Manufacture and Characterization of Polypropylene (PP) and High-Density Polyethylene (HDPE) Blocks for Potential Use as Masonry Component in Civil Construction

The lack of suitable destinations for plastics materials can be a global environmental problem. The alternative use of materials for sustainable construction encourages the standardization of waste and promotes effective social, environmental and economic gains at the local level and ensures savings and income for communities. The aim of this paper is the development, manufacture, and characterization of PP and HDPE recycled polyolefin blocks as masonry components in civil construction. These blocks were manufactured by the rotational molding process. Besides this, the mechanical, physical, impact and flammability properties of the blocks were studied. In conclusion, HDPE showed better behavior than PP in tests realized.


Introduction
Overall, plastic materials have been used regularly in all aspects of daily life. The lack of suitable destination for these materials can be a worldwide environmental problem, especially because plastic materials can take hundreds of years to decompose [1]. On the other hand, the reuse of waste by efficient recycling provides social, environmental, and economic gains and at the local level, it ensures money savings for communities [2]. Also, plastic recycling and demolition waste annually lead to abundant environmental and economic benefits using them as an alternative material in sustainable construction. Besides that, it can promote the solution of sanitary landfill problems and the reduction of carbon emissions [3].
In addition, polypropylene (PP) and high-density polyethylene (HDPE) are relevant polymer wastes because they are polyolefins used in foam sheets and can indicate satisfactory results even with 50% of granules replacing virgin materials [5].
Moreover, PP and HDPE can be reused without getting changes which are known as primary recycling [6]. Nonetheless, they should have been cleaned and uncontaminated [7]. Mechanical recycling can also be used by extrusion, injection, thermoforming, compression molding and rotational molding. The polymeric material is usually in powder form after the revaluation process (collection, cleaning, drying and grinding). In this method, the The calcined alumina used was originated by ALUNORTE-Alumina do Norte S.A. company, from Belém, state of Pará, Brazil. The alumina is less stable than alumina-α. This type of alumina is used as raw material for the aluminum production process, as it uses less energy than its more stable form, called alumina-α.

Three-Dimensional Modeling of Molds for Manufacture of Polymeric Blocks
Firstly, the three-dimensional modeling of the blocks and molds was performed using computational resources from the SketchUp PRO 2017 software, version 17.0.18899 64-bit for the construction of the desired geometries and 3D visualization [36,37].
After this, the stainless-steel mold was made using a sheet with thickness of 3 mm, 2 thread bars of 9.53 mm in diameter with 350 mm and 400 mm of length, high temperature aluminum tapes to aid in sealing, nuts and alleys to fix the mold on the bars. At the aluminum mold, a plate with a single thickness of 1.5 mm, thread bars, nuts and washers were used.
Besides that, a rotational molding machine prototype was used to manufacturing the civil construction blocks. The mold was fed with 1.530 kg of material and the speeds of biaxial rotation were 6 rpm and 9 rpm (translation). The heating time was 50 min and cooling time was 30 min with biaxial rotation up to 60 °C for demolding the block [38]. The calcined alumina used was originated by ALUNORTE-Alumina do Norte S.A. company, from Belém, state of Pará, Brazil. The alumina is less stable than alumina-α. This type of alumina is used as raw material for the aluminum production process, as it uses less energy than its more stable form, called alumina-α.

Three-Dimensional Modeling of Molds for Manufacture of Polymeric Blocks
Firstly, the three-dimensional modeling of the blocks and molds was performed using computational resources from the SketchUp PRO 2017 software, version 17.0.18899 64-bit for the construction of the desired geometries and 3D visualization [36,37].
After this, the stainless-steel mold was made using a sheet with thickness of 3 mm, 2 thread bars of 9.53 mm in diameter with 350 mm and 400 mm of length, high temperature aluminum tapes to aid in sealing, nuts and alleys to fix the mold on the bars. At the aluminum mold, a plate with a single thickness of 1.5 mm, thread bars, nuts and washers were used.
Besides that, a rotational molding machine prototype was used to manufacturing the civil construction blocks. The mold was fed with 1.530 kg of material and the speeds of biaxial rotation were 6 rpm and 9 rpm (translation). The heating time was 50 min and cooling time was 30 min with biaxial rotation up to 60 • C for demolding the block [38].

