cement ratio, curing condition, and dosage of cement and air entraining agent

Annals of Nuclear Energy 38 (2011) 1505–1511

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Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene

Determination of transmission factors of concretes with different water/cement ratio, curing condition, and dosage of cement and air entraining agent c _ Remzi Sß ahin a,⇑, Recep Polat b, Orhan Içelli , Cafer Çelik d a

Dept. of Civil Eng., Faculty of Eng., Atatürk University, Erzurum, Turkey Dept. of Physics, Faculty of Education, Erzincan University, Erzincan, Turkey c _ Dept. of Physics, Faculty of Arts & Science, Yıldız Technical University, Istanbul, Turkey d Dept. of Industrial Eng., Faculty of Eng., Atatürk University, Erzurum, Turkey b

a r t i c l e

i n f o

Article history: Received 13 January 2011 Received in revised form 6 March 2011 Accepted 28 March 2011 Available online 22 April 2011 Keywords: Concrete Transmission factor Radiation Taguchi Method

a b s t r a c t This study focuses on determination of transmission factors of main parameters affecting the properties of both normal- and heavy-weight concrete in order to increase knowledge and understanding of radiation attenuation in concrete at a later age. Water/cement (W/C) ratio, curing condition, cement quantity and air entraining agent (AEA) were selected as the main parameters. Eight energy values have been selected within the energy interval of 30.85–383.85 keV to be used in the radiation source. The Taguchi Method was used as the method of optimization. It was determined in the study that the most important parameter affecting the attenuation of the radiation of the concrete is the W/C ratio and the concretes produced with the lowest level of W/C ratio absorb more radiation. However, it was also determined that there was a combined effect between the W/C ratio and the cement dosage. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction A constant need to produce materials, which can be used under hostile environment with high exposure to radiation, has developed with the current advances in technology (Krocher and Browman, 1984). Material that would be aimed to be used for this purpose should have a high attenuation coefficient. Concrete, which contains water, cement and aggregate, has many of the desired properties for nuclear radiation shielding. Moreover, this material is cheap, easy to prepare in different compositions, and easy to form and to use in construction works. Therefore, this composite material is widely used in building constructions such as nuclear power stations, particle accelerators, and medical hospitals (Kaplan, 1989; Shultis and Faw, 1996). Radiation shielding concrete can be used to attenuate both neutrons and gamma rays, and its effectiveness varies with the composition of the concrete (Kaplan, 1989). The type and quantity of aggregate and the cement dosage in concrete are important factors in terms of the radiation protection properties of concrete (Topçu, 2006). The experimental measurements of the attenuation coefficient, on the other hand, is essential for shield design since it provides basic data including interaction cross-section and half value layer parameters, which determine transport and attenuation of radiation in concrete. The linear attenuation coefficient, which ⇑ Corresponding author. Tel.: +90 533 643 66 31. E-mail address: [email protected] (R. Sßahin). 0306-4549/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.anucene.2011.03.013

is defined as the probability of a radiation interacting with a material per unit path length, is the most important quantity characterizing the penetration and the diffusion of gamma rays in a medium. Its magnitude depends on the incident photon energy, the atomic number and the density of shielding materials (Wood, 1982). The study of the absorption of gamma radiations in materials has also been an important subject in the field of radiation physics and is potentially useful in the development of semi-empirical formulations of high accuracy. Benefiting from the mass attenuation coefficient, a number of related parameters can be derived, such as the mass energy-absorption coefficients, the total interaction cross-section, the molar extinction coefficient, molecular, atomic, electronic cross sections, the effective atomic number, and the effective electron density. In this study, in addition to these parameters, the transmission factors of concrete samples were measured by using the mass attenuation coefficient at different energy intervals. The transmission of gamma-rays through different concrete samples have been measured by using the extremely narrowcollimated-beam transmission method in the range of 30.85– 383.85 keV of energy, as shown in Fig. 1. Several studies such as Abdo (2002), Akkurt et al. (2005, 2006), Bashter (1997), Boncukçuog˘lu et al. (2005), Demir et al. (2010), Demir and Keles (2006), Kharita et al. (2009), Korkut et al. (2010), Shiao and Tsai (1989), Okuno (2005), Yarar and Bayulken (1994) and Yarar (1996) have been performed in order to obtain linear attenuation coefficients and mass attenuation coefficients

