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Experimental study of the production of resin granite and marble using their solid waste

ABSTRACT

Structural materials play an essential role in equipment and constructions, with properties such as strength and stability. Granite and marble are widely used for structural building materials such as cladding, sinks and countertops. It is possible to recycle waste from these rocks in the production of new parts, reducing the environmental impact. In Brazil, there is a high amount of construction and demolition waste, with most of the raw material becoming waste before the product is finished. Studies indicate that the incorporation of ornamental stone waste into cementitious products can significantly reduce environmental impact and improve its sustainability. The present work presents an experimental study for the manufacture of resin granite test specimens with residues from different dosages and resin epoxy levels. Flexural strengths of up to 7, 11, 24 and 28 MPa are achieved for resin contents of 5%, 10%, 15% and 20% respectively. The material has anisotropic characteristics and makes good use of almost all of the size ranges of waste used. Future reverse engineering studies of the resin are also necessary to expand knowledge and further optimize its application.

Keywords
Resin granite; synthetic granite; marble; recycled granite; construction; demolition waste

1. INTRODUCTION

1.1. General introduction

Structural materials play a fundamental role in the efficiency and operation of equipment, responsible for supporting materials, transferring stresses and heat, preventing water absorption, and resisting abrasion from supporting materials. To fulfill these functions, it is essential for these materials to possess appropriate properties such as compressive and flexural strength, good chemical and thermal stability, low electrical conductivity, and low porosity, adapting to each application [1[1] ASHBY, M.F., Materials selection in mechanical design, 3rd ed. London, Butterworth Heinemann, 2005., 2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
].

Due to their characteristics, granite and marble are widely used in structural applications, such as flooring, cladding, and support countertops like sinks and counters [3[3] INSTITUTO DE PESQUISAS TECNOLÓGICAS, Catálogo das rochas ornamentais de São Paulo, São Paulo, IPT, 1990.]. These materials must support the weight of other materials, traffic and various loads with adequate strength and durability, in addition to other properties.

However, the use of these materials has significant environmental impacts, as they are finite and non-biodegradable natural resources, raising concerns about their extraction and disposal. Unfortunately, to date, waste from the extraction of these materials, such as pieces after use, is often disposed of in landfills without proper sorting, making recycling of these materials a challenging task [4[4] RANA, A., KALLA, P., VERMA, H.K., et al., “Recycling of dimensional stone waste in concrete: a review”, Journal of Cleaner Production, v. 135, pp. 312–331, 2016. doi: http://dx.doi.org/10.1016/j.jclepro.2016.06.126.
https://doi.org/10.1016/j.jclepro.2016.0...
, 5[5] YURDAKUL, M., “Natural Stone waste generation from the perspective of natural stone processing plants: an industrial-scale case study in the province of Bilecik, Turkey”, Journal of Cleaner Production, v. 276, pp. 123339, 2020. doi: http://dx.doi.org/10.1016/j.jclepro.2020.123339.
https://doi.org/10.1016/j.jclepro.2020.1...
].

To mitigate the environmental impact, it is possible to use ornamental rock waste in the manufacturing of new marble and granite pieces, reducing energy consumption in the processing and solid waste generation, thereby reducing the environmental impact [6[6] ZULCÃO, R., CALMON, J.L., REBELLO, T.A., et al., “Life cycle assessment of the ornamental stone processing waste use in cemented-based building materials”, Construction & Building Materials, v. 257, pp. 119523, 2020. doi: http://dx.doi.org/10.1016/j.conbuildmat.2020.119523.
https://doi.org/10.1016/j.conbuildmat.20...
].