Methods for Characterization HDPE and PP Materials
The optical microscope, Zeiss Axiocam 105 model, from UFPA, Belém, state of Pará, Brazil, was used for obtaining images of PP and HDPE post-consumer polymers. The Image J software version 1.52b was used to calculate the average particle size of polymers [39]. The density measurements (D) were carried followed by ASTM D792 standard [40,41] at the temperature of 23 • C. The density of the samples was determined by Equation (1): where: a = apparent mass of specimen, without wire or sinker, in air, b = apparent mass of specimen (and of sinker, if used) completely immersed and of the wire partially immersed in liquid, and w = apparent mass of totally immersed sinker (if used) and of partially immersed wire. X-ray diffraction (XRD) analysis was performed with a Bruker D2 Phaser diffractometer at room temperature, from UFPA, Belém, state of Pará, Brazil. The parameters used were: Cu radiation (Kα = 1.540598 Å), 30 kV voltage, 10 mA current, angular scanning range ( • 2θ) = 5-60 • with Ni Kβ filter, at 0.02 • angular step and 0.3 s per step time [42][43][44][45].
The impact strength test was performed by Gunt Hamburg model WP 410, from UFPA, Belém, state of Pará, Brazil. This equipment has a capacity of 300 Nm, hammer weight of 19.8 kg, impact velocity of 5.5 m·s −1 , length of the pendulum of 840 mm, drop angle of 150 • and supports for samples with an opening of 40 mm. It used the measures of the specimens and the procedures for execution of the Charpy impact test [21,50,51]. There was no used notch in the specimen.
In Brazil, there are no standards for polymeric modular building blocks. So, the polymeric blocks were characterized similarly to ceramic blocks. Thus, geometric characteristics (dimensions of the faces, thickness of the septa, external walls, deviation from the square and flatness of the faces) [52], mechanical characteristics (compression strength) [53], water absorption test were realized by ASTM C20-00 and ABNT NBR 15270-1 and ABNT NBR 15270-2 Brazilian standards [52][53][54][55]. Water absorption was a relation between the dry and wet specimen weights and Equation (2) was used: where: Aw is water absorption percentual; Ms is saturated with water specimen masses; Md is dry specimen mass. The flammability properties were tested under vertical UL94 standard burning conditions for observations of the dripping phenomenon. In the experiment, the flame was applied to each specimen for 10 s and removed. Furthermore, once the combustion was extinguished the flame was applied again for 10 s [32,56,57]. The samples were cut from the fabricated PP and HDPE blocks with 5% of alumina filler and without fillers.
In Brazil, the Brazilian standard ABN NBT 15575-1 (2021) establishes fire safety of building components and building systems, in particular sealing systems and walls systems [58]. Moreover, plastics are flammable materials when heated and physical-chemical changes occur by which the materials decompose into volatile products. So, the main focus of the flammability was to evaluate if a certain polymeric material will have the required behavior. The flammability test follows the IEC 60695-11-10, ASTM D635 and UL94 international standards that evaluate points, such as: time to combustion, how long it took to extinguish combustion without intervention, if combustion continues and other tests that will determine the flammability potential and its resistance to flame exposure. Figure 2 shows the modeling of the rotomolded blocks and the modeling of the molds. Initially, the stainless-steel mold was thought of as an option for the material to the molds. However, due to local limitations of material and laboratory, the molds were made with aluminum and blocks without interlocking. So, the stainless-steel mold was able to achieve its purpose which was to develop the rotomolded parts.

Three-Dimensional Modeling
In Brazil, the Brazilian standard ABN NBT 15575-1 (2021) establishes fire safety of building components and building systems, in particular sealing systems and walls systems [58]. Moreover, plastics are flammable materials when heated and physical-chemical changes occur by which the materials decompose into volatile products. So, the main focus of the flammability was to evaluate if a certain polymeric material will have the required behavior. The flammability test follows the IEC 60695-11-10, ASTM D635 and UL94 international standards that evaluate points, such as: time to combustion, how long it took to extinguish combustion without intervention, if combustion continues and other tests that will determine the flammability potential and its resistance to flame exposure. Figure 2 shows the modeling of the rotomolded blocks and the modeling of the molds. Initially, the stainless-steel mold was thought of as an option for the material to the molds. However, due to local limitations of material and laboratory, the molds were made with aluminum and blocks without interlocking. So, the stainless-steel mold was able to achieve its purpose which was to develop the rotomolded parts.

