# Activity Concentration Index Values for Concrete Multistory Residences in Greece Due to Fly Ash Addition in Cement

^{1}

^{2}

^{*}

## Abstract

**:**

^{226}Ra chain is found to be about 1 kBq/kg. Since natural radionuclide concentrations, which are harmful to human health in terms of radiation exposure, exist in fly ash, ACI should be assessed for building materials containing fly ash. The present study evaluates the ACI of concrete containing fly ash cement when used in multistory residential buildings. Results showed that cement produced in Greece by the three main Greek cement production plants, containing lignite fly ash, and used as a material for concrete multistory constructions, should not be considered as “of concern from a radiation protection point of view”. Each country that wishes to evaluate the use of fly ash into constructions should repeat the method for the ACI uncertainty budget proposed in this study, to assess whether it significantly exceeds the reference value (whether it is of concern from a radiation protection point of view).

## 1. Introduction

^{226}Ra chain is found to be about 1 kBq/kg [6,7,8,9,10,11,12]. As has been already discussed [8], there have been significant differences in the results of various studies relative to the concentration of naturally occurring radioisotopes in lignite-produced fly ash. This could be attributed to differences between the sampling approaches followed in each study. In the same context, the following parameters also contribute:

- -
- Intrinsic variation by time of the under-study concentrations, according to which was the exact deposit where the finally burned lignite was originating from.
- -
- Variations among technical characteristics of the different burning processes.

_{x}is the specific (by mass) activity for x contributor, namely the

^{226}Ra series, the

^{232}Th series and

^{40}K, expressed in Bq/kg.

_{γ}index, as mentioned in some of them) or other similar indexes such as the

^{226}Ra equivalent activity concentration (Ra

_{eq}in Bq/kg) and the external hazard index (H

_{ex}, dimensionless as per ACI), when gamma radiation is assessed for concrete or even its constituents [16,17,18,19,20,21,22,23,24,25,26,27]. None of them have proposed a method according to the ISO approach to estimate the uncertainty of the results. Therefore, a producer of construction products/materials or a laboratory contributing to quality control, are not effectively supported to establish a decision rule on whether the product/material is “of concern from a radiation protection point of view”.

^{226}Ra,

^{232}Th and

^{40}K in the granites may not be particularly high, the presence of other radioisotopes in this material is also mentioned, increasing the level of the produced gamma radiation field [36]. In these cases, the fact that the ACI formula (Equation (1)) cannot incorporate the effect from these radioisotopes should also be considered.

## 2. Data and Methods

^{226}Ra and

^{232}Th series of radioisotopes and

^{40}K) concentration but also on a definition uncertainty caused by a lack of knowledge on the exact placement of the construction materials in the residence.

^{226}Ra and

^{232}Th series and

^{40}K in samples from materials which, according to the current Concrete Technology Regulation, constitute the minimum necessary materials so that the mixture can be called concrete. These values are the input data for Equation (3), specifically for estimating the mass specific activity of concrete constituents other than cement containing fly ash.

^{226}Ra,

^{232}Th and

^{40}K, was calculated according to Equation (3), as also presented graphically in Figure 4.

_{i}are the proportions of the three concrete constituents, expressed in kg/m

^{2}of fresh concrete, i.e., exactly as determined according to the concrete composition study.

_{fa}, C

_{fa}are the mass ratio (proportion into cement) and mass specific activity of fly ash and a

_{cem}, C

_{cem}are the mass ratio (proportion into cement) and mass specific activity for the rest of the cement constituents.

_{i}proportions of cement and fly ash were obtained according to the permissible limits imposed by the concurrent Greek legislation.

## 3. Results

_{fa}

_{,}

_{cem}, α

_{cem}) was assumed based on a linear correlation coefficient equal to −1.