According to the Brazilian Association of Public Cleaning and Special Waste Companies (ABRELPE), em 2020 [7[7] ABRELPE, Panorama de resíduos sólidos no Brasil 2021. ABRELPE, 2021, https://abrelpe.org.br/panorama-2021/, accessed in January, 2024.
https://abrelpe.org.br/panorama-2021/...
], approximately 47 million tons of construction and demolition waste (CDW) were collected, highlighting the magnitude of the waste problem in the construction industry [7[7] ABRELPE, Panorama de resíduos sólidos no Brasil 2021. ABRELPE, 2021, https://abrelpe.org.br/panorama-2021/, accessed in January, 2024.
https://abrelpe.org.br/panorama-2021/...
]. Moreover, it is estimated that around 90% of the raw material used in the manufacturing of these products becomes waste even before the products are finished, and 80% of the finished product is discarded in the first 6 months of use [8[8] DOORSSELAER, K.V., The role of ecodesign in the circular economy. In: A. Stefanakis, I. Nikolaou (eds.), Circular Economy and Sustainability, chapter 12, USA, Elsevier, pp. 189–205, 2021. doi: http://dx.doi.org/10.1016/B978-0-12-819817-9.00018-1.
https://doi.org/10.1016/B978-0-12-819817...
, 9[9] SIMÃO, L., SOUZA, M.T., RIBEIRO, M.J., et al., “Assessment of the recycling potential of stone processing plant wastes based on physicochemical features and market opportunities”, Journal of Cleaner Production, v. 319, pp. 128678, 2021. doi: http://dx.doi.org/10.1016/j.jclepro.2021.128678.
https://doi.org/10.1016/j.jclepro.2021.1...
].

About 20 to 30% of the blocks are transformed into powder during the processing of natural granites, estimating that around 2 to 2.5 million tons of waste are generated annually in Brazil [10[10] MARTINS, M.S., “Influência do tipo de resina na fabricação de um compósito de reforço de resíduos de mármore”, Trabalho de Conclusão de Curso, Centro Universitário do Rio Grande do Norte, Natal, 2020.].

Given the importance of finding a better destination for granite and marble waste, other research can also be found, such as applications in red ceramics [11[11] COELHO, A.M.R., SAGGIORO, F.G., SALES JUNIOR, J.C.C., et al., “Evaluation of the potential use of granite waste in products of the red ceramic industry in the state of Amazonas”, Matéria (Rio de Janeiro), v. 27, n. 2, pp. e13209, 2022. doi: http://dx.doi.org/10.1590/s1517-707620220002.1309.
https://doi.org/10.1590/s1517-7076202200...
], in materials and concrete structure [12[12] RAJENDRAN, S., KANAGARAJ, R., “Experimental investigation on granite waste and alccofine in concrete”, Matéria (Rio de Janeiro), v. 28, n. 4, pp. e20230241, 2023. doi: http://dx.doi.org/10.1590/1517-7076-rmat-2023-0241.
https://doi.org/10.1590/1517-7076-rmat-2...
, 13[13] RODRIGUES, H.K.S., OLIVEIRA, H.A., MELO, F.M.C., et al., “Propriedades de um concreto leve estrutural com incorporação de argila expandida e resíduo de granito”, Matéria (Rio de Janeiro), v. 27, n. 1, pp. e13153, 2022. doi: http://dx.doi.org/10.1590/s1517-707620220001.1353.
https://doi.org/10.1590/s1517-7076202200...
], in lightweight aggregates for concrete [14[14] SOUZA, N.S.L., ANJOS, M.A.S., SÁ, M.V.A., et al., “Desenvolvimento de agregados leves a partir de resíduo de corte de pedras ornamentais (granitos e mármores) e argila”, Matéria (Rio de Janeiro), v. 25, n. 1, pp. e-12559, 2020. doi: http://dx.doi.org/10.1590/s1517-707620200001.0884.
https://doi.org/10.1590/s1517-7076202000...
], among others.

According to the Life Cycle Assessment (LCA) conducted by ZULCÃO et al. [6[6] ZULCÃO, R., CALMON, J.L., REBELLO, T.A., et al., “Life cycle assessment of the ornamental stone processing waste use in cemented-based building materials”, Construction & Building Materials, v. 257, pp. 119523, 2020. doi: http://dx.doi.org/10.1016/j.conbuildmat.2020.119523.
https://doi.org/10.1016/j.conbuildmat.20...
], adding 10% of ornamental stone waste to cementitious products can result in about an 8.5% reduction in environmental impact. This also applies to composite materials made of mineral aggregates and resins, which, when aggregates are replaced by waste, can significantly reduce environmental impact.