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ties of the cement are given in Table 1. The locally available siliceous sand and crushed basalt fines were used as fine aggregate. Crushed basalt was separated into two size fractions, 4–8 mm and 8–16 mm, before being used. The particle densities and the water absorption values of the aggregates are given in Table 2. A synthetic detergent type chemical admixture produced in accordance with ASTM C260-01 was used as an air entraining agent (AEA). 2.2. Mixture design and preparation of specimens

Fig. 1. Experimental setup.

for concrete. However, almost all of these studies are concerned with heavy-weight concrete. In this study, normal-weight concrete was selected because of two different reasons. The first is to determine which one of the main parameters affecting the properties of both normal- and heavy-weight concrete (i.e. water/cement ratio, curing condition, cement quantity, and void ratio) is the most effective on the absorption of radiation of concrete. The other reason for its selection is to provide data to researchers, who want to compare mass attenuation coefficient of the normal-weight concrete with that of the heavy-weight concrete. Additionally, since radiation is absorbed by the lead plates covering the normalweight concrete wall in some structural engineering applications (e.g. in hospitals) it would be informative to determine whether the wall also contributes to the absorption of radiation or not.

2. Materials and method 2.1. Materials In all mixtures, the same Ordinary Portland Cement (CEM I 32.5) was used. The 7- and 28-day compressive strengths of the standard CEN cement mortars were 32.1 MPa and 44.0 MPa, respectively. The chemical composition and some physical proper-

Table 1 Chemical composition and physical properties of the cement. Oxides

Composition (%)

Chemical composition Silicon dioxide (SiO2) Aluminum oxide (Al2O3) Ferric oxide (Fe2O3) Calcium oxide (CaO) Magnesium oxide (MgO) Sulfur trioxide (SO3) Loss on ignition

21.0 5.3 3.3 59.2 3.2 2.7 3.8

Physical properties Specific gravity Initial setting time (h) Final setting time (h) Expansion in the Le Chatelier apparatus (mm)

3.03 3.00 3.30 4.00

In this study, 27 different concrete mixtures were prepared. The maximum particle size of the aggregate was kept constant at 16 mm for all the mixtures. The grading curve of the combined aggregate was selected to be between ISO A16 and B16, and it was closer to B16. The ratio of fine-to-coarse aggregate was 57/ 43. A pan-type laboratory mixer was used in the production. In concrete mixtures that do not contain an air entraining agent, the cement was first homogenized using the total amount of mixing water for about one minute in order to obtain a uniform mixture. In concrete mixtures containing air entraining agent, however, the cement was homogenized using half of the total amount of mixing water for 30 s, then, the remaining portion of the mixing water together with the air entraining agent was added and mixed for another 30 s. The sand, crushed basalt fines and the coarse aggregates were added to the cement paste in the given order in both cases and the mixing was sustained for three more minutes. A similar mixing procedure has also been reported in the literature (Marchand et al., 1999; Pigeon and Lachance, 1981). 2.3. The selected parameters and the design of experiments Water–cement ratio (W/C), cement content (C), curing condition (CC) and air-entraining admixture (AEA) were selected as the parameters of investigation. The test parameters and their experimentally studied values and ranges are shown in Table 3. The curing conditions given in Table 3 can be explained as follows: In air (A): Specimens were cured in a water tank saturated with lime at 20 ± 2 °C for 3 days, and then kept at laboratory medium for 2 years, Under plastic sheet (S): Specimens were cured in the same water tank for 3 days, then kept under polyethylene sheet at about 95% relative humidity for 14 days, and then kept at laboratory medium for 2 years, In water (W): Specimens were cured in water saturated with lime at 20 ± 2 °C temperature for 14 days, and then kept at laboratory medium for 2 years. According to Full Factorial Design, 81 (i.e. 34) different mixtures were required in order to investigate the effect of the four parameters at three levels on radiation transmission. Because the number of specimens was too high, The Taguchi Test Method was used to reduce the number of the tests to be applied. Thus, an experimental design consisting of 27 different combinations was selected taking L27 test model into consideration. In an experimental study comprising of four parameters at three levels, it is possible to use the L9 plan with nine different combinations. In order to investigate whether there is a combined effect of the parameters, the L27 (313) plan was selected in this study. The details regarding the experimental design related to the primary and the combined effects of the parameters can be found in the study reported by S ß ahin (2003). According to the Taguchi Method, a control check is done whether the expected results are obtained or not by conducting confirmation experiments under optimum conditions as determined by the analysis of the obtained results at the end of the experiments. However, in this study, since the concrete

