concrete, usually as a partial replacement for Portland cement, although a number of states have also used blended Portland-pozzolan cement.

Virtually all 40 of these states have used fly ash in concrete pavements and shoulders. This same survey indicated that 44 states had specifications for the use of fly ash as a partial replacement for Portland cement in concrete. (3) At the time of this survey, at least eight states did not permit the use of fly ash in either bridge deck or structural concrete.

A number of states also did not permit the use of fly ash in white concrete items, such as curbs, sidewalks, and median barriers, and two states (Arkansas and New Mexico) reported questionable performance experience: Arkansas had temporarily discontinued the use of fly ash in bridge deck concrete, and New Mexico had a temporary moratorium on the use of Class C fly ash in concrete, pending further investigation.

(4)

• The principal benefits ascribed to the use of fly ash in concrete include enhanced workability due to spherical fly ash particles, reduced bleeding and less water demand, increased ultimate strength, reduced permeability and chloride ion penetration, lower heat of hydration, greater resistance to sulfate attack, greater resistance to alkali-aggregate reactivity, and reduced drying shrinkage. (5)
• The main precautions usually associated with the use of fly ash in concrete include somewhat slower early strength development, extended initial setting time, possible difficulty in controlling air content, seasonal limitations during winter months, and quality control of fly ash sources. (5)
• The use of Class F fly ash usually results in slower early strength development, but the use of Class C fly ash does not and may even enhance early strength development.
• MATERIAL PROCESSING REQUIREMENTS
• Source Control
• To ensure the quality of fly ash for use in PCC, the following sources of ash should be avoided:

• Ash from a peaking plant instead of a base loaded plant.
• Ash from plants burning different coals or blends of coal.
• Ash from plants burning other fuels (wood chips, tires, trash) blended with coal.
• Ash from plants using oil as a supplementary fuel.
• Ash from plants using precipitator additives, such as ammonia.
• Ash from start-up or shut-down phases of operation.
• Ash from plants not operating at a “steady state.”
• Ash that is handled and stored using a wet system.

The net result of all these restrictions is that only a relatively low percentage (25 to 30 percent, at most) of all the coal fly ash produced annually is even potentially suitable for use in PCC. Drying or Conditioning When used in blended cement or as a partial replacement for Portland cement in ready-mix concrete, fly ash must be in a dry form and as such requires no processing.

When used as a raw feed material for the production of Portland cement, either dry or conditioned ash can be used. Quality Control Fly ash used in concrete should be as consistent and uniform as possible. Fly ash to be used in concrete should be monitored by a quality assurance/quality control (QA/QC) program that complies with the recommended procedures in ASTM C311.

(6) These procedures establish standards for methods of sampling and frequency of performing tests for fineness, loss on ignition (LOI), specific gravity, and pozzolanic activity such that the consistency of a fly ash source can be certified. Many state transportation agencies, through their own program of sampling and testing, have been able to prequalify sources of fly ash within their own state (or from nearby states) for acceptance in ready-mixed concrete.

1. Prequalification of fly ashes from different sources provides an agency with a certain level of confidence in the event fly ashes from different sources are to be used in the same project.
2. ENGINEERING PROPERTIES Some of the engineering properties of fly ash that are of particular interest when fly ash is used as an admixture or a cement addition to PCC mixes include fineness, LOI, chemical composition, moisture content, and pozzolanic activity.

Most specifying agencies refer to ASTM C618 (2) when citing acceptance criteria for the use of fly ash in concrete. Fineness : Fineness is the primary physical characteristic of fly ash that relates to pozzolanic activity. As the fineness increases, the pozzolanic activity can be expected to increase.

Current specifications include a requirement for the maximum allowable percentage retained on a 0.045 mm (No.325) sieve when wet sieved. ASTM C618 specifies a maximum of 34 percent retained on a 0.045 mm (No.325) sieve. Fineness can also be assessed by methods that estimate specific surface area, such as the Blaine air permeability test (7) commonly used for Portland cement.

Pozzolanic Activity (Chemical Composition and Mineralogy ):Pozzolanic activity refers to the ability of the silica and alumina components of fly ash to react with available calcium and/or magnesium from the hydration products of Portland cement. ASTM C618 requires that the pozzolanic activity index with Portland cement, as determined in accordance with ASTM C311, (6) be a minimum of 75 percent of the average 28-day compressive strength of control mixes made with Portland cement.

• Loss on Ignition : Many state transportation departments specify a maximum LOI value that does not exceed 3 or 4 percent, even though the ASTM criteria is a maximum LOI content of 6 percent.
• 2) This is because carbon contents (reflected by LOI) higher than 3 to 4 percent have an adverse effect on air entrainment.

Fly ashes must have a low enough LOI (usually less than 3.0 percent) to satisfy ready-mix concrete producers, who are concerned about product quality and the control of air-entraining admixtures. Furthermore, consistent LOI values are almost as important as low LOI values to ready-mix producers, who are most concerned with consistent and predictable quality.

Moisture Content : ASTM C618 specifies a maximum allowable moisture content of 3.0 percent. Some of the properties of fly ash-concrete mixes that are of particular interest include mix workability, time of setting, bleeding, pumpability, strength development, heat of hydration, permeability, resistance to freeze-thaw, sulfate resistance, and alkali-silica reactivity.

Workability : At a given water-cement ratio, the spherical shape of most fly ash particles permits greater workability than with conventional concrete mixes. When fly ash is used, the absolute volume of cement plus fly ash usually exceeds that of cement in conventional concrete mixes.

The increased ratio of solids volume to water volume produces a paste with improved plasticity and more cohesiveness. (8) Time of Setting : When replacing up to 25 percent of the Portland cement in concrete, all Class F fly ashes and most Class C fly ashes increase the time of setting. However, some Class C fly ashes may have little effect on, or possibly even decrease, the time of setting.

Delays in setting time will probably be more pronounced, compared with conventional concrete mixes, during the cooler or colder months. (8) Bleeding : Bleeding is usually reduced because of the greater volume of fines and lower required water content for a given degree of workability.

1. 8) Pumpability : Pumpability is increased by the same characteristics affecting workability, specifically, the lubricating effect of the spherical fly ash particles and the increased ratio of solids to liquid that makes the concrete less prone to segregation.
2. 8) Strength Development : Previous studies of fly ash concrete mixes have generally confirmed that most mixes that contain Class F fly ash that replaces Portland cement at a 1:1 (equal weight) ratio gain compressive strength, as well as tensile strength, more slowly than conventional concrete mixes for up to as long as 60 to 90 days.

Beyond 60 to 90 days, Class F fly ash concrete mixes will ultimately exceed the strength of conventional PCC mixes. (5) For mixes with replacement ratios from 1.1 to 1.5:1 by weight of Class F fly ash to the Portland cement that is being replaced, 28-day strength development is approximately equal to that of conventional concrete.

