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REPLACEMENT OF FINE AGGREGATE

BY BOTTOM ASH IN CONCRETE

B Archana1* and C Porchejian1

1 Department of Civil Engineering, PRIST University Pondicherry, India.

*Corresponding author:B Archana � archana.civil11@gmail.com

ISSN 2319 – 6009 www.ijscer.com

Vol. 3, No. 2, May 2014

© 2014 IJSCER. All Rights Reserved

Int. J. Struct. & Civil Engg. Res. 2014

Research Paper

INTRODUCTION

Concrete is a material synonymous withstrength and longevity. It has emerged as thedominant construction material for theinfrastructure needs of the twenty-first century.In addition to being durable, concrete is easilyprepared and fabricated from readily availableconstituents and is therefore widely used in alltypes of structural systems. The challenge forthe civil engineering community in the near

future is to realize projects in harmony with theconcept of sustainable development and thisinvolves the use of high performance materialsand products manufactured at reasonable costwith the lowest possible environmental impactenergy is the main backbone of moderncivilization of the world over, and the electricpower from thermal power stations is a majorsource of energy, in the form of electricity. InIndia, over 70% of electricity generated in India,

This project presents the experimental investigations carried out to study the effect of use ofbottom ash (the coarser material, which falls into furnace bottom in modern large thermal powerplants and constitute about 20% of total ash content of the coal fed in the boilers) as a replacementof fine aggregates. Concrete technology can be improved based on three criteria such asdurability, environmental friendliness for the future of concrete industry, cost of materials andconstruction. The solution for this problem is to use or utilize industrial by-products or solidwastes in producing concrete such as Bottom Ash (BA), Fly Ash (FA), slag, waste glass, silicafume, etc. The various strength properties of the concrete consists of compressive strength,flexural strength and splitting tensile strength. The strength development for various percentages(0-50%) replacement of fine aggregates with bottom ash can easily be equated to the strengthdevelopment of normal concrete at various ages. Bottom ash is usually described asheterogeneous particles consisting of magnetic and paramagnetic metals, glass, synthetic andnatural ceramics, minerals and unburned materials. Reduction in negative effects on economicand environmental problems of concrete industry can be achieved by the use of these concretetechnologies to old conventional methods.

Keywords: Effect, Replacement, Bottomash

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is by combustion of fossil fuels, out of whichnearly 61% is produced by coal-fired plants.This results in the production of roughly 100ton of ash. Most of the ash has to be disposedoff either dry, or wet to an open area.

OBJECTIVES OF THE

PRESENT STUDY

The main objectives for this research are:

i. To determine the optimum content of bottomash as a substitute for fine aggregate (sand)in concrete;

ii. To evaluate the mechanical properties(compressive strength) of concretecontaining bottom ash from power plant assand replacement in concrete; and

iii. To study the porosity of concrete containingbottom ash.

SCOPE OF THE PROJECT

To achieve the aim of the project, necessaryand essential on cement, fine aggregate,coarse aggregate, bottom ash and concreteof different mix need to be carried out. Thesetests required to ascertain the variation, in thebehavior of concrete when bottom ash replacesand as fine aggregate, in differentproportions, while keeping the quantities of allthe ingredients in the concrete mix constant,fine aggregate used for this comparative studyare sand as available and bottom ash asavailable.

BOTTOM ASH

Bottom ash is formed when ash adheres ashot particles to the boiler walls, agglomeratesand then falls to the base of the furnace at atemperature around 12000C (Kim et al., 2006).

Hence the term “Bottom Ash” is coarse, withgrain sizes spanning from sand to gravel,granular, incombustible by-product, and solidmineral residue.

Depending on the boiler furnace types, thebottom ash collected is classified into twotypes: dry bottom ash and wet bottom ash(more commonly referred to as boiler slag).The incombustible mineral elements sticktogether until they are heavy enough causesthem to remove from the bottom of the furnaceseither in a wet or dry condition and istransported to handling areas by conveyor orpipe. It is angular in shape and ranges in colorfrom a medium brown or medium grey toalmost black. Bottom ash is much coarser andmore highly fused than fly ash, but has a similarchemical composition to fly ash. It does nothave any cementations properties due to itslarger sizes.

Utilization of Bottom Ash

Disposal in landfills and surface impoundmentsis most commonly used coal combustionresidues management option. However, thereare many alternative uses, such as the use offly ash in cement. The utilization of coalcombustion residues in these productivealternatives has been increasing steadily. Thecumulative coal combustion residuesutilization rate increased from 24.8% in 1995(ACAA, 1998) to 38.1% in 2003 (ACAA,2005a) as markets for coal combustionresidues increased.

