*3.2. Leaching and Natural Radioactivity Tests*

Table 4 presents the results of a test of the leaching of hazardous substances from waste copper slag in comparison with the requirements of Polish legal regulations (The Ordinance of the Council of Ministers of 18 November 2014 on the conditions to be met when introducing sewage into water or soil and on the substances particularly harmful to the aquatic environment). The tests showed that the content of hazardous substances identified in the water extract does not exceed the permissible concentrations of these components specified in the applicable regulations.

**Table 4.** Hazardous substances released to water extract from waste copper slag.


\* Dissolved organic carbon.

The allowable content of natural radioactive isotopes in raw materials, building materials and waste used in construction is regulated by the Ordinance of the Council of Ministers of 2 January 2007 on requirements concerning the content of natural radioactive isotopes of potassium K-40, radium Ra-226 and thorium Th-228 in raw materials and materials used in buildings intended for human habitation and livestock, as well as in industrial waste used in construction, and control of the content of these isotopes. This ordinance also applies to waste used for the production of cement and concrete (such as fly ash, slag including copper slag used as an abrasive). Raw materials and building materials are qualified on the basis of two activity indicators f1 and f2.

The first of the above-mentioned indicators, f1, identifies the exposure to radiation emitted by natural radionuclides (i.e., the nuclei of radioactive atoms): potassium (K), radium (Ra) and thorium (Th). This indicator takes into account the different activities of individual radioisotopes and is calculated using the Equation (1):

$$f\_1 = \frac{C\_K}{3000 \text{ Bq/kg}} + \frac{C\_{Ra}}{300 \text{ Bq/kg}} + \frac{C\_{Th}}{200 \text{ Bq/kg}} \tag{1}$$

where CK, CRa and CTh are concentration values of potassium 40K, radium 226Ra and thorium 228Th in Bq/kg.

The f2 indicator, calculated according to Equation (2), indicates the radium (Ra) content and indirectly the α radiation intensity emitted by radon (Rn) and products of its radioactive decay present in building materials:

$$f\_2 = \mathbb{C}\_{\mathbb{R}a} \tag{2}$$

The results of tests of natural radioactivity of waste copper slag and coarse aggregate, i.e., granite, carried out using the method described above, are presented in Tables 5 and 6.

**Table 5.** Results of natural radioactivity tests of waste copper slag.


which translates into indicator values f1 and f2: f1 = 1.78 ± 0.05; f2 = 400 ± 12.

**Table 6.** Results of natural radioactivity tests of granite.


which translates into indicator values f1 and f2: f1 = 0.67 ± 0.05; f2 = 35.4 ± 6.1.

According to the abovementioned ordinance, the activity rates f1 and f2 must not exceed by more than 20% the limit values of f1 = 2 and f2 = 400 Bq/kg for industrial waste used in the construction of ground structures built on built-up areas or intended to be built on in a local zoning plan and for the levelling of such areas. This means that the tested waste may be used in the production of concrete for the above-mentioned applications. Apart from testing the natural radioactivity of selected concrete components, samples of the concrete itself were also tested. The results of these tests in the case of concrete without and with waste copper slag are presented in Table 7.

The results presented in Table 7 allow to conclude that despite a relatively high level of values of indicators f1 and f2 obtained in the case of waste copper slag, concrete made with this material has a moderate level of radioactivity, although it is significantly higher than in the case of concrete made without the use of waste copper slag. Another important conclusion is the noticeably higher level of radioactivity of concrete, in which CEM II/B-V cement was used, compared to the series made with other cements and the same type of aggregate. The increased radioactivity of these concrete series should be linked to the presence of fly ash in the cement, which is a material with an increased radioactivity level [27,28,42,43]. Relative and absolute differences in the values of indicators f1 and f2 in the case of CEM II/B-V cement concrete is significantly smaller when waste copper slag is used, which indicates the dominant influence of this component on the radioactivity of the obtained concrete. However, the impact of cement is not negligible and should be taken into account when designing the composition of concrete mix.


**Table 7.** Results of natural radioactivity tests of concrete.

### **4. Discussion**

## *4.1. Assumptions and Calculation Method*

Optimization of the composition of the concrete mix requires taking into account not only the properties of the final composite, but also the need to limit its broadly understood impact on the environment.