1. Class C fly ashes often exhibit a higher rate of reaction at early ages than Class F fly ashes.
2. Some Class C fly ashes are as effective as Portland cement in developing 28-day strength.
3. 9) Both Class F and Class C fly ashes are beneficial in the production of high-strength concrete.
4. However, the American Concrete Institute (ACI) recommends that Class F fly ash replace from 15 to 25 percent of the Portland cement and Class C fly ash replace from 20 to 35 percent.

(10) Heat of Hydration : The initial impetus for using fly ash in concrete stemmed from the fact that the more slowly reacting fly ash generates less heat per unit of time than the hydration of the faster reacting Portland cement. Thus, the temperature rise in large masses of concrete (such as dams) can be significantly reduced if fly ash is substituted for cement, since more of the heat can be dissipated as it develops.

1. Not only is the risk of thermal cracking reduced, but greater ultimate strength is attained in concrete with fly ash because of the pozzolanic reaction.
2. 8) Class F fly ashes are generally more effective than Class C fly ashes in reducing the heat of hydration.
3. Permeability : Fly ash reacting with available lime and alkalies generates additional cementitious compounds that act to block bleed channels, filling pore space and reducing the permeability of the hardened concrete.

(5) The pozzolanic reaction consumes calcium hydroxide (Ca(OH) 2 ), which is leachable, replacing it with insoluble calcium silicate hydrates (CSH). (8) The increased volume of fines and reduced water content also play a role. Resistance to Freeze-Thaw : As with all concretes, the resistance of fly ash concrete to damage from freezing and thawing depends on the adequacy of the air void system, as well as other factors, such as strength development, climate, and the use of deicer salts.

• Special attention must be given to attaining the proper amount of entrained air and air void distribution.
• Once fly ash concrete has developed adequate strength, no significant differences in concrete durability have usually been observed.
• 8) There should be no more tendency for fly ash concrete to scale in freezing and thawing exposures than conventional concrete, provided the fly ash concrete has achieved its design strength and has the proper air void system.

Sulfate Resistance : Class F fly ash will generally improve the sulfate resistance of any concrete mixture in which it is included. (11) Some Class C fly ashes may improve sulfate resistance, while others may actually reduce sulfate resistance (12) and accelerate deterioration.

1. 13) Class C fly ashes should be individually tested before use in a sulfate environment.
2. The relative resistance of fly ash to sulfate deterioration is reportedly a function of the ratio of calcium oxide to iron oxide.
3. 12) Alkali-Silica Reactivity : Class F fly ash has been effective in inhibiting or reducing expansive reactions resulting from the alkali-silica reaction.

In theory, the reaction between the very small particles of amorphous silica glass in the fly ash and the alkalis in the Portland cement, as well as the fly ash, ties up the alkalis in a nonexpansive calcium-alkali-silica gel, preventing them from reacting with silica in aggregates, which can result in expansive reactions.

However, because some fly ashes (including some Class C fly ashes) may have appreciable amounts of soluble alkalis, it is necessary to test materials to be used in the field to ensure that expansion due to alkali-silica reactivity will be reduced to safe levels. (8) Fly ash, especially Class F fly ash, is effective in three ways in substantially reducing alkali-silica expansion: 1) it produces a denser, less permeable concrete; 2) when used as a cement replacement it reduces total alkali content by reducing the Portland cement; and 3) alkalis react with fly ash instead of reactive silica aggregates.

(14) Class F fly ashes are probably more effective than Class C fly ashes because of their higher silica content, which can react with alkalis. Users of Class C fly ash are cautioned to carefully evaluate the long-term volume stability of concrete mixes in the laboratory prior to field use, with ASTM C441 (15) as a suggested method of test.

DESIGN CONSIDERATIONS Mix Design Concrete mixes are designed by selecting the proportions of the mix components that will develop the required strength, produce a workable consistency concrete that can be handled and placed easily, attain sufficient durability under exposure to in-service environmental conditions, and be economical.

Procedures for proportioning fly ash concrete mixes differ slightly from those for conventional concrete mixes. Basic mix design guidelines for normal concrete (16) and high-strength concrete are provided by ACI. (10) One mix design approach commonly used in proportioning fly ash concrete mixes is to use a mix design with all Portland cement, remove some of the Portland cement, and then add fly ash to compensate for the cement that is removed.

1. Class C fly ash is usually substituted at a 1:1 ratio.
2. Class F fly ash may also be substituted at a 1:1 ratio, but is sometimes specified at a 1.25:1 ratio, and in some cases may even be substituted at a 1.5:1 ratio.
3. 5) There are some states that require that fly ash be added in certain mixes with no reduction in cement content.

The percentage of Class F fly ash used as a percent of total cementitious material in typical highway pavement or structural concrete mixes usually ranges from 15 to 25 percent by weight. (5) This percentage usually ranges from 20 to 35 percent when Class C fly ash is used.

• 10) Mix design procedures for normal, as well as high-strength, concrete involve a determination of the total weight of cementitious materials (cement plus fly ash) for each trial mixture that is being investigated in the laboratory.
• The ACI mix proportioning guidelines recommend a separate trial mix for each 5-percent increment in the replacement of Portland cement by fly ash.

If fly ash is to replace Portland cement on an equal weight (1:1) basis, the total weight of cementitious material in each trial mix will remain the same. However, because of differences in the specific gravity values of Portland cement and fly ash, the volume of cementitious material will vary with each trial mixture.

(10) When a Type IP (Portland-pozzolan) or Type I-PM blended cement is used in a concrete mix, fly ash is already a part of the cementing material. There is no need to add more fly ash to a concrete mix in which blended cement is being used, and it is recommended that no fly ash be added in such cases.

The blended cement can be used in the mix design process in essentially the same way as a Type I Portland cement. To select a mix proportion that satisfies the design requirements for a particular project, trial mixes must be made. In a concrete mix design, the water-cement (w/c) ratio is a key design parameter, with a typical range being from 0.37 to 0.50.

When using a blended cement, the water demand will probably be somewhat reduced because of the presence of the fly ash in the blended cement. When fly ash is used as a separately batched material, trial mixes should be made using a water-cement plus fly ash (w/c+f) ratio, sometimes referred to as the water-cementitious ratio, instead of the conventional w/c ratio.

(16) The design of any concrete mix, including fly ash concrete mixes, is based on proportioning the mix at varying water-cementitious ratios to meet or exceed requirements for compressive strength (at various ages), entrained air content, and slump or workability needs.

1. The mix design procedures stipulated in ACI 211.1 provide detailed, step-by-step directions regarding trial mix proportioning of the water, cement (or cement plus fly ash), and aggregate materials.
2. Fly ash has a lower specific gravity than Portland cement, which must be taken into consideration in the mix proportioning process.

Structural Design Structural design procedures for concrete pavements containing fly ash are no different than design procedures for conventional concrete pavements. The procedures are based to a great extent on the design strength of the concrete mix, usually determined by testing after moist curing for 28 days.