- The proportion of cement constituents is reported as a dimensionless number, meaning the mass fraction of constituents and the value of the bounds of possible values [40] refer to the half interval on both sides of the mean to produce a confidence interval of about 99.7% level.
- It should be noted that the range of values considered for the proportion of fly ash addition to cement is a worst-case scenario compared to what is known for the actual construction activity in Greece in the last 20 years. The proportion of fly ash added into cement has decreased in recent years due to a decrease in the production of fly ash by Greek TPPs. In the early years of this twenty-year period, the proportion of fly ash added to cement was approximately up to 15% by mass. In current years, the maximum value of this rate has been reduced to approximately 3%. A range of values for α
_{fa}_{,}_{Ra}_{226}= 0–0.2 (i.e., 0% to 20% fly ash percentage, by mass, in the produced cement) was assumed. Such an interval is so wide to includes any effect of a possible difference in the moisture content of the fly ash between samples’ moisture content when analyzed in a gamma spectroscopy setup for determining^{226}Ra,^{232}Th and^{40}K activity and the moisture content of all other cement constituents, during their mix. - The uncertainty budget in Table 4 leads to confidence intervals at an approximately 95% level presented in Table 5 due to applying the “law of error propagation” [40]. In this context, the bounds (a range) of possible values and a corresponding distribution is assumed to produce the standard uncertainty for each variable that contributes to Equation (4). Standard uncertainties are multiplied by the corresponding sensitivity coefficients. These are the partial derivatives of the applied equation as per the variables for which the sensitivity coefficient is estimated. The right-most column of Table 4 shows the contribution of each variable to the finally estimated uncertainty of the result for each NORM as the square value of the result of this multiplication or the value of the covariance between the two mass proportions. The results presented in Table 4 are the sum of these contributions, which is the square of the combined standard uncertainty relative to the result of Equation (4), for each NORM.
- The values provided in Table 5 are used as input data in calculations provided in Table 6 in relation to the possible values of the mass specific activity of cement containing fly ash. Table 6 provides the uncertainty budget for the estimation of mass specific activity of fresh concrete constituents: cement, aggregate and water. The uncertainty budget presented in these tables refers to Equation (3). It is noted that the ratios of these three concrete constituents have an expected correlation between them, as any decision to increase the ratio of the one, (e.g., of the cement to seek a greater strength in the hardened concrete), leads to a corresponding readjustment of the ratio of at least one or even both the remaining constituents.

## 4. Discussion

^{226}Ra,

^{232}Th and

^{40}K emerged as a prevailing radiological factor as compared to others. It should be noted that

^{40}K concentration in common fresh concrete is unlikely to affect ACI values. Covariances between the proportions of the concrete constituents are also unlikely to affect ACI values. On the other hand, the sensitivity coefficient related to changes in NORMs concentrations in the aggregates is relatively high. The possible addition of aggregates that do not belong to the—usually used in Greece—limestone category, must be considered.

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Exposure of a person to gamma radiation field when standing on the ground, due to gamma radiation emitted from soil (yellow arrows) or standing on the floor of a multistory building with concrete as the main structural element, due to gamma radiation emitted by the radioactivity contained in the surrounding materials (dark grey arrows for radiation produced by the floor and the ceiling concrete slabs and light grey arrows for radiation produced by any perpendicular construction materials’ masses, e.g. masonry).

**Figure 2.**Fishbone diagram of parameters contributing to the estimation of ACI when the 2013/59/Euratom Directive formula is used.

**Figure 3.**Fishbone diagram showing that the activity concentration that influences the inhabitant of a building is related to many types of construction products (materials).

**Figure 4.**Fishbone diagram showing the parameters that contribute to the concentration of NORMs in a concrete mixture.