R. Sßahin et al. / Annals of Nuclear Energy 38 (2011) 1505–1511 Table 2 The densities and water absorption values of aggregates. Type of aggregate

Particle density (g/cm3)

Water absorption (%)

Sand (0–4 mm) Crushed basalt fines (0–4 mm) Basalt (4–8 mm) Basalt (8–16 mm)

2.50 2.60 2.62 2.61

3.90 3.40 2.00 2.30

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where F is the value provided from the F table, a is the level of error, DFMSe is the degrees of freedom of mean square error, m is the degrees of freedom used in the prediction of Yi, N is the total number of experiments, and ni is the number of repetitions in the confirmation experiments. The experimental results that were obtained were analyzed statistically for the evaluation of the effect of each parameter on the optimization criterion. 2.4. Nomenclature coding of the mixtures

Table 3 The parameters and corresponding levels to be studied in experiments. Parameters

Their levels

Water–cement ratio (W/C) Cement content (C, kg/m3) Air-entraining admixture (AEA, %) Curing conditions (CC)

1

2

3

0.50 300 0.00 In water (W)

0.55 350 0.05 In air (A)

0.60 400 0.10 Under plastic sheet (S)

The concrete mixtures were designated with the following codes: the first two digits show the water-to-cement ratio (W/C) in weight expressed in percentage, the letter following the two digits is the curing condition (W = curing in water, S = curing under plastic sheet, and A = curing in air), then the three digits following the letter (W, S or A) show the cement content in kg/m3, the last digit (or digits) shows the air entraining agent (AEA) in 1/10,000 in which 0 = no air entraining; 5 and 10 mean that the AEA is used in ratios of 0.05% and 0.10% of the cement content, respectively. Thus, 50W300/0 indicates, for instance, a mixture that had a W/C ratio of 0.50, was kept under water, was prepared with a cement content of 300 kg/m3, and that contained no AEA. 2.5. Experimental procedure to determine the transmission factor

samples were too old (2 years), rather than conducting a classical confirmation test, one supplementary experiment in addition to the combination experiments as determined in the experimental design was determined. Then, the confirmation experiment was conducted simultaneously with the main experiments under the same conditions. Thus, based on the data obtained from the first 27 experiments the 28th experiment was predicted. After calculating the confidence intervals, the calculated results were compared with the experimental results. The data obtained from the experimental results can be analyzed using a series of formulations in the Taguchi Method. Kackar (1985) pointed out that a number of performance statistics (more than 60) was developed depending on the nature of the problem that was investigated. Since it was aimed to produce concrete with low transmission factors, the performance statistics were selected by taking ‘‘lower is better’’ as an optimization criterion in this study. Thus, the performance statistics were evaluated by using the following equation: n 1X Z S ¼ 10Log Y2 n i¼1 i

! ð1Þ

where ZS is the performance statistics, n is the number of repetitions for an experimental combination and Yi is the performance value of ith experiment. Using the Taguchi Method, the performance value corresponding to the optimum working conditions can be predicted by means of the additive model rather than determining the value experimentally (Phadke et al., 1983):

Y i ¼ l þ X i þ ei

ð2Þ

where l is the overall mean of the performance value, Xi is the fixed effect of the parameter level combination used in the experiment, and ei is the random error in ith experiment. Eq. (2) gives the point estimation, which is calculated by using experimental data in order to determine whether the results of the confirmation experiments are meaningful or not. The required confidence interval at a selected error level may be calculated using Eq. (3) (Ross, 1987):

sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi   1þm 1 Y i  F a:1;DF MSe  MSe  þ N ni

