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Fuel 87 (2008) 1610–1616

Radiological safety aspects of utilizing coal ashes for productionof lightweight concrete

Mark Nisnevich a, Gregory Sirotin a,*, Tuvia Schlesinger b, Ya’akov Eshel a

a Samaria and Jordan Rift R&D Center, Science Park, Ariel 40700, Israelb The College of Judea and Samaria, Science Park, Ariel 40700, Israel

Received 25 March 2007; received in revised form 26 July 2007; accepted 29 July 2007Available online 22 August 2007

Abstract

The present paper reports the results of experiments to develop environmentally and economically friendly structural lightweight con-cretes utilizing coal ashes and other waste materials. The product complies with national and international regulations setting limits onthe activity concentration of natural radioisotopes in building products. The utilization of coal ashes in the building industry carries (inaddition to its economic advantages) a fringe environmental benefit. This utilization reduces the potential damage to the environmentcaused by the radioactivity in the combustion by-products (the ashes) stored in piles and ponds near the power stations prior to theirdisposal. The study deals with the radiological characteristics of coal ashes and lightweight concretes based on these ashes. The ashesare generated at Israel’s power stations from coal supplied from different sources in South Africa, Columbia and Indonesia.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Activity concentration index; Bottom ash; Fly ash; Lightweight concrete; Radioactivity

1. Introduction

The utilization of coal ashes in the building industry haseconomic and environmental advantages. The economicadvantages include: the exploitation of non expensivewaste materials in civil engineering; the reduction of theamount of ashes that have to be disposed; the possibilityto channel coal combustion by-products to the consumermarket. The environmental advantage is: incorporatingof the ashes in solid material (concrete and other buildingproducts) lowering the potential environmental hazard(radioactive air and water pollution) associated with pilesand ponds of ashes stored near the power stations priorto their disposal. Therefore this utilization improves signif-icantly the economic and environmental characteristics ofpower engineering. The incorporation of raw materialscontaining enhanced concentration of natural radioactivity(such as coal ashes) in the consumer products is subject to

0016-2361/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.fuel.2007.07.031

* Corresponding author. Tel./fax: +972 3 936 6834.E-mail address: siroting@yosh.ac.il (G. Sirotin).

legal control due to the inherent potential risk of exposingmembers of the public to ionizing radiation originated inthe product. One of the efficient ways to utilize coal ashesfor production of consumer products with an allowablelevel of radioactivity is their use in the concrete industry.This paper considers the results of research and develop-ment of environmentally friendly lightweight concretebased on large quantities of bottom ash and fly ash. Theresearch is distinguished from our earlier studies relatedto this problem. Firstly, it is based on data collected duringsystematic and continuous sampling and testing of fly ashand bottom ash produced in Israel’s power stations. Theseutilize coals being supplied from sources located in SouthAfrica, South America (Columbia) and Indonesia. Thisstudy supplies therefore more comprehensive data on thevariability of the radiological characteristics of coal ashes,especially those of bottom ash. Secondly, in addition to thedata on the radioactivity of the coal ashes, we report theresults of studying the radioactivity of lightweight con-cretes based on combined use of two types of coal ashes:bottom ash and fly ash. Thirdly, the methods used for

M. Nisnevich et al. / Fuel 87 (2008) 1610–1616 1611

controlling and lowering the radioactivity in concrete ele-ments (structures) developed in this study are alsoreported. Based on these methods, the radioactivity con-tent expected in concrete elements (structures) containingcoal ashes from different sources can be predicted. Thesepredictions were confirmed by actual laboratory and fieldmeasurements. The evaluation of radioactivity in coalashes supplied to the building industry enables the predic-tion of the radioactivity in the building elements (struc-tures) based on these ashes. This has a potential for: (i)the optimal implementation of ashes in concrete technol-ogy; (ii) broadening the market of coal ashes for use inthe high performance lightweight concrete; (iii) productionof environmentally friendly lightweight concrete based oncoal ashes while complying with radiation safetyregulations.

