Increasing Shielding Capabilities of Cement Mortars by Fly Ash Addition

IOSIF LINGVAY1, GEORGETA VELCIU1, DANIEL LINGVAY2, ADRIANA MARIANA BORS3*, ADRIANA MOANTA4 1.National Institute for Research and Development in Electrical Engineering INCDIE ICPE-CA, 313, Splaiul Unirii, 030138, Bucharest, Romania 2.Sapientia Hungarian University of Transylvania, Faculty of Sciences and Arts, 4 Calea Turzii , 400193, Cluj Napoca, Romania 3.ICPE SA, 313 Splaiul Unirii, 030138, Bucharest, Romania 4SC CEPROCIM SA, 6 Preciziei, 062203, Bucharest, Romania

In the perspective of sustainable development, requires the provision of healthy working and living conditions in a clean environment, the problem of neutralization of waste by reusing it becomes a priority [1][2][3][4][5].
A significant share of the thermal and electrical energy demand of mankind is produced by burning fuels in thermoelectric power plants.
One may notice from these studies that, due to its cavernous morphology [12, 17,18], low density and surface area, the fly ash addition in concrete and cement mortars leads to a decrease in thermal conductivity and densitywithout significant changes in the characteristics mechanical [14,16,[19][20][21][22][23].
It is also noted that the fly ash addition changes the electrical and dielectric characteristics of concrete and mortar cement [15,18].
On the other hand, it was highlighted the high capacity of fly ash to contain oil products and phenolic pollutants from wastewater [24].
As a result of the technological developments, the electricity consumption shows a continuous trend of growth -which leads to the continuous increase of the level of environmental pollution by electromagnetic fields of anthropogenic origin (electromagnetic pollution of the environment).
Numerous studies have pointed out that, by altering the mechanism and kinetics of natural electrochemical processes [26], electromagnetic fields of anthropogenic origin have complex effects (in the vast majority of negative cases) on both living matter [27] and materials used in construction and installations [28,29].
In the last decades, the share of reactive electric consumers, especially those operating in switching mode, has increased significantly [67 -74], which leads to increased reactive powers and harmonic signals (odd multiples of industrial frequency) [73,74] transited through the electrical networks. In these conditions, electromagnetic fields generated by electric lines (and operating in living and / or working spaces) are complex.
Thus, in the ELF domain over the fundamental component (at the industrial frequency), a series of harmonic components overlap (in a wide spectrum of frequencies, predominantly those up to about 3 kHz).
Certainly, without electricity and related transmission and distribution lines, modern life cannot be conceived, the radiation in the ELF domain being proportional to the powers transited and implicitly to the operating voltage of lines.
Reducing disturbances in the ELF domain by reducing power / operating voltage lines is not plausible (economic considerations) [75].
In these conditions, the protection against the effects of ELF consists in the elaboration and implementation of materials with increased capability of shielding in the civil and industrial constructions (mitigation of electromagnetic disturbing fields [76][77][78]). In view of these considerations, the purpose of the paper is to evaluate the electromagnetic shielding capacity by calculating the attenuation constant á from the data of the experimental determinations obtained by magnetic measurements and dielectric spectroscopy performed on samples of cement mortars with various fly ash additions.

Experimental part
For the comparative assessment of the shielding capacity of cement mortars with various flay ash additions (between 0 and 40 %), were prepared (as described in [18]) samples with parallel planes faces of parallelepiped shaped having the dimensions 5 x 5 x 2 cm.
The cement used was Portland, CEM I grade I quality, according to SR EN 197-1: 2011. The river sand used was washed and sifted (0-2 mm) with a SiO 2 content of over 90 %. Fly ash was collected from the thermo electric power plant from Govora (Romania) and had a grain size of less than 0.5 mm (95 % fraction with < 0.1 mm diameter).
By the X-ray fluorescence spectroscopy (XRF) technique, with WDXRF-S8 Tiger equipment, determined the oxidic percentage compositions of both fly ash and mortar samples obtained.
The dielectric characteristics of the mortar samples were determined in the 50 Hz -3 kHz range by dielectric spectroscopy technique with an AMTEK -1296 Dielectric interface -Solartron Analytical.
In order to ensure good contact with the measuring electrodes, the 5 x 5 cm parallel planes of the mortar samples were contacted ohmically by colloidal silver paste brushing and heat treatment for ½ hour in a thermostat oven at 90 °C.
The magnetic characteristics determination [79] was made by the measurement scheme described in [80] with an automatic RLC impedance bridge of HP4284A -Agilent type. In order to magnetic permeability determine of the mortar samples, a 0.2 mm thick textolite plate was winding over which 1000 spirals of enameled copper wire of 0.2 mm (4 layers over a length of approx. 5 cm).
Various frequencies in the ELF field (50 Hz -3 kHz), were measured using the automatic RLC bridge but also, the inductance and coil impedance with and without the mortar samples introduced into the housing.
From the values obtained following the experimental determinations the real magnetic permeability component of each mortar sample was calculated (according to the mathematical model described in [80]).

