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Technical report

Natural radioactivity and human exposure by raw materials and end productfrom cement industry used as building materials

Z. Stojanovska a,*, D. Nedelkovski a, M. Ristova b

a Laboratory for Radioecology, Institute of Public Health, Skopje 1000, The Former Yugolav Republic of Macedoniab Physics Department, Faculty of Natural Sciences and Mathematic, University in Skopje, The Former Yugolav Republic of Macedonia

a r t i c l e i n f o

 Article history:

Received 4 October 2008

Received in revised form

8 June 2010

Accepted 11 June 2010

Keywords:

Natural radioactivity

Building materials

Raw materials

CementsGamma spectrometry

a b s t r a c t

During the manufacturing process in the cement industry, raw materials of different levels of naturalradioactivity are utilized. In this study we present the radiological impact of cements as a building

material and the different raw materials used in their manufacture. A total of 218 samples of rawmaterials and their end product cements were collected from the cement industry of Macedonia (The

Former Yugoslav Republic) during the period 2005e2007. The specific activities, evaluated by gammaspectrometry analysis, showed the highest mean specific activity in fly ash (226Ra, 107Æ 45 Bq kgÀ1;232Th, 109Æ 30 Bq kgÀ1; 40K, 685Æ 171 Bq kgÀ1), which is used as a raw material. However, the final

cement product usually has relatively lower activity compared with the activity of the raw material andthe mean specific activity of the final cement products were lower (226Ra, 42Æ 10 Bq kgÀ1; 232Th, 28

Æ 6 Bq kgÀ1; 40K, 264Æ 50 Bq kgÀ1). The radium equivalent activity and the hazard index were calculatedfor each sample to assess the radiation hazard. The mean annual effective dose originating from the

cements was found to be 111Æ 22 mSv yÀ1, which is below the recommended EC limit of 300 mSv yÀ1.Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Cement is a widely used building material. Hence, it is of a greatbenefit for the entire society to examine the radioactivity of the raw

materials used in its manufacture. Evaluation of the specific activity(Bq kgÀ1) of these raw materials is an important issue, for they couldbe a source of considerable indoor dose rate. They consist mainly of the natural occurring uranium (238U) and thorium (232Th) series, andpotassium (40K). In the 238U series, the contribution of the radio-

nuclides in the first half of the series between 238U and 230Th isnegligible relative to the second half comprising 226Ra to 210Pb.Consequently the measurement of the activities of  226Ra, 232Th and40K in all the component materials is relevant to a study of cement.

Naturally radioactive materials, manufactured products andindustrial residues are widely used in the cement industry as rawmaterials. Residues from industrial processes such as fly ash fromcoal-fired power plants produced in large quantities can be recy-

cled and used as a supplement in cement production. This processcould yield technological, economical and environmental benefits,but if not subject to regular control, can yield elevated indoorradioactivity exposure rates.

The safety requirements for building materials refer to theexcess exposure rate caused by these materials in addition toterrestrial and cosmic radiation. In this study, safety requirementsproposed by the European Commission (EC, 1999) have been

examined. The basic concept in determination of the excess expo-sure rate consists of (1) determination of the total exposureresulting from the building material including the background and

(2) background subtraction (Markkanen, 1995).

2. Materials and methods

  2.1. Sampling and sample preparation

The samples included the following: cement collected since2005 on a monthly basis from the Cement Factory in Skopje; 218samples (of which 49 were fly ash samples) from the deposits of two power plants, REK Bitola Flyash I and REK Oslomej Flyash II; 45

samples from Pozzolana (originating from Strmos-Pozzolana I andCesinovo-Pozzolana II), 16 natural gypsum samples, 42 clinkersamples and 66 cement samples. The specifications of the cements

under investigation are given in Table 1. The cement CEM I, wellknown as Portland cement, is produced by grinding clinker(96e97%) and natural gypsum (3e4%) and other two types of cement, CEM II/AeM and CEM II/BeM, containing additional

* Corresponding author. Tel.: þ389 2 3125044; fax: þ389 2 3223354.