2. Radiological aspects of generation, storage, and utilization

of coal ashes

The amount of coal ashes accumulated at power stationsis consistently increasing and posing a significant hazard tothe environment. Fly ash and bottom ash, by-products ofcoal combustion, contain enhanced concentration of thenatural radionuclides 40K, 238U and 232Th and their decayproducts (the level of 238U is usually estimated by the pres-ence of 226Ra) [1]. In addition, the short lived daughtersproduct of 226Ra radioisotope 222Rn (radon gas) must beconsidered. These radionuclides emit alpha particles, betaparticles, and gamma rays, and are therefore a source ofionizing radiation. Exposure to such radiation is consid-ered to pose a hazard to human health. Building productsbased on coal ashes are classified by the relevant EuropeanCommission Directorate for Radiation Protection as mate-rials with enhanced radioactivity [2].

Accumulation of coal ashes stored in piles and pondscan lead to the exposure of the public to ionizing radiationvia the following pathways: (i) external exposure of localworker to gamma radiation; (ii) internal exposure of therespiratory tract due to inhalation of radon gas and itsdecay products; (iii) internal exposure due to inhalationand/or ingestion of coal ash dust particles.

Inhalation of radon gas and fine particles of coal ash isthe main route of internal exposure to fly ash. Meij [3]notes that inhalable particles include fly ash particles pass-ing through a 400 mesh (38 lm) sieve. Fly ash complyingwith the requirement set by ASTM C618-05 [4] comprisesmore than 55% of such particles. The amount of fine respi-rable particles in the ash is significantly lower (above 5%).However, these particles are capable of penetrating lungalveoli and they stay in the respiratory tract for a long per-iod of time.

Internal radiation caused by the inhalation of radon gasand radioactive fly ash dust is regarded as a significanthealth hazard because most of the related exposure is dueto high linear energy transfer (LET) alpha particles emittedby 226Ra and 222Rn and by its short lived decay products

such as 218Po and 214Po. 232Th also forms alpha emittingradioactive decay products.

Taking into account the radiological characteristics ofcoal ashes as described above, the requirements for coalash utilization must include lowering its environmentalhazard. For this goal, the following measures can beapplied: (i) limiting the amount and the exposure time ofcoal ash piles to the open environment; (ii) avoiding thespread of coal ash into water, soil, and air pathways; (iii)control of the activity concentration of radionuclides inconsumer products based on coal ashes.

One of the effective ways to utilize coal ash while com-plying with these requirements is to use them in the build-ing industry, i.e. in the production of building materials,predominantly concrete. The advantages of this utilizationare:

(i) The possibility to control the concentration of radio-nuclides in the building products (elements and struc-tures) and lowering it to level below the limitationsset by international recommendations and/ornational legislations.

(ii) Bonding the fine particles of coal ashes with cementin the concrete, eliminating their spread in waterand air and lowering the radon emanation. (It shouldbe noted that utilization of coal ashes in structuralfills and beddings of roads and buildings does notexclude totally their spread in water and air).

3. Utilizing coal ashes for the production of lightweight

concrete

A novel technology of combined utilization of highvolumes of both coal ashes – bottom ash and fly ash –for lightweight concrete production was developed atThe College of Judea and Samaria (Ariel, Israel) [5–7].Characteristics of the lightweight concrete produced andthe bottom ash and fly ash used for this production aredescribed below. Among other variables, we studied theradiological characteristics of the coal ashes. The aimof our study was the production of environmentallyfriendly concrete based on coal ashes with enhancedradioactivity.

3.1. Radiological characteristics of coal ashes used inexperiments

3.1.1. Samples of coal ashes

Samples of fly ash and bottom ash were taken from theproducts of combustion of coals from the main sourcessupplied to Israel (South Africa, Columbia, and Indone-sia). Table 1 presents data on the chemical analysis of thecoals. For sampling, one of Israel’s power stations with apulverized dry-bottom boiler was selected. The coal ashesfrom the different coals were produced using the same coalcombustion and transport of coal ash techniques.

