An Innovative Absorption Propagation System Hollow Block Made of Concrete Modified with Styrene–Butadiene Rubber and Polyethylene Terephthalate Flakes to Reduce the Propagation of Mechanical Vibrations in Walls

This paper discusses an innovative APS hollow block wall with a frame made of concrete modified with recycled materials. The technical data of the hollow block, the percentages of the recycled materials, including SBR rubber granules and PET flakes in the modified concrete, and the composition of the concrete modified with this mixture of recycled additives, are presented. To demonstrate the effectiveness of the solution in reducing mechanical vibrations, the effect of the interaction of different frequencies of the mechanical wave on reducing these vibrations was evaluated for APS blocks and Alpha comparison blocks. The test was carried out on a developed test stand dedicated to dynamic measurements for sixteen frequencies in the range from 8 to 5000 Hz, forcing a sinusoidal course of vibrations. The results are presented graphically and show that the new type of APS hollow block wall was much more effective in reducing mechanical vibrations. This efficiency was in the range from 10 to 51% for 12 out of the tested 16 frequencies. For the frequencies of 8, 16, 128, and 2000 Hz, the values were obtained with a difference of 3.58% in favor of the APS hollow block. In addition, the study of the damping effectiveness of the APS hollow blocks, in relation to the vibrations generated by an M-400 impact mill, showed that the APS block wall had a higher damping efficiency of 16.87% compared to the Alpha hollow block for the signal reading on the floor next to the mill, and 18.68% for the signal reading on the mill body. The modified concrete used in the production of the APS hollow blocks enabled the effective use of two recycled materials, SBR rubber and polyethylene terephthalate, in the form of PET flakes.


Introduction
Commonly used concrete wall hollow blocks are used for erecting the exterior and interior structural walls of buildings, especially underground floors. Their role in the construction of the wall, like that of clay blocks, consists of the transfer of vertical loads to the foundation [1,2]. This is provided by the concrete frame of the hollow block, which usually has alternately shaped through-holes. There are studies in the literature that have examined concrete with the addition of SBR (styrene-butadiene rubber) granules obtained from the processing of used car tires [3][4][5][6], polyethylene terephthalate in the form of PET (Poli(EtylenoTereftalanu)) flakes, or granules from used plastic bottles [7][8][9][10][11], but few publications have studied concrete modified with these two additives [12][13][14]. Contemporary concrete mix designs take into account waste management [8,12,[15][16][17] and the use of "substitutes" that could replace some of the components needed to produce a cement matrix composite material. This is an important aspect of sustainable building [18]. Environmental protection is an important issue that should be taken into account in scientific studies. Examples of such activity may be seen in publications [19][20][21][22]. deviations were determined based on the standards in [68,69]. Permissible dimensiona deviations are within category D1 of the standard [68] and amount to +3/−5 mm for length width, and height. Standards [68,69] also specify the shape conditions to be met by a concrete masonry element, i.e., they allow such an element to have indentations, a joint system, roundness, or sharp edges. All these conditions are met by a new type of concrete hollow block-the APS. Located inside the block, the through-holes D are designed in such a way that it is possible to reduce mechanical vibrations by dissipating the propagating mechanical wave directly in the block as a result of its multiple reflections. The through-holes D are located inside the block throughout its height C and described by an arc L1 with a radius R with central symmetry. On the side of the hollow block with a width B are grooves W. The APS block is designed to allow for a combination of the side-by-side placement of the blocks rotated by 180 degrees alternately. The detailed dimensions in the horizontal section of the developed hollow concrete wall block are shown in Figure 2, while an example of the APS hollow block is shown in Figure 1b. Below are the technical data of the new type of APS block- Table 1, the percentage shares of the SBR rubber granulates and PET flakes used in the modified concrete of the Located inside the block, the through-holes D are designed in such a way that it is possible to reduce mechanical vibrations by dissipating the propagating mechanical wave directly in the block as a result of its multiple reflections. The through-holes D are located inside the block throughout its height C and described by an arc L1 with a radius R with central symmetry. On the side of the hollow block with a width B are grooves W. The APS block is designed to allow for a combination of the side-by-side placement of the blocks, rotated by 180 degrees alternately. The detailed dimensions in the horizontal section of the developed hollow concrete wall block are shown in Figure 2, while an example of the APS hollow block is shown in Figure 1b. deviations were determined based on the standards in [68,69]. Permissible dimensiona deviations are within category D1 of the standard [68] and amount to +3/−5 mm for length width, and height. Standards [68,69] also specify the shape conditions to be met by a con crete masonry element, i.e., they allow such an element to have indentations, a joint sys tem, roundness, or sharp edges. All these conditions are met by a new type of concret hollow block-the APS.
(a) (b) Located inside the block, the through-holes D are designed in such a way that it i possible to reduce mechanical vibrations by dissipating the propagating mechanical wav directly in the block as a result of its multiple reflections. The through-holes D are locate inside the block throughout its height C and described by an arc L1 with a radius R wit central symmetry. On the side of the hollow block with a width B are grooves W. The AP block is designed to allow for a combination of the side-by-side placement of the block rotated by 180 degrees alternately. The detailed dimensions in the horizontal section o the developed hollow concrete wall block are shown in Figure 2, while an example of th APS hollow block is shown in Figure 1b. Below are the technical data of the new type of APS block- Table 1, the percentag shares of the SBR rubber granulates and PET flakes used in the modified concrete of th Below are the technical data of the new type of APS block- Table 1, the percentage shares of the SBR rubber granulates and PET flakes used in the modified concrete of the APS block- Table 2, and the composition of the concrete modified with a mixture of recycling additives: SBR rubber granulate and PET flakes for a volume of 1 m 3 of the concrete mix for the APS block- Table 3. Photos showing the materials used in the tests are presented in Figure 3.   The compressive strength test for the modified concrete of the APS hollow block was carried out on cubic samples perpendicular to the forming direction and centrally in relation to the centered pressure plates of the compression press, using a Toni Technik ZWICK type 2030 testing machine (Figure 4a) that meets the standard requirements PN-EN 12390-4 [71]. A constant sample loading rate of 1.0 MPa/s was used. The distribution of the additive mix in the modified concrete of the APS hollow blocks, obtained from the sample after the test, is shown in Figure 4b.  The average compressive strengths obtained in the test and the corresponding strength classes are presented in Table 4. The compressive strength of the APS hollow block is given in Table 1. The compressive strength test for the modified concrete of the APS hollow block was carried out on cubic samples perpendicular to the forming direction and centrally in relation to the centered pressure plates of the compression press, using a Toni Technik ZWICK type 2030 testing machine (Figure 4a) that meets the standard requirements PN-EN 12390-4 [71]. A constant sample loading rate of 1.0 MPa/s was used. The distribution of the additive mix in the modified concrete of the APS hollow blocks, obtained from the sample after the test, is shown in Figure 4b.  The compressive strength test for the modified concrete of the APS hollow block was carried out on cubic samples perpendicular to the forming direction and centrally in relation to the centered pressure plates of the compression press, using a Toni Technik ZWICK type 2030 testing machine ( Figure 4a) that meets the standard requirements PN-EN 12390-4 [71]. A constant sample loading rate of 1.0 MPa/s was used. The distribution of the additive mix in the modified concrete of the APS hollow blocks, obtained from the sample after the test, is shown in Figure 4b.  The average compressive strengths obtained in the test and the corresponding strength classes are presented in Table 4. The compressive strength of the APS hollow block is given in Table 1. The average compressive strengths obtained in the test and the corresponding strength classes are presented in Table 4. The compressive strength of the APS hollow block is given in Table 1.
The target concrete mix used to make the APS block was selected in the design process (experimental method), in which control concretes were designed at the beginning. After their modification with a mixture of recycling additives, taking into account various amounts of SBR granulate fraction, the target composition was selected, according to Table 3, the most effective in terms of the compressive strength.
Based on the calculated percentages of the individual fractions of the composed aggregate mixture, a grain size curve was plotted between the limiting curves ( Figure 5). The target concrete mix used to make the APS block was selected in the design process (experimental method), in which control concretes were designed at the beginning. After their modification with a mixture of recycling additives, taking into account various amounts of SBR granulate fraction, the target composition was selected, according to Table  3, the most effective in terms of the compressive strength.
Based on the calculated percentages of the individual fractions of the composed aggregate mixture, a grain size curve was plotted between the limiting curves ( Figure 5).