ð3Þ

Transmission factors based on attenuation coefficients of the concrete with different W/C ratios, curing conditions, cement quantities, and AEA contents were measured by narrow beam transmission geometry. The distance of the source-sample and the sample-detector were set to 12 mm and 4 mm, respectively. 30.854, 35, 53.135, 80.997, 276.400, 302.840, 356.010, and 383.850 keV gamma rays of a 133Ba (10 mCi) radioactive source were used to transmit the rays on concretes samples. The radioactive sources were shielded by pinhole lead collimators in order to obtain a narrow beam. The intensities of the gamma rays were measured using a high-resolution Si(Li) detector (FWHM of 160 eV at 5.96 keV) and data were collected into 2048 channels of a multichannel analyzer. All the peak areas were evaluated from the same channel interval at the background level of each spectrum. The spectra were collected for a period of 18,000 s for 133 Ba. The measurements were repeated five times in order to reduce the statistical error. In this study, much effort has been spent to reduce the sources of error during the transmission measurements. In an ideal transmission experiment, all photons must be sent to the absorber sample within parallel beams. In order to ensure this and to reduce the number of counted photons that would be exposed to Compton and coherent scattering at low angles, the way between the primer exciter and the absorber sample was kept narrow and long using a suitable collimator. Scattering angle was determined within the interval of 0–0.00436° with gravimetric method that uses a suitable source collimator having 2 mm in active diameter. The distance between concrete sample and the detector was 4 mm. The secondary sample-source distance was set to 12 mm, which was determined by measuring Ka X-ray intensities at different distances. On the other hand, since sample base affects background, multiple scattering and dead time, lt < 1 condition (where l is linear attenuation coefficients and t is the thickness of material) was satisfied for present samples. In this way, it was aimed that the mentioned effects could be negligible. In order to separate Compton and coherent peak in small angle and strip spectrum, the method reported by S ß ahin et al. (1996) has been used. In addition, long-time periods were selected during counts in order to reduce errors arising from counting statistics. Ratios of background counts/total counts were attempted to be reduced

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Table 4 Mass thickness of the concrete specimens (g/cm2). Concrete number

1

2

3

4

5

6

7

8

9

Mass thickness Concrete number Mass thickness Concrete number Mass thickness

2.0257 10 1.5186 19 1.8527

2.0454 11 2.0731 20 1.9026

1.8625 12 1.8155 21 1.6349

1.9755 13 1.8076 22 2.1188

1.8588 14 1.7486 23 1.9849

1.8337 15 1.9539 24 2.0089

1.4505 16 1.8788 25 1.8604

1.8418 17 1.8023 26 1.8896

1.9076 18 2.1061 27 1.5429

for each measurement. However, during the experimental studies, there is a systematic and/or operating error for each state. The errors in the measurements were mainly due to the counting statistics, non-uniformity of the absorber, impurity content of the samples and the scattered photons reaching the detector. These errors were attributed to be less than 1% for the statistical errors, sample thickness, sample weighting, geometric factor, and source intensity, and 2% for systematic errors. The standard deviation (±) was determined for each measurement by multiplying the calculated value of 0.0316 by the experimental values. 2.5.1. The total mass attenuation coefficients The total mass attenuation coefficients, lt, are given as follows;

 

 

l 1 I0 ln ¼ t q I

ðcm2 =gÞ

ð4Þ

where I0 and I are the intensity of the beam before and after passing through the absorber, respectively. t is the mass thickness of concrete given in Table 4 which is formulated as t = m/pr2. Here, m is the substance quantity (g) and r is the radius of the sample. 2.5.2. The transmission factors When an X-ray beam passes through an absorber, it is attenuated. The degree of attenuation depends on the amount of scattering and on various absorption process parameters. Lambert’s law states that equal paths in the same absorbing medium attenuate

equal fractions of radiation. The fraction of transmission, I/I0 or T, is determined by the following equation:

