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Doses and radiation risks estimation of adding steel slag to asphalt for road construction in Qatar
Construction and Building Materials 228 (2019) 116741
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Doses and radiation risks estimation of adding steel slag to asphalt for road construction in Qatar M.S. Al-Kawari a, M. Hushari b,⇑ a b
Center for Environmental and Municipal Studies, Ministry of Municipality and Environment, Department of Radiation and Chemical Protection, Doha, Qatar Radiation and Chemical Protection Department, Ministry of Municipality and Environment, Department of Radiation and Chemical Protection, Doha, Qatar
h i g h l i g h t s Steel slag recycling is the best selection from environmental and health point of view. The use of slag as aggregate for roads construction, soil stabilization, and base for the surfacing of flexible pavement are good selection. Using gamma spectroscopy is the best selection technique for measuring radioactivity. Measurements and risk calculation are depend strongly on the exposure scenario and models used. It is recommended to use the slag under beneath of the surface layer.
a r t i c l e
i n f o
Article history: Received 3 November 2018 Received in revised form 6 July 2019 Accepted 16 August 2019
Keywords: Natural occurring radioactive materials Slag Hazard Hazard index Gamma ray Dose equivalent Steel Intake
a b s t r a c t Roughly annual production of slag in Qatar is 350ktp/a. For the purpose of exposure evaluation about 2 million tons slag considered. For radioactivity estimation of produced slag, samples taken from steel slag pile randomly, the slag samples prepared for measurements by low background Gamma ray spectroscopy system equipped with high-purity germanium (HPGe). The presence of isotopes 40 K, 232Th (228Ra), 226Ra and 238U were determined and effective dose for public and workers have been estimated according to exposure scenario. The presence of natural isotopes seem to be in normal concentration and comparable with the published data. The main concentration of Th-232 and Ra-226 are 135.176 and 273.176 Bq/Kg respectively. For the purpose of compression,the radioactivity in normal gabbro have been analyzed. The results of gabbro analyses for 40 K, 232Th (228Ra), 226Ra are 25, 0.7 and 10 Bq/kg respectively. Radiation risk estimation were done for two sets of asphalt samples including the loose asphalt and asphalt cores from the Qatar Steel trials with different ratio (20%,40, and 50%) of slag ,the same ratios used for making concrete block samples. Radioactivity’s, radiation exposure and hazard index were measured and calculated for each case. The calculated absorbed dose value for the 20% slag asphalt is 26.13 lSv/y, and 78.12 lSv/y for the 40% slag asphalt, For extreme conditions at full occupancy factor (indoor with direct contact with human), the dose values are 134.68 and 396.6 lSv/y for the 20% and 40% slag asphalt, respectively. Two case studies were considered for the dose estimation to the public when steel slag aggregate used to replace 40% of total aggregate weight in asphalt applications. In the case studies, the Uranium (U-238) decay chain was considered in the analysis which takes into account all radionuclides in the chain including Radium (Ra-226), Radon (Rn-222) and Lead (Pb-210). The first case study was made for a car park constructed of asphalt pavement. Steel slag aggregate was used to fully replace the coarse aggregate, i.e. replacing 40% of the total normal gabbro, The dose to an adult from external exposure from the ground is 0.08 lSv/y. The second case study considered a children’s playing area made with 40% slag asphalt pavement. Similar to the car park, The doses to 10-year old children from playing on the 40% slag asphalt. The total dose from external irradiation from the play area is 2 lSv/y. It is recommended that loose steel slag aggregate may not use internally in direct contact with humans. However, it could be used in external construction applications below the ground surface. Asphalt made with up to 40% steel slag aggregate could be safely used in road applications in cities. However, concrete made with up to 50% slag aggregate could be safely used in construction applications. Ó 2019 Elsevier Ltd. All rights reserved.
⇑ Corresponding author. E-mail addresses: [email protected] (M.S. Al-Kawari), mmhushari@mme. gov.qa (M. Hushari). https://doi.org/10.1016/j.conbuildmat.2019.116741 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
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1. Review of national and international related regulation natural occurring radioactive material (NORM) in different by-products: The primary legislations for Radiation Safety in Qatar are Decree No.31, 2002, on Radiation Protection. According to this decree Ministry of Municipality and Environment (MME) have the authority to supervise the regulation and control of the use of radioactive material and sources and protection against the associated hazards, the hazardous materials (radioactive material and chemicals) and hazardous waste in Qatar, which are stated in the Decree No. 30 (2002) [1,2]. The decision of the MME No. 45 of 2013 issuing, management of (NORM) resulting mainly from the oil and gas industry. However, this Decision applicable for all NORM sources. The limit of the main radioactive materials (Ra-226 and Ra-228) concentration are 0.185 Bq/g for contaminated soil for depth not >15 cm and 5.55 Bq/g for deeper soil with the dose equivalent He for general of public <1 mSv/y from all sources and from all pathways [2,6] as seen in Fig. 1. The Standardization Affairs has established the Decision No 1-12382-2013 and Guideline No 7-18421-2014; they established Gamma Index (Ic) for Control and Release of NORM [3–5]. This index is used to assess exceeding of action levels and was calculated from activity concentration measurements of (226Ra), (232Th), (40 K) and 137Cs from fallout. It is a screening tool for identifying materials that might become of health concern when used for construction .Values of Iyr 1 corresponds to an annual effective dose of less than or equal to 1 mSv, while Iyr 0.5 corresponds to annual effective dose less or equal to 0.3 mSv. If the activity indices Ic1 and Ic2, is 1 or<1, the material can be used, so far as radioactivity is concerned, without restriction. The activity index Ic1 for materials used in building construction is
Ic1 ¼
CTh CRa CK þ þ 200 300 3000
The activity index Ic2 for materials used in high way road (asphalt), street, and related construction is:
Ic2 ¼
CTh CRa CK þ þ 500 700 8000
of critical group which exposed under realistic conditions, but does not include radon exposure [7–11]. Constraint of 0.3 mSv per year above background from any single source of radioactivity, May applied. Ground outdoor radon exhalation limits should less than (0.74 Bq/S.m2), averaged over the entire area of the used unit as waste or material pile, or impoundment, etc. Indoor radon limited to 200 Bq/m3 in areas that are occupied or occupied able. According to ICRP 107 the main concentration for exclusion, exemption and/or clearance of most important radionuclides U &Th series is 1 Bq/g and K-40 is 10 Bq/g [12–16]. When calculating TEDE to the average member of the critical group. The dose shall determine the peak annual TEDE dose expected within the first 1000 years after using NORM materials, there is not a ‘‘TEDE meter” available for measuring the total dose over 1000 years after disposing. Therefore, mathematical models used to estimate TEDE. These mathematical models are generally dependent on environmental pathways of intakes The dose rate D is calculated using the following equation:
nGy D ¼ 0:427CRa þ 0:662CTh þ 0:043CK h
where: CRa, CTh and CK are the activity concentrations of 226Ra, 232Th and 40 K in Bq/kg, respectively. 2. Exposures from slag Workers Exposures from slag storage could be result from direct exposure to gamma radiation and Slag dust released from large storage piles of slag, by wind-driven re-suspension. Doses to members of the public from slag heaps were assumed to result from many exposure pathways: Inhalation of radionuclides, external irradiation, inhalation of radionuclides re-suspended from a surface deposit, external irradiation by deposited radionuclides and direct external irradiation by the slagheap. The pathway analysis for deriving slag concentration guidelines from a dose limit has four parts: Source analysis, environmental transport analysis, dose/exposure analysis, and scenario analysis. 3. Radionuclide concentrations and source Terms, measurements and evaluation:
where: CTh, CRa, CK and are the activity concentration values of 232Th, 226Ra, and 40 K, expressed in Bq/kg. The International standard for control and release of NORM is depend on Primary exposure limit of 1 mSv/year as a Total Effective Dose Equivalent(TEDE)above background, to average member
In rough estimate the total amount of slag generation >350ktpa in normal operation, where the main equipment production capacity of slag >20ktpm/shift. For the purpose of exposure evaluation the total slag volume over 10 years:1–2 million tons slag considered.
Fig. 1. Collection of molten slag, weathering and processing.
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741
samples were taken from different mixture, depth and percentage of slag, asphalts, and concrete. Mixing steel slag, with 50% of Gabbro and 4% of Bitumen with asphalt used as road base. in construction of 200 m road was at Messeed city at Qatar its mechanical and strain stress measurements was conducted by specialist, then 5 core from the surface to the bottom of road to measure (NORM) radioactivity. Our main goal is to reach the optimum mixture of steel slag, with different percentage of Gabbro and Bitumen with asphalt to use them as road base in acceptable ratio. For the purpose of compression and establishing base line, many samples of clean normal Aggregate of crude materials used in road paving.