In the calculations using the EIPI method, emissions, consumption of raw materials and rarity of their occurrence were assumed according to the data presented in the article [37]. The value of PI is evaluated on the basis of the sum of normalized values of selected concrete properties. The compressive strength and sorptivity tested after 28 days were used for calculations. The reference values were adopted at the same level as in [37], i.e., fcm = 60 MPa i S = 0.120 cm/h0.5. As another concrete property, the air permeability kT, measured with a Torrent apparatus on specimens dried at 65 ◦C, was included in the evaluation. As a reference value, the limit used for exposure classes XC4, XD1, XD2a, XF1 and, XF2 in Swiss Standard SIA 262 (SIA 262/1 Annex E) [39], i.e., 2.0 <sup>×</sup> <sup>10</sup>–16 <sup>m</sup>2, was used.

Equation (3), which contains the abovementioned concrete parameters, was used to calculate PI without taking into account radioactivity. The relevant quotients from normalization are multiplied by the respective weighting coefficients, whose values were taken as: *wfcm* = 0.4, *wkT* = 0.3 and *wS* = 0.3 in the present study. The sum of the weighting coefficients should be equal to unity so that a concrete mix with reference values of selected properties will give a PI value of 1:

$$PI = \frac{f\_{cm}}{60 \text{ MPa}} \times w\_{fcm} + \frac{0.120 \text{ cm}/h^{0.5}}{\text{S}} \times w\_{\text{S}} + \frac{2.0 \times 10^{-16} m^2}{kT} \times w\_{kT} \tag{3}$$

In the further concrete assessment, the values of indicators f1 and f2 were taken into account in the PI calculations. In their case, the reference values were adopted according to the Ordinance mentioned above, i.e., f1 = 2 and f2 = 400 Bq/kg. To calculate so extended PI values Equation (4) was used:

$$PI = \frac{f\_{\rm cm}}{60 \,\text{MPa}} \times w\_{f\text{cm}} + \frac{0.120 \,\text{cm}/\text{h}^{0.5}}{\text{S}} \times w\_{\text{S}} + \frac{2.0 \times 10^{-16} m^2}{kT} \times w\_{kT} + \frac{2}{f\_1} \times w\_{f1} + \frac{400}{f\_2} \times w\_{f2} \tag{4}$$

The higher values of PI the analysed concrete achieves, the more desirable engineering properties it possesses. The weighting coefficients in Equation (4), were assumed in a few variants which are presented and described in the next subsection.

The value of EI is calculated according to Equation (5) as the square root of the sum of the normalized total emission of CO2 and the normalized total raw materials usage both multiplied by weights that sum to one:

$$EI = \sqrt{\frac{EM}{490 \text{ kg} / m^3} \times w\_{EM} + \frac{RM}{2000 \text{ kg} / m^3} \times w\_{RM}}\tag{5}$$

To normalize the values of total emission of CO2 (EM) and usage of raw materials (RM), which have to be calculated first, they are divided by the reference values. The reference values in this study were assumed as in [37] and equal approximately 490 kg of CO2 emission and 2000 kg/m3 of raw materials usage per cubic metre of concrete. The weighting coefficients were assumed as: *wEM* = 0.5 and *wRM* = 0.5.

A lower EI value means that analysed concrete is more environmentally friendly. Results of the calculations the EI for analysed concrete mixtures are presented in Table 8 and repeated in Table 9.

A comprehensive evaluation of concrete, taking into account both its ecological impact (EI) and engineering performance (PI), is expressed by Gross Ecological and Performance Indicator (GEPI), which is calculated using Equation (6):

$$GEPI = \sqrt{EI^2 + \frac{1}{PI^2}}\tag{6}$$

**Table 8.** EI, PI and GEPI values without taking into account natural radiation.




When designing a concrete mix in practice, a low GEPI is aimed for concrete with favourable concurrent EI and PI, while a high GEPI should be avoided.

It should be stressed very clearly here that the comparison of different variants of the designed concrete mixtures using the EIPI method in engineering practice will be only reasonable, if all the technical parameters of the concrete obtained from the designed concrete mixtures, taken into account in the PI calculations, meet the specified limit requirements defined by the construction designer or the relevant regulations or standards.