Table 1Chemical analysis of coal samples

Chemicalcomposition,%

Source of coal

SouthAfrica-12005

SouthAfrica-22005

SouthAfrica-32005

Columbia-1 2005

Indonesia-1 2005

Ash 14.50 13.80 15.00 8.73 4.20Volatile

matter28.60 28.60 28.20 37.82 44.20

Carbon 72.40 72.40 71.80 74.19 76.07Hydrogen 4.11 4.37 3.84 5.13 5.35Nitrogen 1.78 1.70 1.67 1.46 1.70Sulfur 0.19 0.68 0.06 0.15 0.64Chlorine 0.04 0.04 0.03 0.03 0.10Oxygen 6.56 6.75 7.11 9.97 12.28

Note. The table is complied using data obtained from the laboratory ofThe Israel Electric Corporation.

1612 M. Nisnevich et al. / Fuel 87 (2008) 1610–1616

Fly ash was conveyed to a silo and supplied to custom-ers in dry condition; therefore fly ash samples were not pro-cessed before testing. Bottom ash was conveyedhydraulically to the storehouse; accordingly, its moisturecontent reached 50% and above. Wet samples of bottomash were dried to a constant mass for laboratory testsand to a water content equal to the level of water absorp-tion for field tests. Our earlier study established that the drysurface of the bottom ash particles prevents formation ofcement lumps [8]. Cement lumps forming on the wet sur-face of bottom ash particles lowers the concrete strength.All samples of the fly ash and bottom ash are taken fromthe process streams at the thermal power station.

3.1.2. Fly ash

The chemical analysis of the fly ash samples are pre-sented in Table 2. The samples of fly ash studied met themain requirements of ASTM C618, Class F. The sum ofSiO2 + Al2O3 + Fe2O3 was greater than 80% (standardrequirement of ASTM C618 is min. 70%). The value ofSO3 was 1.70 to 3.46% (standard requirement of ASTM

Table 2Chemical analysis of fly ash samples

Chemicalcomposition,%

Source of the coal

SouthAfrica-12005

SouthAfrica-22005

SouthAfrica-32005

Columbia-1 2005

Indonesia-1 2005

SiO2 46.14 44.00 47.53 60.57 52.46Al2O3 32.28 33.27 31.40 19.89 26.24Fe2O3 4.13 4.30 3.45 8.08 9.75CaO 9.73 10.32 8.20 2.66 2.02MgO 1.98 2.37 1.98 2.36 2.69TiO2 1.67 1.46 1.57 1.01 0.92K2O 0.50 0.52 0.46 2.26 2.18Na2O 0.17 0.26 0.15 0.64 0.26SO3 1.70 2.98 3.46 2.15 2.02P2O5 2.50 2.27 2.48 0.22 0.42

Note. The table is compiled using data obtained from the laboratory ofThe Israel Electric Corporation.

C618 is max. 5%). Loss of ignition of ashes from sourcesin South Africa was about 3% and from sources in Colum-bia and Indonesia about 9% (standard requirement ofASTM C618 is max. 6%). Content of total CaO was 2.02to 10.32%, complying with requirement set by ASTMC618 for fly ash of Class F (max. 10%). It is note thatthe coals with a higher volume of ash (South Africa)formed ashes with higher CaO content (8.20–10.32%) com-pared with CaO content of 2.02–2.66% in the ashes formedfrom the other coals (Columbia and Indonesia). Not morethan 30% of sample particles were retained on the 45 lm(325 meshes) sieve. The standard requirement of ASTMC618 is max. 34%. The specific surface (Blaine) of all sam-ples was at least 380 m2/kg.

Activity concentrations of 226Ra, 232Th, and 40K in flyash sampled in 2005–2006 are presented in Table 3. Eachvalue in the Table 3 is the result of the determination ofthe activity concentration of the relevant radionuclide inthe sample from a given source. The determination of theactivity concentration was performed with 95% confidencelevel related to the statistical counting errors, which arealso presented in Table 3. All radiological measurementsreported in this paper were conducted at the Soreq NuclearResearch Center (Yavneh, Israel). From the table it can beseen that activity concentration values in the fly ash sam-ples in this study have a wide distribution. The variationis both among ashes of coals imported from one country,as well as among ashes produced from coals imported fromdifferent countries.