E-mail address: stojanovskazdenka@gmail.com (Z. Stojanovska).

Contents lists available at ScienceDirect

Radiation Measurements

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / r a d m e a s

1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.

doi:10.1016/j.radmeas.2010.06.023

Radiation Measurements 45 (2010) 969e972

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This dependence is based on the estimation that 1 Bq kgÀ1 of 226Ra, 1.43 Bq kgÀ1 of 232Th and 0.077 Bq kgÀ1 of 40K produce equalgamma dose rates. For safe use of building materials, the maximumvalue of the Raeq should be less than 370 Bq kgÀ1 (UNSCEAR, 1993,2000). The calculated Raeq values for raw materials and for cement

samples are presented in Table 4. The mean value of Raeq for thecements studied (111Æ22 Bq kgÀ1) is below the set limit of 370 Bq kgÀ1 but higher for Pozzolana II (372Æ 74 Bq kgÀ1). The

radium equivalent concentration in fly ash and Pozzolana wasfound to be about 3e4 times higher than those in Portland cement,which is in agreement with the ratios reported by Kovler et al.(2005).

  3.2. Gamma index

In order to assess whether the safety requirements for buildingmaterials are being fulfilled, a gamma index proposed by theEuropean Commission (EC, 1999) was used. It is defined as,

I g ¼C Ra

300þ

C Th

200þ

C K3000

; (2)

where, C Ra, C Th and C K are the specific activities of 226Ra, 232Th and

40K, respectively.The gamma index should also take into account typical ways

and amounts in which the material is used in a building. The limitvalues depend on the dose criteria, the way and amount of thematerial and the manner in which it was used in a building and

construction. For material used in bulk amounts I g 1 correspondsto an absorbed gamma dose rate of 1 mSv yÀ1 (EC, 1990).

Assessment of the internal hazard, originating from the alphaactivity of building materials, requires calculations of the alpha

index or internal hazard index. In this study the alpha index wascalculated by using the following equation, proposed by Righi andBruzzi (2006),

I a ¼C Ra

200; (3)

where, C Ra, is thespecific activityof 226Ra. The safe use of materialsinbuilding construction requires I a to be less than 1. This limit corre-sponds to the action level specific activity for 222Rn which is

200 Bq kgÀ1 for future building construction (EC, 1990). The distri-bution of I g and I a for the different samples in this study is shown in

Fig.1 where it canbe seen that thecalculated mean values of I g (0.37)and I a (0.21) for the cements are below the limits for safe use.

 3.3. Indoor absorbed dose

The activity indexes presented above are used for assessingwhether the safety requirements are being fulfilled for materialswhich might be of concern. Any actual decision for restriction of useof materials should be based on a separate dose assessment into

a scenario for the materials to be used (EC, 1999).The European Commission has proposed a scenario (RP 112) for

the calculation of the annual effective dose in a concrete room withdimensions: 4 m 5 m 2.8 m. Thethickness anddensity of walls are

20 cm and 2350 kg m

À3, respectively. The conversion factor used for

calculation of theabsorbed gamma doserate D (nGy hÀ1) correspondsto 0.92 nGy hÀ1 per Bq kgÀ1 for 226Ra, 1.1 nGy hÀ1 per 1 Bq kgÀ1 for232Th and 0.08 nGy hÀ1 per 1 Bq kgÀ1 for 40K (Markkanen, 1995; EC,1999),

D ¼ 0:92Â C Ra þ 1:1Â C Th þ 0:08Â C K; (4)

where C Ra, C Th and C K are the specific activities of 226Ra, 232Th and40K, respectively.

To assess the excess gamma dose rate, originating from thebuilding materials in the proposed scenario room, the gamma doserate from sources of naturally occurring radioactivity should be

subtracted. A background dose rate of 50 nGy hÀ1 corresponding toan average outdoor value in Europe was used.