1. CONSTRUCTION PROCEDURES
2. Material Handling and Storage
3. When fly ash is used as a mineral admixture, the ready-mix producer typically handles fly ash in the same manner as Portland cement, except that fly ash must be stored in a separate silo from the Portland cement.
4. Mixing, Placing, and Compacting

Certain fly ashes will reduce the effectiveness of air entraining agents, requiring a higher dosage to meet specifications. Therefore, the concrete producer must ensure that the proper amount of air entraining admixture is added during mixing, so that the air content of the concrete is within specified limits.

1. The air content of the concrete must be carefully checked and adjusted during production to ensure that it remains within those limits.
2. As with any concrete, excessive vibration should be avoided because it may reduce the air content of the in-place concrete.
3. 5) Placement and handling of fly ash concrete is in most respects similar to that of normal concrete.

Fly ash concrete using Class F fly ash has a slower setting time than normal concrete. As a result, finishing operations may have to be delayed, possibly by 1 to 2 hours, depending on the temperature. Also, fly ash concrete surfaces may tend to be more sticky than normal concrete during placement and finishing, although properly proportioned concrete mixes containing fly ash should benefit workability and finishing.

• 5) Normal procedures for screeding, finishing, edging, and jointing of conventional PCC are also applicable to fly ash concrete.
• Curing The slower strength development of concrete containing Class F fly ash may require that the moisture be retained in the concrete for a longer period of time than what is normally required for conventional concrete.

The proper application of a curing compound should retain moisture in the concrete for a sufficient period of time to permit strength development. Normal curing practices should be adequate for concrete containing Class F fly ash. Scheduling of pavement construction should allow adequate time for the desired or specified strength gain prior to the placement of traffic loads, the onset of freeze-thaw cycles, and the application of deicing salts because of the detrimental effect of cold weather on strength gain.

Some states, such as Wisconsin, have a construction cut-off date beyond which fly ash is not permitted to be used in concrete until the following spring. There is less of a concern with the use of Class C fly ash in cold weather than Class F fly ash. Rather than relying on a cut-off date, the percentage of fly ash could be reduced during colder weather, or other measures (such as additional Portland cement, or the possible use of high-early strength cement, or a chemical accelerator) could be taken to maintain or improve strength development under low temperature conditions.

Normal construction practices for cold weather concreting (such as heated aggregates and mixing water, reducing the slump of the concrete, covering the poured concrete with insulation material, and using space heaters for inside pours) are also applicable for concrete containing some fly ash.

(18) Quality Control The most important quality control consideration concerning the use of fly ash in PCC mixes is to ensure that the air content of the freshly mixed concrete is within specified limits and does not fluctuate to any greater extent than a normal PCC mix. To ensure that such is the case, air content testing of fly ash concrete mixes may initially need to be done at a greater frequency than with normal PCC mixes.

Another important quality control consideration in freshly mixed PCC is its workability, as determined by performing slump tests. Slump testing of fly ash concrete can be done at the same frequency as for normal PCC mixes. UNRESOLVED ISSUES An improved means of classifying and specifying fly ash sources for use as a mineral admixture in PCC is needed.

There are considerable laboratory and limited field data that indicate that high percentage (50 to 70 percent) Class F or Class C fly ash, in combination with a high range water reducing admixture, produces concrete with exceptional compressive strength. (19) Trial usage of high percentage fly ash concrete mixes is needed in order to be able to evaluate the field performance of these mixes.

Class F fly ash may have cementitious ability when blended with other by-products such as cement kiln dust prior to being introduced into a concrete mix. Additional data are needed on the characteristics and long-term performance of concrete mixes in which a blend of fly ash and other cementitious (or pozzolanic) by-products is used.

As a consequence of the Clean Air Act, many coal-fired power plants are being equipped with low NO x burners. The short-term effect of burning coal in a low NO x burner appears to be an increase in the LOI of the fly ash. The coal ash industry is developing comparative information on the characteristics and engineering properties of ASTM C618 sources of fly ash before and after installation of low NO x burners.

Some fly ash sources do not have acceptable LOI values once low NO x burners have been installed and put into operation. REFERENCES

1. ASTM C595-92a. “Standard Specification for Blended Hydraulic Cements,” American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994.
2. ASTM C618-92a. “Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan For Use as Mineral Admixture in Portland Cement Concrete,” American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994.
3. Collins, Robert J. and Stanley K. Ciesielski. Recycling and Use of Waste Materials and By-Products in Highway Construction, National Cooperative Highway Research Program Synthesis of Highway Practice No.199. Transportation Research Board, Washington, DC, 1994.
4. Collins, Robert J. and Stanley K. Ciesielski. Recycling and Use of Waste Materials and By-Products in Highway Construction – Volume 2, National Cooperative Highway Research Program Technical Appendix to Synthesis of Highway Practice No.199, Transportation Research Board, Washington, DC, 1994.
5. American Coal Ash Association. Fly Ash Facts for Highway Engineers, Federal Highway Administration, Report No. FHWA-SA-94-081, Washington, DC, December, 1995.
6. ASTM C311-92. “Standard Methods of Sampling and Testing Fly Ash or Natural Pozzolans for Use as a Mineral Admixture in Portland Cement Concrete.” American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994.
7. ASTM C204. “Test Method for Fineness of Portland Cement by Air Permeability Apparatus,”American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994.
8. Halstead, Woodrow J. Use of Fly Ash in Concrete, National Cooperative Highway Research Program Synthesis of Highway Practice No.127, Transportation Research Board, Washington, DC, 1986.
9. Cook, James E. A Ready-Mixed Concrete Company’s Experience with Class C Ash, National Ready-Mix Concrete Association, Publication No.163, Silver Spring, Maryland, April, 1981.
10. ACI 211.4R-93. “Guide for Selecting Properties for High-Strength Concrete with Portland Cement and Fly Ash,” ACI Manual of Concrete Practice, Part 1. American Concrete Institute, Detroit, Michigan, 1996.
11. Hester, J.A. “Fly Ash in Roadway Construction,” Proceedings of the First Ash Utilization Symposium,U.S. Bureau of Mines, Information Circular No.8348, Washington, DC, 1967, pp.87-100.
12. Dunstan, E.R., Jr. “A Possible Method for Identifying Fly Ashes That Will Improve Sulfate Resistance of Concrete,” Cement, Concrete and Aggregates, Volume 2, No.1, American Society for Testing and Materials, West Conshohocken, Pennsylvania, 1980.
13. Helmuth, Richard. Fly Ash in Cement and Concrete, Portland Cement Association, Publication No. SP040.01T, Skokie, Illinois, 1987.
14. Guide to Alkali-Aggregate Reactivity, Mid-Atlantic Regional Technical Committee of the National Ready-Mix Concrete Association, Silver Spring, Maryland, 1993.
15. ASTM C441. “Standard Test Method for Effectiveness of Mineral Admixtures or Ground Blast-Furnace Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction.” American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994.
16. ACI 211.1. “Standard Practice for Selecting Proportions for Normal, Heavyweight and Mass Concrete,” ACI Manual of Concrete Practice, Part 1. American Concrete Institute, Detroit, Michigan, 1996.
17. ASTM C39. “Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens,” American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994.
18. Cold-Weather Concreting, Portland Cement Association, Publication No. IS154.06T, Skokie, Illinois, 1980
19. Naik, Tarun R., Vasanthy Sivasunduram, and Shiw S. Singh. “Use of High-Volume Class F Fly Ash for Structural-Grade Concrete,” Transportation Research Record No.1301, Washington, DC, 1991.

| | : User Guidelines for Waste and Byproduct Materials in Pavement Construction

What is the grade of fly ash?