Recycling SBR and PET Materials
The use of recycling materials in the APS block included SBR rubber granulate and PET flakes in the amounts indicated in Table 2. The rubber granules were obtained from the processing of used car tires, while the PET flakes were obtained from used plastic bottles. The physical and chemical properties of the SBR rubber granules used in the tests are listed in Table 5. The basic physical and chemical properties of the polyethylene terephthalate in the form of PET flakes are presented in Table 6. Table 5. Physical and chemical properties of SBR rubber granules. Classification according to [72].

Recycling SBR and PET Materials
The use of recycling materials in the APS block included SBR rubber granulate and PET flakes in the amounts indicated in Table 2. The rubber granules were obtained from the processing of used car tires, while the PET flakes were obtained from used plastic bottles. The physical and chemical properties of the SBR rubber granules used in the tests are listed in Table 5. The basic physical and chemical properties of the polyethylene terephthalate in the form of PET flakes are presented in Table 6. Table 5. Physical and chemical properties of SBR rubber granules. Classification according to [72].

Comparative Alpha Hollow Block
An Alpha 25 concrete hollow block was used as a comparison for the mechanical vibration reduction tests. It was purchased from the C.J. Blok Sp. z o. o. from Głogów Małopolski, Poland. The comparative hollow block accepted for testing had external dimensions of length × width × height, respectively, equal to 490 × 240 × 240 mm. These dimensions were identical to the dimensions of the new type of APS hollow concrete block. The area of the through-holes in the Alpha block was 1176 cm 2 and was also comparable to the area of the holes in the new APS block, which was 1124 cm 2 . The basic dimensions of the Alpha block are shown in Figure 6 [74], while an example of the Alpha hollow block is shown in Figure 7.

Comparative Alpha Hollow Block
An Alpha 25 concrete hollow block was used as a comparison for the mechanical vibration reduction tests. It was purchased from the C.J. Blok Sp. z o. o. from Głogów Małopolski, Poland. The comparative hollow block accepted for testing had external dimensions of length × width × height, respectively, equal to 490 × 240 × 240 mm. These dimensions were identical to the dimensions of the new type of APS hollow concrete block. The area of the through-holes in the Alpha block was 1176 cm 2 and was also comparable to the area of the holes in the new APS block, which was 1124 cm 2 . The basic dimensions of the Alpha block are shown in Figure 6 [74], while an example of the Alpha hollow block is shown in Figure 7.  Alpha concrete hollow blocks are intended for the construction of foundation walls in land and water construction. They meet the conditions of standard EN 771-3:2011 + A1:2015 [68]. The basic technical data of the Alpha block are presented in Table 7 [74]. Alpha concrete hollow blocks are intended for the construction of foundation wall in land and water construction. They meet the conditions of standard EN 771-3:2011 A1:2015 [68]. The basic technical data of the Alpha block are presented in Table 7 [74].