Research such as that conducted by LOVO et al. [2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
], RAMOS et al. [15[15] RAMOS, D.T.L., PALLONE, E.M.J.A., PURQUERIO, B.M., et al., “Design and construction of a pin-on-disc bench for wear testing”, Cerâmica, v. 60, n. 355, pp. 443–448, Jul. 2014. doi: http://dx.doi.org/10.1590/S0366-69132014000300018.
https://doi.org/10.1590/S0366-6913201400...
], and SILVA et al. [16[16] SILVA, T.L.C., CARVALHO, E.A.S., BARRETO, G.N.S., et al., “Characterization of artificial stone developed with granite waste and glass waste in epoxy matrix”, Journal of Materials Research and Technology, v. 26, pp. 2528–2538, 2023. doi: http://dx.doi.org/10.1016/j.jmrt.2023.08.045.
https://doi.org/10.1016/j.jmrt.2023.08.0...
] investigated different synthetic granites in epoxy resin matrices with varying dosages. This resulted in efficient materials and proper disposal of their waste. The present study aims to contribute another option of synthetic granite in an epoxy matrix, focusing on low-cost applications.

“Granite” and “marble” are generic commercial terms used to define rocks employed in similar applications with similar properties, such as gneisses, migmatites, syenites, gabbros, among others [3[3] INSTITUTO DE PESQUISAS TECNOLÓGICAS, Catálogo das rochas ornamentais de São Paulo, São Paulo, IPT, 1990.]. This study focuses on the general issue and application of materials with similar properties, rather than specific details of each type.

For general application, where flexural strength is highly relevant, granite and marble show similar results, as observed in works such as LOVO et al. [2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
] and CABRAL [17[17] CABRAL, T.B., “Estudo acerca da viabilidade de confecção de granitos e mármores sintéticos de baixo custo na construção civil a partir de resíduos de pedras ornamentais”, Trabalho de Conclusão de Curso, Caraguatatuba, 2022.].

The conducted study uses mixed granite waste as an example, with approximate colors, often containing fragments of marble and other rocks. It is a utilized material, where, for the intended application, there is usually no need for extensive separation.

This work presents a theoretical and experimental study of the production of sustainable resin-treated granites and marbles through their solid waste. Analyzing factors from waste generation, environmental impact, dosage influence, processing, flexural strength to enable application. Presenting literature reviews and an experimental study of making and analyzing test specimens with different resin dosages and contents.

1.2. Fundamental concepts for optimal dosage of resinized granites and marbles

Regardless of how aggregates are bonded by a binder, whether it be cement or resin, combining aggregate sizes in the best way possible will be crucial for optimal performance.

Starting with the analysis of the particle size distribution of aggregates is interesting for the dosing planning of the test specimen for various reasons, especially to produce a test specimen with sufficient desired performance and strength, as well as to plan for a better utilization of the residues [18[18] FALCÃO BAUER, L.A., Materiais de construção, 6. ed., Rio de Janeiro, LTC, 2019, vol. 1., 19[19] CALLISTER, W.D., Materials science and engineering: a introduction, 7th ed., USA, John Wiley & Sons, Inc., 2007.].

The correct particle size distribution can reduce the void content of the test specimen, thereby increasing its general resistance, such as traction and compression [18[18] FALCÃO BAUER, L.A., Materiais de construção, 6. ed., Rio de Janeiro, LTC, 2019, vol. 1., 19[19] CALLISTER, W.D., Materials science and engineering: a introduction, 7th ed., USA, John Wiley & Sons, Inc., 2007.], consequently improving its resistance to flexion, which is so important for structural plate applications such as sinks and countertops, as is often the case with granite and marble applications [3[3] INSTITUTO DE PESQUISAS TECNOLÓGICAS, Catálogo das rochas ornamentais de São Paulo, São Paulo, IPT, 1990.].

Several factors can interfere in the processing of aggregates with less energy expenditure and less environmental impact, such as equipment, climate, terrain, type of material, and desired particle sizes [20[20] OZCELIK, M., “Energy consumption analysis for natural aggregate processing and its results (Atabey, Isparta, Turkey)”, Mining of Mineral Deposits, v. 12, n. 3, pp. 80–86, 2018. doi: http://dx.doi.org/10.15407/mining12.03.080.
https://doi.org/10.15407/mining12.03.080...
]. Therefore, processing the material for less time, with a grain size that is not as small as possible, can result in a lower environmental impact. However, the maximum size will be delimited not only by what fits into the molds but also by a size that fills the mold in the best way, with proper fluidity, resulting in fewer voids and good strength [18[18] FALCÃO BAUER, L.A., Materiais de construção, 6. ed., Rio de Janeiro, LTC, 2019, vol. 1., 19[19] CALLISTER, W.D., Materials science and engineering: a introduction, 7th ed., USA, John Wiley & Sons, Inc., 2007.].