Classification – Two classes of fly ash are defined by American Society for Testing and Materials (ASTM) C618: Class F fly ash and Class C fly ash. The chief difference between these classes is the amount of calcium, silica, alumina, and iron content in the ash.

• The chemical properties of the fly ash are largely influenced by the chemical content of the coal burned (i.e., anthracite, bituminous, and lignite ).
• Not all fly ashes meet ASTM C618 requirements, although depending on the application, this may not be necessary.
• Fly ash used as a cement replacement must meet strict construction standards, but no standard environmental regulations have been established in the United States.

Seventy-five percent of the fly ash must have a fineness of 45 µm or less, and have a carbon content, measured by the loss on ignition (LOI), of less than 4%. In the US, LOI must be under 6%. The particle size distribution of raw fly ash tends to fluctuate constantly, due to changing performance of the coal mills and the boiler performance.

1. This makes it necessary that, if fly ash is used in an optimal way to replace cement in concrete production, it must be processed using beneficiation methods like mechanical air classification.
2. But if fly ash is used as a filler to replace sand in concrete production, unbeneficiated fly ash with higher LOI can be also used.

Especially important is the ongoing quality verification. This is mainly expressed by quality control seals like the Bureau of Indian Standards mark or the DCL mark of the Dubai Municipality.

What is the standard colour of ash brick?

Beautify Home with Red Fly Ash Bricks We all know the foundation of every house should be strong, but what if the base would be stylish as well as tough! Yes, now this can be possible with Harden Bricks.Fly ash bricks are generally gray in color and they can be identified by their unique look.

But Harden Bricks gives a twist to this usual gray colour. Introducing red fly ash bricks, but why is it necessary? Well, we can come to this point later, but first let’s talk about the unique features of fly ash bricks.Fly ash bricks are always better than conventional red bricks in terms of strength, durability, and cost.

Fly ash bricks are a byproduct, so it’s eco-friendly and energy-efficient that can reduce the mercury pollution. The bricks are compact and uniform in shape, size and colour.The most useful advantage of fly ash bricks is they have high strength, so these bricks can be undoubtedly used for construction.Uniform size of each block and thickness of the joints helps reduce the plaster consumption compared to clay bricks.

This saves cement consumption to 25% – 30%.Fly ash bricks have calcium oxide in it that makes the brick bonding excellent. Due to lesser water absorption, the building walls would be safe from dampness.So, these advantages make fly ash a demanding product in the construction sector.Now coming to the point why red fly ash bricks are necessary! Beautification Red fly ash bricks can be used to give a different look to houses.

Due to the uniformity, the bricks look attractive. The colour red makes the bricks more striking and stylish. This red brick wall gives a different look where you don’t need to paint. No Plaster Needed Don’t need to apply plaster on the bricks as the bricks itself work as your home’s design element.Harden Bricks comes with an innovative idea that not only gives your house a beautiful look, but makes your house strong as well.

Is flyash brick waterproof?

There is no doubt that in comparison with red bricks, fly ash bricks are structurally stronger, more durable, better insulators, water-resistant, etc. But not using them so usually has, especially in India, a whole lot of reasons : Firstly, though fly ash bricks save the cost of the project as a whole, they are still more expensive than red bricks, and the poor majority doesn’t like the idea.

• Secondly, flay ash bricks are not easily available everywhere, and red bricks are.
• Getting fly ash bricks transported adds to their cost, which already was higher.
• Thirdly, only modular sizes are feasible.
• Larger bricks are very brittle.
• The outer surface is harder as compared to the inner core, which can lead to cracking in the future if a few bricks are cut out to allow running of pipes, wiring, etc.

Fourthly, laborers aren’t very familiar here with fly ash. Many builders, therefore, consider it a bad choice. Fifthly, fly ash bricks buildings get quite cold in winter since it doesn’t absorb much heat. Sixthly, fly ash bricks are only good if care for quality in production has been taken.

Is code for testing of fly ash bricks?

The minimum average wet compressive strength of pulverized fuel ash-lime bricks shall not be less than the one specified for each class in 4.1 when tested as described in IS 3495 ( Part 1).

Which is code is used for fly ash?

As per clause 5.2 of IS 456-2000 Plain and Reinforced cement concrete code of practice, flyash (conforming to IS: 3812 Part–1 ) up to 35% can be used as part replacement of OPC in the concrete.

What is the strength of fly ash brick?

The compressive strength of flyash brick is three times greater than the normal clay brick. The minimum compressive strength of clay brick is 3.5 N/mm².So as the flyash brick has compressive strength of 10-12 N/mm².

Which is better AAC or fly ash bricks?

Comparative Study of AAC block with Fly ash brick and Burnt Clay Brick | Gandhian Young Technological Innovation Award India is a rapidly developing country and the infrastructure of the country also growing fast according to the rise in population and increase in constructional activities considering the improvement in the standard of living. hence in a modern days everyone needs to be a perfect construction materials for the masonry work which will be full-fill the requirement such as time consumption, economical, eco-friendly, earthquake resist, cheap and ease of work.

on that requirement there are different types of bricks used in masonry works but from them which material is more reliable in construction of masonry work,the material which will be full-fill the above all requirement which plays an important role in developing of a country.aac blocks can be extensively used in all building constructional activities similar to that of common burnt clay bricks and fly ash bricks.

the aac blocks are comparatively lighter in weight and stronger than common clay bricks and fly ash bricks. about 180 billion tones of common burnt clay bricks are consumed annually approximately 340 billion tones of clay- about 5000 acres of top layer of soil dug out for bricks manufacture, soil erosion, emission from coal burning or fire woods which causes deforestation are the serious problems posed by brick industry.

Use of aac blocks and fly ash bricks instead of clay bricks reduce the annually consumption of clay from the top layer of soil. unlike clay bricks, making of which uses top fertile soil, the aac block and fly ash bricks use fly ash generated as waste by thermal power plants as raw material and thus use of these helps in conserving of top fertile soil.

but due to high density, high thermal conductivity and high water absorption properties of fly ash bricks, it is not reliable for construction work than aac blocks. in this project, we are comparing aac blocks with fly ash bricks and burnt clay bricks on the basis of laboratory test like water absorption test, density test and compressive strength test.

Is fly ash stronger than cement?