Research of the Reduction in Mechanical Vibrations
Mechanical waves are generated by the interaction of at least two bodies and als arise during the vibration of a medium [75]. The impact caused by the movement of ma chinery or equipment is also of a wave nature and is transmitted through the ground, fo example, to the foundations of buildings [76][77][78]. Consequently, mechanical vibrations ar generated, causing the movement of the medium in which they were generated [79,80 This results in the transmission of mechanical energy and its propagation in the buildin structure. This has a negative impact not only on the building, but also on the people in side the building. To reduce these mechanical vibrations propagating through the soil me dium to the foundation walls, a new type of concrete wall hollow block, APS, was de signed [67]. It is a hollow block with a modified recycled concrete frame and a patented solution for its internal structure, with curvilinear through-holes and locks.
The measurement of vibrations allows for the observation of complex, non-sinusoi dal waveforms, which, after a frequency analysis, can be presented in the form of an am plitude spectrum. For a quantitative description of these vibrations, peak-to-peak value are taken, from which it is possible to determine the maximum value qimax of the differenc in the positive deviation qi(+) and negative deviation qi(-) of the signal at the measuremen points P1 to P6, according to

Research of the Reduction in Mechanical Vibrations
Mechanical waves are generated by the interaction of at least two bodies and also arise during the vibration of a medium [75]. The impact caused by the movement of machinery or equipment is also of a wave nature and is transmitted through the ground, for example, to the foundations of buildings [76][77][78]. Consequently, mechanical vibrations are generated, causing the movement of the medium in which they were generated [79,80]. This results in the transmission of mechanical energy and its propagation in the building structure. This has a negative impact not only on the building, but also on the people inside the building. To reduce these mechanical vibrations propagating through the soil medium to the foundation walls, a new type of concrete wall hollow block, APS, was designed [67]. It is a hollow block with a modified recycled concrete frame and a patented solution for its internal structure, with curvilinear through-holes and locks.
The measurement of vibrations allows for the observation of complex, non-sinusoidal waveforms, which, after a frequency analysis, can be presented in the form of an amplitude spectrum. For a quantitative description of these vibrations, peak-to-peak values are taken, from which it is possible to determine the maximum value q imax of the difference in the positive deviation qi (+) and negative deviation qi (-) of the signal at the measurement points P 1 to P 6 , according to On this basis, it is possible to assess the displacements of the selected points of the tested hollow block as a result of the mechanical wave propagation, i.e., as a result of the vibration transmission [81]. The measure of damping is the relative mean damping values w tm , determined according to Equation (2).
where q m is the average level of vibration obtained after integrating the signal function q(t), obtained in the time interval from the beginning to the end of the measurement, respectively, for points P 2 to P 6 of the back wall of the hollow block, according to Figure 8b. For each of the above measurement points, the value of the average vibration level was determined, and the arithmetic mean was calculated from these values, thus obtaining the average vibration level, denoted as q m in Equation (2), whereas q m1 is the average level of the vibration, obtained in the time interval from the beginning to the end of the measurement, for point P 1 of the front wall of the hollow block, according to Figure 8a.
average vibration level, denoted as qm in Equation (2), whereas qm1 is the average level of the vibration, obtained in the time interval from the beginning to the end of the measurement, for point P1 of the front wall of the hollow block, according to Figure 8a.
To determine the proportional relationship with the energy carried by the evoked signal, the root mean square level RMS is calculated according to Equation (3) [81].
where t1 and t2 are the start and end time of the measurement, respectively, and the q(t) signal function and qm are the mean values of the vibrations obtained after integrating the signal function. The calculation of the relative mean damping as a root mean square (RMS) value of the vibration for wts blocks shows a proportional relationship with the energy transformed by the signal. Root mean square takes into account the temporal history of the signal waveform and the amplitude [80,82]. Calculations for a series of three Alpha blocks and a series of three APS new-type hollow blocks were performed in accordance with Equation (4): where qs and qs1 are the values of the root mean square level RMS, for points P2 to P6 of the back wall of the hollow block and point P1 of the front wall of the hollow block, respectively, according to Figure 8.

Description of the Stand for Measuring the Effectiveness of Damping Hollow Blocks
A test stand was built to study the propagation of mechanical vibrations through concrete wall blocks according to Figure 9. The block wall was placed on the floor by To determine the proportional relationship with the energy carried by the evoked signal, the root mean square level RMS is calculated according to Equation (3) [81].
where t 1 and t 2 are the start and end time of the measurement, respectively, and the q(t) signal function and q m are the mean values of the vibrations obtained after integrating the signal function. The calculation of the relative mean damping as a root mean square (RMS) value of the vibration for w ts blocks shows a proportional relationship with the energy transformed by the signal. Root mean square takes into account the temporal history of the signal waveform and the amplitude [80,82]. Calculations for a series of three Alpha blocks and a series of three APS new-type hollow blocks were performed in accordance with Equation (4): where q s and q s1 are the values of the root mean square level RMS, for points P 2 to P 6 of the back wall of the hollow block and point P 1 of the front wall of the hollow block, respectively, according to Figure 8.

Description of the Stand for Measuring the Effectiveness of Damping Hollow Blocks
A test stand was built to study the propagation of mechanical vibrations through concrete wall blocks according to Figure 9. The block wall was placed on the floor by connecting it to the ground with cement mortar. For the tests, three three-row walls were built using the Alpha and APS blocks, respectively. The extreme blocks in the first and second rows of each wall were positioned in a direction perpendicular to the axis of the wall (Figure 9b), thus creating additional bracing for the wall hollow block tested, which was located in the second row in the center of the erected wall (Figure 9a). connecting it to the ground with cement mortar. For the tests, three three-row walls were built using the Alpha and APS blocks, respectively. The extreme blocks in the first and second rows of each wall were positioned in a direction perpendicular to the axis of the wall (Figure 9b), thus creating additional bracing for the wall hollow block tested, which was located in the second row in the center of the erected wall (Figure 9a).
(a) (b)  Accelerometers were attached to each test block studied, according to Figure 8. Six accelerometers were placed on each test block, one on the front wall at point P 1 and five on the back wall at points P 2 to P 6 . The first accelerometer, labelled P 1 , was located at the center of the front wall of the hollow block, directly at the point of the force application ( Figure 8a). The remaining accelerometers, P 2 to P 6 , were placed on the back wall of the hollow block, as shown in Figure 8b. The positions of the accelerometers were adopted in the same way for all the tested Alpha and APS hollow wall blocks.