Some examples include grout, which recommends aggregates much smaller than the space, for reasons of being poured from a great height, requiring high fluidity [21[21] MOHAMAD, G., Construções em alvenaria estrutural: materiais, projeto e desempenho, 2. ed. ampl. e revisada conforme a NBR 16868/2020, São Paulo, Blucher, 2020.]. Or in the case of the production of concrete block pieces, where the NBR 6136 standard [22[22] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 6136: Blocos Vazados de Concreto Simples para Alvernaria - Requisitos. Rio de Janeiro, ABNT, 2016.] limits the maximum aggregate value to half the thickness of the block walls.

Combining different size ranges of aggregates can provide better compactness. Smaller aggregates can fill the voids of larger aggregate [18[18] FALCÃO BAUER, L.A., Materiais de construção, 6. ed., Rio de Janeiro, LTC, 2019, vol. 1.]. See an example in Figure 1.

Figure 1:
Particle size distribution and void volume (adapted from Kosmatka et al., 2003 [23[23] KOSMATKA, S.H., KERKHOFF, B., PANARESE, W., “Aggregates for concrete”, In: PORTLAND CEMENT ASSOCIATION, Design and Control of Concrete Mixes, 14th ed., Illinois, PCA, pp. 79–103, 2003.]).

A continuous distribution of particle sizes can hinder compactness due to the “wall effect.” To facilitate mobility, it is preferable to have a discontinuous distribution of particle sizes, with the absence of certain sizes, achieving a 10:1 ratio between larger and smaller particles [24[24] OLIVEIRA, I.R., STUDART, A.R., PILEGGI, R.G., et al. Dispersão e empacotamento de partículas: princípios e aplicações em processamento cerâmico, São Paulo, Fazendo Arte Editorial, 2000.].

Combining different size ranges of aggregates can provide better compactness. Smaller aggregates can fill the voids of larger aggregates [18[18] FALCÃO BAUER, L.A., Materiais de construção, 6. ed., Rio de Janeiro, LTC, 2019, vol. 1.]. See an example in Figure 1. This corroborates old studies like that of FERET [25[25] FERET, R., Sur la compacité des mortiers hydrauliques, Anmales Ponts et Chaussées, 7. Serie, IV, n. 21, 1892, https://gallica.bnf.fr/ark:/12148/bpt6k4085589/f4.item, accessed in January, 2024.
https://gallica.bnf.fr/ark:/12148/bpt6k4...
], who also achieved better compactness when using combinations of sands with a ratio of 10.

FERET [25[25] FERET, R., Sur la compacité des mortiers hydrauliques, Anmales Ponts et Chaussées, 7. Serie, IV, n. 21, 1892, https://gallica.bnf.fr/ark:/12148/bpt6k4085589/f4.item, accessed in January, 2024.
https://gallica.bnf.fr/ark:/12148/bpt6k4...
] studied a mixture of coarse (5 to 2 mm), medium (2 to 0.5 mm), and fine (less than 0.5 mm) sand aggregates for mortars and obtained the best compactness result of 0.734 with 80% coarse sand and 20% fine sand, dispensing with the use of medium sand for better compactness of this combination.

Other factors such as the shape coefficient can affect the development of the best aggregate dosage; for example, if the material is more rounded or more parallel [18[18] FALCÃO BAUER, L.A., Materiais de construção, 6. ed., Rio de Janeiro, LTC, 2019, vol. 1.]. These factors require a more specific evaluation and are suggested for future work. Therefore, the dosage will depend significantly on the desired application and the raw material obtained.

The resin matrix, in turn, binds the aggregates, also entering their voids, cooperating in supporting the tensile loads in which the aggregates have low resistance. Thus, improving the properties of the composite [18[18] FALCÃO BAUER, L.A., Materiais de construção, 6. ed., Rio de Janeiro, LTC, 2019, vol. 1.20[20] OZCELIK, M., “Energy consumption analysis for natural aggregate processing and its results (Atabey, Isparta, Turkey)”, Mining of Mineral Deposits, v. 12, n. 3, pp. 80–86, 2018. doi: http://dx.doi.org/10.15407/mining12.03.080.
https://doi.org/10.15407/mining12.03.080...
]. Therefore, the best possible combinations to optimize voids and resin usage are always sought. We conclude this section by presenting two examples of synthetic granite research that tested different dosages.