Samples of steel slag were taken from the pile as random samples. The slag samples prepared for Gamma ray spectrometry analysis, crushed, grained, homogenized, quartered to the quantity of 1.0 kg and dried at 378 K for 24 h, transferred to standard counting vessels (Marnilly backer) of 1000 cm3 and weighed, but for cores samples the measurement done directly. The loaded vessels were sealed and all gamma emitters have been measured. Measurements were conducts by low background Gamma ray spectroscopy system equipped with CANBERRA detector of highpurity germanium (HPGe). System calibrated using prepared standards that their matrixes resemble to steel slug matrix. The detector has a resolution of 2.5 keV and relative efficiency of 30% for 1.332 MeV gamma energy of 60Co. The spectral data analyzed using the ‘‘Genie 2000 Gamma Analysis Software package”. The specific radioactivity of 226Ra under the peak energy of 186.21 keV is the sum of 235U under the peak energy of 185.7 keV and peak energy of 226Ra alone. Also 226Ra activities calculated from the activity measured from the 609.4 keV peak and other progeny peaks. 232Th activities were determined from the average concentrations of 238.6 keV peak of its 212Pb and 911.1 keV peak of its 228Ac or by 208TI gamma-ray emission probability corrected for 212Bi a decay branching ratio of 35.94%. Activities of 40 K were calculated from the 1460.7 keV peak, activities of 137Cs were calculated from the 661.6 keV peak in the samples. Activities of 238U were calculated from the 235U activities assuming the 235U/238U activity ratio of 0.046. 235U activities were calculated from the 186 keV peak. Limit of detection (LD) or (MDA) which is the minimum detectable activity was calculated according to Currie (14). Method at 95% confidence level and was estimated at the base of know efficiency, counting time, energy intensity and sample mass. The cores
3.1. Background measurements The measurements of back ground radiation of normal gabbro in Qatar have been done. The radionuclide in the samples of normal gabbro measured. The presence of natural isotopes 40 K, 232Th (228Ra), 226Ra and 238U were determined and effective dose for public and workers have been estimated according to exposure scenario. The presence of natural isotopes in the measured samples seem to be in normal concentration and comparable with the published data. Some samples of 100% slag were measured, the samples and the normal gabbro were treated, hazard and dose index calculated for both, the measurements results seen in Table 1. It is clear from this table all the index (dose and hazard index) exceeding the limits for 100% slag The summary of hazards index and dose for workers, general public and critical groups estimated as it similar to slag where Fig. 2 and Table 2 show the concentration index.
Table 1 Radio activity analysis of clean materials (Gabbro) and 100% slag. ID
Date
40 K
232Th
226Ra
137Cs
D(mSv.y-1)
Hex
clean material for road building
Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gab Avg
05/03/2016 03/03/2016 04/04/2017 05/04/2017 07/06/2017
14 25 4 24 11 7.8 14.3
0.7 0.7 0.7 0.38 6 0.7 1.53
7 10 8 7.5 8 8
<0.3 <0.3 <0.3 <0.8 ,0.8 <0.3
4.0544 5.808 4.051 4.486 7.861 4.2148 1.6278
0.024 0.034 0.025 0.027 0.047 0.026 0.0089
pure slag from Qatar Steel
Slag Slag Slag Slag Slag AVG Slag
5.8 7.8 20 7 6 9.32
172 168 170 140 183 166.6
291 271 260 300 295 283.4
<0.1 <0.1 <0.8 <0.3 <0.1
238.370 227.268 224.42 221.081 247.369
1.452 1.382 1.363 1.353 1.505
03/03/2016 07/06/2016 05/04/2016 04/04/2016
Fig. 2. The low background Gamma spectroscopy and sample preparation laboratories.
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741
Table 2 Show the dose and hazard index for Gabbro. Hazard index (I_c2)
Hazard index (I_c1)
D(dose index)(nGy/h)
226Ra (Bq/Kg)
232Th (Bq/Kg)
40 K (Bq/Kg)
Sample Description
Month
0.014 0.013 0.012 0.013 0.019 0.013 0.021 0.025 0.015 0.014 0.014 0.007 0.010 0.006 0.008 0.017 0.012 0.014
0.034 0.030 0.029 0.032 0.045 0.032 0.052 0.060 0.036 0.034 0.035 0.018 0.023 0.014 0.020 0.040 0.029 0.033
4.382 3.839 3.788 4.054 5.808 4.051 6.803 7.861 4.725 4.365 4.439 2.274 2.939 1.781 2.617 5.165 3.697 4.270
7 7 7 7 10 8 7.5 8 4.4 8.1 7.7 4 5.1 3.5 4.3 9.5 6 6.712
1 0.7 0.7 0.7 0.7 0.7 3.88 6 3 0.07 0.7 0.4 0.5 0.4 0.4 0.7 1 1.268
17 9 7.8 14 25 4 24 11 20 20 16 7 10 0.5 12 15 11 13.135
Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro
Nov-14 Dec-14 Jan-15 Feb-15 Mar-15 Apr-15 May-15 Jun-15 May-16 Jun-16 Jul-16 Aug-16 Sep-16 Oct-16 Nov-16 Dec-16 Jan-17 Average
Variaon of K-40 Concentraon(Bq/Kg )from Nov,2014 to Jan2017.
Variaon of Th-232 concen. from Nov.2014 to Jan2017 40 30 20 10 0
17 15 13 11 9
7
5
3
Varaiaon of Ra-226 concen. from Nov.2014 to Jan 2017
200
400
150
300
100
200
50
100
0 17 15 13 11 9 7 5 3 1 232Th (Bq/Kg)
1
0 17 15 13 11 9 7 5 3 1
AVG
226Ra (Bq/Kg)
AVG
Fig. 3. Show The variation of K-40, Th-232 and Ra-226 for the measuring period of Nov2014 to Jan2017 of Slag samples.
3.2. Radiation routine tests Radioactivity levels in the steel slag aggregate have been measured on a monthly basis. Radiation Levels measured for steel slag and gabbro (as a control) samples are given in Fig. 3. The results cover measurements from November 2014 to June 2015, then from May 2016 to January 2017 in Fig. 4 The Fig. 3 above illustrate the variation of K-40, Th-232 and Ra-226 for the measuring period of Nov2014 to Jan2017, the variation of 40 indicate that the average K-40 concentration was 12.5, and its ranging from 30 Bq/Kg to about 5 Bq/Kg. Where the main concentration of Th- 232 and Ra-226 were 135.176 and 273.176 Bq/Kg respectively.
K-40,Th232,and Ra-226 concentraon (Bq/Kg)for Gabbro samples taken from Nov 2014 to Jan2017
3.3. Radiation of the slag site trials 30 25 20 15 10 5 0
40K (Bq/Kg)
232Th (Bq/Kg)
The main observations are that the trend of these two radionuclide’s are similar, and it seem that the trend indicate that since Jan 2015 seem that the both concentration dropped down which mean the source of steel ore might changed. The radioactivity results of the routine testing were analysed and the data evaluated for compliance with the dose and external hazard indices of the Qatari regulations. The results for gabbro analyses are given in Table 2. The table clearly showed that the Dose index and all hazard (internal and external) are accepted and this is in accordance with natural background in Qatar. Where the Table 3 present the Dose and hazards indexes, which is clear that the use of 100% slag for all type of use, are irregular. The table also show that radium concentration is higher than the reference level in Qatar so all 100% slag should be not accepted for use in road construction and as well as building materials.
226Ra (Bq/Kg)
Fig. 4. Comparison of variation of K-40. Th-232and Ra-226 in Gabbro samples.
The steel slag aggregate used in the full-scale production of unbound subbase materials, asphalt road subbase, and precast concrete units (crash barriers, soakaways etc.). The following samples from the slag products obtained for radioactivity testing: Loose slag samples (0–5, 5–10, and 10–20 mm diameter) Loose asphalt and asphalt cores for the control asphalt (gabbro), 20% slag asphalt, and 40% slag. Concrete cores for the control concrete (gabbro), 20% slag, and 50% slag.
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741 Table 3 the Dose and hazards indexes of slag’s sample collected from Nov2014 to Jan2017. Hazard index (I_c2)
Hazard index (I_c1)
D(dose index)(nGy/h)
226Ra (Bq/Kg)
232Th (Bq/Kg)
40 K (Bq/Kg)
Sample Description
Month
0.756 0.772 0.760 0.726 0.714 0.788 0.709 0.714 0.765 0.492 0.530 0.546 0.572 0.568 0.510 0.784 0.552 0.662
1.820 1.860 1.832 1.750 1.723 1.900 1.702 1.723 1.833 1.152 1.271 1.310 1.372 1.361 1.219 1.885 1.327 1.591
236.800 242.116 238.370 227.750 224.420 247.369 221.081 224.420 237.975 147.802 164.926 170.070 178.080 176.604 158.134 245.025 172.463 206.671
290 292 291 271 260 295 300 260 330 325 230 235 245 250 230 315 225 273.1765
170 177 172 168 170 183 140 170 145 13 100 105 110 105 90 165 115 135.1765
10 6 5.8 19 20 6 7 20 25 9.8 12 5 15 8 8 30 6 12.50588
Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag
Nov-14 Dec-14 Jan-15 Feb-15 Mar-15 Apr-15 May-15 Jun-15 May-16 Jun-16 Jul-16 Aug-16 Sep-16 Oct-16 Nov-16 Dec-16 Jan-17 AVG
The slag samples were collected from the road site trials in Qatar Steel premises in Messeed. The grinded specimens were measured by Gamma ray spectroscopy. Table 4 shows the results of radioactivity measured in collected samples. The measurement of activity concentrations of 226Ra, 232Thand 40 K in the sample from the studied areas varies from 140 Bq kg1 to 15 Bq kg1 for K-40, from all samples type. Where the activity of Ra-226 ranging from about zero to about 120 Bq kg1 and from about100 Bq kg1 to about 3 Bq kg1. The radiation measurements results in Table 4 show that all the values are within the Qatari and International regulations of <185 Bq/kg. A zero value refers to the value lower, the radiation exposure and radiation risk were estimated for the various construction applications made with slag aggregate. The Gamma index for the activity concentration is also calculated to assess suitability of the slag products for use in construction road in the cities (Ic1) and outside cities (Ic2). The radiation exposure and radiation risk were estimated for the various construction applications made with slag aggregate. The Gamma index for the activity concentration is also calculated to assess suitability of the slag products for use in cities (Ic1) and outside cities (Ic2) as well as dose estimation seen in Table 5.