The variations of activity concentrations values of theradionuclides above as measured in the ashes tested inour experiments were compared with data published inthe worldwide technical literature [2,9–14]. The statisticalanalysis of the most complete data of European Commis-sion Directorate for Radiation Protection [2] revealed thatthe values of activity concentration of 226Ra in the ashesgenerated in 10 European continental countries werereported in the range of 158 ± 62 Bq/kg (95% confidence).

Table 3Activity concentrations of radionuclides 226Ra, 232Th, and 40K in fly ashsamples

Sample Source of coal Activity concentrations, Bq/kg

226Ra 232Th 40K

1 South Africa-1 2005 151 ± 15 125 ± 8 178 ± 252 2006 205 ± 17 193 ± 10 167 ± 193 South Africa-2 2005 213 ± 21 215 ± 12 148 ± 234 South Africa-3 2005 200 ± 17 202 ± 10 204 ± 225 2006 248 ± 21 202 ± 10 163 ± 196 Columbia 2005 107 ± 10 81 ± 5 380 ± 407 2006 94 ± 8 62 ± 3 489 ± 468 Columbia-2 2006 142 ± 13 110 ± 6 175 ± 219 Indonesia-1 2005 150 ± 17 146 ± 10 271 ± 3610 2006 55 ± 5 58 ± 3 488 ± 47

Average 156 ± 13 139 ± 8 266 ± 30

Note. Radiological evaluation was carried out at the Soreq NuclearResearch Center (Israel).

M. Nisnevich et al. / Fuel 87 (2008) 1610–1616 1613

The values of the activity concentration of 226Ra presentedin Table 3 fall within this range, i.e. are similar to the datareported in these countries. Activity concentration of 226Rain coal ashes generated at UK power stations is reported tobe in range 70–150 (predominantly 100–150) Bq/kg, whichis below the mean EU value [9].

3.1.3. Bottom ash

The grading of bottom ash samples was close to themain requirements for fine and combined fine and coarseaggregates. The loose bulk density of the samples (600 to730 kg/m3) met requirements established by ASTM C332[15] (Group II aggregates) and ASTM C330 [16] for light-weight insulating concrete and structural concrete,respectively.

The activity concentrations of radionuclides 226Ra,232Th, and 40K in the samples of bottom ashes tested arepresented in Table 4. These data indicate also as having awide distribution among ashes produced from coal sourceslocated in one country, as well as among ashes producedfrom coal sources located in different countries. Data pre-sented in the technical literature related to the radioactivityof bottom ash in different countries are deficient and thuswe were unable to make a comparison.

3.2. Radiological characteristics of other constituents of the

concrete

3.2.1. Radioactivity of the cement

The activity concentrations of radionuclides in the sam-ple of cement (portland cement close to ASTM C150 [17],Type 1, used in our experiment were: 46 ± 4, Bq/kg,19 ± 0.1 Bq/kg, 94 ± 11 Bq/kg, for 226Ra, 232Th, and40K, respectively. The relatively high activity concentrationof 226Ra in the cement is partly explained by the use of flyash as an additive during cement production (5%), but ismainly due to the use of components with enhanced radio-activity (clay, gypsum, etc.) in the clinker composition.Similar mean results were also obtained by analysis of

Table 4Activity concentrations of radionuclides 226Ra, 232Th, and 40K in bottomash samples

Sample Source of coal Activity concentrations (Bq/kg)

226Ra 232Th 40K

1 South Africa-1 2005 241 ± 26 221 ± 14 146 ± 242 2006 199 ± 16 168 ± 8 155 ± 143 South Africa-2 2005 103 ± 4 104 ± 8 62 ± 124 South Africa-3 2005 160 ± 21 140 ± 11 103 ± 295 2006 242 ± 22 194 ± 11 122 ± 176 Columbia-1 2005 39 ± 6 23 ± 2 199 ± 347 2006 79 ± 6 53 ± 3 348 ± 298 Columbia-2 2006 113 ± 9 76 ± 4 285 ± 249 Indonesia-1 2005 204 ± 23 181 ± 12 135 ± 2610 2006 70 ± 6 77 ± 4 333 ± 31

Average 145 ± 14 139 ± 8 189 ± 24

Note. Radiological evaluation was carried out at the Soreq NuclearResearch Center (Israel).

the data from reference [2] concerning the radioactivity ofcement produced in 12 European countries (226Ra –50 ± 39 Bq/kg). Hence, the activity of the cement contrib-utes to the total radioactivity of the concrete and must betaken into account as an additional source of activitybesides the coal ashes.