Recent studies with three different combinations of particle sizes were conducted by RAMOS et al. [15[15] RAMOS, D.T.L., PALLONE, E.M.J.A., PURQUERIO, B.M., et al., “Design and construction of a pin-on-disc bench for wear testing”, Cerâmica, v. 60, n. 355, pp. 443–448, Jul. 2014. doi: http://dx.doi.org/10.1590/S0366-69132014000300018.
https://doi.org/10.1590/S0366-6913201400...
] for a resin-bonded composite material, which experimentally achieved the best compaction with large (7 to 12 mm), medium (2 to 4 mm), and fine (0.3 to 1.2 mm) sizes, using 30%, 20%, and 50%, respectively.

Also, for a resin composite, LOVO et al. [2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
] outlined a diagram of the best compaction with three value ranges—large (1.2 to 2 mm), medium (0.3 to 0.6 mm), and fine (0.1 to 0.2 mm)—using the same proportions of 50%, 15%, and 35%, respectively. The result was obtained by performing 66 mixtures, following ABNT NBR 12173 [26[26] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 12173: Fine-grained Refractory Materials -Determination Bulk Specific Gravity, Rio de Janeiro, ABNT, 2012.] and ABNT NBR 248 [27[27] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 248: Aggregate Materials –Determination Bulk Composition, Rio de Janeiro, ABNT, 2003.]. In this case, 19% of the total mass of residues was added to ensure minimal resin consumption.

Although using much more resin, 30%, reducing its environmental benefit slightly, the study by SHISHEGARAN et al. [28[28] SHISHEGARAN, A., SAEEDI, M., MIRVALAD, S., et al., “The mechanical strength of the artificial stones, containing the travertine wastes and sand”, Journal of Materials Research and Technology, v. 11, pp. 1688–1709, 2021. doi: http://dx.doi.org/10.1016/j.jmrt.2021.02.013.
https://doi.org/10.1016/j.jmrt.2021.02.0...
] achieved flexural strength values of up to 67 MPa.

Additionally, some patents can be found for the production of these materials, such as the patent by HO [29[29] HO, H.C., Processo para obtenção de massa para simulação de pedra nobre em revestimento de superfícies do tipo mármore artificial e produto obtido, Patente nº BRPI0901144A2, 2010. https://patents.google.com/patent/BRPI0901144A2/pt?oq=PI0901144, accessed in January, 2024.
https://patents.google.com/patent/BRPI09...
], which presents a very specific mix for industrial stairs. Other patents, such as those by LÓPEZ and GUERRERO [30[30] LÓPEZ, J.M.B., GUERRERO, J.A.J., Method for the production of solid surfaces for construction, Patente nº EP2889437A1, 2012. https://patents.google.com/patent/EP2889437A1/de?oq=EP2889437A1, accessed in January, 2024.
https://patents.google.com/patent/EP2889...
] and LOPEZ et al. [31[31] LOPEZ, J.M., HERNANDEZ, L.G., GUERRERO, J.A.J., Stratified, agg lomerated artificial stone articles with polymerisable resin and process for its manufacturing by vacuum vibro-compression system, Patente nº US20180194164A1, 2013. https://patents.google.com/patent/US20180194164A1/en?oq=US20180194164A1, accessed in January, 2024.
https://patents.google.com/patent/US2018...
], patent manufacturing and finishing methods for the material.

2. MATERIALS AND METHODS

2.1. Processing of raw materials

The raw material was obtained through donations of granite and marble fragments and residues from local businesses in Caraguatatuba city, State of São Paulo in southwest of Brazil. These companies often find themselves with excess material and incur transportation costs for disposal in municipal landfills.

The required amount of material was broken into smaller fragments and residues with a hammer, which were then stored for subsequent analysis and particle size separation. The presented procedure is simple and cost-effective, primarily used for producing small pieces or samples. Similar processes are employed by small businesses and artisans for crafting in limited quantities. It is evident that for larger quantities, industrial machines such as crushers or grinders may offer a more cost-effective solution.

2.2. Granulometric analysis

The residues, already in smaller sizes, were sieved in a sequence of openings, from the largest to the smallest, of 19, 9, 4.8, 2.4, 1.2, 0.6, and 0.3 mm, with the aid of a vibrating table. Figure 2 illustrates an example of how the granite aggregates are retained in the sieves, similar to the gravel used in concrete. The material retained on each sieve was weighed, and the results of the particle size analysis will be discussed in the following sections.