Polymeric Blocks Produced
The designed bars were effective in fixing the mold on the spider and the mold sealing with the help of high-temperature aluminum tape prevented material runoff. Despite the mold having an angle inclination in the male and female cavities, there was a small difficulty in the demold of the female cavity. The PP blocks had a surface finish with a discrete gloss and voids in their surfaces in the male cavities and in the upper corners acquired from the stainless-steel mold. The aluminum mold contributed to the surface finishing with accentuated shine, reduced number of voids on its surfaces, and similar porosity in both materials, however, it presented a regular surface with final surface quality.
The aluminum mold had no material run off and a 9 kg reduction in mold mass occurred. There was no difficulty in demolding, with the need to disassemble only the upper or lower part, making the part slide over the mold, facilitating the demolding of the rotomolded block.
The blocks had dimensions of 39 cm in length, 19 cm in height and 14 cm in thickness (width) (Figure 2).
The HDPE blocks show a surface with moderate gloss and its porosity was reduced by stainless-steel molds. The aluminum mold contributed to a smooth surface with high

Polymeric Blocks Produced
The designed bars were effective in fixing the mold on the spider and the mold sealing with the help of high-temperature aluminum tape prevented material runoff. Despite the mold having an angle inclination in the male and female cavities, there was a small difficulty in the demold of the female cavity. The PP blocks had a surface finish with a discrete gloss and voids in their surfaces in the male cavities and in the upper corners acquired from the stainless-steel mold. The aluminum mold contributed to the surface finishing with accentuated shine, reduced number of voids on its surfaces, and similar porosity in both materials, however, it presented a regular surface with final surface quality.
The aluminum mold had no material run off and a 9 kg reduction in mold mass occurred. There was no difficulty in demolding, with the need to disassemble only the upper or lower part, making the part slide over the mold, facilitating the demolding of the rotomolded block.
The blocks had dimensions of 39 cm in length, 19 cm in height and 14 cm in thickness (width) (Figure 2).
The HDPE blocks show a surface with moderate gloss and its porosity was reduced by stainless-steel molds. The aluminum mold contributed to a smooth surface with high gloss and reduced porosity compared to the other developed blocks, there were no material dispositions, closing all corners in both metals used in Figure 2c PP rotomolded block and Figure 2d HDPE rotomolded block. As a smaller particle size material was used, a better sintering propagation was obtained, producing flat and regular surfaces with final surface quality.
The blocks made by PP had more production more economical than HDPE blocks, because they do not require a second grinding in the regrind of the polymer, reducing the final cost. They can be used with or without finishing materials such as glass tablets and metal profiles, because of their low porosity and smooth surface and overlapping regardless of the material used for the finishing.

Optical Microscopy
From Optical microscopy, no bubbles were identified in the blocks, which are the main defects reported for the rotomolding process. This fact indicates that the technique used in the processing was efficient [21]. Both materials show comparable thermal behavior. The polypropylene block showed porosity and texturing on the outer surface and great roughness on the inner surface in Figure 3a,b,e,f. The polyethylene pieces showed little porosity and a smooth outer surface and less roughness and a tangle on the inner surface in Figure 3c,d,g,h.
metal profiles, because of their low porosity and smooth surface and overlapping regardless of the material used for the finishing.

Optical Microscopy
From Optical microscopy, no bubbles were identified in the blocks, which are the main defects reported for the rotomolding process. This fact indicates that the technique used in the processing was efficient [21]. Both materials show comparable thermal behavior. The polypropylene block showed porosity and texturing on the outer surface and great roughness on the inner surface in Figure 3a,b,e,f. The polyethylene pieces showed little porosity and a smooth outer surface and less roughness and a tangle on the inner surface in Figure 3c,d,g,h.
In the case of semicrystalline polymers, the cooling rate causes more effect on the crystallization phenomenon and the growth rate of the spherulites and their size [24]. The particles have different shapes after revaluation of the PP particles. So, the average area value of PP was calculated and equal value of 10.15 mm and for the HDPE particles, the average area value of HDPE was 1.53 mm. A wide particle size distribution compensates for the low packing density of large particles and leads to smaller bubble sizes in the melt [59]. However, the irregular particle shape decreases the sintering efficiency in PP, leading to a lesser efficient sintering process than HDPE [60].