3.4. Radiation in asphalt Two sets of asphalt samples were tested including the loose asphalt (from the plant) and asphalt cores from the Qatar Steel trials in Messeed. In order to estimate the annual effective dose rate in air, a conversion coefficient from the absorbed dose in air to the effective dose received by an adult was considered. This value published in United Nations Scientific Committee on the Effects of Atomic Radiation report (UNSCEAR, 2000) to be 0.7 Sv/Gy for environmental exposure to gamma rays of moderate energy. The value of the occupancy factor is related to the degree of exposure; fulltime exposure. The annual effective dose equivalent (AEDE) is determined using the following equation:
AEDEðlSv =yÞ ¼ ðnannuGy=hÞ 8760h=y
0:2ðoccupancy factor outsideÞ 0:7ðSv =GyÞ 103
When applying the above equation for an outside occupancy factor, the absorbed dose for the control samples (without slag) indicated a negligible dose of 1 lSv/y. The calculated absorbed dose value for the 20% slag asphalt is 26.13 lSv/y, and 78.12 lSv/ y for the 40% slag asphalt [17–20].
Table 4 Radio-analysis results of slag road trials. Concentration (Bq/kg)
Loose asphalt mix (Control)
Loose asphalt mix(20% slag)
Loose asphalt mix(40% slag)
asphalt cores
Concrete cores
Loose slag
Loss slag
Sample cod.
K-40
Pb-212
Bi-214
Pb-214
Ra-226
Ac-228
Pa-234 m
U-235
1–11 1–12 1–13 1–14 1–15 1–16 1–17 1–18 1–19 4D Control 7D20% Slag 11D 40% Slag 1F Control 3E 20% Slag 2C 50% Slag 0–5 mm 5–10 mm 10–20 mm
18 ± 2 17 ± 2 15 ± 2 16 ± 1 16 ± 1 17 ± 1 17 ± 2 20 ± 1 19 ± 2 20 ± 1 18 ± 2 19 ± 2 162 ± 7 97 ± 5 125 ± 6 16 ± 1 12 ± 3 140 ± 2 22 ± 2
– 1 ± 0.2 – 28 ± 2 27 ± 2 30 ± 2 79 ± 6 72 ± 6 75 ± 6 2 ± 0.2 26 ± 2 34 ± 3 4 ± 0.3 77 ± 6 55 ± 4 92 ± 4 94 ± 5 32 ± 3 29 ± 2
– 1 ± 0.1 1 ± 0.1 30 ± 1 33 ± 1 34 ± 1 77 ± 2 71 ± 2 77 ± 2 5 ± 0.2 36 ± 1 45 ± 1 6 ± 0.3 71 ± 2 53 ± 2 111 ± 2 113 ± 3 122 ± 3 36 ± 1
1 ± 0.2 1 ± 0.1 1 ± 0.2 30 ± 1 31 ± 2 34 ± 2 78 ± 4 70 ± 4 77 ± 4 4 ± 0.3 36 ± 2 46 ± 3 6 ± 0.4 75 ± 4 52 ± 3 114 ± 4 118 ± 4 124 ± 4 37 ± 2
– 1 ± 0.1 – – – 26 ± 12 72 ± 34
– – – 31 ± 1 29 ± 1 31 ± 1 80 ± 2 74 ± 2 78 ± 2 3 ± 0.2 26 ± 1 35 ± 1 4 ± 0.3 76 ± 2 54 ± 2 96 ± 2 98 ± 2 96 ± 2 29 ± 1
– – –
– – – 3 ± 0.3 3 ± 0.3 2±1 6±2 8±1 5±2 – 4±1 5±2 – 5±2 6±1 5±1 5±1 8±1 3±1
64 ± 34 – 69 ± 8 – 14 ± 4 83 ± 32 102 ± 11 131 ± 16 32 ± 27 108 ± 18 34 ± 15
18 ± 1 38 ± 8 89 ± 17 54 ± 14 56 ± 18 – 21 ± 12 42 ± 11 – 105 ± 22 57 ± 17 126 ± 13 146 ± 27 134 ± 13 24 ± 9
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741
Table 5 dose and hazard index for all sample collected (19 sample). Hazard index (I_c2)
Hazard index (I_c1)
D(dose index) (nGy/h)
226Ra (Bq/Kg)
232Th (Bq/Kg)
40 K (Bq/Kg)
Sample Code Number
Sample
0.002
0.006
0.774
0
0
18
1 11
Loose asphalt mix (Control)
0.004 0.002 0.064 0.060 0.101 0.265 0.151 0.250 0.009 0.153 0.072 0.048 0.283 0.269 0.381 0.243 0.364 0.109
0.009 0.005 0.160 0.150 0.247 0.646 0.377 0.610 0.022 0.366 0.181 0.121 0.689 0.652 0.922 0.601 0.887 0.266
1.158 0.645 21.210 19.886 32.355 84.435 49.848 79.781 2.846 47.449 23.987 15.592 89.924 84.677 120.177 79.056 115.688 34.662
1 0 0 0 26 72 0 64 0 69 0 14 83 102 131 32 108 34
0 0 31 29 31 80 74 78 3 26 35 4 76 54 96 98 96 29
17 15 16 16 17 17 20 19 20 18 19 162 97 125 16 12 140 22
1 12 1 13 1 14 1 15 1 16 1 17 1 18 1 19 4D Control 7D 20% Slag 11D 40% Slag 1F Control 3E 20% Slag 2C 50% Slag 0–5 mm 5–10 mm 10–20 mm
For extreme conditions at full occupancy factor (indoor with direct contact with human), the dose values are 134.68 and 396.6 lSv/y for the 20% and 40% slag asphalt, respectively. This condition is unlikely to occur for humans to stay exposed in direct contact to slag radiation from asphalt for 100% of their time, but was considered to assess the extreme conditions. The radioactivity results and the analysis conducted confirm that the absorbed doses for all tested slag asphalt specimens are within the Qatari regulation permissible limit of 1 mSv/y (1000 lSv/y). There for up to 40% steel slag aggregate could be safely used for road construction in residential and urban areas could have an occupancy factor of 1.
Loose asphalt mix (20% slag) Loose asphalt mix (40% slag) asphalt cores
Concrete cores
Loose slag
loss slag
3.7. Car parking The first case study was made for a car park constructed of asphalt pavement. Steel slag aggregate was used to fully replace the coarse aggregate, i.e. replacing 40% of the total imported gabbro, in full pavement layers. In this scenario, the most significant pathway is likely to be from external exposure. Accordingly, doses from external irradiation to the public from the slag asphalt car park were determined using the following equation:
Dext ¼ AR Fslag DCexr; R T where:
3.5. Radiation in concrete The concrete radiation measurements results with 0–20, of the 50% slag aggregate as replacement of gabbro’s. The Ra-226 concentrations for the Control (core 1F), 20% slag (3E), and 50% slag (2C) were 14, 83, and 102 Bq/kg, respectively (less than the Qatar permissible value of 185 Bq/kg). The dose index for the three concrete mixtures was <1 mSv/y, considering 2000 working exposure per year. The Gamma activity index was always <1 for Ic1 and Ic2, indicating potential use in residential and urban areas. An additional internal hazard index (Hin) was calculated this index is considered when the application is in direct contact with humans. The hazard of this index is due to the inhalation of Radon that can lead to respiratory diseases and cancer. The Hin values calculated for the Control (core 1F), 20% slag (3E), and 50% slag (2C) were 0.13, 0.76, and 0.79, respectively. Whilst the Hin values are less than the Qatari permissible limit of 1, the RCPD-MME recommended not using slag concrete in buildings with direct contact of humans.
Dext: Dose from external irradiation in a car park 1 m above the ground (Sv/y) AR:Activity concentration of radionuclide R in slag (Bq/g) Fslag Fraction of slag used in asphalt surface materials (0.4) DCext, R: Dose coefficient for external exposure for radionuclide R (Sv/h per Bq/g) T: Duration of exposure, 100 h/y is assumed, based on 15 min per day Values for DCext, and R were determined using energy specific dose equivalent rates from IAEA (1992), appropriate for a plane surface of the car park. Doses to members of the public from the car park paved with 40% slag asphalt are given in Table 6. Both U-238 and Th-232 decay chains contribute to the external dose, with a higher contribution from Th-232 (62%) compared to 38% from U-238 decay chain. The does values take into account all members of the decay chain and were calculated using dose conversion factors of 0.039x10-8 and 0.06x10-8 for U-238 and Th-232, respectively as seen in Table 7.
3.6. Case studies Two case studies were considered for the dose estimation to the public when steel slag aggregate was used to replace 40% of total aggregate weight in asphalt applications. In the case studies, the Uranium (U-238) decay chain was considered in the analysis which takes into account all radionuclides in the chain including Radium (Ra-226), Radon (Rn-222) and Lead (Pb-210).
Table 6 Doses from 40% slag asphalt car parking to the public. Radionuclide
External Dose
Radionuclide contribution %
U-238 Th-232 total
2.88.10–8 4.8.10–8 7.68.10–8
38% 68% 100%
M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741 Table 7 Dose estimation for children play area made with 40% slag asphalt.