Testing with a Modal Hammer and Discussion of the Results
The hollow concrete wall blocks, i.e., the Alpha comparative hollow block and the new APS hollow block, were subjected to the modal hammer test. A PCB modal hammer, model 086C03 PCB Piezotronics (manufactured: PCB Piezotronics, Depew, NY, USA), was used, with a transducer-readable frequency range of up to 8000 Hz and a force amplitude range of 2200 N ( Figure 10). Accelerometers were attached to each test block studied, according to Figure 8. Six accelerometers were placed on each test block, one on the front wall at point P1 and five on the back wall at points P2 to P6. The first accelerometer, labelled P1, was located at the center of the front wall of the hollow block, directly at the point of the force application ( Figure 8a). The remaining accelerometers, P2 to P6, were placed on the back wall of the hollow block, as shown in Figure 8b. The positions of the accelerometers were adopted in the same way for all the tested Alpha and APS hollow wall blocks.

Testing with a Modal Hammer and Discussion of the Results
The hollow concrete wall blocks, i.e., the Alpha comparative hollow block and the new APS hollow block, were subjected to the modal hammer test. A PCB modal hammer, model 086C03 PCB Piezotronics (manufactured: PCB Piezotronics, Depew, NY, USA), was used, with a transducer-readable frequency range of up to 8000 Hz and a force amplitude range of 2200 N ( Figure 10). The nature and distribution of the excitation force pulse F over time, when hitting a concrete wall block with a PCB 086C03 modal hammer, is shown in Figure 11. A dedicated plate was selected for the modal hammer, with the goal of obtaining a signal that allowed for the determination of a clear pulse distribution profile. The impact with the modal hammer was repeated until the maximum pulse force F was obtained, ranging from 400 to 415 N. Three trials were thus determined for each series of blocks, in which the discrepancy in the signals was less than 1%. Acceleration values were read from the six accelerometers numbered from P1 to P6, arranged according to the diagram shown in Figure 8. The results were read using the Sirius DEWESoft'X3 program (manufactured: Dewesoft, Trbovlje, Slovenia). The nature and distribution of the excitation force pulse F over time, when hitting a concrete wall block with a PCB 086C03 modal hammer, is shown in Figure 11. A dedicated plate was selected for the modal hammer, with the goal of obtaining a signal that allowed for the determination of a clear pulse distribution profile. The impact with the modal hammer was repeated until the maximum pulse force F was obtained, ranging from 400 to 415 N. Three trials were thus determined for each series of blocks, in which the discrepancy in the signals was less than 1%. Acceleration values were read from the six accelerometers numbered from P 1 to P 6 , arranged according to the diagram shown in Figure 8. The results were read using the Sirius DEWESoft'X3 program (manufactured: Dewesoft, Trbovlje, Slovenia). block, through a 288D01 PCB PIEZOTRONIC force sensor (Manufactured: PCB Piezotronics, Depew, NY, USA) with a frequency range of up to 5 kHz and a maximum measured force of 2224 N ( Figure 9, point 6, and Figure 8a).
Accelerometers were attached to each test block studied, according to Figure 8. Six accelerometers were placed on each test block, one on the front wall at point P1 and five on the back wall at points P2 to P6. The first accelerometer, labelled P1, was located at the center of the front wall of the hollow block, directly at the point of the force application (Figure 8a). The remaining accelerometers, P2 to P6, were placed on the back wall of the hollow block, as shown in Figure 8b. The positions of the accelerometers were adopted in the same way for all the tested Alpha and APS hollow wall blocks.

Testing with a Modal Hammer and Discussion of the Results
The hollow concrete wall blocks, i.e., the Alpha comparative hollow block and the new APS hollow block, were subjected to the modal hammer test. A PCB modal hammer, model 086C03 PCB Piezotronics (manufactured: PCB Piezotronics, Depew, NY, USA), was used, with a transducer-readable frequency range of up to 8000 Hz and a force amplitude range of 2200 N ( Figure 10). The nature and distribution of the excitation force pulse F over time, when hitting a concrete wall block with a PCB 086C03 modal hammer, is shown in Figure 11. A dedicated plate was selected for the modal hammer, with the goal of obtaining a signal that allowed for the determination of a clear pulse distribution profile. The impact with the modal hammer was repeated until the maximum pulse force F was obtained, ranging from 400 to 415 N. Three trials were thus determined for each series of blocks, in which the discrepancy in the signals was less than 1%. Acceleration values were read from the six accelerometers numbered from P1 to P6, arranged according to the diagram shown in Figure 8. The results were read using the Sirius DEWESoft'X3 program (manufactured: Dewesoft, Trbovlje, Slovenia). Figure 11. Impulse distribution of excitation force F in time t when hit with a PCB 086C03 modal hammer on a hollow concrete block.
As a result of the modal hammer test, acceleration amplitudes were recorded for the individual measurement points located on the walls of the Alpha and APS blocks, in accordance with Figure 8. The test was conducted for audible frequencies of up to 20,000 Hz. The graphs are presented for frequencies of up to 4000 Hz. No measurable accelerations were observed above this frequency.