NOTE : An updated version of this article is available. Please to access it. – By Arnie Rosenberg Dr. Arnie Rosenberg is a former research director at Grace Construction Products and now a guest researcher at the National Institute for Standards and Testing, working on the characterization of fly ash. All precast concrete producers can now use a group of materials called “fly ash” to improve the quality and durability of their products. Fly ash improves concrete’s workability, pumpability, cohesiveness, finish, ultimate strength, and durability as well as solves many problems experienced with concrete today–and all for less cost. Fly ash, however, must be used with care. Without adequate knowledge of its use and taking proper precautions, problems can result in mixing, setting time, strength development, and durability. What Is Fly Ash? Fly ash is a group of materials that can vary significantly in composition. It is residue left from burning coal, which is collected on an electrostatic precipitator or in a baghouse. It mixes with flue gases that result when powdered coal is used to produce electric power. Since the oil crisis of the 1970s, the use of coal has increased. In 1992, 460 million metric tons of coal ash were produced worldwide. About 10 percent of this was produced as fly ash in the United States. In 1996, more than 7 million metric tons were used in concrete in the U.S. Economically, it makes sense to use as much of this low-cost ash as possible, especially if it can be used in concrete as a substitute for cement. Coal is the product of millions of years of decomposing vegetable matter under pressure, and its chemical composition is erratic. In addition, electric companies optimize power production from coal using additives such as flue-gas conditioners, sodium sulfate, oil, and other additives to control corrosion, emissions, and fouling. The resulting fly ash can have a variable composition and contain several additives as well as products from incomplete combustion. Most fly ash is pozzolanic, which means it’s a siliceous or siliceous-and-aluminous material that reacts with calcium hydroxide to form a cement. When portland cement reacts with water, it produces a hydrated calcium silicate (CSH) and lime. The hydrated silicate develops strength and the lime fills the voids. Properly selected fly ash reacts with the lime to form CSH–the same cementing product as in portland cement. This reaction of fly ash with lime in concrete improves strength. Typically, fly ash is added to structural concrete at 15-35 percent by weight of the cement, but up to 70 percent is added for mass concrete used in dams, roller-compacted concrete pavements, and parking areas. Special care must be taken in selecting fly ash to ensure improved properties in concrete. Standards There are two classes of fly ash: “F” is made from burning anthracite and/or bituminous coal, and “C” is produced from lignite or subbituminous coal. In Canada, there is a further distinction. When the lime content is 8-20 percent, it is classified Cl, and when it is higher, it is class C. In the United States and other parts of the world where U.S. standards have been adopted, the chemical part of the specification requires only a combined total of silica, alumina, and iron oxide. It does not specify the amount of silica that reacts with lime to produce added strength. The alumina content could be high in fly ash, which could be detrimental because more sulfate to control its reactivity might be required. Sulfate is added to the cement to control only the setting reactions of the aluminates and ferrites in the cement. However, the amount is limited because expansive reactions are possible after the concrete has set. This amount of sulfate does not take into account the extra aluminates that can be added when fly ash is used. Too much iron oxide will retard the setting time. Although in ASTM C618, the loss on ignition listed in the table of requirements is less than 6 percent, a footnote actually allows up to 12 percent. Incomplete combustion products such as carbon, which affects air entrainment, water-cement ratio, set, and the concrete’s color, could cause this ignition loss. Fly ash is considered to have met C618’s requirements if the 7- or 28-day strength of a sample with 20 percent fly ash reaches 75 percent of the control strength in an ASTM C109 test. Both class C fly ash and slag have about 35 percent silica and much lower calcium oxide than portland cement. In most cases, lower calcium oxide means better durability. In some fly ash, alumina and iron oxide can be quite high, leading to lower strength and unusual setting time problems. The carbon content was reported in some to be so high that it was beyond the special footnoted exception in ASTM C618. Advantages The advantages of using fly ash far outweigh the disadvantages. The most important benefit is reduced permeability to water and aggressive chemicals. Properly cured concrete made with fly ash creates a denser product because the size of the pores are reduced. This increases strength and reduces permeability. Today, there are at least two ways to make fly ash more beneficial: a dry process that involves triboelectric static separation and a wet process based on froth flotation. These procedures generally lower the carbon content and the LOI of fly ash. The cost of an additional storage bin should be easily covered by the reduction in the cost of the concrete and the added benefits to the concrete. Low-carbon fly ash or the use of a better air-entraining agent at a higher-than-usual addition rate can control the problem of freeze-thaw durability. Advantages in Fresh Concrete Since fly ash particles are spherical and in the same size range as portland cement, a reduction in the amount of water needed for mixing and placing concrete can be obtained. In precast concrete, this can be translated into better workability, resulting in sharp and distinctive corners and edges with a better surface appearance. This also makes it easier to fill intricate shapes and patterns. Fly ash also benefits precast concrete by reducing permeability, which is the leading cause of premature failure. The use of fly ash can result in better workability, pumpability, cohesiveness, finish, ultimate strength, and durability. The fine particles in fly ash help to reduce bleeding and segregation and improve pumpability and finishing, especially in lean mixes. Advantages in Hardened Concrete Strength in concrete depends on many factors, the most important of which is the ratio of water to cement. Good quality fly ash generally improves workability or at least produces the same workability with less water. The reduction in water leads to improved strength. Because some fly ash contains larger or less reactive particles than portland cement, significant hydration can continue for six months or longer, leading to much higher ultimate strength than concrete without fly ash. There have been several cases in which the early strength of concrete was low, particularly where a significant portion–30 percent or more–of the portland cement was replaced with fly ash. This need not be a serious problem today, since set time is also controlled by many other factors that can be altered to compensate for added fly ash, if necessary. The observed slow set and low early strength obtained with fly ash has caused a reduction in the amount of this mineral admixture used in concrete. Although some fly ash materials will reduce early strength and slow the setting time it does not have to be the case today. Some fly ash actually accelerates set. The addition of accelerators, plasticizers and/or a small amount of additional CSF, as well as the proper beneficiated fly ash, can mitigate this problem. Properly proportioned concrete containing fly ash should create a lower cost. Because of the reduced permeability and reduced calcium oxide in properly selected fly ash, it should be less susceptible to the alkali-aggregate reaction. Sulfate and other chemical attacks are reduced when fly ash is added. Fly ash, which has little effect on creep, has been suspected of contributing to corrosion because it reacts with the calcium hydroxide. Fly ash, in fact, does not materially reduce alkalinity, and the reduced permeability helps to protect the concrete from chloride penetration, the cause of rebar corrosion (see Rosenberg’s article on corrosion in the Fall 1999 issue of MC Magazine). A superplasticizer combined with fly ash can be used to make high-performance and high-strength concrete. Concrete containing fly ash generally performs better than plain concrete in drying shrinkage tests. Disadvantages The quality of fly ash is important–but it can vary. Poor-quality fly ash can have a negative effect on concrete. The principle advantage of fly ash is reduced permeability at a low cost, but fly ash of poor quality can actually increase permeability. Some fly ash, such as that produced in a power plant, is compatible with concrete. Other types of fly ash must be beneficiated, and some types cannot be improved sufficiently for use in concrete. Some concrete will set slowly when fly ash is used. Though this might be perceived as a disadvantage, it can actually be a benefit by reducing thermal stress. When cement sets, it produces 100 calories per gram so that the temperature of a structure may rise 135 degrees. Certain fly ash can be used to keep the temperature from rising too high (less than 45 degrees). However, concrete with fly ash can set up normally or even rapidly, since many other factors control the set and strength development. Freeze-thaw durability may not be acceptable with the use of fly ash in concrete. The amount of air entrained in the concrete controls the freeze-thaw durability, and the high carbon content in certain fly ash products absorbs some air entraining agents, reducing the amount of air produced in the concrete, making the concrete susceptible to frost damage. High-carbon fly ash materials tend to use more water and darken the concrete as well. It is not recommended to use a high-carbon (greater than 5 percent) content fly ash, but if it must be used, the proper air content can be reached by increasing the dosage of an air-entraining agent. Slow set and low early strength need not be consequences of using fly ash. Most of the time, high- fineness and low-carbon fly ash will result in high early strength. Sometimes, additional lime, an accelerator or a superplasticizer will be needed. Fly ash also can be mixed with a small amount of condensed silica fume (CSF) to improve set or early-strength properties. Certainly, careful attention to the mix design and water content is always necessary to obtain proper set and early strength development. Precasters should try to obtain fly ash with as high a silica content as possible. Silica reacts with lime from cement to produce strength and reduce permeability (class F fly ash should have 50 percent silica content; class C should have 35 percent silica content). Ask that the water requirement be less than the control, that the color, density and fineness have a minimum variation (<5 percent) and that the strength activity index at 3, 7 and 28 days be 90 percent of the control. If protection from the alkali aggregate reaction is needed, then the fly ash should be tested in ASTM C 441 with 25 percent of the cement replaced with the fly ash. Some class C fly ash will not protect against the alkali-aggregate reaction. Lastly, it is important for the precast concrete producer to test the mix design continually, because fly ash is a group of materials that comes from burning coal. : Using Fly Ash in Concrete