K-40 U-238(Ra-226) Th-232 Total
7
4. Radiation risk assessment for different gabbro’s percentage
Dose conversion factor (Sv/yperBg/g)
Radionuclides concentration(Bq/g)
Absorbed Dose (Sv/y)
5.6 108 6.44 107 7.70 107
1.7 102 7.2 102 8.0 102
1.9 107 9.27 106 12.3 106 21.8 106
3.8. Radionuclide external do The dose to an adult from external exposure from the ground is 7.682 108 Sv/y, equivalent to 0.08 lSv/y. The calculated dose value is much lower than the Qatari regulation limit of 0.3 mSv/y (300 lSv/y) from a single source. It is therefore concluded that the 40% slag in asphalt car parking adds a very small dose, which is within the acceptable range of the Qatari regulations to the public. 3.9. Children’s play area The second case study considered a children’s playing area made with 40% slag asphalt pavement. Similar to the car park, the most significant pathway in this scenario is from external exposure. However, this pathway is more applicable to children (up to 10 year olds) rather than adults in the car park. The external irradiation is calculated from the same equation as the car park with the only difference that the exposure duration is increased to 200 h per year. The doses to 10-year old children from playing on the 40% slag asphalt. The total dose from external irradiation from the play area is 2 lSv/y. The excess dose, from using 40% slag aggregate in the surfacing materials will be <2lSv/y, which is lower than the limit of 10 lSv/y to be exempted dose from regulation. The results show clearly that the dose from external irradiation from the asphalt play area is 22 lSv/y which is much lower than the Qatari regulation limit of 0.3 mSv/y (equivalent to 300 lSv/y) from a single source. Results from the children’s play area and the car parking confirm the use of 40% slag aggregate in asphalt applications is safe for humans with negligible risk to children and adults.
Risk assessment methods are generally used for determining the allowable radiation concentration and dose. A software ‘‘RESRAD” was used in this investigation for assessing the radiological doses resulting from the slag materials, which considers external exposure, ingestion, internal and inhalation pathways. The risk assessment was conducted on an asphalt road constructed with 40% slag aggregate. The slag asphalt is considered to be laid within the top 300 mm layers of the road pavement, with the purpose of estimating the total effective dose equivalent to an individual over 1000 years. The following parameters are used for the dose calculation: The concentrations of radionuclides are K-40 = 17, Th-232 = 80, and Ra-226 = 72 Bq/kg, as obtained from Table 5 for the loose asphalt specimen (1–17). The dose conversion factor for external radiation is determined from the ICRP 107 (2010) for each radionuclide as (risk/y)/(mBq/g). The studied area is 10,000 m2 with an outdoor occupancy of 0.1 (200 h per year). The unrestricted zone is 1 m thick, related to the ground water level, and is assumed to remain constant during the study period. All pathways are considered, including Radon inhalation .The dose calculation was made for the period of 1, 2, 3, 4, 5, 6, 10, 13, and 1000 years, which are the main periods for risk assessment. The 1000 year is considered because it represents the half-life of the most important radionuclides from exposure point of view. External and internal exposures from all pathways up to 1000 years are presented in Fig. 5. The results show that the maximum dose from all nuclides is <1.5 lSv/y and occurs within the first 10 years of construction. The total dose decreases with time to below 1.0 lSv/y after 700 years of exposure. The results confirm that the total exposure from 40% slag pavement, considering all pathways, over 1000 year is negligible compared to national and international standards. Further analysis was conducted to assess the risk associated with the use of steel slag aggregate in asphalt pavement, which relates to the probability of having cancer due to exposure to radioactive materials used in road construction. Fig. 6 shows the excess cancer risk from all radionuclides and pathways for 40% slag asphalt up to 1000 years of exposure. Fig. 6 shows the maximum
Fig. 5. External and internal exposures from 40% slag asphalt up to 1000 years.
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741
Fig. 6. Cancer risk from using 40% slag asphalt in roads.
risk achieved is 3.4 106 and occurs after 10 years from construction. The risk is reduced with time to reach less 3.0 106 after 500 years from construction. The value of 3.0 106 fatal cancer risk (i.e. 3 persons every million) is considered extremely low compared to the annual death rate from other activities. Annual death rate is the most common scale used for understanding and comparing the risk from exposure to radiation. Data from the US Bureau of Labor Statistics (2016) published the Census of Fatal Occupational Injuries (CFOI) rate from various activities in 2015. The average risk of dying from mining, quarrying, and oil and gas extraction is 11.7 in 100,000, 10.1 in 100,000 from construction activities, and 2.3 in 100,000 from manufacturing. The risk value for the use of steel slag is therefore negligible in comparison to these activities. Based on the radioactivity analysis conducted in this study by the RCPD, the Ministry of Municipality and Environment issued a No Objection Letter (Appendix A) for the use of 20% slag aggregate in asphalt (below the wearing course) and precast concrete (below the ground) provided compliance with the national and international regulations. The 20% permission is an initial step to start utilizing steel slag aggregate in various construction applications and is intended to encourage an increase in uptake to 40% slag after implementing a safe system for monitoring in practice. 5. Summary and conclusions The data on the concentration of radioisotopes for the steel slag showed a wide variation over the last 3 years, mainly in Radium Ra-226 and Thorium Th-232 concentrations, the two isotopes with significant levels of radioactivity. This change may be attributed to possible variation of iron sources. Loose steel slag aggregate may not use internally in direct contact with humans. However, it could be used in external construction applications below the ground surface. Asphalt made with up to 40% steel slag aggregate could be safely used in road applications in cities. However, from an environmental point of view, its use in the surface layer is not recommended. Concrete made with up to 50% slag aggregate could be safely used in construction applications, however, it is not recommended for use indoors with direct contact with humans. Precast concrete applications below
the ground surface or in open areas are recommended. Two case studies were considered for the use of steel slag aggregate in car parking and children’s playing areas. Where the slag used to replace 40% of the imported gabbro in asphalt and the results indicated safe use in both applications with negligible risk to children and adults. Radiation risk assessment showed very low risk (<3 106 fatal cancer risk) (i.e. 3 persons every million), which is considered extremely low compared to other exposure activities. The permitted content of slag could be increase to 40% in safe use in Asphalt. Our results are in well agreements with all international considerable studies and we recommend strongly using slag in asphalt outside and inside the cities especially in high ways construction. Declaration of Competing Interest None. Acknowledgements The authors are grateful to the Ministry of Municipality & Environment and the Public Works Authority (Ashghal) for their valuable contribution and support the project. The authors are also grateful to the Radiation Chemicals & Protection Department for carrying out the radioactivity investigation, Also to Qatar Steel who funded the project. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2019.116741. References [1] Ziauddin A. Khan, Rezqallah H. Malkawi, Khalaf A. Al-Ofi, Nafisullah Khan 2002. Review of steel slag utilization in Saudi Arabia, The 6th Saudi engineering conference KFUPM Dhahran. [2] A.T. Al-Kinani, M. Hushari, I.A. Alsadig, H. Al-Sulaiti, Measurements of recycling steel slug at Qatar Steel using low-level Gamma-ray Spectrometry and calculation of risk factors.Dannish, J. Res. Environ. Stud. 2 (4) (2015) 28–36. [3] The European Slag Association, Legal Status of Slags, Position Paper, 2006.
M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741 [4] E.O. Agbalagba, R.A. Onoja, Evaluation of natural radioactivity in soil, sediment and water samples of Niger Delta (Biseni) flood plain lakes, Nigeria, J. Environ. Radioactiv. 102 (2011) 667–671. [5] Rohit Mehra, Surinder Singh, Kulwant Singh, Assessment of the average effective dose from the analysis of Ra-226, Th-232and K-40 in soil samples from Punjab, India, Geochem. J. 45 (2011) 497–503. [6] UNSCEAR (200) Sources and Effects of Ionizing Radiation Report of United Nations Scientific Committee on the Effect of Atomic Radiation. United Nations, New York. [7] J. Beretka, P.J. Mathew, Natural radioactivity of Australian building materials, industrial wastes and byproducts, Health Phys. 48 (1985) 87–95. [8] A.K. Sam, N. Abbas, Assessment of radioactivity and associated hazards in local and imported cement types used in Sudan, Rad. Protect. Dosimet. 88 (225– 260) (2010) 2000s. [9] F.A. Ibrahim, I.A. Mohammad, Soil radioactivity levels and radiation hazard assessment in the highlands of northern Jordan, Rad. Measure. 44 (2009) 102– 110. [10] STUK, GUIDE ST 12.2/17 December 2010,The radioactivity of building materials and ash. [11] M. Tufail, N. Akhtar, S. Jaried, T. Hamid, Natural radioactivity hazards of building bricks fabrication from soil of two districts of Pakistan, J. Radiol. Protect. 27 (2007) 481–492. [12] S. Turhan, L. Gunduz, Determination of specific activity of 226Ra, 232Th and 40K for assessment of radiation hazards from Turkish pumice samples, J. Environ. Radiat. (2007), https://doi.org/10.1016/j .jenvrad. 2007 .08. 002. [13] H.M. Taskin, P. Karavus, A. Ay, S. Touzogh, Hindiroglu, G. Karaham, Radionuclide concentration in soil and lifetime cancer risk due to the gamma radioactivity in Kirklareli, Turkey, J. Environ. Radioactiv. 100 (2009) 49–53.