Results and discussions
The XRF determinations results, namely the fly ash oxide composition used, and the mortar samples with various experimental fly ash contents are shown in table 1.
Analysing the data presented in Table 1 it is noted that the main ash constituents used are SiO 2 , Al 2 O 3 , Fe 2 O 3 in total of 84.63 %, which according to [17,81] it is recommended for use in concrete and mortar. There is also a relatively high content of Fe 2 O 3 (13.83 % -higher than in cements and sands commonly used in construction).
XRD-X-ray diffraction studies on the ashes used [12, 18] indicated that Fe 2 O 3 is found in the form of magnetic hematite described in [79]. In figure 1, the results determination by the dielectric spectroscopy, respectively evolution the dielectric loss, tgδ δ δ δ δ, at different frequencies in the ELF domain, are presented synthetically depending on the fly ash and Fe 2 O 3 content of the investigated samples.
The shielding capacity of the materials, expressed by the shielding constant, α α α α α, [Np/m] (Np is a logarithmic unit for the measurement of physical field and power quantities, such as gain and loss of electronic signals) is calculated according to the electrical characteristics and magnetic properties of materials with relation (1): (1) in which: αthe attenuation constant; ω -pulsation (ω = 2πf), f -frequency; µ'the real component of magnetic permeability; The relation between the imaginary component and the real dielectric permittivity represents, tgδ δ δ δ δ, respectively (2): (2) In figure 2 the real component evolution of the dielectric permeabilityε ε ε ε ε'resulting from the performed determinations by dielectric spectroscopy, is presented.
In figure 3 the magnetic determinations results, respectively the evolution at different frequencies of the applied measurement signal of the real component of the magnetic permeability, µ', are presented, depending on the fly ash and Fe 2 O 3 content of the investigated mortar samples.
From (1) and (2)  The increase recorded at 50 Hz from 531 Np/m to 7580 Np/m is approx. 14.5 times, and at 3 kHz (the 60 th harmonic of industrial frequency 50 Hz) the increase is from 3168 Np/m to 66264 Np / m, that is approx. 21 times.
In figure 5. The evolution of the frequency m attenuation constant at different fly ash concentrations in the investigated mortar samples is presented.
By the comparative analysis of the figure 4 and figure 5, in correlation with the data from table 1, it is observed that by the addition of ash from thermal power plants (hazardous waste resulting from thermoelectric power plants) in concrete and mortar of Portland cement there more beneficial effects are obtained for the environment and the quality of life, namely: -reducing the specific consumption of cement in construction (particularly energy-intensive raw material) and implicitly substantial energy savings with the noxious related emissions into the atmosphere -including CO 2 ; -the recovery of ash from thermoelectric power plants and its blocking in concrete and mortars, thus reducing the costs of ash treatment and storage as well as air ash (fly ash) air pollution; -decrease of thermal conductivity of mortars and concrete and implicitly reduction of the energy consumption necessary for thermal comfort [18]; The increase in the shielding capacity of concrete and mortars by the addition of fly ash from thermoelectric power plants is explained by the relatively high content of Fe 2 O 3 (microstructured hematite) -which suggests that in the case of fly ash species richer in Fe 2 O 3 the shielding efficiency increases accordingly.

Conclusions
By magnetic and dielectric determinations samples of cement mortar have been characterized in the ELF domain with various fly ash additions.
Following experimental data processing, an increase in shielding capacity in the ELF domain was observed by the fly ash addition to microstructured hematite Fe 2 O 3 in the investigated mortar samples. This increase in shielding capacity was recorded 14.5 times at an addition of up to 40 % fly ash at 50 Hz and up to 21 times at 3 kHz.