Indicative Types of Cement That the Producer Provides in Year 2023 | Cement Producer | Commenting on the Presence of Fly Ash in Cement (As Product) |
---|---|---|

CEM II/B-M (P-W-L) 32.5N | HERACLES | Natural pozzolana—calcareous fly ash—limestone: 21–35% |

CEM II/B-M(W-P-LL) 32.5N | TITAN | Natural pozzolana—calcareous fly ash—limestone: 21–35% |

CEM IV/B(P-W) 32.5 (sulfate resistant) | HALYPS | Natural pozzolana—calcareous fly ash—limestone: 36–55% |

**Table 2.**Data retrieved from previous works on the potential concentrations of naturally occurring radioisotopes (

^{226}Ra,

^{232}Th and

^{40}K) in fly ash produced during lignite combustion in Greek ΤPPs.

Lignite Origin According to Reference | NORM Concentrations [Bq/kg] | ||
---|---|---|---|

^{226}Ra | ^{232}Th | ^{40}K | |

Megalopolis (Region of Peloponnese) [7,8,9,42,43] | 293–1058 | 4–89 | 308–590 |

Ptolemais and Kardia (Region of Western Macedonia) [7,8] | 204–825 | <90 | 162–299 |

Aliveri (Evia, Region of Central Greece) [7] | 257–357 | 0.6–2.0 | - |

Cement producers [31,44] | 200–1400 | 34–84 | <650 |

Greek lignite according to all references | 200–1400 | <90 | <650 |

**Table 3.**NORM mass specific concentrations in concrete constituents according to papers related construction materials produced in Greece.

What Was Measured? | NORM Concentrations [Bq/kg] | ||
---|---|---|---|

^{226}Ra | ^{232}Th | ^{40}K | |

Limestone [31] | 5–7 | 4–10 | 86–128 |

Pozzolanic materials [31] | 34–40 | 19–53 | 298–424 |

Gypsum [31] | 5–9 | <LoD * | <LoD |

Clinker [31] | 12–18 | 5–23 | 102–180 |

Cement not containing fly ash [32] | 96 | 22 | 200 |

Total of no fly ash cement constituents | 5–96 | <53 | <424 |

Cement containing fly ash [32] | 215–218 | 11–26 | 222–330 |

Cement (in general) [12] | 15–218 | 10–41 | 32–457 |

Sand [31] | 7–15 | <9.9 | <60 |

Aggregates (in general) [12] | 3–46 | 3–56 | 19–1048 |

Aggregates [12,31] | 3–46 | <56 | <1048 |

Water [42] | <2 | <2 | <100 |

**Table 4.**Uncertainty budget for the calculation of the confidence interval for the values of the specific activity of

^{226}Ra,

^{232}Th and

^{40}K in cement to which lignite ash has been added.

Factor | Mean Value | Bounds of Possible Values | Distribution of Possible Values | Standard Uncertainty | Sensitivity Coefficient | Contribution to the Uncertainty of the Result |
---|---|---|---|---|---|---|

^{226}Ra | ||||||

α_{fa,Ra226} | 0.1 | 0.1 | Rectangular | 0.06 | 800 Bq/kg | 2133 (Bq/kg)^{2} |

α_{cem,Ra226} | 0.9 | 0.1 | Rectangular | 0.06 | 50 Bq/kg | 9 (Bq/kg)^{2} |

C_{fa,Ra226} | 800 Bq/kg | 600 Bq/kg | Triangular | 245 Bq/kg | 0.1 | 600 (Bq/kg)^{2} |

C_{cem,Ra226} | 50 Bq/kg | 46 Bq/kg | Triangular | 19 Bq/kg | 0.9 | 292 (Bq/kg)^{2} |

Cov(α_{fa,Ra226}, α_{cem,Ra226}) | −288 (Bq/kg)^{2} | |||||

C_{fa,cem,Ra226} | 125 Bq/kg | 2746 (Bq/kg)^{2} | ||||

^{232}Th | ||||||

α_{fa,Th232} | 0.1 | 0.1 | Rectangular | 0.06 | 45 Bq/kg | 7 (Bq/kg)^{2} |

α_{cem,Th232} | 0.9 | 0.1 | Rectangular | 0.06 | 27 Bq/kg | 3 (Bq/kg)^{2} |

C_{fa,Th232} | 45 Bq/kg | 45 Bq/kg | Triangular | 18 Bq/kg | 0.1 | 3 (Bq/kg)^{2} |