3.2.2. Radioactivity of aggregates

Enhanced activity concentrations of radionuclides wasestablished in some types of dense (granite) and porous(tuff, pumice) igneous rocks. Activity concentrations ofradionuclides in sedimentary rocks and natural sand areessentially lower. For example, activity concentration mea-sured the in the dolomite unprocessed crushed sand (UCS)from Israel’s source were 17 ± 1 Bq/kg, 1 ± 0.2 Bq/kg and12 ± 3 Bq/kg, for 226Ra, 232Th, and 40K, respectively.Thus, the evaluation of radioactivity in aggregates for usein concrete in combination with coal ashes is alsonecessary.

3.3. Radiological evaluation of lightweight concretes based

on coal ashes

The examples of technical characteristics of lightweightconcretes containing coal ashes are presented below. Bot-tom ash (BA) as a porous aggregate and fly ash (FA) asan additive to the cement from above Source No. 3 (SouthAfrica – 2) were used as main raw materials for the manu-facture of concretes. Relative specific gravity of fly ash was2.25, specific surface (Blaine) was 385 m2/kg; loose bulkdensity of bottom ash was 600 kg/m3. UCS sample usedas a strengthening and diluting material for lowering radio-activity of the concrete was taken from a local dolomitequarry. Apparent density of UCS was 2.6 g/cm3. Portlandcement (C) close to requirements set by ASTM C150, Type1 was used in experiments (relative specific gravity – 3.15;Blaine – 370 m2/kg; 28-day compressive strength of stan-dard prisms – 41.5 MPa).

The following concrete proportions were used in theexamples below. Cement content was accepted as 335 kg/m3 according to ASTM C330 (this standard was used toevaluate the density and strength of the concrete for struc-tural purposes). The ratio FA/(C + FA) on data of our ear-lier researches was accepted as 0.5 for all concreteproportions. The effect of replacing part of bottom ashwith UCS on properties of the lightweight concrete wasstudied for a UCS/(BA + UCS) ratio range between 0and 1. All concrete mixtures were prepared at a constantconsistence characterized by a Vebe time of 15 s [18].

The technical characteristics of the concretes obtainedwere as follows. The density of specimens was in the range1200–2000 kg/m3, the strength was in the range 10–36 MPa, i.e. the concrete complied with the requirementsset by ASTM C332 for insulating concrete made withGroup II aggregates and with the requirements set by BS206–1 [19] for strength class LC 8/9 and for density classesD 1.2 and D 1.4; and with the requirements set by ASTM

Ratio UCS/(BA+UCS)

100

90

80

70

60

50

40

30 0

226Ra232Th

40KAct

ivity

con

cent

ratio

ns o

f ra

dion

uclid

es, B

q/kg

1.0 0.9 0.80.7 0.60.5 0.40.30.20.1

Δ

Fig. 1. Effect of the ratio UCS/(BA + UCS) on the activity concentrationsof radionuclides 226Ra, 232Th, and 40K in lightweight concrete based oncoal ash.

1614 M. Nisnevich et al. / Fuel 87 (2008) 1610–1616

C330 for structural lightweight concrete with density inrange 1680–1840 kg/m3 (17–28 MPa) and with require-ments set by BS EN 206–1 for strength classes LC 12/13–LC 35/38 and for density classes D1.6–D2. The averagethermal conductivity of the specimens of insulating con-crete was 0.35 W/moK complying with the requirementsset by ASTM C332 for concrete made with Group IIaggregates.

Evaluation of the activity concentrations of the radio-nuclides 226Ra, 232Th, and 40K was made for all lightweightconcrete proportions considered above. To forecast theradioactivity in the concrete, the following data were used:the activity concentrations of radionuclides in samples ofbottom ash and fly ash from source No 3 (South Africa –2), in the cement and UCS described above (3.2), the con-crete proportions, used in the experiments and the densityof the concrete specimens, respectively. The effect of the rel-ative value of UCS which replaced part of BA, expressed asUCS/(BA + UCS), on the activity concentrations of radio-nuclides in the concrete is presented in Fig. 1. The plotillustrates the essential role of the ratio UCS/(BA + UCS)used as a factor of controlling and lowering the radioactiv-ity of the lightweight concrete. The possibility to controlthe radioactivity of concrete by means of proportioningactive and non-active constituents is based on the additivityof the activities in concrete components [20].