Assessment of the Efficiency of Hollow Block Damping
The damping effectiveness of the new type of APS concrete wall block compared to the Alpha reference block was tested in the frequency range from 8 Hz to 5000 Hz. The test was carried out on a test stand, as shown in Figure 9, for the selected sixteen frequencies, which were, respectively, 8, 16, 32, 64, 128, 256, 512, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, and 5000 Hz. A sinusoidal waveform of the vibration was forced, and the signal from the accelerometers was recorded at a sampling rate of 200 kHz, using Siemens LMS TestLab software. Three Alpha hollow concrete blocks and three APS blocks were tested. Using Formulas (1) and (2), the peak-to-peak acceleration values, RMS values, and relative mean damping values were calculated w tm for each frequency.
Based on the arithmetic mean, the relative mean damping values were calculated w tma at points P 2 to P 6 . For the selected sixteen considered frequencies, the damping values for the Alpha and APS blocks were calculated. A comparison based on the arithmetic mean of the values w tma obtained for the measurement points P 2 to P 6 for the relative mean damping values w tma in the excitation frequency range of 8 ÷ 5000 Hz for the Alpha and APS blocks is shown in Figure 12. Figure 11. Impulse distribution of excitation force F in time t when hit with a PCB 086C03 modal hammer on a hollow concrete block.
As a result of the modal hammer test, acceleration amplitudes were recorded for the individual measurement points located on the walls of the Alpha and APS blocks, in accordance with Figure 8. The test was conducted for audible frequencies of up to 20,000 Hz. The graphs are presented for frequencies of up to 4000 Hz. No measurable accelerations were observed above this frequency.

Assessment of the Efficiency of Hollow Block Damping
The damping effectiveness of the new type of APS concrete wall block compared to the Alpha reference block was tested in the frequency range from 8 Hz to 5000 Hz. The test was carried out on a test stand, as shown in Figure 9, for the selected sixteen frequencies, which were, respectively, 8, 16, 32, 64, 128, 256, 512, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, and 5000 Hz. A sinusoidal waveform of the vibration was forced, and the signal from the accelerometers was recorded at a sampling rate of 200 kHz, using Siemens LMS TestLab software. Three Alpha hollow concrete blocks and three APS blocks were tested. Using Formulas (1) and (2), the peak-to-peak acceleration values, RMS values, and relative mean damping values were calculated for each frequency. Based on the arithmetic mean, the relative mean damping values were calculated 〈 〉 at points P2 to P6. For the selected sixteen considered frequencies, the damping values for the Alpha and APS blocks were calculated. A comparison based on the arithmetic mean of the values 〈 〉 obtained for the measurement points P2 to P6 for the relative mean damping values 〈 〉 in the excitation frequency range of 8 ÷ 5000 Hz for the Alpha and APS blocks is shown in Figure 12. The comparison of the relative mean damping values of the new type of APS block with those of the Alpha block revealed that only for the frequencies of 8 Hz, 16 Hz, 128 Hz, and 2000 Hz was the difference small, up to 3.58%. For the other frequencies, a comparison of the relative mean damping values showed a higher efficiency of the APS block, which ranged from 10% to 51%, as shown in Figure 12. An analysis of the relative mean damping values based on the arithmetic mean of the measurements for points P2 to P6 〈 〉 revealed that the Alpha block, for each excitation frequency studied, had lower The comparison of the relative mean damping values of the new type of APS block with those of the Alpha block revealed that only for the frequencies of 8 Hz, 16 Hz, 128 Hz, and 2000 Hz was the difference small, up to 3.58%. For the other frequencies, a comparison of the relative mean damping values showed a higher efficiency of the APS block, which ranged from 10% to 51%, as shown in Figure 12. An analysis of the relative mean damping values based on the arithmetic mean of the measurements for points P 2 to P 6 w tma revealed that the Alpha block, for each excitation frequency studied, had lower damping values than those of the APS. The Alpha hollow block achieved high damping values for the frequencies of 2000 Hz, 4500 Hz, and 5000 Hz and they were, respectively, 45%, 60%, and 44%, but were still lower than the damping for the APS hollow blocks.
In other cases, the relative mean damping did not exceed 30%. At low frequencies of 8 to 256 Hz, the concrete blocks of the new type achieved relative mean damping values greater than several to ca. 30%, and for higher frequencies, the damping definitely increased and reached values of up to 80% in favor of the APS blocks. Based on the comparison of the damping of the new type of APS blocks with the Alpha blocks, it can be concluded that only for the frequency of 2000 Hz was the damping of the new type of hollow blocks comparable with the Alpha blocks and within 45-55%. In other cases, the new type of APS hollow blocks was significantly better at reducing mechanical vibrations.
Based on Equation (4), the relative mean RMS damping w tsa in the excitation frequency range of 8 ÷ 5000 Hz for the Alpha and APS hollow blocks was calculated for the arithmetic mean of the measurements at points P 2 to P 6 located on the back wall of the tested hollow blocks. The results are shown in Figure 13. damping values than those of the APS. The Alpha hollow block achieved high damping values for the frequencies of 2000 Hz, 4500 Hz, and 5000 Hz and they were, respectively, 45%, 60%, and 44%, but were still lower than the damping for the APS hollow blocks. In other cases, the relative mean damping did not exceed 30%. At low frequencies of 8 to 256 Hz, the concrete blocks of the new type achieved relative mean damping values greater than several to ca. 30%, and for higher frequencies, the damping definitely increased and reached values of up to 80% in favor of the APS blocks. Based on the comparison of the damping of the new type of APS blocks with the Alpha blocks, it can be concluded that only for the frequency of 2000 Hz was the damping of the new type of hollow blocks comparable with the Alpha blocks and within 45-55%. In other cases, the new type of APS hollow blocks was significantly better at reducing mechanical vibrations.
Based on Equation (4), the relative mean RMS damping 〈 〉 in the excitation frequency range of 8 ÷ 5000 Hz for the Alpha and APS hollow blocks was calculated for the arithmetic mean of the measurements at points P2 to P6 located on the back wall of the tested hollow blocks. The results are shown in Figure 13. The comparison of the relative mean RMS damping 〈 〉 in the band of the analyzed frequencies showed that the new APS hollow wall block was more effective in reducing mechanical impacts than the Alpha block. Only for the frequencies of 128 Hz and 256 Hz, both considered hollow wall blocks, was similar relative mean RMS damping 〈 〉 shown.