C_{cem,Th232} | 27 Bq/kg | 27 Bq/kg | Triangular | 11 Bq/kg | 0.9 | 98 (Bq/kg)^{2} |

Cov(α_{fa,Th232}, α_{cem,Th232}) | −9 (Bq/kg)^{2} | |||||

C_{fa,cem,Th232} | 29 Bq/kg | 102 (Bq/kg)^{2} | ||||

^{40}k | ||||||

α_{fa,K40} | 0.1 | 0.1 | Rectangular | 0.06 | 325 Bq/kg | 380 (Bq/kg)^{2} |

α_{cem,K40} | 0.9 | 0.1 | Rectangular | 0.06 | 212 Bq/kg | 162 (Bq/kg)^{2} |

C_{fa,K40} | 325 Bq/kg | 325 Bq/kg | Triangular | 133 Bq/kg | 0.1 | 177 (Bq/kg)^{2} |

C_{cem,K40} | 212 Bq/kg | 212 Bq/kg | Triangular | 87 Bq/kg | 0.9 | 6130 (Bq/kg)^{2} |

Cov(α_{fa,K40}, α_{cem,K40}) | −496 (Bq/kg)^{2} | |||||

C_{fa,cem,K40} | 223 Bq/kg | 6353 (Bq/kg)^{2} |

**Table 5.**Estimated 95% confidence intervals for NORM mass specific concentrations (Bq/kg) in cement produced in Greece during the year 2023.

Estimated for | C_{fa,cem} (Bq/kg) |
---|---|

^{226}Ra | (1.2 ± 1.0) × 10^{2} |

^{232}Th | 29 ± 20 |

^{40}K | (2.2 ± 1.6) × 10^{2} |

**Table 6.**Uncertainty budget for the calculation of the confidence interval for the values of the specific activity of

^{226}Ra,

^{232}Th and

^{40}K in fresh concrete.

Factor | Mean Value | Bounds of Possible Values | Distribution of Possible Values | Standard Uncertainty | Sensitivity Coefficient | Contribution to the Uncertainty of the Result |
---|---|---|---|---|---|---|