What is Class C flyash?

Class C Fly Ash CLASS C FLY ASH Composition Class C fly ash is designated in ASTM C 618 and originates from subbituminous and lignite coals. Its composition consists mainly of calcium, alumina, and silica with a lower loss on ignition (LOI) than Class F fly ash. Additional chemical properties are listed in Table 1.

Table 1. Class C fly ash Chemical Composition
Property	Requirements (ASTM C618), %
SiO 2 plus Al 2 O 3 plus Fe 2 O 3, min	50
SO 3, max	5
Moisture content, max	3
Loss on Ignition, max	6

Replacement

When used in portland cement, Class C fly ash can be used as a portland cement replacement ranging from 20-35% of the mass of cementitious material. Advantages When used as a portland cement replacement, Class C fly ash offers the following advantages when compared to unmodified portland cement:

Increased early and late compressive strengths Increased resistance to alkali silica reaction (ASR) when >15% is added Less heat generation during hydration Increased pore refinement Decreased permeability Decreased water demand Increased workability Decreased cost ($80/ton for portland cement vs. $30/ton for fly ash).

Cautions When using Class C fly ash as a portland cement replacement, it is important to know several precautions. The time of set may be slightly delayed. Also, the fine aggregate fraction of the concrete will need to be modified because fly ash has a lower bulk specific gravity than does portland cement and therefore occupies more volume for the same mass.

1. Class C fly ash must replace at least 25% of the portland cement to mitigate the effects of alkali silica reaction.
2. If using any organic admixtures such as air entrainment, the amount added must be modified since the carbon (LOI) in the fly ash adsorbs organic compounds.
3. Finally, if the fly ash has a high calcium content, it should not be used in sulfate exposure applications.

When using this or any other alternative cementing material with portland cement, it is necessary to create trial mixtures to ensure proper proportioning for the desired properties. : Class C Fly Ash

How many types of flyash are there?

Two classes of fly ash are defined in ASTM C618: 1) Class F fly ash, and 2) Class C fly ash.

What are the two classes of flyash?

When used as a mineral admixture in concrete, fly ash is classified as either Class C or Class F ash based on its chemical composition.

Which is Better Class C or Class F fly ash?

Class C and Class F fly ashes reduced compressive and flexural strengths of concrete mixture at early ages. Compared to Class C fly ash, Class F fly ash and concrete with higher ash contents produced more pronounced reductions. Both types of ash showed a decrease in the rate of strength gain.

What color is fly ash?

William Hime Sometimes color provides an esthetic emotion like the specialty “warm tone” portland cements of some years ago and today’s proprietary colored mortar cements. Today, there are pigments of all sorts—mineral and chemical—and colored concrete is becoming more popular.

• Such is the case with a bank building where, anchored at each concrete floor level, are rectangular granite units laid end to end.
• The granite is splotched with olive-colored minerals so at a distance it looks like dollar bills end to end girdling each floor—a delight to its bank firm owner.
• Most of the time color variances are ignored, and some are even desired.

But sometimes they are so frustrating, resulting in litigation. Bernard Erlin How about a brick-masonry building where mortar joint color is embarrassingly different than an approved mock-up; a pink concrete abutment face, a surprise when forms were removed; driveway and floor slab surfaces mottled various shades of gray; unacceptable variegated greenish-blue concrete flatwork surfaces; concrete block walls spotted with various gray shades and deemed an architectural dilemma.

1. You can probably add to the list, however, the causes for these usually are explainable.
2. Portland cement and fly ash are fine powders and act like pigments—a good portion of the particles are in the submicron size range.
3. Portland cement’s ferrite mineral phase (C4AF, brownmillerite) can be light brown, amber, deep brown, reddish brown, greenish brown, or almost black.

Its dicalcium silicate mineral phase (C2S, belite) can be colorless, olive green, green, orange, light brown, medium brown, and deep brown. Its tricalcium silicate mineral phase (C3S, alite), although usually colorless, can sometimes have a gray overtone.

1. White portland cements usually have a distinct green, brown, or blue overtone that sometimes make their manufacturing sources traceable.
2. Fly ash is also a fine powder and, like portland cement, has different intrinsic particle colors that vary from gray, brown, green, olive, yellow, amber, red, to yellow brown.

Aggregate fines are a pigment. Their effects on color vary depending upon color and concentration. Hydration changes things, particularly when using admixtures. For example, the light yellow tone masonry mock-up joints versus the deeper yellow tone building joints resulted because calcium chloride, although not permitted by specification, was used in the building’s jointing mortar.

The different gray concrete block variations resulted because of variable amounts of fly ash contamination, proved with petrographic proof. This point was later acknowledged by the block manufacturer who blamed poor fly ash storage control at his block manufacturing plant, an admission that ended a trial (that should never have started).

The pink concrete surface resulted because of a phenolic-based coating on wood forms. The upgrade was unappreciated until its nonadverse cause was diagnosed and the concrete’s future projected. As anticipated, the upgrade was temporary; the gray soon returned when the surface carbonated with no adverse effects.