Density
The results of the density analysis by the pycnometer method, performed at the temperature of 27 °C of distilled water with its density of 1.0 g/m 3 , show that the revalued post-consumer packaging presented values of 1.0 g.m -3 for PP and 1.0 g.m -3 for HDPE. Therefore, with the results obtained, it was possible to measure and to compare the values established by ASTM D792 standard. Thus, the values obtained were analogous in with the standard. This standard informs values independent of virgin or processed materials, In the case of semicrystalline polymers, the cooling rate causes more effect on the crystallization phenomenon and the growth rate of the spherulites and their size [24]. The particles have different shapes after revaluation of the PP particles. So, the average area value of PP was calculated and equal value of 10.15 mm and for the HDPE particles, the average area value of HDPE was 1.53 mm. A wide particle size distribution compensates for the low packing density of large particles and leads to smaller bubble sizes in the melt [59]. However, the irregular particle shape decreases the sintering efficiency in PP, leading to a lesser efficient sintering process than HDPE [60].

Density
The results of the density analysis by the pycnometer method, performed at the temperature of 27 • C of distilled water with its density of 1.0 g/m 3 , show that the revalued post-consumer packaging presented values of 1.0 g.m −3 for PP and 1.0 g.m −3 for HDPE. Therefore, with the results obtained, it was possible to measure and to compare the values established by ASTM D792 standard. Thus, the values obtained were analogous in with the standard. This standard informs values independent of virgin or processed materials, showing that there was no adulteration with cheaper material and ensuring the homogeneity of the rotomolded materials [41]. As the PP and HDPE polymers used have similar densities, the same amount of material was used in the molds, standardizing the block development process.  polymers, there was a difference in the diffraction intensity of the peaks compared to the post-consumer ones, resulting in a reduction in intensity and to indicating that this disparity caused changes in crystallinity [71]. Therefore, a shift to smaller angles occurs, indicating the effect of thermomechanical degradation on crystal morphology [72]. So, solving technical problems with the rotational molding machine, three types of molds were developed to obtain a mass reduction in the mold.
Moreover, it can analyze rotomolded parts with aluminum, stainless steel, and glass mold. Thus, it was observed that there was no expressive change in the peak intensities in the PP samples in Figure 5a. Besides that, the same did not occur with HDPE samples in which the stainless-steel mold showed a disparity compared to the other analyzed molds Figure 5b. The mold cooling time may have influenced the HDPE recrystallization.     (20) [68][69][70]. In both samples of rotomolded PP and HDPE polymers, there was a difference in the diffraction intensity of the peaks compared to the post-consumer ones, resulting in a reduction in intensity and to indicating that this disparity caused changes in crystallinity [71]. Therefore, a shift to smaller angles occurs, indicating the effect of thermomechanical degradation on crystal morphology [72]. So, solving technical problems with the rotational molding machine, three types of molds were developed to obtain a mass reduction in the mold.

Mechanical Behavior and Characterization of Masonry Blocks
Moreover, it can analyze rotomolded parts with aluminum, stainless steel, and glass mold. Thus, it was observed that there was no expressive change in the peak intensities in the PP samples in Figure 5a. Besides that, the same did not occur with HDPE samples in which the stainless-steel mold showed a disparity compared to the other analyzed molds Figure 5b. The mold cooling time may have influenced the HDPE recrystallization.

Flexural Strength
It was calculated the modulus of elasticity (E) and maximum strain (ε) from the flexural test. It was shown 302 MPa for PP with 2 mm·min −1 (PP2), 266 MPa for 5 mm·min −1 (PP5) and 83 MPa for 10 mm·min −1 (PP10) for the respective 22 mm, 19 mm and 20 mm. I addition to, the values of 91 MPa for HDPE in 2 mm·min −1 (HDPE2), 76 MPa for 5 mm·min −1 (HDPE5) and 26 MPa for 10 mm·min −1 were obtained (PEAD10) for the modulus of elasticity in respective 26 mm, 22 mm and 19 mm for strain ((ε) reported in Table 1. It is observed that the sample PP exhibits modulus of elasticity values higher than HDPE at the several strain rates studied. As expected, the strain rates change the flexural strengths and modulus of elasticities, in especial for the PP material. With the increase of rates, the E was reduced. Thus, a variation was observed under the influence of the strain rate applied in the tests illustrated in Figure 6. It was observed that PP2 samples showed highest flexural strength of blocks tested.
In the flexural test, the samples of PP2 from literature showed better results with materials recycled by rotational molding, now according to a work performed by rotational molding with virgin polyethylene and was performed the flexion test of the external It was observed that PP2 samples showed highest flexural strength of blocks tested. In the flexural test, the samples of PP2 from literature showed better results with materials recycled by rotational molding, now according to a work performed by rotational molding with virgin polyethylene and was performed the flexion test of the external surface, showed a value close to 17.5 MPa [73]. Despite being the same process, the samples of the rotationally molded blocks have porosity and interstitial spaces between the structures, facilitating the agglutination of other materials on the external surfaces of the blocks, such as cement and external and internal finishing materials in walls.