T¼

I ¼ elt t I0

ð5Þ

lt, mass attenuation coefficient, can be obtained from the measured values of I/I0 and t. 3. Results and discussion The unit weights and the transmission factors of the specimens obtained from the experiments were listed in Table 5. The results

Table 6 Optimum levels of the parameters and major combined effect among the parameters. Energy level (keV)

Parameters W/C

30 35 53 80 276 302 356 383

0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50

C (43) (43) (39) (69) (69) (69) (68) (65)

350 350 350 350 400 350 400 400

(12) (5) (6) (5) (9)

AEA

CC

Combined effect

0,05 (6) 0,05 0,00 0,10 0,10 0,10 0,10 0,10

A A (6) W S S S S S

W/C  C W/C  C W/C  C W/C  C W/C  C W/C  C W/C  C W/C  C

(24) (13) (24) (12) (9) (10) (10) (13)

Table 5 Unit weights of the specimens and results of experimental transmission factors.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Code

Unit weight (kg/m3)

55W300/0 55A300/5 55S300/10 55A350/0 55S350/5 55W350/10 55S400/0 55W400/5 55A400/10 60W300/0 60A300/5 60S300/10 60A350/0 60S350/5 60W350/10 60S400/0 60W400/5 60A400/10 50W300/0 50A300/5 50S300/10 50A350/0 50S350/5 50W350/10 50S400/0 50W400/5 50A400/10

2291 2268 2239 2306 2266 2162 2286 2238 2195 2309 2260 2190 2260 2235 2192 2268 2197 2170 2228 2276 2231 2320 2299 2226 2312 2254 2211

Energy (keV) 30.854

35

53.135

80.997

276.400

302.840

356.010

383.850

0.00076 0.00079 0.00328 0.00061 0.00171 0.00234 0.00588 0.00277 0.00288 0.00340 0.00033 0.00416 0.00098 0.00176 0.00203 0.00263 0.00231 0.00250 0.00121 0.00184 0.00144 0.00012 0.00027 0.00052 0.00022 0.00023 0.00064

0.0148 0.0078 0.0183 0.0076 0.0155 0.0193 0.0361 0.0229 0.0164 0.0319 0.0076 0.0232 0.0105 0.0030 0.0170 0.0200 0.0188 0.0144 0.0126 0.0149 0.0069 0.0012 0.0023 0.0046 0.0023 0.0033 0.0039

0.0119 0.1609 0.2122 0.1473 0.2268 0.1999 0.3019 0.2275 0.2531 0.2985 0.1536 0.2329 0.1585 0.2131 0.2222 0.2512 0.2371 0.2813 0.2061 0.2057 0.0583 0.0351 0.0420 0.0387 0.0409 0.0414 0.0490

0.4416 0.4636 0.5303 0.4357 0.5077 0.4953 0.5721 0.5365 0.4958 0.5550 0.4237 0.5482 0.4398 0.5027 0.5081 0.5399 0.5240 0.5089 0.4886 0.5031 0.1176 0.0906 0.0981 0.1071 0.0988 0.0973 0.1072

0.7345 0.6654 0.6625 0.6160 0.6333 0.6820 0.7912 0.7812 0.5583 0.5960 0.7828 0.6846 0.6303 0.6314 0.6288 0.6847 0.6308 0.5148 0.5635 0.6780 0.1376 0.0814 0.1611 0.1456 0.1049 0.1273 0.1192

0.7382 0.6818 0.7555 0.7543 0.7478 0.7151 0.7309 0.7398 0.7943 0.7099 0.6324 0.8215 0.6541 0.6724 0.7872 0.8137 0.7624 0.8744 0.7563 0.6829 0.1446 0.1461 0.1195 0.1409 0.1572 0.1498 0.1565

0.7510 0.6907 0.7310 0.6905 0.7343 0.6909 0.7758 0.7298 0.6606 0.7590 0.6636 0.7570 0.6858 0.7442 0.7462 0.7204 0.7592 0.7134 0.7423 0.7426 0.1511 0.1513 0.1417 0.1617 0.1495 0.1369 0.1546

0.6629 0.6089 0.7260 0.5691 0.6700 0.6244 0.6213 0.6576 0.5763 0.6096 0.5332 0.5343 0.4804 0.6018 0.5428 0.5396 0.5188 0.5271 0.6446 0.6355 0.1552 0.1049 0.0878 0.1389 0.1188 0.0911 0.0837

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Fig. 2. S/N graphs of the parameters.