4. Radiological safety of lightweight concretes (structures)

based on coal ashes

The radiological safety of building materials (structures)based on coal ashes is ensured by complying with limita-tions set by international recommendations and nationallegislations [21–24]. International recommendations (ICRP1999) permit to choose an effective dose increment con-straint in the range 0.3–1.0 mSv/y for prolonged exposureto natural radiation by a member of the public. The effec-tive dose takes into account, in addition to the energyabsorbed in the body due to exposure to radiation, also

the relative biological harm and the susceptibility to harmof different biological tissues.

Evaluation of the radiological safety of the lightweightconcrete (structure) in our study was performed in viewof Israel’s standard SI 5098 [25] setting limits on the con-centration of natural radioactive element in building prod-ucts. SI 5098 is based on a total annual effective doseincrement of 0.3 mSv/y due to all the routes of exposureto radiation originated in a building product This includesthe dose increment (in top of a reference level) to the resi-dents of a building due to external and internal radiationcaused by using a given novel building material (structure).The reference level was selected as 0.15 mSv/y. This refer-ence dose was estimated as the dose to residents of build-ings caused by the presence of natural radio nuclides inconventional building materials (structures) used in civilengineering in Israel before 1990. The value of 0.3 mSv/yselected for the permitted dose increment corresponds tothe minimum constraint level set by the ICRP on sourcesof prolonged exposure [23]. Thus, the total dose due toradioactivity in building products is limited by SI 5098 to0.45 mSv/y [26].

For practical goals, the evaluation of the compliance ofa specific building material (structure) with the limitationsof international recommendations and/or with the nationalstandards is carried out using activity concentration indexi. This index is expressed in terms of activity concentrationsof three major natural radionuclides: 226Ra, 232Th, and40K:

i ¼ Cð226RaÞAð226RaÞ

þ Cð232ThÞAð232ThÞ

þ Cð40KÞAð40KÞ

ð1Þ

where: C(226Ra), C(232Th) and C(40K) are the activity con-centrations of 226Ra, 232Th and 40K in the building materialtested, respectively; A(226Ra), A(232Th) and A(40K) are thelimiting values set for the activity concentrations of theseradionuclides in the building elements (structure); and i isthe activity concentration index. The activity concentrationlimit A(iX) is the activity concentration value for radionu-clide iX, which, if present in a building article (structure),will cause, on its own, a specified additional annual doseto the residents of a standard building built of these build-ing articles (structures).

To comply with the regulations (based on the annualdose increment constraint of 0.3 mSv/y) the activity con-centration index i, calculated for the product tested, mustcomply with the criterion: i 6 1.

The activity concentrations limits A(iX) depend on thelimit set on the effective dose increment in national legisla-tions. The limiting values set for activity concentrations bystandard SI 5098 are defined for different thickness andeffective density (including pores and hollows) of the build-ing structure, as well for the different radon emanation e.The radon emanation e is defined as the fraction of theradon generated within the building product which escapesfrom the product into the open air (note: half of this

Table 5Characteristics of concrete articles based on coal ashes

Characteristic Masonry units Masonry units Ceiling units

Dimensions, cm 20 · 20 · 40 20 · 20 · 40 20 · 20 · 50Density, kg/m3 845 875 700Activity

concentrations ofthe radionuclidesin the concrete,Bq/kg

226 Ra 101–93 88–93 91–93232Th 81–82 73–78 76–7740K 98–84 84–79 80–72Radon emanation, % 0.5 0.7 1.1Activity

concentrationindex i

0.88 0.87 0.73

M. Nisnevich et al. / Fuel 87 (2008) 1610–1616 1615

amount is assumed to dissipate into the residential livingspace. The rest of the radon remains locked in the productand its decay products is the source of the gamma radiationcausing exposure to the residents of the living space). Theemanation e is calculated from the value of radon exhala-tion E, Bq per m2 s, using equation:

E ¼ e � C � k � d � d ð2Þwhere: C is the activity concentration of 226Ra in the build-ing material, Bq/kg; k is the decay constant of radon(7.6 · 10�3 h�1); d is the density of material, kg/m3; d isthickness of the wall, m.