Impact Test
The PP block showed a 0.62 kJ·m −2 value and the HDPE block presented a 2.48 kJ·m −2 value reported in Figure 7. For HDPE pure the impact strength is 6 kj.m -2 [21] and 3 kj.m -2 for PP pure [50]. So, both types of polymers studied had a decrease of values of impact strength related to HDPE pure and PP pure. This behavior is expected because of the porosity of recycled blocks and reduction of intensity in the crystallographic planes of both recycled polymers. The reprocessing impacts the mechanical strengths [72].

Geometric Characteristics
Determination of the face dimensions, effective dimensions, deviation from the square (D) and from the flatness of the faces (F) and thickness of the external walls and septa of the blocks.
In the test for determining the thickness of the external walls, it can observe the measurements of the measures of the block of PP with 40 mm and HDPE 44 mm corresponding to the values of the external septa met the minimum requirements, according to the tolerance of the sum of 20 mm minimum of the external septa in Table 2. Related to the determination of the measures of the faces, the measurements of width 136 mm for PP and 137 mm for HDPE, height 191 mm for PP and HDPE and length of 385 mm in both samples of PP and HDPE were obtained. The average tolerance was od ±3 mm for width, height and length.  For HDPE pure the impact strength is 6 kJ·m −2 [21] and 3 kJ·m −2 for PP pure [50]. So, both types of polymers studied had a decrease of values of impact strength related to HDPE pure and PP pure. This behavior is expected because of the porosity of recycled blocks and reduction of intensity in the crystallographic planes of both recycled polymers. The reprocessing impacts the mechanical strengths [72].

Geometric Characteristics
Determination of the face dimensions, effective dimensions, deviation from the square (D) and from the flatness of the faces (F) and thickness of the external walls and septa of the blocks.
In the test for determining the thickness of the external walls, it can observe the measurements of the measures of the block of PP with 40 mm and HDPE 44 mm corresponding to the values of the external septa met the minimum requirements, according to the tolerance of the sum of 20 mm minimum of the external septa in Table 2. Related to the determination of the measures of the faces, the measurements of width 136 mm for PP and 137 mm for HDPE, height 191 mm for PP and HDPE and length of 385 mm in both samples of PP and HDPE were obtained. The average tolerance was od ±3 mm for width, height and length. Sd ( In the test for determining deviations from the square, it can observe the measurements of the PP block with 1.5 mm and HDPE with 1 mm, to meeting the tolerance of 3 mm maximum.
In the determination of the flatness of the faces, the values were for the blocks of PP 1.31 mm and HDPE 2 mm the average of the analyzed blocks met the minimum requirements of maximum tolerance of 3 mm deviation. Thus, the rotomolded blocks were accepted as to the analysis of the geometric characteristics not presenting deformities outside the requirements. Unlikely the certified and non-certified ceramic blocks for masonry sealing, commercialized in the region of Chapecó in the state of Santa Catarina, Brazil about 30% did not meet the requirements as to the geometric characteristics [52,53,74].

Water Absorption Test
As expected there was no water absorption in PP and HDPE blocks. The Brazilian standards establish maximum values of 20-22% for ceramic blocks [52,53]. This property is interesting to avoid problems of lack of water tightness and presence of humidity in components or parts of edification.
As an example, PP and HDPE blocks with geopolymer showed water absorption from 13% to 20% [55]. The authors believe this difference is due to the size of particles of polymers.