Test Results of Free Vibration
The results for the tested Alpha and APS blocks as a result of the modal hammer impacts are shown in Figures 14 and 15, in the form of an amplitude acceleration spectrum of amplitude in the time domain and a spectrum of amplitude in the frequency domain. The application of the force causing the vibration occurred at a distance of 1 cm from the accelerometer P1 (Figure 8). The characteristics of the applied force are shown in Figure 8. The measuring points P2 and P3 were set on the right side of the back wall of the hollow blocks at the narrow rib. The measuring points P4 and P5 were set on the left side of the back wall of the hollow blocks, close to the wider rib. The arrangement of the accelerometers at the selected points is shown in Figures 8 and 16. Figure 13. Relative mean RMS damping w tsa [%] between point P 1 -front wall and points P 2 to P 6 -rear wall based on the arithmetic mean of measurements for Alpha and APS blocks in the frequency range of 8 ÷ 5000 Hz.
The comparison of the relative mean RMS damping w tsa in the band of the analyzed frequencies showed that the new APS hollow wall block was more effective in reducing mechanical impacts than the Alpha block. Only for the frequencies of 128 Hz and 256 Hz, both considered hollow wall blocks, was similar relative mean RMS damping w tsa shown.

Test Results of Free Vibration
The results for the tested Alpha and APS blocks as a result of the modal hammer impacts are shown in Figures 14 and 15, in the form of an amplitude acceleration spectrum of amplitude in the time domain and a spectrum of amplitude in the frequency domain. The application of the force causing the vibration occurred at a distance of 1 cm from the accelerometer P 1 (Figure 8). The characteristics of the applied force are shown in Figure 8. The measuring points P 2 and P 3 were set on the right side of the back wall of the hollow blocks at the narrow rib. The measuring points P 4 and P 5 were set on the left side of the back wall of the hollow blocks, close to the wider rib. The arrangement of the accelerometers at the selected points is shown in Figures 8 and 16.   (Figure 16) revealed the highest acceleration amplitudes on accelerometers P4 and P5 placed on the rib for a frequency of 1478. 63 Hz. An analysis of the data from the P1 and P6 accelerometers at the centers of the front and back panels found identical frequencies in two peaks, a lower one at around 1475 Hz, and a higher one at around 1827 Hz. For a frequency of 1475 Hz, with a maximum input acceleration amplitude at P1 of 0.7 m/s 2 , the value of the acceleration at P6 on the back wall was half of the input value, at 0.348 m/s 2 .
The test was carried out for a new type of concrete wall hollow block (APS) induced with a force of 400 N using a modal hammer. The vibration extinction time was ca. 0.08 s. The acceleration amplitude in the frequency domain is shown in the second column of Figure 15. The maximum acceleration value was up to 50 m/s 2 , with a frequency range of 0 ÷ 4000 Hz. A comparison of the data from accelerometers P1 and P6 placed at the geometric centers of the front and rear walls allowed for the determination of the maximum acceleration amplitude at the input at P1 at the level of 0.65 m/s 2 and at the output at P6 at the level of 0.516 m/s 2 . At higher frequencies, there were also decreases in the acceleration amplitudes at point P6 compared to point P1. Comparing the data of the accelerometers placed on the left side (P4, P5) and on the right side (P2, P3) of the rear wall of the hollow block (Figure 16), lower acceleration amplitudes were observed on the accelerometers P4 and P5 located on the rib for the frequencies of 915 Hz, 1563 Hz, 1892 Hz, 2248 Hz, and 3001 Hz.
A free vibration plot was obtained for both types of blocks as a result of using a modal hammer with a force of 400 N. The vibration extinction time for the Alpha block was about 0.1 s, while that for the new APS block was about 0.08 s. These values were read assuming that the vibration extinction cut-off point occurred at a = 2 m/s 2 -see Table 8. A comparison of the new concrete blocks with the Alpha block revealed that the vibration extinction time was reduced by 25% compared to the Alpha block.  Figure 14, which demonstrated a similar character (regardless of the location of the accelerometer) in the frequency range of 0 ÷ 4000 Hz. An increase in the vibration amplitudes at similar frequencies was observed for all the selected points: about 1424 Hz, 1825 Hz, 2428 Hz, and 2715 Hz. A comparison of the data from the accelerometers placed on the left side (P 4 , P 5 ) and the right side (P 2 , P 3 ) of the rear wall of the block (Figure 16) revealed the highest acceleration amplitudes on accelerometers P 4 and P 5 placed on the rib for a frequency of 1478. 63 Hz. An analysis of the data from the P 1 and P 6 accelerometers at the centers of the front and back panels found identical frequencies in two peaks, a lower one at around 1475 Hz, and a higher one at around 1827 Hz. For a frequency of 1475 Hz, with a maximum input acceleration amplitude at P 1 of 0.7 m/s 2 , the value of the acceleration at P 6 on the back wall was half of the input value, at 0.348 m/s 2 .
The test was carried out for a new type of concrete wall hollow block (APS) induced with a force of 400 N using a modal hammer. The vibration extinction time was ca. 0.08 s. The acceleration amplitude in the frequency domain is shown in the second column of Figure 15. The maximum acceleration value was up to 50 m/s 2 , with a frequency range of 0 ÷ 4000 Hz. A comparison of the data from accelerometers P 1 and P 6 placed at the geometric centers of the front and rear walls allowed for the determination of the maximum acceleration amplitude at the input at P 1 at the level of 0.65 m/s 2 and at the output at P 6 at the level of 0.516 m/s 2 . At higher frequencies, there were also decreases in the acceleration amplitudes at point P 6 compared to point P 1 . Comparing the data of the accelerometers placed on the left side (P 4 , P 5 ) and on the right side (P 2 , P 3 ) of the rear wall of the hollow block (Figure 16), lower acceleration amplitudes were observed on the accelerometers P 4 and P 5 located on the rib for the frequencies of 915 Hz, 1563 Hz, 1892 Hz, 2248 Hz, and 3001 Hz.
A free vibration plot was obtained for both types of blocks as a result of using a modal hammer with a force of 400 N. The vibration extinction time for the Alpha block was about 0.1 s, while that for the new APS block was about 0.08 s. These values were read assuming that the vibration extinction cut-off point occurred at a = 2 m/s 2 -see Table 8. A comparison of the new concrete blocks with the Alpha block revealed that the vibration extinction time was reduced by 25% compared to the Alpha block. Furthermore, a comparison of the readings from the accelerometers placed at measurement points P 1 to P 6 for the new type of APS blocks showed that all the amplitude readings were lower than those from the accelerometers placed on the Alpha block. This demonstrated the effectiveness of the solution presented.