Figure 2:
Particle size separation of each range of granite residue sizes.

2.3. Preparation and analysis of test samples

The particle size analysis discussed in the results, along with the literature, contributed to the planning of the dosage for the study test specimens, as presented in Table 1. Particle size ranges below the sieve 0.3 mm were not used.

Table 1:
Dosage of test specimens (present work).

The resin used was a low-viscosity epoxy type from the brand OHANA, with a ratio of 2:1 resin to catalyst/hardener. The total curing time for the resin to reach adequate strength, according to the manufacturer, is 7 days. The amount of resin used was 5%, 10%, 15%, and 20% by mass relative to the total mass of the test specimen, aiming to better understand the influence of resin in these mixtures. Each type of sample was named with a letter representing the group followed by the percentage of resin, with the sample from the A group/mixture with 5% resin named as A5, and so forth. Six samples of each type were prepared.

The desired mixtures were manually blended in a container and then filled into molds of 40 × 40 × 160 mm for subsequent flexural testing after a curing time of 7 days. The samples were weighed, and their densities were measured using a precision balance with a precision of 0.0001 g.

2.4. Flexural strength analysis

Although the C-580 standard [32[32] AMERICAN SOCIETY FOR TESTING AND MATERIALS, C-580: Standard Test Method for Flexural Strength and Modulus of Elasticity of Chemical- Resistant Mortars, Grouts, Monolithic Surfacings, and Polymer Concretes, West Conshohocken, ASTM, 2018.] establishes criteria for flexural analyses of similar materials, such as polymeric concretes or grouts, it stipulates a very small specimen size of 4 mm that does not perfectly simulate the material studied here—synthetic granite, which has aggregates with much larger dimensions than the specimen.

For this reason, the flexural strength of the material was analyzed using dimensions of 40 × 40 × 160 mm to assess its flexural strength. These specimen dimensions are closer to the approximate thickness (20 to 30 mm) typically used in structural applications, mainly as support benches such as sinks and counters, in which flexural behavior is more representative of its commercial use. Additionally, the choice of this size is practical, as equipment and molds of this standard size for flexural testing are more readily available in engineering laboratories. These dimensions are also commonly used for flexural testing of mortar, guided by the NBR 13279 standard [33[33] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 13279: Argamassa para Assentamento e Revestimento de Paredes e Tetos – Determinação da Resistência à Tração na Flexão e Compressão, Rio de Janeiro, ABNT, 2005.]. Therefore, other standards, such as support span, were also adapted in accordance with NBR 13279 [33[33] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 13279: Argamassa para Assentamento e Revestimento de Paredes e Tetos – Determinação da Resistência à Tração na Flexão e Compressão, Rio de Janeiro, ABNT, 2005.].

3. RESULTS AND DISCUSSION

3.1. Particle size analysis

After the screening of the processed residues as described in the materials and methods, the following particle size distribution results were obtained, as shown in Figure 3.

Figure 3:
Particle size distribution of the ground raw material.

Comparing the size ranges with particle size distributions already conducted in the literature, it is possible to find a similarity in scale with the study by LOVO et al. [2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
], with only one order of magnitude difference, but maintaining the size ratio between the largest and smallest aggregates. Therefore, this approximate size range from the sieves was chosen to create the mixture for the “Group A” of samples, which is presented in Table 2 and Figure 4.

Table 2:
Aggregate dosages of the study and comparison with reference mixture.
Figure 4:
Selected sieves for the preparation of test specimens.

Upon analyzing Figure 5, it is noticeable that there are particle size ranges that differ by almost 10 times in size, specifically those from 9 to 4.8 mm and from 1.2 to 0.3 mm. Considering the quantities measured in the particle size analysis, the amount of larger aggregates is also higher than that of the smaller ones, facilitating the filling of voids by the smaller range. As seen in the previous literature section, the optimal ratio would be 80/20.

Figure 5:
Resin-infused granite samples manufactured with different resin contents, sets A and B.

However, the particle size analysis indicates that the amount obtained from recycling the residues has a proportion of larger residues to smaller ones of 70/30. With the aim of disposing of the remaining residues, the decision was made to experiment with the 70/30 ratio. Even though it is not the ideal combination of coarse and fine aggregates, a slight drop in flexural strength would still yield values well above natural granite, while still utilizing almost all of obtained residue ranges. This was confirmed by the tests, see the flexural results in section 3.3.