Problem Of Coal Ash

The value of coal is absolutely opposite by theenvironmental issues. The negative aspectsof mining operation can lead to confirmations

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among citizen group, government agenciesand the mining industry. The conflicts tend tobe centered on the following issue:

i. Destruction of landscape

ii. Destruction of agriculture and forest lands

iii. Dust

iv. Sedimentation erosion

PROPERTIES OF BOTTOM ASH

Information regarding the physical, chemical,and engineering properties of coal combustionresidues is required before these materialscan be safely effectively utilized. The physicaland engineering properties, in particular, areimportant parameters affecting the behaviorof coal combustion residues in variousengineering applications. Informationconcerning the chemical composition isimportant for addressing the potentialenvironmental impacts associated with coalcombustion residues utilization and disposal.Most of the researchers has accentuated thatbottom ash has quite alterable physical,chemical, and engineering characteristics. Itis not only varying from one plant to another,but also from day to day production within asingle plant over time.

Therefore, these characteristics reported byresearchers just can be taken as referencesand not absolutes. Power plant’s operatingparameters play an important role in thevalidation on the characteristics of bottom ashfrom a given source. As long as it remainsconstant, laboratory data tested on thesebottom ashes can be recognized as valid. It isimportant to insure that the samples obtained

are representative of the entire supply (NationalResearch Council, 2006). There are twodifferent types of bottom ash: dry bottom ashand wet bottom ash (boiler slag). Basically, wetbottom ash tends to have more regularcharacteristics than dry bottom ash becauseof wet bottom ash is solidified from the moltenslag while dry bottom ash is the straightforwardproduct of flaming process.

MATERIALS AND METHODS

Cement

Portland cement concrete is foremost amongthe construction materials used in civilengineering projects around the world. Thereasons for its often use are varied, but amongthe more important are the economic andwidespread availability of its constituents, itsversatility and adaptability, as evidenced bythe many types of construction in which it isused, and the minimal maintenancerequirements during service (Mindess et al.,2003). Concrete is unique Among majorconstruction materials in that it is generallydesigned specifically for a particular, projectusing locally available materials (Lay, 1990).

Fineness Test

This experiment is carried out to check theproper grinding of cement. The cement whichis produced by an industry is checked for itsquality, that either it is good for certain type ofconstruction or it doesn’t possess that muchstrength. For example, for RCC and otherheavy load bearing structures such as bridgesit is essential that the cement which is beingused in the concrete should have the ability toprovide the required strength, while in the PCCstructures it is not so much critical.

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The ability to provide strength of a certaintype of cement is checked by finding thefineness of that cement, because the finenessof cement is responsible for the rate ofhydration and hence the rate of gain of strengthand also the rate of evolution of heat.

If the cement is fine then greater is itscohesiveness, which is the property, requiredin the concrete because it gives compactnessto the concrete. Usually cement loses 10% ofits strength within one month of itsmanufacturing.

Sieving Method

This method serves only to demonstrate thepresence of coarse cement particles. Thismethod is primarily suited to checking andcontrolling production process. The finenessof cement is measured by sieving it onstandard sieves. The proportion of cement ofwhich the grain sizes are larger than thespecified mesh size is thus determined

Standard Consistency Test

Mix about 25% water by weight of dry cementthoroughly to get a cement paste. Total timeTake 400 g of cement and place it in theenameled tray taken to obtain thoroughly mixedwater cement paste, i.e., “Gauging time”should not be more than 3 to 5 min. Fill thevicatmould, resting upon a glass plate, with thiscement paste. After filling the mould completely,smoothen the surface of the paste, making itlevel with top of the mould. Place the wholeassembly (i.e., mould + cement paste + glassplate) under the rod bearing plunger. Lowerthe plunger gently so as to touch the surface ofthe test block and quickly release the plungerallowing it to sink into the paste. Measure thedepth of penetration and record it.

Prepare trial paste with varyingpercentages of water content and follow thesteps as described above, until the depth ofpenetration becomes 33 to 35 mm.

Normal consistency of cement = 33%

Setting Time Test

We need to calculate the initial and final settingtime as per IS: 4031 (Part 5) – 1988. To doso, we need Vicat apparatus conforming toIS: 5513 – 1976, Balance, whose permissiblevariation at a load of 1000 g should be +1.0 g,Gauging trowel conforming to IS: 10086 –1982.

i) Prepare a cement paste by gauging thecement with 0.85 times the water requiredto give a paste of standard consistency.

ii) Start a stop-watch, the moment water isadded to the cement.

iii)Fill the Vicatmould completely with thecement paste gauged as above, the mouldresting on a nonporous plate and smoothoff the surface of the paste making it levelwith the top of the mould. The cement blockthus prepared in the mould is the test block.