^{226}Ra | ||||||

α_{fa,cem} | 320 kg/m^{2} | 40 | Triangular | 16 | 0.03 | 0.33 (Bq/kg)^{2} |

α_{agg} | 1500 kg/m^{2} | 200 | Triangular | 82 | −0.005 | 0.16 (Bq/kg)^{2} |

α_{w} | 164 kg/m^{2} | 52 | Triangular | 21 | −0.01 | 0.1 (Bq/kg)^{2} |

C_{fa,cem,Ra226} | 125 Bq/kg | 42 | 0.14 | 35 (Bq/kg)^{2} | ||

C_{agg,Ra226} | 24 Bq/kg | 22 | Triangular | 9 | 0.79 | 50 (Bq/kg)^{2} |

C_{w, Ra226} | 2 Bq/kg | 2 | Triangular | 1 | 0.07 | 0.003 (Bq/kg)^{2} |

Cov(α_{fa,cem}, α_{agg}) (r = −0.2, is assumed) | 0.09 (Bq/kg)^{2} | |||||

Cov(α_{fa}_{,}_{cem}, α_{w}) (r = 0.5, is assumed) | −0.18 (Bq/kg)^{2} | |||||

Cov(α_{a}_{gg}, α_{w}) (r = −0.2, is assumed) | −0.05 (Bq/kg)^{2} | |||||

C_{con,Ra226} | 35 Bq/kg | - | 85 (Bq/kg)^{2} | |||

^{232}Th | ||||||

α_{fa,cem} | 320 kg/m^{2} | 40 | Triangular | 16 | 0.001 | 0.0004 (Bq/kg)^{2} |

α_{agg} | 1500 kg/m^{2} | 200 | Triangular | 82 | 0.0007 | 0.004 (Bq/kg)^{2} |

α_{w} | 164 kg/m^{2} | 52 | Triangular | 21 | −0.01 | 0.05 (Bq/kg)^{2} |

C_{fa,cem,Th232} | 29 Bq/kg | 10 | 0.14 | 2 (Bq/kg)^{2} | ||

C_{agg,Th232} | 28 Bq/kg | 28 | Triangular | 11 | 0.79 | 81 (Bq/kg)^{2} |

C_{w,Th232} | 2 Bq/kg | 2 | Triangular | 0,8 | 0.07 | 0.003 (Bq/kg)^{2} |

Cov(α_{fa,cem}, α_{agg}) (r = −0.2, is assumed) | −0.0005 (Bq/kg)^{2} | |||||

Cov(α_{fa}_{,}_{cem}, α_{w}) (r = 0.5, is assumed) | −0.004 (Bq/kg)^{2} | |||||

Cov(α_{agg}, α_{w}) (r = −0.2, is assumed) | 0.006 (Bq/kg)^{2} | |||||

C_{con,Th232} | 26 Bq/kg | - | 83 (Bq/kg)^{2} | |||

^{40}k | ||||||

α_{fa,cem} | 320 kg/m^{2} | 40 | Triangular | 16 | −0.10 | 3 (Bq/kg)^{2} |

α_{agg} | 1500 kg/m^{2} | 200 | Triangular | 82 | 0.03 | 7 (Bq/kg)^{2} |

α_{w} | 164 kg/m^{2} | 52 | Triangular | 21 | −0.17 | 14 (Bq/kg)^{2} |

C_{fa,cem,K40} | 223 Bq/kg | 78 | 0.14 | 119 (Bq/kg)^{2} | ||

C_{agg,K40} | 524 Bq/kg | 524 | Triangular | 214 | 0.79 | 28,422 (Bq/kg)^{2} |

C_{w,K40} | 50 Bq/kg | 50 | Triangular | 20 | 0.07 | 2 (Bq/kg)^{2} |

Cov(α_{fa,cem}, α_{agg}) (r = −0.2, is assumed) | 2 (Bq/kg)^{2} | |||||

Cov(α_{fa}_{,}_{cem}, α_{w}) (r = 0.5, is assumed) | 6 (Bq/kg)^{2} | |||||

Cov(α_{a}_{gg}, α_{w}) (r = −0.2, is assumed) | 4 (Bq/kg)^{2} | |||||

C_{con,K40} | 448 Bq/kg | - | 28,580 (Bq/kg)^{2} |

**Table 7.**Estimated 95% confidence intervals for NORM mass specific concentrations (Bq/kg) in concrete produced in Greece during the year 2023.

Estimated for | C_{con} (Bq/kg) |
---|---|

^{226}Ra | 35 ± 18 |

^{232}Th | 26 ± 18 |

^{40}K | (4.5 ± 3.4) × 10^{2} |

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## Share and Cite

**MDPI and ACS Style**

Gavela, S.; Papadakos, G.
Activity Concentration Index Values for Concrete Multistory Residences in Greece Due to Fly Ash Addition in Cement. *Eng* **2023**, *4*, 2926-2940.
https://doi.org/10.3390/eng4040164

**AMA Style**

Gavela S, Papadakos G.
Activity Concentration Index Values for Concrete Multistory Residences in Greece Due to Fly Ash Addition in Cement. *Eng*. 2023; 4(4):2926-2940.
https://doi.org/10.3390/eng4040164

**Chicago/Turabian Style**

Gavela, Stamatia, and Georgios Papadakos.
2023. "Activity Concentration Index Values for Concrete Multistory Residences in Greece Due to Fly Ash Addition in Cement" *Eng* 4, no. 4: 2926-2940.
https://doi.org/10.3390/eng4040164