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[14] A.S. Murray, M.J. Aitken, Analysis of low-level natural radioactivity in small mineral samples for use in thermoluminiscence dating, using high resolution gamma spectrometry, Int. Appl. Radiat. Isot. 39 (1998) 145–158. [15] L.A. Currie, Limits for qualitative detection and quantitative determination, Anal. Chem. 40 (1968) 586–593. [16] Ziauddin A. Khan, Rezqallah H. Malkawi, Khalaf A. Al-Ofi, Nafisullah Khan Review of steel slag utilization in Saudi Arabia, The 6th Saudi engineering conference KFUPM Dhahran December 200. [17] Steel Slag as A Road Construction Material Mohd. Rosli Hainina, Md. Maniruzzaman A. Aziza,b*, Zulfiqar Alia, Ramadhansyah Putra Jayaa, Moetaz M. El-Serganyc, HaryatiYaacobaaDepartment of Geotechnics and Transportation, Faculty of Civil Engineering, UniversitiTeknologi Malaysia, 81310 UTM Johor Bahru, Johor Malaysia. BUTM Construction Research Centre (CRC), UniversitiTeknologi Malaysia, 81310 UTM Johor Bahru, Johor Malaysia, Ce-School of Health and Environmental Studies, Hamdan Bin Mohamed Electronic University, UAE. [18] The International Commission on Radiological Protection (2010). The 2007 recommendations of the international commission on radiological protection. ICRP Publication 103, available on (http://www.icrp.org/docs/ICRP_ Publication_103- Annals_of_the_ICRP_37 (2-4)-Free_extract.pdf) [19] UK Environment Agency. Quality Protocol for Steel Slag – End of waste criteria for the production and use of steel slag aggregates in construction applications. Draft Document for Consultation, March 2014. 28pp. https://consult.environmentagency. gov.uk/portal/ho/waste/quality_protocol/ steel_slag?pointId=2837038 [20] UK Environment Agency. Technical Report for steel slag aggregates – manufacturing and applications, February 2014, pp. 46 https://consult. environmentagency gov.uk/portal/ho/waste/quality protocol/steel slag pointed2837038
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Doses and radiation risks estimation of adding steel slag to asphalt for road construction in Qatar M.S. Al-Kawari a, M. Hushari b,⇑ a b
Center for Environmental and Municipal Studies, Ministry of Municipality and Environment, Department of Radiation and Chemical Protection, Doha, Qatar Radiation and Chemical Protection Department, Ministry of Municipality and Environment, Department of Radiation and Chemical Protection, Doha, Qatar
h i g h l i g h t s Steel slag recycling is the best selection from environmental and health point of view. The use of slag as aggregate for roads construction, soil stabilization, and base for the surfacing of flexible pavement are good selection. Using gamma spectroscopy is the best selection technique for measuring radioactivity. Measurements and risk calculation are depend strongly on the exposure scenario and models used. It is recommended to use the slag under beneath of the surface layer.
a r t i c l e
i n f o
Article history: Received 3 November 2018 Received in revised form 6 July 2019 Accepted 16 August 2019
Keywords: Natural occurring radioactive materials Slag Hazard Hazard index Gamma ray Dose equivalent Steel Intake
a b s t r a c t Roughly annual production of slag in Qatar is 350ktp/a. For the purpose of exposure evaluation about 2 million tons slag considered. For radioactivity estimation of produced slag, samples taken from steel slag pile randomly, the slag samples prepared for measurements by low background Gamma ray spectroscopy system equipped with high-purity germanium (HPGe). The presence of isotopes 40 K, 232Th (228Ra), 226Ra and 238U were determined and effective dose for public and workers have been estimated according to exposure scenario. The presence of natural isotopes seem to be in normal concentration and comparable with the published data. The main concentration of Th-232 and Ra-226 are 135.176 and 273.176 Bq/Kg respectively. For the purpose of compression,the radioactivity in normal gabbro have been analyzed. The results of gabbro analyses for 40 K, 232Th (228Ra), 226Ra are 25, 0.7 and 10 Bq/kg respectively. Radiation risk estimation were done for two sets of asphalt samples including the loose asphalt and asphalt cores from the Qatar Steel trials with different ratio (20%,40, and 50%) of slag ,the same ratios used for making concrete block samples. Radioactivity’s, radiation exposure and hazard index were measured and calculated for each case. The calculated absorbed dose value for the 20% slag asphalt is 26.13 lSv/y, and 78.12 lSv/y for the 40% slag asphalt, For extreme conditions at full occupancy factor (indoor with direct contact with human), the dose values are 134.68 and 396.6 lSv/y for the 20% and 40% slag asphalt, respectively. Two case studies were considered for the dose estimation to the public when steel slag aggregate used to replace 40% of total aggregate weight in asphalt applications. In the case studies, the Uranium (U-238) decay chain was considered in the analysis which takes into account all radionuclides in the chain including Radium (Ra-226), Radon (Rn-222) and Lead (Pb-210). The first case study was made for a car park constructed of asphalt pavement. Steel slag aggregate was used to fully replace the coarse aggregate, i.e. replacing 40% of the total normal gabbro, The dose to an adult from external exposure from the ground is 0.08 lSv/y. The second case study considered a children’s playing area made with 40% slag asphalt pavement. Similar to the car park, The doses to 10-year old children from playing on the 40% slag asphalt. The total dose from external irradiation from the play area is 2 lSv/y. It is recommended that loose steel slag aggregate may not use internally in direct contact with humans. However, it could be used in external construction applications below the ground surface. Asphalt made with up to 40% steel slag aggregate could be safely used in road applications in cities. However, concrete made with up to 50% slag aggregate could be safely used in construction applications. Ó 2019 Elsevier Ltd. All rights reserved.
⇑ Corresponding author. E-mail addresses: [email protected] (M.S. Al-Kawari), mmhushari@mme. gov.qa (M. Hushari). https://doi.org/10.1016/j.conbuildmat.2019.116741 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.
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1. Review of national and international related regulation natural occurring radioactive material (NORM) in different by-products: The primary legislations for Radiation Safety in Qatar are Decree No.31, 2002, on Radiation Protection. According to this decree Ministry of Municipality and Environment (MME) have the authority to supervise the regulation and control of the use of radioactive material and sources and protection against the associated hazards, the hazardous materials (radioactive material and chemicals) and hazardous waste in Qatar, which are stated in the Decree No. 30 (2002) [1,2]. The decision of the MME No. 45 of 2013 issuing, management of (NORM) resulting mainly from the oil and gas industry. However, this Decision applicable for all NORM sources. The limit of the main radioactive materials (Ra-226 and Ra-228) concentration are 0.185 Bq/g for contaminated soil for depth not >15 cm and 5.55 Bq/g for deeper soil with the dose equivalent He for general of public <1 mSv/y from all sources and from all pathways [2,6] as seen in Fig. 1. The Standardization Affairs has established the Decision No 1-12382-2013 and Guideline No 7-18421-2014; they established Gamma Index (Ic) for Control and Release of NORM [3–5]. This index is used to assess exceeding of action levels and was calculated from activity concentration measurements of (226Ra), (232Th), (40 K) and 137Cs from fallout. It is a screening tool for identifying materials that might become of health concern when used for construction .Values of Iyr 1 corresponds to an annual effective dose of less than or equal to 1 mSv, while Iyr 0.5 corresponds to annual effective dose less or equal to 0.3 mSv. If the activity indices Ic1 and Ic2, is 1 or<1, the material can be used, so far as radioactivity is concerned, without restriction. The activity index Ic1 for materials used in building construction is
Ic1 ¼
CTh CRa CK þ þ 200 300 3000
The activity index Ic2 for materials used in high way road (asphalt), street, and related construction is:
Ic2 ¼
CTh CRa CK þ þ 500 700 8000
of critical group which exposed under realistic conditions, but does not include radon exposure [7–11]. Constraint of 0.3 mSv per year above background from any single source of radioactivity, May applied. Ground outdoor radon exhalation limits should less than (0.74 Bq/S.m2), averaged over the entire area of the used unit as waste or material pile, or impoundment, etc. Indoor radon limited to 200 Bq/m3 in areas that are occupied or occupied able. According to ICRP 107 the main concentration for exclusion, exemption and/or clearance of most important radionuclides U &Th series is 1 Bq/g and K-40 is 10 Bq/g [12–16]. When calculating TEDE to the average member of the critical group. The dose shall determine the peak annual TEDE dose expected within the first 1000 years after using NORM materials, there is not a ‘‘TEDE meter” available for measuring the total dose over 1000 years after disposing. Therefore, mathematical models used to estimate TEDE. These mathematical models are generally dependent on environmental pathways of intakes The dose rate D is calculated using the following equation:
nGy D ¼ 0:427CRa þ 0:662CTh þ 0:043CK h
where: CRa, CTh and CK are the activity concentrations of 226Ra, 232Th and 40 K in Bq/kg, respectively. 2. Exposures from slag Workers Exposures from slag storage could be result from direct exposure to gamma radiation and Slag dust released from large storage piles of slag, by wind-driven re-suspension. Doses to members of the public from slag heaps were assumed to result from many exposure pathways: Inhalation of radionuclides, external irradiation, inhalation of radionuclides re-suspended from a surface deposit, external irradiation by deposited radionuclides and direct external irradiation by the slagheap. The pathway analysis for deriving slag concentration guidelines from a dose limit has four parts: Source analysis, environmental transport analysis, dose/exposure analysis, and scenario analysis. 3. Radionuclide concentrations and source Terms, measurements and evaluation:
where: CTh, CRa, CK and are the activity concentration values of 232Th, 226Ra, and 40 K, expressed in Bq/kg. The International standard for control and release of NORM is depend on Primary exposure limit of 1 mSv/year as a Total Effective Dose Equivalent(TEDE)above background, to average member
In rough estimate the total amount of slag generation >350ktpa in normal operation, where the main equipment production capacity of slag >20ktpm/shift. For the purpose of exposure evaluation the total slag volume over 10 years:1–2 million tons slag considered.