Discussion of the Nature of the Research
An example of the analysis of the effectiveness of the APS block damping was performed for conditions occurring at the Faculty of Civil Engineering at the Częstochowa University of Technology, where the source of high-intensity vibrations is an M-400 pneumatic impact mill with a capacity of 11 kW, which is designed for grinding bulk materials. It is driven by an SKF-160M-2A motor (Manufactured: Fumo-Ostrzeszów, Ostrzeszów, Poland) and powered by 400 V, with a rated rotor speed of 3000 rpm. To determine its dynamic impact on the external environment, measurements were taken while the mill was operated. During the vibration measurements, the device was loaded with 20 kg of loose material in the form of fine aggregate with a fraction of 2÷8 mm. Due to the positioning of the impact mill directly on the concrete floor in the laboratory, measurements were taken at two points, (1) on the floor and (2) on the body of the mill, in accordance with Figure 17. The test was performed using accelerometers, which indicated the acceleration values over time in three directions, x, y, and z; the results were read using the Simens LMS TestLab 17 program.
For the test results, Fourier FFT transform was performed to transform the signal from the time domain to the frequency domain. This made it possible to present a frequency representation of the signal, and the signal spectrum contained information about the "signal frequency content". The resulting transformation can be interpreted as the determination of the measure of the correlation for individual harmonic functions, i.e., checking "how much" of a particular "frequency" is contained in the signal.

Determination of the Nature of Mechanical Vibrations
To determine the nature of the mechanical vibrations of the M-400 impact mill, measurements were made with a triaxial accelerometer. The signal values recorded on the floor at the mill are shown in Figure 18. In Figure 18d, the resultant for the measurements taken is additionally determined. Acceleration graphs for each axis from the sensor set on the mill body are shown in Figure 19. The resultant from the measurements taken is also determined here (see Figure 19d). For the test results, Fourier FFT transform was performed to transform the s from the time domain to the frequency domain. This made it possible to present quency representation of the signal, and the signal spectrum contained information the "signal frequency content". The resulting transformation can be interpreted as th termination of the measure of the correlation for individual harmonic functions checking "how much" of a particular "frequency" is contained in the signal.

Determination of the Nature of Mechanical Vibrations
To determine the nature of the mechanical vibrations of the M-400 impact mill, m urements were made with a triaxial accelerometer. The signal values recorded on the at the mill are shown in Figure 18. In Figure 18d, the resultant for the measurements is additionally determined. Acceleration graphs for each axis from the sensor set o mill body are shown in Figure 19. The resultant from the measurements taken is als termined here (see Figure 19d). By analyzing the readings from a sensor placed on the floor at the mill, the vibrations with the highest amplitude were obtained in the x-direction, and they were 0.32 m/s 2 ( Figure 18). These were sinusoidal vibrations, which are a consequence of the operating characteristics of the analyzed device. The y-and z-directions also showed sinusoidal oscillations, with their values being an order of magnitude smaller than those measured in the x-direction.
The readings from a sensor placed on the body of the mill indicated vibrations with the highest amplitude also in the x-direction. Their value was 9.97 m/s 2 ( Figure 19). These were sinusoidal vibrations. In the y-and z-directions, half the vibration was obtained, but with the same sinusoidal waveform.  By analyzing the readings from a sensor placed on the floor at the mill, the vibrations with the highest amplitude were obtained in the x-direction, and they were 0.32 m/s 2 (Figure 18). These were sinusoidal vibrations, which are a consequence of the operating characteristics of the analyzed device. The y-and z-directions also showed sinusoidal       Based on the tests performed, the relative mean damping values w tma were calculated for the frequency range from 8 to 5000 Hz and the relative mean RMS damping w tsa for the Alpha and APS blocks, taking into account the signal generated by an M-400 pneumatic impact mill in two variants: 1-with a measurement on the floor next to the mill and 2-with a measurement on the mill body. A signal analysis was performed for three directions, x, y, and z, and their resultants.

Simulation of Damping of Selected Signals
A comparison of the relative mean damping values w tma for the tested hollow blocks is shown in Figure 24, and for the relative mean RMS damping w tsa , the comparison is shown in Figure 25. Based on the tests performed, the relative mean damping values 〈 〉 were calculated for the frequency range from 8 to 5000 Hz and the relative mean RMS damping 〈 〉 for the Alpha and APS blocks, taking into account the signal generated by an M-400 pneumatic impact mill in two variants: 1-with a measurement on the floor next to the mill and 2-with a measurement on the mill body. A signal analysis was performed for three directions, x, y, and z, and their resultants.
A comparison of the relative mean damping values 〈 〉 for the tested hollow blocks is shown in Figure 24, and for the relative mean RMS damping 〈 〉 , the comparison is shown in Figure 25.   Based on the tests performed, the relative mean damping values 〈 〉 were calculated for the frequency range from 8 to 5000 Hz and the relative mean RMS damping 〈 〉 for the Alpha and APS blocks, taking into account the signal generated by an M-400 pneumatic impact mill in two variants: 1-with a measurement on the floor next to the mill and 2-with a measurement on the mill body. A signal analysis was performed for three directions, x, y, and z, and their resultants.
A comparison of the relative mean damping values 〈 〉 for the tested hollow blocks is shown in Figure 24, and for the relative mean RMS damping 〈 〉 , the comparison is shown in Figure 25.   A comparison of the simulated damping for the signal measured on the floor at the leg of the M-400 pneumatic impact mill during its operation, at a distance of 75 cm from its axis (point 1 in Figure 17), shows that the relative mean RMS damping w tsa for the Alpha block was 23.11%, while that for the APS block was 39.98%. On the mill body, at a distance of 40 cm from its axis (point 2 in Figure 17), it was found that the relative mean RMS damping w tsa for the Alpha block was 14.92%, while for the APS block, it was at a level more than twice as high, at 33.60%. In this case, more than a 100% improvement in the vibration reduction efficiency was achieved.
For the signal generated by the operation of the M-400 pneumatic impact mill, read from a sensor set at the mill on the floor, the APS block absorbed 16.87% more signal compared to the Alpha block, while for the signal read from a sensor set on the mill body, the APS block absorbed 18.68% more signal compared to the Alpha block. A simulation of the damping of the impact mill signal showed that, for both signals analyzed, the damping of the APS blocks was significantly higher compared to the Alpha comparison block.