The phenolic coating was like applying phenolphthalein, an indicator of carbonation, to the surface. Phenolphthalein turns uncarbonated paste variable shades of pink. The greenish-blue flatwork surface, as could best be determined, was due to trace amounts of chrome in the portland cement. The mottled gray flatwork surfaces resulted because of restricted hydration of the portland cement’s ferrite phase, a result of finishing manipulations that squeezed water from the immediate concrete surface region, thus resulting in a darker gray color.

Concrete made with portland cement manufactured using iron slag as a component of its raw feed, and concrete made using ground granulated blast-furnace, initially will result in dark bluish-green paste. With time, the color will change to a warm-tone brown that results when an iron sulfide component oxidizes.

Color variations can be related to variable fine porosities of portland cement paste. Such porosity varies with water-cement or water-cementitious materials ratios. For example, light impinging on paste is either absorbed or diffracted depending upon the paste’s pore size. If that size is smaller than the wavelength of impinging light, the light will be absorbed and surfaces will appear dark.

On the other hand, if the pore size is larger than the wavelength of impinging light, the light rays bounce (or diffract) between surfaces; some will be directed away from the surface and the surface will appear light. That’s why wet concrete is darker than dry concrete.

Let it dry, it loses its optical continuity and becomes lighter. Aside from purposeful chemical and mineral pigment additions, concrete color can be influenced by: color intrinsic to cementitious materials; hydration effects on cement and fly ash minerals; chemical admixtures; water-cement and cementitious materials ratios; aggregate fines; and finishing manipulations.

William Hime is a principal with Wiss, Janney, Elstner Associates and began working as a chemist at PCA over 54 years ago. Bernard Erlin is president of The Erlin Co. (TEC), Latrobe, Pa., and has been involved with all aspects of concrete for over 48 years.

What are the fly ash requirements?

Fly Ash Properties – Fineness. The fineness of fly ash is important because it affects the rate of pozzolanic activity and the workability of the concrete. Specifications require a minimum of 66 percent passing the 0.044 mm (No.325) sieve. Specific gravity.

1. Although specific gravity does not directly affect concrete quality, it has value in identifying changes in other fly ash characteristics.
2. It should be checked regularly as a quality control measure, and correlated to other characteristics of fly ash that may be fluctuating.
3. Chemical composition.
4. The reactive aluminosilicate and calcium aluminosilicate components of fly ash are routinely represented in their oxide nomenclatures such as silicon dioxide, aluminum oxide and calcium oxide.

The variability of the chemical composition is checked regularly as a quality control measure. The aluminosilicate components react with calcium hydroxide to produce additional cementitious materials. Fly ashes tend to contribute to concrete strength at a faster rate when these components are present in finer fractions of the fly ash.

1. Sulfur trioxide content is limited to five percent, as greater amounts have been shown to increase mortar bar expansion.
2. Available alkalis in most ashes are less than the specification limit of 1.5 percent.
3. Contents greater than this may contribute to alkali-aggregate expansion problems.
4. Carbon content.

LOI is a measurement of unburned carbon remaining in the ash. It can range up to five percent per AASHTO and six percent per ASTM. The unburned carbon can absorb air entraining admixtures (AEAs) and increase water requirements. Also, some of the carbon in fly ash may be encapsulated in glass or otherwise be less active and, therefore, not affect the mix.

How do you activate fly ash?

Conclusions –

1. 1. Chemical compounds, Na 2 SO 4 and Ca(OH) 2, can activate fly ash–cement mixture. It is evidenced, compared to non-activated fly ash–cement blend, by: shortening of induction period and intensification of period related to precipitation of C–S–H, increasing total heat released after 48 h of hydration, higher amount of bound water, reduction of Ca(OH) 2 and quicker precipitation of hydrated products resulting from faster development of pozzolanic activity.
2. 2. Ettringite is one of the hydration products, formed in higher amount in chemically activated mix as an effect of introduction of sulfate.
3. 3. Chemical activators accelerate cement hydration and enhance reactivity of fly ash grains. In activated fly ash–cement binder, synergic effect takes place.
4. 4. In early hydration hours, the presence of cement is mainly responsible for activating effect of fly ash–cement mixture. During 24 h of hydration, fly ash starts to react.
5. 5. Two kinds of Ca(OH) 2 can be present in activated fly ash–cement system: hydroxide introduced as component of activating mixture and the one precipitated as cement hydration product.
6. 6. The knowledge about kinetics of chemical and physical processes of hydration/activation and products that are formed is key factor to develop new more ecological binders which could replace cement in the future. Results of investigation on other ways of activation of such systems (i.e., very high volume fly ash mixtures) will be discussed in next works.

Does fly ash react with water?

Introduction – The use of fly ash in portland cement concrete (PCC) has many benefits and improves concrete performance in both the fresh and hardened state. Fly ash use in concrete improves the workability of plastic concrete, and the strength and durability of hardened concrete.

Improved workability. The spherical shaped particles of fly ash act as miniature ball bearings within the concrete mix, thus providing a lubricant effect. This same effect also improves concrete pumpability by reducing frictional losses during the pumping process and flat work finishability. Figure 3-1: Fly ash improves workability for pavement concrete. Decreased water demand. The replacement of cement by fly ash reduces the water demand for a given slump. When fly ash is used at about 20 percent of the total cementitious, water demand is reduced by approximately 10 percent. Higher fly ash contents will yield higher water reductions. The decreased water demand has little or no effect on drying shrinkage/cracking. Some fly ash is known to reduce drying shrinkage in certain situations. Reduced heat of hydration. Replacing cement with the same amount of fly ash can reduce the heat of hydration of concrete. This reduction in the heat of hydration does not sacrifice long-term strength gain or durability. The reduced heat of hydration lessens heat rise problems in mass concrete placements.

Benefits to Hardened Concrete. One of the primary benefits of fly ash is its reaction with available lime and alkali in concrete, producing additional cementitious compounds. The following equations illustrate the pozzolanic reaction of fly ash with lime to produce additional calcium silicate hydrate (C-S-H) binder:

	(hydration)
Cement Reaction:	C 3 S +	H → C-S-H + CaOH
Pozzolanic Reaction:	CaOH +	S → C-S-H
	silica from ash constituents

ul> Increased ultimate strength. The additional binder produced by the fly ash reaction with available lime allows fly ash concrete to continue to gain strength over time. Mixtures designed to produce equivalent strength at early ages (less than 90 days) will ultimately exceed the strength of straight cement concrete mixes (see Figure 3-2).

Figure 3-2: Typical strength gain of fly ash concrete.

Reduced permeability. The decrease in water content combined with the production of additional cementitious compounds reduces the pore interconnectivity of concrete, thus decreasing permeability. The reduced permeability results in improved long-term durability and resistance to various forms of deterioration (see Figure 3-3)

Figure 3-3: Permeability of fly ash concrete.