For assessment of the annual effective doses DE (mSv yÀ1

), theconversion coef ficient from absorbed dose in air to effective dose

was taken to be 0.7 SvGyÀ1, and the indoor occupancy time wastaken to be 7000 h per year (EC, 1999; UNSCEAR, 1993, 2000).Hence, the annual effective dose was calculated using the followingequation:

DE ¼ DÂ 0:7Â 7000: (5)

The results obtained for annual effective doses from different raw

materials and cements are presented in the Table 4. It can be seenthat the maximum values of the annual effective dose are associatedwith thefly ash samples and Pozzolana, which is consistent with the

  Table 4

Estimated radium equivalent and annual dose.

Sample N  Raeq (BqkgÀ1) DE (mSv yÀ1)

Min Max MeanÆ SD Min Max MeanÆ SD

Gypsum 16 7.3 12.7 9.1Æ 1.5 Lower than background

Fly ash I 20 232 468 314Æ 74 687 1665 1030Æ 314

Fly ash II 29 232 444 357Æ 54 629 1489 1141Æ 213

Pozzolana I 17 111 239 178Æ 31 202 684 457Æ 121

Pozzolana II 28 266 555 372Æ 74 774 1837 1175Æ 273Clinker 42 64 119 85Æ 13 9 234 94Æ 52

CEM I 19 69 100 82Æ 10 31 155 86Æ 38

CEM II/AeM 28 93 138 116Æ 13 128 313 224Æ 53

CEM II/BeM 19 115 148 130Æ 9 213 351 279Æ 38

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

1,1

1,2

1,3

Gypsum Fly ash I Fl y ash II Pozzolana I Pozzolana II Clinker Cement I Cement II Cement III Cement IV

     G    a    m    m    a     /    a     l    p     h    a

     i    n     d    e    x

Gamma index

 Alpha index

Fig. 1. Gamma and alpha index in raw materials and cements.

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other results in this study. According to this scenario the meanannual effective dose in the concrete room, where cement is used as

a raw material is 200Æ 89 mSv yÀ1. According to the EC recommen-dation, this value is below the limit of 300 mSv yÀ1 for safe use.

4. Conclusions

In this study we have found that the highest values for the mean

activity concentrations are in fly ash (226Ra, 107Æ45BqkgÀ1, 232Th,109Æ 30BqkgÀ1; 40K, 685Æ171 Bq kgÀ1), the specific activities of which are above the world mean values for building materials (50,50 and 500 Bq kgÀ1 for 226Ra, 232Th and 40K, respectively; UNSCEAR,

1993). However, the mean specific activities of the cement products(226Ra, 42Æ10 Bq kgÀ1; 232Th, 28Æ 6 BqkgÀ1; 40K, 264Æ 50BqkgÀ1) are similar to those reported by other investigators(Papastefanou et al., 2005; Rizzo et al., 2001; Turhan, 2007). The

main contributors to the overall specific activities in the materialsexamined in this study are attributed to fly ash and Pozzolana and if these raw materials are used as additives in cement production,theiractivity concentration should be carefully monitored. However, the

mean value of Raeq for cements (111Æ22BqkgÀ

1) is below therecommended level of 370 Bq kgÀ1. The mean values of  I g and I a forcements were found to be 0.37 and 0.21, respectively, which is belowthe limit for safe use. Although the mean values of the annual

effective dose for Pozzolana and fly ash are estimated to be higherthan the acceptable level their diluted concentration (< 30%) in thecements gives rise to an annual effective dose that does not exceedthe recommended limits. Finally, the mean annual effective dose

from the cements was estimated to be 200Æ 89 mSv yÀ1, which isbelow the limit of 300 mSv yÀ1 for safe use. Taking into account theEC recommendation, the results from this research have shown thatthere is no significant radiation risk from the use of the cements

investigated in this study.

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