### *4.2. Results Analysis and Discution*

The results of calculations conducted without taking into account the influence of radioactive nuclide content on the PI value are presented in Figure 1. The PI and EI values calculated under this assumption are presented in Table 8 together with the GEPI values calculated on their basis. Series with CEM III cement are characterized by the most favourable EI value due to lower clinker content than in other cements, resulting in a lower consumption of natural resources and a lower carbon dioxide emission. The highest PI values were achieved by the CI66F and CIII66F series. This is mainly due to higher tightness than in other series, which consists of the lowest values of sorptivity and one of the lowest values of air permeability. The overall assessment based on GEPI values indicates as the best series CIII66F (GEPI = 0.897) and CIII66 (GEPI = 1.001). The CI0 series (GEPI = 1.480) and CI66 series (GEPI = 1.314) were the least favourable from the point of view of the complete score.

In the next stage of the assessment, the impact of the radioactive nuclides contained in the concrete was also taken into account. This was done by using Equation (4) in the calculations of PI values. Four variants differing in the values of weights for the components of the formula taking into account indicators f1 and f2 were used in the calculations. Their influence on PI value was differentiated by assigning to them in the calculations a sum of weights equal to 0.3 (variants S) or 0.7 (variants B). Additional differentiation was based on taking equal weight values (variants S1 and B1) and assigning about twice as much weight to the f2 indicator in relation to the f1 indicator (variants S2 and B2). The list of adopted values of weights is presented in Table 9 and the obtained GEPI results are presented in Table 10.

**Figure 1.** Ecological Index plotted against reciprocal of Performance Index in variant 0.


**Table 10.** Results of GEPI calculations.

The analysis of the obtained results showed a clear but small variation in the calculated PI values obtained in the individual variants. Regardless of the adopted variant, the mutual proportions of GEPI values obtained in the case of individual series remained very close to each other. Therefore, it was found pointless to present in detail the results of EI and PI calculations of all variants and to

visualize them in the figures. Only the results of calculations obtained in variant B2 were selected, in which the influence of natural radioactivity of concrete on the result of PI calculations was the greatest. The results obtained in this variant are presented in Table 11 and Figure 2.


**Table 11.** EI, PI and GEPI values taking into account the natural radiation-variant B2.

**Figure 2.** Ecological Index plotted against the reciprocal of the performance index in variant B2.

As can be seen, the weight variation in the adopted variants had the greatest impact on the GEPI values for CEM II cement concrete, regardless of the type of fine aggregate and plasticiser used, and for waste copper slag, regardless of the type of cement. However, this variation, understood as the difference between the highest and the lowest GEPI value, reaches a maximum of less than 12%.

The significantly lower natural radioactivity of concrete with CEM I and CEM III without the use of waste copper slag caused PI in these two series to be high, several times higher than in series with the same type of cement and waste. It is also about three times higher than that of CII0 series, in which cement with increased natural radioactivity due to fly ash content is used. CIII0 concrete (GEPI = 0.768) proved to be the best with such established assessment criteria. Despite increased natural radioactivity, mixtures with the waste and blast furnace slag cement were ranked in the next two places (GEPI = 0.822 and GEPI = 0.826). The worst results were obtained in the case of the series with CEM I cement and waste copper slag (GEPI = 0.953 and GEPI = 0.944). This allows us to state that the use of waste copper slag improves the performance of concrete so much that it reduces the negative impact of increased radioactivity in the assessment performed by the EIPI method.

It should be taken into account that when PI is calculated on the basis of other parameters (selected properties, reference values, weights), it is not possible to directly compare PI and GEPI results obtained in the calculation of the different variants. The comparisons make sense between the different concrete mixes assessed on the basis of the criteria adopted for the specific variant and adapted to the requirements of the specific conditions of concrete exploitation and, for example, the limitations related to natural radioactivity. The variant calculations of the impact of natural radioactivity of concrete on the PI value presented in the paper were aimed at analysing various variants of the differentiation of the weights and their impact on the final assessment of the concrete.

Despite favourable results of the calculations of GEPI values due to the relatively high natural radioactivity of waste copper slag, however, within acceptable limits, the authors do not recommend the use of concrete with this material for the construction of buildings intended for permanent human presence. This type of concrete materials can be used, e.g., for erecting farm buildings or road pavements (bottom layer) and structures (bridges, overpasses, etc.).