Fig. 1. Collection of molten slag, weathering and processing.
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741
samples were taken from different mixture, depth and percentage of slag, asphalts, and concrete. Mixing steel slag, with 50% of Gabbro and 4% of Bitumen with asphalt used as road base. in construction of 200 m road was at Messeed city at Qatar its mechanical and strain stress measurements was conducted by specialist, then 5 core from the surface to the bottom of road to measure (NORM) radioactivity. Our main goal is to reach the optimum mixture of steel slag, with different percentage of Gabbro and Bitumen with asphalt to use them as road base in acceptable ratio. For the purpose of compression and establishing base line, many samples of clean normal Aggregate of crude materials used in road paving.
Samples of steel slag were taken from the pile as random samples. The slag samples prepared for Gamma ray spectrometry analysis, crushed, grained, homogenized, quartered to the quantity of 1.0 kg and dried at 378 K for 24 h, transferred to standard counting vessels (Marnilly backer) of 1000 cm3 and weighed, but for cores samples the measurement done directly. The loaded vessels were sealed and all gamma emitters have been measured. Measurements were conducts by low background Gamma ray spectroscopy system equipped with CANBERRA detector of highpurity germanium (HPGe). System calibrated using prepared standards that their matrixes resemble to steel slug matrix. The detector has a resolution of 2.5 keV and relative efficiency of 30% for 1.332 MeV gamma energy of 60Co. The spectral data analyzed using the ‘‘Genie 2000 Gamma Analysis Software package”. The specific radioactivity of 226Ra under the peak energy of 186.21 keV is the sum of 235U under the peak energy of 185.7 keV and peak energy of 226Ra alone. Also 226Ra activities calculated from the activity measured from the 609.4 keV peak and other progeny peaks. 232Th activities were determined from the average concentrations of 238.6 keV peak of its 212Pb and 911.1 keV peak of its 228Ac or by 208TI gamma-ray emission probability corrected for 212Bi a decay branching ratio of 35.94%. Activities of 40 K were calculated from the 1460.7 keV peak, activities of 137Cs were calculated from the 661.6 keV peak in the samples. Activities of 238U were calculated from the 235U activities assuming the 235U/238U activity ratio of 0.046. 235U activities were calculated from the 186 keV peak. Limit of detection (LD) or (MDA) which is the minimum detectable activity was calculated according to Currie (14). Method at 95% confidence level and was estimated at the base of know efficiency, counting time, energy intensity and sample mass. The cores
3.1. Background measurements The measurements of back ground radiation of normal gabbro in Qatar have been done. The radionuclide in the samples of normal gabbro measured. The presence of natural isotopes 40 K, 232Th (228Ra), 226Ra and 238U were determined and effective dose for public and workers have been estimated according to exposure scenario. The presence of natural isotopes in the measured samples seem to be in normal concentration and comparable with the published data. Some samples of 100% slag were measured, the samples and the normal gabbro were treated, hazard and dose index calculated for both, the measurements results seen in Table 1. It is clear from this table all the index (dose and hazard index) exceeding the limits for 100% slag The summary of hazards index and dose for workers, general public and critical groups estimated as it similar to slag where Fig. 2 and Table 2 show the concentration index.
Table 1 Radio activity analysis of clean materials (Gabbro) and 100% slag. ID
Date
40 K
232Th
226Ra
137Cs
D(mSv.y-1)
Hex
clean material for road building
Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gab Avg
05/03/2016 03/03/2016 04/04/2017 05/04/2017 07/06/2017
14 25 4 24 11 7.8 14.3
0.7 0.7 0.7 0.38 6 0.7 1.53
7 10 8 7.5 8 8
<0.3 <0.3 <0.3 <0.8 ,0.8 <0.3
4.0544 5.808 4.051 4.486 7.861 4.2148 1.6278
0.024 0.034 0.025 0.027 0.047 0.026 0.0089
pure slag from Qatar Steel
Slag Slag Slag Slag Slag AVG Slag
5.8 7.8 20 7 6 9.32
172 168 170 140 183 166.6
291 271 260 300 295 283.4
<0.1 <0.1 <0.8 <0.3 <0.1
238.370 227.268 224.42 221.081 247.369
1.452 1.382 1.363 1.353 1.505
03/03/2016 07/06/2016 05/04/2016 04/04/2016
Fig. 2. The low background Gamma spectroscopy and sample preparation laboratories.
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741
Table 2 Show the dose and hazard index for Gabbro. Hazard index (I_c2)
Hazard index (I_c1)
D(dose index)(nGy/h)
226Ra (Bq/Kg)
232Th (Bq/Kg)
40 K (Bq/Kg)
Sample Description
Month
0.014 0.013 0.012 0.013 0.019 0.013 0.021 0.025 0.015 0.014 0.014 0.007 0.010 0.006 0.008 0.017 0.012 0.014
0.034 0.030 0.029 0.032 0.045 0.032 0.052 0.060 0.036 0.034 0.035 0.018 0.023 0.014 0.020 0.040 0.029 0.033
4.382 3.839 3.788 4.054 5.808 4.051 6.803 7.861 4.725 4.365 4.439 2.274 2.939 1.781 2.617 5.165 3.697 4.270
7 7 7 7 10 8 7.5 8 4.4 8.1 7.7 4 5.1 3.5 4.3 9.5 6 6.712
1 0.7 0.7 0.7 0.7 0.7 3.88 6 3 0.07 0.7 0.4 0.5 0.4 0.4 0.7 1 1.268
17 9 7.8 14 25 4 24 11 20 20 16 7 10 0.5 12 15 11 13.135
Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro Gabbro
Nov-14 Dec-14 Jan-15 Feb-15 Mar-15 Apr-15 May-15 Jun-15 May-16 Jun-16 Jul-16 Aug-16 Sep-16 Oct-16 Nov-16 Dec-16 Jan-17 Average
Variaon of K-40 Concentraon(Bq/Kg )from Nov,2014 to Jan2017.
Variaon of Th-232 concen. from Nov.2014 to Jan2017 40 30 20 10 0
17 15 13 11 9
7
5
3
Varaiaon of Ra-226 concen. from Nov.2014 to Jan 2017
200
400
150
300
100
200
50
100
0 17 15 13 11 9 7 5 3 1 232Th (Bq/Kg)
1
0 17 15 13 11 9 7 5 3 1
AVG
226Ra (Bq/Kg)
AVG
Fig. 3. Show The variation of K-40, Th-232 and Ra-226 for the measuring period of Nov2014 to Jan2017 of Slag samples.
3.2. Radiation routine tests Radioactivity levels in the steel slag aggregate have been measured on a monthly basis. Radiation Levels measured for steel slag and gabbro (as a control) samples are given in Fig. 3. The results cover measurements from November 2014 to June 2015, then from May 2016 to January 2017 in Fig. 4 The Fig. 3 above illustrate the variation of K-40, Th-232 and Ra-226 for the measuring period of Nov2014 to Jan2017, the variation of 40 indicate that the average K-40 concentration was 12.5, and its ranging from 30 Bq/Kg to about 5 Bq/Kg. Where the main concentration of Th- 232 and Ra-226 were 135.176 and 273.176 Bq/Kg respectively.
K-40,Th232,and Ra-226 concentraon (Bq/Kg)for Gabbro samples taken from Nov 2014 to Jan2017
3.3. Radiation of the slag site trials 30 25 20 15 10 5 0
40K (Bq/Kg)
232Th (Bq/Kg)
The main observations are that the trend of these two radionuclide’s are similar, and it seem that the trend indicate that since Jan 2015 seem that the both concentration dropped down which mean the source of steel ore might changed. The radioactivity results of the routine testing were analysed and the data evaluated for compliance with the dose and external hazard indices of the Qatari regulations. The results for gabbro analyses are given in Table 2. The table clearly showed that the Dose index and all hazard (internal and external) are accepted and this is in accordance with natural background in Qatar. Where the Table 3 present the Dose and hazards indexes, which is clear that the use of 100% slag for all type of use, are irregular. The table also show that radium concentration is higher than the reference level in Qatar so all 100% slag should be not accepted for use in road construction and as well as building materials.
226Ra (Bq/Kg)
Fig. 4. Comparison of variation of K-40. Th-232and Ra-226 in Gabbro samples.
The steel slag aggregate used in the full-scale production of unbound subbase materials, asphalt road subbase, and precast concrete units (crash barriers, soakaways etc.). The following samples from the slag products obtained for radioactivity testing: Loose slag samples (0–5, 5–10, and 10–20 mm diameter) Loose asphalt and asphalt cores for the control asphalt (gabbro), 20% slag asphalt, and 40% slag. Concrete cores for the control concrete (gabbro), 20% slag, and 50% slag.