Conclusions and Summary of the Research
The paper presented an innovative APS concrete wall block and provided technical data on this new type of block, the percentages of the SBR rubber granules and PET flakes used in the modified concrete, and the composition of the concrete modified with this mixture of recycled additives (SBR rubber granules and PET flakes) per 1 m 3 volume of concrete mix.
To demonstrate the effectiveness of the solution in reducing mechanical vibrations, the effect of the interaction of different frequencies of the mechanical wave on reducing these vibrations was evaluated for comparison blocks (Alpha) and innovative wall blocks (APS). The test was performed on a test stand construed for dynamic measurements following the propagation of a mechanical wave, thus determining the damping efficiency of the blocks. The study was conducted for sixteen frequencies: 8, 16, 32, 64, 128, 256, 512, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, and 5000 Hz.
The comparison of the relative mean damping values of the APS block with those of the Alpha block showed that, for low frequencies of 8 Hz, 16 Hz, and 128 Hz and frequencies of 2000 Hz, respectively, the difference in damping was up to 3.58% in favor of the new type of hollow block (APS). For the other frequencies tested, the comparison of the damping of the APS block with the Alpha block ranged from 10% to 51%, confirming its usefulness in reducing mechanical vibrations. The analysis of the relative mean damping values revealed that the Alpha block, for each excitation frequency tested, was less effective at damping the signal than the new type (APS). Significant damping was obtained for the Alpha block for frequencies of 2000, 4500, and 5000 Hz. They were over 45%, 60%, and 44%, respectively. For the other frequencies tested, the Alpha block showed significantly lower damping values, which did not exceed 30% compared to the new APS block. The comparison Alpha block and the APS block were also subjected to a modal hammer test. This allowed for an analysis of the nature of the free vibration for each block tested. Based on the acceleration amplitudes read from the accelerometers placed on the front and rear walls of the tested blocks, the new APS block was found to have a 25% shorter impact pulse extinction time compared to the Alpha block.
A simulation of the damping of the vibrations forced by the M-400 pneumatic impact mill was also carried out for the tested Alpha and APS blocks. Based on the resultant readings from the accelerometers located on the body of the impact mill and the floor at the mill, the nature of the interactions was determined, and an analysis of the damping efficiency of the test blocks was carried out. For the signal measured on the mill body, the relative mean RMS damping w tsa was evaluated, which was 14.92% for the Alpha block and 33.60% for the APS block. On the floor directly at the mill, the value of w tsa for the Alpha block was 23.11%, while for the APS block it was 39.98%. This demonstrated the greater effectiveness of the new type of concrete wall block (APS) in reducing mechanical vibrations compared to the Alpha block. In conclusion, the research on the reduction in mechanical interactions, both in terms of the sixteen frequencies studied and with regard to the effectiveness of the solution studied at damping the vibrations forced by the operation of the M-400 pneumatic impact mill, showed that the new type of APS concrete wall hollow block is an effective alternative to other types of concrete matrix blocks used for structural wall masonry and can significantly improve the comfort of buildings subjected to mechanical vibrations. Furthermore, the developed solution effectively uses recycled materials in the form of SBR rubber granules from, for example, used car tires, and PET flakes from used food packaging, to produce modified concrete for a new type of APS concrete wall hollow block.
The developed APS wall hollow block is an innovative solution protected by Patent No PL 235427 B1 [67]. In order to obtain its effectiveness at reducing the vibrations presented in this study, a purely mechanical approach was needed, resulting from the use of the geometry of the internal space of the hollow block, through the proper design of its through-holes and butt locks to reduce the vibration energy. This required many numerical analyses, which took into account sublime research methods. In the course of the numerical research prior to obtaining the patent protection, a preliminary strength assessment was also performed, which was confirmed at the stage of experimental verification, both in the study of the concrete mix modified with recycling additives and the prototype series of the APS hollow blocks. An additional test confirming the effectiveness of the developed solution, based on a non-traditional approach to the design of concrete hollow blocks, was the simulation of vibrations generated by the M-400 pneumatic impact mill, intended for grinding loose materials. For the developed solution, the reduction in the signal for the APS wall block was greater than that of the comparative Alpha hollow block, by 16.87% from the signal reading on the floor next to the mill and by 18.68% from the signal reading from the mill body, in accordance with Figure 17. In this way, the effectiveness of the vibration reduction in the internal structure of the hollow block was demonstrated, which was also observed at the stage of testing sinusoidal excitations in the range from 8 to 5000 Hz.
To sum up, it can be stated that the APS concrete hollow block discussed in this paper, designed with a concrete mix modified with recycling additives (SBR and PET), not only meets the standard criteria for this type of construction product, but also has an innovative solution for its internal structure, showing a greater efficiency (compared to the Alpha hollow block) in reducing propagating vibrations. This was the most important design intention, which, on the basis of the research cited here, can be considered as meeting the expectations of our work.

Patents
The authors obtained, in Poland, a patent for the invention: Ażurowy pustakścienny

Conflicts of Interest:
The authors declare no conflict of interest.