Initial Setting Time

Place the test block under the rod bearing theneedle. Lower the needle gently in order tomake contact with the surface of the cementpaste and release quickly, allowing it topenetrate the test block. Repeat the proceduretill the needle fails to pierce the test block to apoint 5.0 ± 0.5 mm measured from the bottomof the mould. The time period elapsing betweenthe time, water is added to the cement and thetime, the needle fails to pierce the test block by5.0 ± 0.5 mm measured from the bottom of themould, is the initial setting time.

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Specific Gravity of Cement

1. Determine and record the weight of theempty clean and dry pycnometer, wp.

2. Place 10 g of a dry soil sample (passedthrough the sieve no. 10) in the pycnometer.Determine and record the weight of thepycnometer containing the dry soil, wps.

3. Add distilled water to fill about half to three-fourth of the pycnometer. Soak the samplefor 10 min.

4. Apply a partial vacuum to the contents for10 min, to remove the entrapped air.

5. Stop the vacuum and carefully remove thevacuum line from pycnometer.

6. Fill the pycnometer with distilled (water tothe mark), clean the exterior surface of thepycnometer with a clean, dry cloth.Determine the weight of the pycnometer andcontents, wb.

7. Empty the pycnometer and clean it. Thenfill it with distilled water only (to the mark).Clean the exterior surface of the pycnometerwith a clean, dry cloth. Determine the weightof the pycnometer and distilled water, wa.

8. Empty the pycnometer and clean it.

Specific gravity of cement = 3.15.

Fine Aggregate

The composition of sand is highly variable,depending on the local rock sources andconditions, but the most common constituentof sand in inland continental settings and non-tropical coastal settings is silica (silicondioxide, or SiO2), usually in the form of quartz.

The second most common type of sand iscalcium carbonate, for example aragonite,

which has mostly been created, over the pasthalf billion years, by various forms of life, likecoraland shellfish. It is, for example, the primaryform of sand apparent in areas where reefshave dominated the ecosystem for millions ofyears like the Caribbean.

In terms of particle size as used bygeologists, sand particles range in diameterfrom 0.0625 mm (or 1D16 mm) to 2 mm. Anindividual particle in this range size is termeda sand grain. Sand grains are between gravel(with particles ranging from 2 mm up to 64 mm)and silt (particles smaller than 0.0625 mmdown to 0.004 mm). The size specificationbetween sand and gravel has remainedconstant for more than a century, but particlediameters as small as 0.02 mm wereconsidered sand under the Albert Atterbergstandard in use during the early 20th century. A1953 engineering standard published by theAmerican Association of State Highway andTransportation Officials set the minimum sandsize at 0.074 mm. A 1938 specification of theUnited States Department of Agriculture was0.05 mm. Sand feels gritty when rubbedbetween the fingers (silt, by comparison, feelslike flour).

Bottom Ash

Bottom ash obtained from thermal power plantat Neyveliin India was used in the investigation.The specific gravity of bottom ash was 1.68.

Physical Properties

Bottom ashes have angular particles with avery porous surface texture. Bottom ashparticles range in size from a fine gravel to afine sand with very low percentages of silt-claysized particles. The ash is usually a well-graded material, although variations in particle

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size distribution may be encountered in ashsamples taken from the same power plant atdifferent times. Bottom ash is predominantlysand-sized, usually with 50 to 90% passing a4.75 mm (No. 4) sieve, 10 to 60% passing a0.42 mm (No. 40) sieve, 0 to 10% passing a0.075 mm (No. 200) sieve, and a top sizeusually ranging from 19 mm (3/4 in) to 38.1mm (1-1/2 in). Table 1 compares the typicalgradations of bottom ash and boiler slag.

the low pH of bottom ash and boiler slag, thesematerials could exhibit corrosive properties.When using bottom ash or boiler slag in anembankment, backfill, sub base, or evenpossibly in a base course, the potential forcorrosion of metal structures that may comein contact with the material is of concern andshould be investigated prior to use.

Tests for Bottom Ash

Sieve Analysis

Sieve analysis (or gradation test) is a practiceor procedure used (commonly used in civilengineering) to assess the particle sizedistribution (also called gradation) of a granularmaterial.

Mix Proportions

Five mixture proportions were made. First wascontrol mix (without bottom ash), and the otherfour mixes contained bottom ash. Fineaggregate (sand) was replaced with bottomash by weight. The proportions of fineaggregate replaced ranged from 20% to 50%.Mix proportions are given in Table . The controlsmix without bottom ash was proportioned asper Indian standard Specifications IS: 10262-1982 to obtain a 28-days cube compressivestrength of 33.3 MPa. Hand mixing was donefor the concrete mixes.