50W300/0 50A300/5

0.8

0.8

50S300/10

fit curve for 55W300/0

50A350/0

fit curve for 50W300/0

50S350/5 50W350/10

Transmission Factor

Transmission Factor

50S400/0

0.6

50W400/5 50A400/10

0.4

0.6

0.4

55W300/0 55A300/5

0.2

55S300/10 55A350/0

0.2

55S350/5 55W350/10 55S400/0

0.0

55W400/5 55A400/10

0.0

50 0

100

200

300

400

Incident photon energy (keV)

100

150

200

250

300

350

400

Incident photon energy (keV) Fig. 4. Transmission factors of the concrete mixtures with moderate water–cement ratio (0.55).

Fig. 3. Transmission factors of the concrete mixtures with low water–cement ratio (0.50).

of the optimization, which was carried out using these data based on the ‘‘lower is better’’ criterion, were given in Table 6 and Fig. 2. Table 6 shows the most effective level of the parameters, effectiveness percentage of these levels on the results (only the results higher than 5% were given in the parentheses) and the combined effects of the parameters obtained by ANOVA. In Fig. 2, the maximum points show the optimum level of the parameters while the slopes of the lines indicate the degrees of efficiency of the parameters. The sharpest slope indicates the most important parameter in Fig. 2. The following results can be deduced from Table 6 and Fig. 2: The most effective parameter on radiation attenuation of the normal-weight concrete is the W/C ratio. This applies to all energy levels. The order of the parameters other than the W/C has changed in different energy levels. Although a definitive ranking cannot be carried out for the energy levels below 53 keV, the dosage of cement (C) was determined to be the second most effective parameter for up to energy levels of 80 keV. The effectiveness of AEA and

CC has remained fairly low levels, especially for higher energy levels closer to the upper limit of 80 keV. The lowest level (i.e. 0.50) of the W/C ratio can be considered to be the most effective ratio for all energy levels. The degree of efficiency of this ratio became more evident with increasing energy levels. The efficiency percentage of the ratio of 0.50 is 41 ± 2% for lower photon energy levels of 53 keV, and is 67 ± 2% for higher photon energy levels of 80 keV (see Table 6). High levels of cement dosage (350–400 kg/m3) in the concrete, on the other hand, have increased the attenuation of the radiation. The density of concrete increased with decreasing W/C ratio. It can be determined from Table 6 that the average unit weights of the concrete specimens are 2262 kg/m3, 2250 kg/m3 and 2231 kg/ m3 for ratios of 0.50, 0.55 and 0.60, respectively. These results show that the radiation attenuation of the concrete increased in direct proportion to the density of the concrete. In other words, highdensity concrete attenuates more radiation. In fact, it is well known that the density of concrete increases with increasing cement dosage. However, since air entraining agent (AEA) that was used in this study mixed thoroughly with the concrete having high

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0.8

0.4 60W300/0 60A300/5

0.22672 0.08857–0.36487 0.1386

0.6

356.010

Transmission Factor

fit curve for 60W300/0

0.16995 0.05055–0.28935 0.1541

383.850

1.0

60S300/10

0.2

60S350/5 60W350/10 60S400/0

302.840

60W400/5 60A400/10

Incident photon energy (keV)

276.400

Fig. 5. Transmission factors of the concrete mixtures with high water–cement ratio (0.60).

The predicted values and the confidence intervals determined by Eqs. (2) and (3), respectively, were displayed in Table 7 for one extra mixture that was produced in order to determine the conformity of the test results. In Table 7, the results obtained from Eq. (2) were given in the column denoted as the ‘‘predicted value’’. It can be seen from Table 7 that almost all of the experimental results of the specimen coded 50W400/10 (arbitrarily selected) are within 95% confidence level. These results indicate that the experiments that are not conducted according to the selected experimental design can be predicted, and that the Taguchi Method is a verified experimental design technique.