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741 Table 3 the Dose and hazards indexes of slag’s sample collected from Nov2014 to Jan2017. Hazard index (I_c2)
Hazard index (I_c1)
D(dose index)(nGy/h)
226Ra (Bq/Kg)
232Th (Bq/Kg)
40 K (Bq/Kg)
Sample Description
Month
0.756 0.772 0.760 0.726 0.714 0.788 0.709 0.714 0.765 0.492 0.530 0.546 0.572 0.568 0.510 0.784 0.552 0.662
1.820 1.860 1.832 1.750 1.723 1.900 1.702 1.723 1.833 1.152 1.271 1.310 1.372 1.361 1.219 1.885 1.327 1.591
236.800 242.116 238.370 227.750 224.420 247.369 221.081 224.420 237.975 147.802 164.926 170.070 178.080 176.604 158.134 245.025 172.463 206.671
290 292 291 271 260 295 300 260 330 325 230 235 245 250 230 315 225 273.1765
170 177 172 168 170 183 140 170 145 13 100 105 110 105 90 165 115 135.1765
10 6 5.8 19 20 6 7 20 25 9.8 12 5 15 8 8 30 6 12.50588
Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag Slag
Nov-14 Dec-14 Jan-15 Feb-15 Mar-15 Apr-15 May-15 Jun-15 May-16 Jun-16 Jul-16 Aug-16 Sep-16 Oct-16 Nov-16 Dec-16 Jan-17 AVG
The slag samples were collected from the road site trials in Qatar Steel premises in Messeed. The grinded specimens were measured by Gamma ray spectroscopy. Table 4 shows the results of radioactivity measured in collected samples. The measurement of activity concentrations of 226Ra, 232Thand 40 K in the sample from the studied areas varies from 140 Bq kg1 to 15 Bq kg1 for K-40, from all samples type. Where the activity of Ra-226 ranging from about zero to about 120 Bq kg1 and from about100 Bq kg1 to about 3 Bq kg1. The radiation measurements results in Table 4 show that all the values are within the Qatari and International regulations of <185 Bq/kg. A zero value refers to the value lower, the radiation exposure and radiation risk were estimated for the various construction applications made with slag aggregate. The Gamma index for the activity concentration is also calculated to assess suitability of the slag products for use in construction road in the cities (Ic1) and outside cities (Ic2). The radiation exposure and radiation risk were estimated for the various construction applications made with slag aggregate. The Gamma index for the activity concentration is also calculated to assess suitability of the slag products for use in cities (Ic1) and outside cities (Ic2) as well as dose estimation seen in Table 5.
3.4. Radiation in asphalt Two sets of asphalt samples were tested including the loose asphalt (from the plant) and asphalt cores from the Qatar Steel trials in Messeed. In order to estimate the annual effective dose rate in air, a conversion coefficient from the absorbed dose in air to the effective dose received by an adult was considered. This value published in United Nations Scientific Committee on the Effects of Atomic Radiation report (UNSCEAR, 2000) to be 0.7 Sv/Gy for environmental exposure to gamma rays of moderate energy. The value of the occupancy factor is related to the degree of exposure; fulltime exposure. The annual effective dose equivalent (AEDE) is determined using the following equation:
AEDEðlSv =yÞ ¼ ðnannuGy=hÞ 8760h=y
0:2ðoccupancy factor outsideÞ 0:7ðSv =GyÞ 103
When applying the above equation for an outside occupancy factor, the absorbed dose for the control samples (without slag) indicated a negligible dose of 1 lSv/y. The calculated absorbed dose value for the 20% slag asphalt is 26.13 lSv/y, and 78.12 lSv/ y for the 40% slag asphalt [17–20].
Table 4 Radio-analysis results of slag road trials. Concentration (Bq/kg)
Loose asphalt mix (Control)
Loose asphalt mix(20% slag)
Loose asphalt mix(40% slag)
asphalt cores
Concrete cores
Loose slag
Loss slag
Sample cod.
K-40
Pb-212
Bi-214
Pb-214
Ra-226
Ac-228
Pa-234 m
U-235
1–11 1–12 1–13 1–14 1–15 1–16 1–17 1–18 1–19 4D Control 7D20% Slag 11D 40% Slag 1F Control 3E 20% Slag 2C 50% Slag 0–5 mm 5–10 mm 10–20 mm
18 ± 2 17 ± 2 15 ± 2 16 ± 1 16 ± 1 17 ± 1 17 ± 2 20 ± 1 19 ± 2 20 ± 1 18 ± 2 19 ± 2 162 ± 7 97 ± 5 125 ± 6 16 ± 1 12 ± 3 140 ± 2 22 ± 2
– 1 ± 0.2 – 28 ± 2 27 ± 2 30 ± 2 79 ± 6 72 ± 6 75 ± 6 2 ± 0.2 26 ± 2 34 ± 3 4 ± 0.3 77 ± 6 55 ± 4 92 ± 4 94 ± 5 32 ± 3 29 ± 2
– 1 ± 0.1 1 ± 0.1 30 ± 1 33 ± 1 34 ± 1 77 ± 2 71 ± 2 77 ± 2 5 ± 0.2 36 ± 1 45 ± 1 6 ± 0.3 71 ± 2 53 ± 2 111 ± 2 113 ± 3 122 ± 3 36 ± 1
1 ± 0.2 1 ± 0.1 1 ± 0.2 30 ± 1 31 ± 2 34 ± 2 78 ± 4 70 ± 4 77 ± 4 4 ± 0.3 36 ± 2 46 ± 3 6 ± 0.4 75 ± 4 52 ± 3 114 ± 4 118 ± 4 124 ± 4 37 ± 2
– 1 ± 0.1 – – – 26 ± 12 72 ± 34
– – – 31 ± 1 29 ± 1 31 ± 1 80 ± 2 74 ± 2 78 ± 2 3 ± 0.2 26 ± 1 35 ± 1 4 ± 0.3 76 ± 2 54 ± 2 96 ± 2 98 ± 2 96 ± 2 29 ± 1
– – –
– – – 3 ± 0.3 3 ± 0.3 2±1 6±2 8±1 5±2 – 4±1 5±2 – 5±2 6±1 5±1 5±1 8±1 3±1
64 ± 34 – 69 ± 8 – 14 ± 4 83 ± 32 102 ± 11 131 ± 16 32 ± 27 108 ± 18 34 ± 15
18 ± 1 38 ± 8 89 ± 17 54 ± 14 56 ± 18 – 21 ± 12 42 ± 11 – 105 ± 22 57 ± 17 126 ± 13 146 ± 27 134 ± 13 24 ± 9
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741
Table 5 dose and hazard index for all sample collected (19 sample). Hazard index (I_c2)
Hazard index (I_c1)
D(dose index) (nGy/h)
226Ra (Bq/Kg)
232Th (Bq/Kg)
40 K (Bq/Kg)
Sample Code Number
Sample
0.002
0.006
0.774
0
0
18
1 11
Loose asphalt mix (Control)
0.004 0.002 0.064 0.060 0.101 0.265 0.151 0.250 0.009 0.153 0.072 0.048 0.283 0.269 0.381 0.243 0.364 0.109
0.009 0.005 0.160 0.150 0.247 0.646 0.377 0.610 0.022 0.366 0.181 0.121 0.689 0.652 0.922 0.601 0.887 0.266
1.158 0.645 21.210 19.886 32.355 84.435 49.848 79.781 2.846 47.449 23.987 15.592 89.924 84.677 120.177 79.056 115.688 34.662
1 0 0 0 26 72 0 64 0 69 0 14 83 102 131 32 108 34
0 0 31 29 31 80 74 78 3 26 35 4 76 54 96 98 96 29
17 15 16 16 17 17 20 19 20 18 19 162 97 125 16 12 140 22
1 12 1 13 1 14 1 15 1 16 1 17 1 18 1 19 4D Control 7D 20% Slag 11D 40% Slag 1F Control 3E 20% Slag 2C 50% Slag 0–5 mm 5–10 mm 10–20 mm
For extreme conditions at full occupancy factor (indoor with direct contact with human), the dose values are 134.68 and 396.6 lSv/y for the 20% and 40% slag asphalt, respectively. This condition is unlikely to occur for humans to stay exposed in direct contact to slag radiation from asphalt for 100% of their time, but was considered to assess the extreme conditions. The radioactivity results and the analysis conducted confirm that the absorbed doses for all tested slag asphalt specimens are within the Qatari regulation permissible limit of 1 mSv/y (1000 lSv/y). There for up to 40% steel slag aggregate could be safely used for road construction in residential and urban areas could have an occupancy factor of 1.
Loose asphalt mix (20% slag) Loose asphalt mix (40% slag) asphalt cores
Concrete cores
Loose slag
loss slag
3.7. Car parking The first case study was made for a car park constructed of asphalt pavement. Steel slag aggregate was used to fully replace the coarse aggregate, i.e. replacing 40% of the total imported gabbro, in full pavement layers. In this scenario, the most significant pathway is likely to be from external exposure. Accordingly, doses from external irradiation to the public from the slag asphalt car park were determined using the following equation:
Dext ¼ AR Fslag DCexr; R T where:
3.5. Radiation in concrete The concrete radiation measurements results with 0–20, of the 50% slag aggregate as replacement of gabbro’s. The Ra-226 concentrations for the Control (core 1F), 20% slag (3E), and 50% slag (2C) were 14, 83, and 102 Bq/kg, respectively (less than the Qatar permissible value of 185 Bq/kg). The dose index for the three concrete mixtures was <1 mSv/y, considering 2000 working exposure per year. The Gamma activity index was always <1 for Ic1 and Ic2, indicating potential use in residential and urban areas. An additional internal hazard index (Hin) was calculated this index is considered when the application is in direct contact with humans. The hazard of this index is due to the inhalation of Radon that can lead to respiratory diseases and cancer. The Hin values calculated for the Control (core 1F), 20% slag (3E), and 50% slag (2C) were 0.13, 0.76, and 0.79, respectively. Whilst the Hin values are less than the Qatari permissible limit of 1, the RCPD-MME recommended not using slag concrete in buildings with direct contact of humans.