Preparation and Casting of TestSpecimens

The 150 mm concrete cubes were cast forcompressive strength, 150 × 300 mm cylindersfor splitting tensile strength and 101.4 × 101.4× 508 mm beams for flexural strength. Aftercasting, all the test specimens were finishedwith a steel trowel. All the test specimens werestored at temperature of about 30oC in the

Table 1: Physical Property of Bottom Ash

S. No Characteristics Test Result

1 Colour Grey to black in colour

2 Specific gravity 1.68

3 Bulk density 1120kg/m3

4 Fineness modulus 2.73

Chemical Properties

Bottom ash and boiler slag are composedprincipally of silica, alumina, and iron, withsmaller percentages of calcium, magnesium,sulfates, and other compounds. Thecomposition of the bottom ash or boiler slagparticles is controlled primarily by the sourceof the coal and not by the type of furnacepresents a chemical analysis of selectedsamples of bottom ash and boiler slag fromdifferent coal types and different regions.

Bottom ash or boiler slag derived fromlignite or sub-bituminous coals has a higherpercentage of calcium than the bottom ash orboiler slag from anthracite or bituminous coals.Although sulfate is usually very low (less than1.0%), unless pyrites have not been removedfrom the bottom ash or boiler slag.

Due to the salt content and, in some cases,

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casting room. They were demolded after 24h, and were put into a water-curing tank.

RESULTS AND DISCUSSION

The various aspects studied include (i) theeffect of bottom ash on workability(Compaction Factor) of fresh concrete; (ii) theeffect on compressive, flexural and splittingtensile strength using bottom ash in varyingpercentages as a partial replacement of fineaggregates.

Compressive Strength

Compressive strength of concrete mixes madewith and without bottom ash was determinedat 7, 28, 56, 90 days. The test results are givenin Table 1 and Figures 1a and 1b. The gain ofcompressive strength by different types ofbottom ash concrete with respect to theircompressive strength at the age of 90 daysvaries from 56-65% at 7 days 75-85% at 28days and varies between 86-90% at 56 days.The bottom ash concrete gains strength at aslower rate in the initial period and acquiresstrength at Splitting Tensile Strength of theConcrete with age.

CONCLUSION

The workability of concrete decreased with theincrease in bottom ash content due to theincrease in water demand, which isincorporated by increasing the content ofsuperplasticizer. The density of concretedecreased with the increase in bottom ashcontent due to the low specific gravity ofbottom ash as compared to fine aggregates.

Compressive strength, Splitting tensilestrength and Flexural strength of fineaggregates replaced bottom ash concretespecimens were lower than control concretespecimens at all the ages. The strengthdifference between bottom ash concretespecimens and control concrete specimensbecame less distinct after 28 days.

Compressive strength, Splitting tensilestrength and Flexural strength of fine aggregatereplaced bottom ash concrete continue toincrease with age for all the bottom ashcontents. Mix containing 30% and 40% bottomash, at 90 days, attains the compressive

Figure 1: Compressive Strength ofConcrete Mixes Mad with Bottom Ash

Figure 2: Compressive Strength ofConcrete Mixes Mad without Bottom Ash

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strength equivalent to 108% and 105% ofcompressive strength of normal concrete at 28days and attains flexural strength in the rangeof 113-118% at 90 days of flexural strength ofnormal concrete at 28 days. The time requiredto attain the required strength is more forbottom ash concrete.

REFERENCES

1. S M Gupta Civil Engineering Department,National Institute of Technology,Kurukshetra 136119, India.

2. Commercial Applications Of WeEnergies Bottom Ash-CCP Handbook.

3. Effect of Coal Bottom Ash As SandReplacement on the Properties OfConcrete With Different W/C Ratio- M PKadam, Y D Patil2Al-Manaseer.

4. Properties of High-calcium Dry BottomAsh Concrete, ACI Materials Journal,(1997)90-101.

5. Ghafoori N and Yuzheng C (1998),“Laboratory-made Roller CompactedConcretes Containing Dry Bottom Ash:Part II - long term durability”, ACIMaterials Journal, pp. 244-251.

6. Jaturapitakkul C and Cheerarot R (2003),“Development of Bottom Ash AsPozzolanic Material”, Journal OfMaterials In Civil Engineering, Jan-Feb.pp. 48-53.

7. Pera J, Coutaz L, Ambroise J andChababbet M, Use of Incinerator BottomAsh in Concrete.