Compressive Strength
The PP block's compressive strength is higher than the HDPE block's compression strength, as can be seen in Table 2. So, the PP blocks showed a compression strength 50% higher than the HDPE blocks. It was found that the PP blocks after the test, suffered ruptures on the left and right sides with the ruptures similar to ceramic materials after the compression strength test observed in the study [75,76].
The HDPE blocks showed local elastic deformation, forming an appreciable lateral deformation not occurring rupture of the block, after the removal of the applied load. The samples tend to return to their initial shape, indicating that the HDPE blocks have a larger elastic phase than the PP ones.
It can be observed in Figure 7a the block at the beginning of the test, in Figure 7b the block receiving a load and suffering a local elastic deformation on the sides of the block. In the Figure 7c, the block returned to its initial shape after the removal of the load applied on it and its recovery after the tests. This did cause a permanent residual deformation as in the study of [77] and indicated a longer elastic deformation than the PP block.
HDPE presents a ductile behavior when subjected to compression and its compressive strength is adjacent, when compared to the strength of concrete and wood. Therefore, the application of HDPE would be a robust structural element to be submitted to compression [78].
A steel mesh with a diameter of 3.4 mm was added to the blocks as reinforcement to increase the compressive strength. The Figure 7a shows a structure developed for the reinforcement of the blocks. Also, the Figure 7b exhibit the mold with the frame inside waiting for the material to be poured to explore a possible increase in compression strength.
The HDPE blocks reinforced with the metal mesh showed better compressive strength than the HDPE blocks without reinforcement Figure 8c

UL 94 Vertical Flammability Test
It was observed that the samples without the incorporation of alumina in the blocks, suffer ignition followed by a flaming drip on the cotton in the second application of the flame to the specimen, characterizing it as the materials with the classification according to UL 94 Vertical of V-2 ( Figure 9ab).
In Figure 10a the PP sample without flames and the cotton fiber with flames after contexture and in Figure 10b the same occurred with HDPE, characterizing the two materials PP and HDPE as V-2.
However, in the samples with 5% incorporation of alumina, the flame retardant in the HDPE and PP blocks in the first application of the flame for 10 s, the set of specimens sustains the flame for only 5 s and goes out. After this, in the second application of the flame for 10 s the flame sustains for only 5 s and goes out, with no dripping of the material on the cotton. Thus, reaching the UL-94 vertical classification as V-0, referring to the classification requirements and in Figure 10c the PP sample with 5% alumina without dripping. Figure 9c illustrates the cotton fiber without flame due to the material being classified as V-0.  The filled PET bottle-based blocks can be a good alternative to solve the increase of compressive strength, by adding concrete inside the rotomolded blocks. Another solution would be to add sisal or cabuya fiber changing the elastic properties of the matrix polymer resulting in lower plastic deformation and higher elasticity, accompanied by shorter recovery times [77].
Although the rotomolded blocks do not meet the requirements corresponding to the mechanical strength according to the standard adapted for ceramic blocks.

UL 94 Vertical Flammability Test
It was observed that the samples without the incorporation of alumina in the blocks, suffer ignition followed by a flaming drip on the cotton in the second application of the flame to the specimen, characterizing it as the materials with the classification according to UL 94 Vertical of V-2 (Figure 9a,b).

UL 94 Vertical Flammability Test
It was observed that the samples without the incorporation of alumina in the blocks, suffer ignition followed by a flaming drip on the cotton in the second application of the flame to the specimen, characterizing it as the materials with the classification according to UL 94 Vertical of V-2 ( Figure 9ab).
In Figure 10a the PP sample without flames and the cotton fiber with flames after contexture and in Figure 10b the same occurred with HDPE, characterizing the two materials PP and HDPE as V-2.
However, in the samples with 5% incorporation of alumina, the flame retardant in the HDPE and PP blocks in the first application of the flame for 10 s, the set of specimens sustains the flame for only 5 s and goes out. After this, in the second application of the flame for 10 s the flame sustains for only 5 s and goes out, with no dripping of the material on the cotton. Thus, reaching the UL-94 vertical classification as V-0, referring to the classification requirements and in Figure 10c the PP sample with 5% alumina without dripping. Figure 9c illustrates the cotton fiber without flame due to the material being classified as V-0.