Dext: Dose from external irradiation in a car park 1 m above the ground (Sv/y) AR:Activity concentration of radionuclide R in slag (Bq/g) Fslag Fraction of slag used in asphalt surface materials (0.4) DCext, R: Dose coefficient for external exposure for radionuclide R (Sv/h per Bq/g) T: Duration of exposure, 100 h/y is assumed, based on 15 min per day Values for DCext, and R were determined using energy specific dose equivalent rates from IAEA (1992), appropriate for a plane surface of the car park. Doses to members of the public from the car park paved with 40% slag asphalt are given in Table 6. Both U-238 and Th-232 decay chains contribute to the external dose, with a higher contribution from Th-232 (62%) compared to 38% from U-238 decay chain. The does values take into account all members of the decay chain and were calculated using dose conversion factors of 0.039x10-8 and 0.06x10-8 for U-238 and Th-232, respectively as seen in Table 7.
3.6. Case studies Two case studies were considered for the dose estimation to the public when steel slag aggregate was used to replace 40% of total aggregate weight in asphalt applications. In the case studies, the Uranium (U-238) decay chain was considered in the analysis which takes into account all radionuclides in the chain including Radium (Ra-226), Radon (Rn-222) and Lead (Pb-210).
Table 6 Doses from 40% slag asphalt car parking to the public. Radionuclide
External Dose
Radionuclide contribution %
U-238 Th-232 total
2.88.10–8 4.8.10–8 7.68.10–8
38% 68% 100%
M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741 Table 7 Dose estimation for children play area made with 40% slag asphalt.
K-40 U-238(Ra-226) Th-232 Total
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4. Radiation risk assessment for different gabbro’s percentage
Dose conversion factor (Sv/yperBg/g)
Radionuclides concentration(Bq/g)
Absorbed Dose (Sv/y)
5.6 108 6.44 107 7.70 107
1.7 102 7.2 102 8.0 102
1.9 107 9.27 106 12.3 106 21.8 106
3.8. Radionuclide external do The dose to an adult from external exposure from the ground is 7.682 108 Sv/y, equivalent to 0.08 lSv/y. The calculated dose value is much lower than the Qatari regulation limit of 0.3 mSv/y (300 lSv/y) from a single source. It is therefore concluded that the 40% slag in asphalt car parking adds a very small dose, which is within the acceptable range of the Qatari regulations to the public. 3.9. Children’s play area The second case study considered a children’s playing area made with 40% slag asphalt pavement. Similar to the car park, the most significant pathway in this scenario is from external exposure. However, this pathway is more applicable to children (up to 10 year olds) rather than adults in the car park. The external irradiation is calculated from the same equation as the car park with the only difference that the exposure duration is increased to 200 h per year. The doses to 10-year old children from playing on the 40% slag asphalt. The total dose from external irradiation from the play area is 2 lSv/y. The excess dose, from using 40% slag aggregate in the surfacing materials will be <2lSv/y, which is lower than the limit of 10 lSv/y to be exempted dose from regulation. The results show clearly that the dose from external irradiation from the asphalt play area is 22 lSv/y which is much lower than the Qatari regulation limit of 0.3 mSv/y (equivalent to 300 lSv/y) from a single source. Results from the children’s play area and the car parking confirm the use of 40% slag aggregate in asphalt applications is safe for humans with negligible risk to children and adults.
Risk assessment methods are generally used for determining the allowable radiation concentration and dose. A software ‘‘RESRAD” was used in this investigation for assessing the radiological doses resulting from the slag materials, which considers external exposure, ingestion, internal and inhalation pathways. The risk assessment was conducted on an asphalt road constructed with 40% slag aggregate. The slag asphalt is considered to be laid within the top 300 mm layers of the road pavement, with the purpose of estimating the total effective dose equivalent to an individual over 1000 years. The following parameters are used for the dose calculation: The concentrations of radionuclides are K-40 = 17, Th-232 = 80, and Ra-226 = 72 Bq/kg, as obtained from Table 5 for the loose asphalt specimen (1–17). The dose conversion factor for external radiation is determined from the ICRP 107 (2010) for each radionuclide as (risk/y)/(mBq/g). The studied area is 10,000 m2 with an outdoor occupancy of 0.1 (200 h per year). The unrestricted zone is 1 m thick, related to the ground water level, and is assumed to remain constant during the study period. All pathways are considered, including Radon inhalation .The dose calculation was made for the period of 1, 2, 3, 4, 5, 6, 10, 13, and 1000 years, which are the main periods for risk assessment. The 1000 year is considered because it represents the half-life of the most important radionuclides from exposure point of view. External and internal exposures from all pathways up to 1000 years are presented in Fig. 5. The results show that the maximum dose from all nuclides is <1.5 lSv/y and occurs within the first 10 years of construction. The total dose decreases with time to below 1.0 lSv/y after 700 years of exposure. The results confirm that the total exposure from 40% slag pavement, considering all pathways, over 1000 year is negligible compared to national and international standards. Further analysis was conducted to assess the risk associated with the use of steel slag aggregate in asphalt pavement, which relates to the probability of having cancer due to exposure to radioactive materials used in road construction. Fig. 6 shows the excess cancer risk from all radionuclides and pathways for 40% slag asphalt up to 1000 years of exposure. Fig. 6 shows the maximum
Fig. 5. External and internal exposures from 40% slag asphalt up to 1000 years.
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M.S. Al-Kawari, M. Hushari / Construction and Building Materials 228 (2019) 116741
Fig. 6. Cancer risk from using 40% slag asphalt in roads.
risk achieved is 3.4 106 and occurs after 10 years from construction. The risk is reduced with time to reach less 3.0 106 after 500 years from construction. The value of 3.0 106 fatal cancer risk (i.e. 3 persons every million) is considered extremely low compared to the annual death rate from other activities. Annual death rate is the most common scale used for understanding and comparing the risk from exposure to radiation. Data from the US Bureau of Labor Statistics (2016) published the Census of Fatal Occupational Injuries (CFOI) rate from various activities in 2015. The average risk of dying from mining, quarrying, and oil and gas extraction is 11.7 in 100,000, 10.1 in 100,000 from construction activities, and 2.3 in 100,000 from manufacturing. The risk value for the use of steel slag is therefore negligible in comparison to these activities. Based on the radioactivity analysis conducted in this study by the RCPD, the Ministry of Municipality and Environment issued a No Objection Letter (Appendix A) for the use of 20% slag aggregate in asphalt (below the wearing course) and precast concrete (below the ground) provided compliance with the national and international regulations. The 20% permission is an initial step to start utilizing steel slag aggregate in various construction applications and is intended to encourage an increase in uptake to 40% slag after implementing a safe system for monitoring in practice. 5. Summary and conclusions The data on the concentration of radioisotopes for the steel slag showed a wide variation over the last 3 years, mainly in Radium Ra-226 and Thorium Th-232 concentrations, the two isotopes with significant levels of radioactivity. This change may be attributed to possible variation of iron sources. Loose steel slag aggregate may not use internally in direct contact with humans. However, it could be used in external construction applications below the ground surface. Asphalt made with up to 40% steel slag aggregate could be safely used in road applications in cities. However, from an environmental point of view, its use in the surface layer is not recommended. Concrete made with up to 50% slag aggregate could be safely used in construction applications, however, it is not recommended for use indoors with direct contact with humans. Precast concrete applications below
the ground surface or in open areas are recommended. Two case studies were considered for the use of steel slag aggregate in car parking and children’s playing areas. Where the slag used to replace 40% of the imported gabbro in asphalt and the results indicated safe use in both applications with negligible risk to children and adults. Radiation risk assessment showed very low risk (<3 106 fatal cancer risk) (i.e. 3 persons every million), which is considered extremely low compared to other exposure activities. The permitted content of slag could be increase to 40% in safe use in Asphalt. Our results are in well agreements with all international considerable studies and we recommend strongly using slag in asphalt outside and inside the cities especially in high ways construction. Declaration of Competing Interest None. Acknowledgements The authors are grateful to the Ministry of Municipality & Environment and the Public Works Authority (Ashghal) for their valuable contribution and support the project. The authors are also grateful to the Radiation Chemicals & Protection Department for carrying out the radioactivity investigation, Also to Qatar Steel who funded the project. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.conbuildmat.2019.116741. References [1] Ziauddin A. Khan, Rezqallah H. Malkawi, Khalaf A. Al-Ofi, Nafisullah Khan 2002. Review of steel slag utilization in Saudi Arabia, The 6th Saudi engineering conference KFUPM Dhahran. [2] A.T. Al-Kinani, M. Hushari, I.A. Alsadig, H. Al-Sulaiti, Measurements of recycling steel slug at Qatar Steel using low-level Gamma-ray Spectrometry and calculation of risk factors.Dannish, J. Res. Environ. Stud. 2 (4) (2015) 28–36. [3] The European Slag Association, Legal Status of Slags, Position Paper, 2006.
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