Improved durability. The decrease in free lime and the resulting increase in cementitious compounds, combined with the reduction in permeability enhance concrete durability. This affords several benefits:

Improved resistance to ASR. Fly ash reacts with available alkali in the concrete, which makes them less available to react with certain silica minerals contained in the aggregates. Improved resistance to sulfate attack. Fly ash induces three phenomena that improve sulfate resistance:

Fly ash consumes the free lime making it unavailable to react with sulfate The reduced permeability prevents sulfate penetration into the concrete Replacement of cement reduces the amount of reactive aluminates available

Improved resistance to corrosion. The reduction in permeability increases the resistance to corrosion.

Figure 3-4: Fly ash concrete is used in severe exposure applications such as the decks and piers of Tampa Bay’s Sunshine Skyway Bridge.

What color is fly ash in concrete?

William Hime Sometimes color provides an esthetic emotion like the specialty “warm tone” portland cements of some years ago and today’s proprietary colored mortar cements. Today, there are pigments of all sorts—mineral and chemical—and colored concrete is becoming more popular.

• Such is the case with a bank building where, anchored at each concrete floor level, are rectangular granite units laid end to end.
• The granite is splotched with olive-colored minerals so at a distance it looks like dollar bills end to end girdling each floor—a delight to its bank firm owner.
• Most of the time color variances are ignored, and some are even desired.

But sometimes they are so frustrating, resulting in litigation. Bernard Erlin How about a brick-masonry building where mortar joint color is embarrassingly different than an approved mock-up; a pink concrete abutment face, a surprise when forms were removed; driveway and floor slab surfaces mottled various shades of gray; unacceptable variegated greenish-blue concrete flatwork surfaces; concrete block walls spotted with various gray shades and deemed an architectural dilemma.

1. You can probably add to the list, however, the causes for these usually are explainable.
2. Portland cement and fly ash are fine powders and act like pigments—a good portion of the particles are in the submicron size range.
3. Portland cement’s ferrite mineral phase (C4AF, brownmillerite) can be light brown, amber, deep brown, reddish brown, greenish brown, or almost black.

Its dicalcium silicate mineral phase (C2S, belite) can be colorless, olive green, green, orange, light brown, medium brown, and deep brown. Its tricalcium silicate mineral phase (C3S, alite), although usually colorless, can sometimes have a gray overtone.

White portland cements usually have a distinct green, brown, or blue overtone that sometimes make their manufacturing sources traceable. Fly ash is also a fine powder and, like portland cement, has different intrinsic particle colors that vary from gray, brown, green, olive, yellow, amber, red, to yellow brown.

Aggregate fines are a pigment. Their effects on color vary depending upon color and concentration. Hydration changes things, particularly when using admixtures. For example, the light yellow tone masonry mock-up joints versus the deeper yellow tone building joints resulted because calcium chloride, although not permitted by specification, was used in the building’s jointing mortar.

1. The different gray concrete block variations resulted because of variable amounts of fly ash contamination, proved with petrographic proof.
2. This point was later acknowledged by the block manufacturer who blamed poor fly ash storage control at his block manufacturing plant, an admission that ended a trial (that should never have started).

The pink concrete surface resulted because of a phenolic-based coating on wood forms. The upgrade was unappreciated until its nonadverse cause was diagnosed and the concrete’s future projected. As anticipated, the upgrade was temporary; the gray soon returned when the surface carbonated with no adverse effects.

1. The phenolic coating was like applying phenolphthalein, an indicator of carbonation, to the surface.
2. Phenolphthalein turns uncarbonated paste variable shades of pink.
3. The greenish-blue flatwork surface, as could best be determined, was due to trace amounts of chrome in the portland cement.
4. The mottled gray flatwork surfaces resulted because of restricted hydration of the portland cement’s ferrite phase, a result of finishing manipulations that squeezed water from the immediate concrete surface region, thus resulting in a darker gray color.

Concrete made with portland cement manufactured using iron slag as a component of its raw feed, and concrete made using ground granulated blast-furnace, initially will result in dark bluish-green paste. With time, the color will change to a warm-tone brown that results when an iron sulfide component oxidizes.

1. Color variations can be related to variable fine porosities of portland cement paste.
2. Such porosity varies with water-cement or water-cementitious materials ratios.
3. For example, light impinging on paste is either absorbed or diffracted depending upon the paste’s pore size.
4. If that size is smaller than the wavelength of impinging light, the light will be absorbed and surfaces will appear dark.

On the other hand, if the pore size is larger than the wavelength of impinging light, the light rays bounce (or diffract) between surfaces; some will be directed away from the surface and the surface will appear light. That’s why wet concrete is darker than dry concrete.

Let it dry, it loses its optical continuity and becomes lighter. Aside from purposeful chemical and mineral pigment additions, concrete color can be influenced by: color intrinsic to cementitious materials; hydration effects on cement and fly ash minerals; chemical admixtures; water-cement and cementitious materials ratios; aggregate fines; and finishing manipulations.

William Hime is a principal with Wiss, Janney, Elstner Associates and began working as a chemist at PCA over 54 years ago. Bernard Erlin is president of The Erlin Co. (TEC), Latrobe, Pa., and has been involved with all aspects of concrete for over 48 years.

What happens if you inhale fly ash?

Coal ash can contain particulates (a mixture of solid particles and liquid droplets found in the air), volatile and semi-volatile organic compounds, and heavy metals. These chemical compounds can cause skin irritation (dermatitis). Inhalation (breathing in) of these compounds can cause respiratory irritation and irritation of the eyes, nose, and throat.

Ingestion (eating or swallowing) of these compounds can cause nausea, vomiting, and diarrhea. Some of the compounds found in coal ash can cause cancer after continued long-term ingestion and inhalation. When a natural disaster occurs, contamination from coal ash can affect drinking water systems. Public water systems monitor and control for these types of contaminants.

Private well owners should contact their local public health authority to find out if they should test their wells for these contaminants. Coal ash is produced mainly from burning coal in coal-fired power plants. Two main by-products of coal ash combustion (the process of burning it) result from coal-fired operations:

Fly ash is a very fine, powdery residue from coal-fired plants (like factories). Fly ash is captured in the stack. Onsite coal ash ponds should mainly consist of fly ash, which is made up of heavy metals (for example, mercury, arsenic, copper, and chromium ). Fly ash may pose an inhalation hazard when dry. Dry fly ash can cause respiratory irritation similar to flu-like symptoms. Bottom ash is a heavier, coarse material captured at the bottom of the coal furnace. Bottom ash can contain cresol and semivolatile organic compounds such as polycyclic aromatic hydrocarbons, Bottom ash is unlikely to be in coal ash ponds because it is typically disposed of immediately after combustion and sent to a landfill.

The U.S. Environmental Protection Agency regulates coal ash under the Resource Conservation and Recovery Act external icon (RCRA) and the Clean Water Act. RCRA regulates management of hazardous and nonhazardous solid waste in the United States. To learn more about coal ash and how EPA regulates it, visit here: https://www.epa.gov/coalash/coal-ash-basics external icon For resources for Emergency Responders, visit: https://www.atsdr.cdc.gov/substances/ToxEmergency.asp For more about Emergency Response and Preparedness, visit: https://www.cdc.gov/nceh/emergency.htm