Technical, Economic, Environmental Feasibility, and Industrial Scale Production
One of the main advantages of reuse in civil construction is the reduction of nonrenewable raw materials, such as aggregates and materials in the manufacture of cement. This optimizes the environmental damage caused by the extraction of raw materials and also represents a lower financial cost, since the material of these recycled polyolefins would be a raw material that is discarded every day as waste. That is why there is a growing interest in studying and improving the research on the incorporation of such material, thus providing security for the use of blocks and developing the interest of other companies to increase and invest in the recycling sector.
Therefore, when we observe the results of the large-scale manufacturing of recycled polyolefin blocks compared to conventional blocks, we conclude that there is a considerable financial advantage, especially if the company obtains the residue as a donation.
The results obtained with the characterization tests are difficult to obtain similarities if there is no similarity of the methods used in this present paper. Due to the difficulty of numerous tests with rotomolded parts with several variables to be analyzed such as rotation speed, material size and translation, heating time and amount of material.
The notable results in this study were the achievement of filling the corners of the pieces, as they are not rounded, which makes it difficult to fill in the rotational molding process and total elastic recovery of the HDPE pieces, after the compression tests.
Also, using the standardization that was used in this study, it will be possible to perform repeatability, we recommend for future studies the use of an industrial scale rotational molding machine, since the one used in this study was a laboratory scale, which brought some limitations and allowed the production of a part in each cycle. If an adaptation is made that makes it possible to store several molds in the machine's oven, it would facilitate the production of the parts and, as a consequence, the tests. We indicate the use of a thicker aluminum plate for making the molds, as the one used in this study needed some care in the release process so as not to cause damage to the mold due to the thickness of the plate according to the release of several pieces. However, in the samples with 5% incorporation of alumina, the flame retardant in the HDPE and PP blocks in the first application of the flame for 10 s, the set of specimens sustains the flame for only 5 s and goes out. After this, in the second application of the flame for 10 s the flame sustains for only 5 s and goes out, with no dripping of the material on the cotton. Thus, reaching the UL-94 vertical classification as V-0, referring to the classification requirements and in Figure 10c the PP sample with 5% alumina without dripping. Figure 9c illustrates the cotton fiber without flame due to the material being classified as V-0.

Technical, Economic, Environmental Feasibility, and Industrial Scale Production
One of the main advantages of reuse in civil construction is the reduction of nonrenewable raw materials, such as aggregates and materials in the manufacture of cement. This optimizes the environmental damage caused by the extraction of raw materials and also represents a lower financial cost, since the material of these recycled polyolefins would be a raw material that is discarded every day as waste. That is why there is a growing interest in studying and improving the research on the incorporation of such material, thus providing security for the use of blocks and developing the interest of other companies to increase and invest in the recycling sector.
Therefore, when we observe the results of the large-scale manufacturing of recycled polyolefin blocks compared to conventional blocks, we conclude that there is a considerable financial advantage, especially if the company obtains the residue as a donation.
The results obtained with the characterization tests are difficult to obtain similarities if there is no similarity of the methods used in this present paper. Due to the difficulty of numerous tests with rotomolded parts with several variables to be analyzed such as rotation speed, material size and translation, heating time and amount of material.
The notable results in this study were the achievement of filling the corners of the pieces, as they are not rounded, which makes it difficult to fill in the rotational molding process and total elastic recovery of the HDPE pieces, after the compression tests.
Also, using the standardization that was used in this study, it will be possible to perform repeatability, we recommend for future studies the use of an industrial scale rotational molding machine, since the one used in this study was a laboratory scale, which brought some limitations and allowed the production of a part in each cycle. If an adaptation is made that makes it possible to store several molds in the machine's oven, it would facilitate the production of the parts and, as a consequence, the tests. We indicate the use of a thicker aluminum plate for making the molds, as the one used in this study needed some care in the release process so as not to cause damage to the mold due to the thickness of the plate according to the release of several pieces.

Conclusions
Conclusions can be drawn:

•
It was possible to produce the blocks with PP and HDPE materials, increasing the life cycle of the packaging by rotational molding. • Aluminum mold proved to major material and it reached a reduction of 9 kg of the total mold weight and offered no difficulties in the demold.

•
The compressive strength of HDPE rotomolded blocks with 1.53 mm particle diameter was 0.6 MPa and PP blocks with 10.15 mm particle diameter were 0.9 MPa. Therefore, HDPE block would be an excellent material for use in modular construction, in special considering the lightweight material in comparison with traditional ones (ceramic).

•
In order for the rotomolded blocks to be applied in civil construction they need to pass a flammability test, so that in case of fire, the fire does not spread through the dripping of the pieces. Therefore, the blocks with the addition of 5% alumina as fireretardant obtained a V-0 classification. Thus, obeying the requirements of the vertical flammability test of the ASTM UL 94 standard can be used in civil construction.

•
The increase in the speed of the flexural tests has a great influence on the results obtained in this study. The results obtained show that there was a reduction in the extracted values with increasing speed in the flexural tests.