For determining the annual dose to a resident in a stan-dard room constructed of given building materials (struc-tures), theoretical models and computer code weredeveloped [27]. The code takes into account the gammaradiation and radon exhalation. Thus, the standard SI5098 provides an estimation of fitness of the concrete(structure) based on coal ash to the civil engineeringrequirements.

An example of examining the potential compliance ofspecific building product with the requirements of SI5098 in the stage of designing its constituents is presentedin Fig. 2. The diagram in the figure presents the predictedvalue of the activity concentration index i for hollowmasonry units designed to be produced with fly ash andbottom ash from 10 different sources. For the calculationswe used the activity concentration of 226Ra, 232Th, and 40Kin these ashes as presented in Tables 3 and 4 for fly ash andbottom ash, respectively. The activity concentration valueswe assumed for the other constituents of the concrete(cement, aggregates, etc) are presented in 3.2 above. Theconcrete constituents assumed for all designed masonryunits were (kg/m3): cement – 300, fly ash – 300, bottomash – 600, unprocessed crushed sand – 300. The densityof hardened concrete (including the water for hydrationof the cement) was designed to be 1600 kg/m3. Themasonry units were designed to be hollow with uniformdimensions and shape (dimensions 200 · 200 · 400 mm,concrete content in units – 59%). The emanation of radone was assumed to be 0.01(1%).

Sam

ples

of

coal

ash

es

from

Tab

les1

and

2

Activity concentration index i

10 9

8 7 6 5 4

3 2

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.8 1.0 1.1 1.2 1.3

Fig. 2. Diagram of predicted activity concentration index i for masonryunits with different coal ashes.

The example illustrates a possibility to forecast theradioactivity of the concrete elements (structures) if theradioactivity of coal ashes and other constituents used,the concrete proportion and the characteristic of buildingelements (structures) are known. This example illustratesthat lightweight concrete based on coal ashes and non-active aggregate additive such as unprocessed crushed sandhas a potential for mass production. However to ensurecompliance with radiation safety requirements for the useof high percentages of coal ash in the production of light-weight concrete, a careful preliminary radiological evalua-tion of the ashes and other constituents is required.

5. Example of industrial production of ecologically friendly

lightweight concrete based on coal ashes and unprocessed

crushed sand

The example below demonstrates the efficiency of usingcoal ash with enhanced radioactivity for industrial produc-tion of hollow lightweight masonry units and ceiling unitscomplying with standard SI 5098 (Table 5). For this indus-trial production, coal ashes from the source South Africa-2above (Tables 3 and 4, respectively) and unprocessedcrushed sand from the source above (3.2) were used. Coalashes content in the concrete reached 55%. Data of activityconcentrations of 226Ra, 232Th, and 40K in the concreteused for producing the masonry and ceiling units, valuesof radon emanation e from the masonry and ceiling units,and values of activity concentration index i according tostandard SI 5098, are presented in Table 5.

The results confirm a potential for industrial use of thelightweight concrete for effective utilization of coal ashes.

6. Conclusion

The production of environmentally friendly lightweightconcretes based on the combined use of the bottom ashand fly ash, classified as materials with enhanced radioac-tivity, and non-active aggregate such as by-products fromstone quarries, has potential for utilization of coal ashes.The main advantages of the suggested technology are:

1616 M. Nisnevich et al. / Fuel 87 (2008) 1610–1616

1. Increasing the amounts of both fly ash and bottom ashutilized in the production of high-performance light-weight thermal insulating, thermal insulating/structural,and structural concretes.

2. Broadening the coal ash market and lowering the con-sumption of natural and artificial lightweightaggregates.

3. Production of environmentally friendly lightweight con-crete elements (structures).

4. Improving the environmental characteristics of powerengineering.

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