Table 7 Confirmity tests results.

3.1. Results of the confirmation tests

30.854

Energy (keV)

35.0

53.135

80.997

cement dosage (Sßahin, 2003), the specimens with high AEA content and high cement content had a lower unit weight. Therefore, the expected increase in the density of concrete with increasing cement content could not be determined definitively. Theoretical values of the mass attenuation coefficients are not calculated since no accurate result for elemental analysis of modular sand was available. However, the experimental transmission fractions are illustrated in Figs. 3–5, which are classified according to their level for the W/C ratio. As it can be seen from the figures, the transmission factors increase exponentially with increasing energy supplied by 133Ba in the range of 30.85–276.85 keV. At energy levels higher than 276.85 keV, the transmission fractions decrease with increasing energy, especially in concrete samples with W/ C = 0.55 and 0.60. The maximum rates of increase were around 0.10 for the concrete samples with W/C ratio of 0.50 (except for the specimens coded 50W300/0 and 50A300/5) and were in the range of 0.60–0.80 for the concrete samples with W/C ratio of 0.55 and 0.60. In this study, the combined effects (i.e. interactions) have been identified among the parameters. The interaction, which is more evident below energy levels of 53 keV, is most pronounced between the W/C ratio and the C.

0.15854 0.04803–0.26905 0.0945

400

0.18039 0.07737–0.28341 0.0955

300

0.1027 0.03134–0.17406 0.0349

200

0.01135 0.01052–0.01218 0.0024

100

0.00097 0.0000–0.0022 0.00011

0

Predicted value Confidence interval (%95) Experimental result

0.0

0.27590 0.12272–0.42908 0.1185

60A350/0

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4. Conclusions The number of reinforced concrete building containing any source of radiation is increasing every day. Therefore, as is done in this study, application of nuclear physics research on concrete technology is important to determine the radiation resistance of concrete. Within the framework of this study, it can be concluded that the most important parameter affecting the attenuation of radiation of normal-weight concrete is the water/cement ratio. This parameter is followed by the cement content. Curing conditions and air entraining agents have little effect in comparison to the W/C ratio and the amount of cement. Moreover, it was also determined that there was a combined effect between the two parameters. Therefore, more investigation regarding this interaction is required. The concrete having the lowest W/C ratio and higher levels of cement content (350–400 kg/m3) attenuate more radiation. It can also be deduced form the study that, when the number of test parameters is high, Taguchi Method provides an appropriate methodology for parameter reduction and the most effective parameter can be determined by the optimization of the parameters. References Abdo, A.E., 2002. Calculation of the cross-sections for fast neutrons and gamma-rays in concrete shields. Ann. Nucl. Energy 29, 1977–1988. Akkurt, I., Mavi, B., Akkurt, A., Basßyig˘it, C., Kılınçarslan, S., Yalım, H.A., 2005. Study on Z dependence of partial and total mass attenuation coefficients. J. Quant. Spectrosc. Radiat. Transfer 94 (3–4), 379–385. Akkurt, I., Basßyig˘it, C., Kılınçarslan, S., Mavi, B., Akkurt, A., 2006. Radiation shielding of concretes containing different aggregates. Cem. Concr. Compos. 28, 153–157. Bashter, I.I., 1997. Calculation of radiation attenuation coefficients for shielding concretes for shielding concretes. Ann. Nucl. Energy 24, 1389–1401. _ Boncukçuog˘lu, R., Içelli, O., Erzeneog˘lu, S., Kocakerim, M.M., 2005. Comparison of radioactive transmission and mechanical properties of portland cement and a modified cement with trommel sieve waste. Cem. Concr. Res. 35 (6), 1082–1087. Demir, D., Keles, G., 2006. Radiation transmission of concrete including boron waste for 59.54 and 80.99 keV gamma rays. Nucl. Instrum. Methods Phys. Res. Sect. B 245, 501–504.

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