This approach maximizes the utilization of the remaining residues, forming a second experimental mix called “GROUP B,” with aggregate sizes slightly smaller than those in Group A. In an effort to use the least amount of resin possible, combinations of resin quantities at 5%, 10%, 15%, and 20% by mass of aggregates were tested for each mix.

3.2. Preparation and analysis of test specimens

Examples of samples produced as described in materials and methods are presented in Figure 5. It is possible to observe numerous pores and stone protrusions on the top side of the mold, while on the bottom, leveling was easier due to resin flow. This indicates a certain difficulty in material compaction in the mold, given that the resin initiates its setting process very quickly, within 10 minutes according to the manufacturer.

The resin ends up concentrating at the bottom of the material, leading to a non-uniform distribution of elements along the cross-section. This makes the studied material anisotropic [19[19] CALLISTER, W.D., Materials science and engineering: a introduction, 7th ed., USA, John Wiley & Sons, Inc., 2007.], where its properties, such as flexural strength, can vary in different directions.

It is important to mention that natural or resinous granites are used in different finishes and applications in construction, where their aesthetics are also considered in the selection process.

The possibility of applying pigments to the resin provides a greater variety of tones than natural stone often cannot offer. Samples with low resin content and more porous characteristics can be used where a more rustic finish is desired, provided they exhibit adequate strength and properties for the intended application.

It is also possible to grind and polish surfaces to achieve a smoother and glossier appearance if desired. Alternatively, the bottom surface, where the resin accumulates in higher concentration, can be used as the exposed surface. The rougher side can be chosen for the hidden or bonded part, thus having a larger surface area and, consequently, a larger contact area.

Therefore, a future study of these anisotropic characteristics of the composite, as well as other features such as finish, roughness, and surface hardness, is suggested, as these factors can often play a role in material selection for specific applications.

Despite all the application possibilities, in most cases, a more uniform and less porous material is generally sought. This can be achieved by reducing the material’s particle size to improve its compaction, which proved challenging due to the viscosity of the resin.

However, it is important to note that when there is no need for lower porosity in the piece, working with the material closer to its origin, with as few processes as possible, becomes an economic and environmental advantage, provided it maintains adequate strength.

After the preparation of the test specimens, they were weighed, and their densities were calculated, as presented in Figure 6.

Figure 6:
Relative density of samples.

The samples from Group A with up to 10% resin showed lower density, as expected. These samples were produced with aggregates from larger size ranges, reducing fluidity and complicating compaction in the mold, leading to a higher number of pores.

From 15% onward, there was a reversal of behavior, with Group A samples exhibiting higher density. This aligns with the study by LOVO et al. [2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
], which achieved good compactness of samples with a similar aggregate combination to that of Group A. This increase in density, hence a decrease in pores, affects their flexural strength, as demonstrated in the following section.

3.3. Flexural strength analysis

The flexural strength results are presented in Table 3 and Figure 7. The presented results reach values close to the literature on resin-infused granites and marbles, such as CABRAL [17[17] CABRAL, T.B., “Estudo acerca da viabilidade de confecção de granitos e mármores sintéticos de baixo custo na construção civil a partir de resíduos de pedras ornamentais”, Trabalho de Conclusão de Curso, Caraguatatuba, 2022.], who achieved up to 14 MPa for 10% resin, and LOVO et al. [2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
], who achieved around 27 MPa with 19% resin. LOVO et al. [2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
] even reached 51 MPa flexural strength for resin-infused granites reinforced with carbon fibers. However, the study’s ­intention is to focus on a low-cost material for small applications where reinforcement with carbon fibers or other ­materials may impact cost-effectiveness.

Table 3:
Flexural strength (MPa) of resin-infused granite specimens.
Figure 7:
Flexural strength (MPa) as a function of resin content for each mixture.

In addition to epoxy resin, other resins are also commonly found in the literature, such as polyester resin, which in the work of RIBEIRO et al. [34[34] RIBEIRO, C.E.G., RODRIGUEZ, R.J.S., CARVALHO, E.A., “Microstructure and mechanical ­properties of artificial marble”, Construction & Building Materials, v. 149, pp. 149–155, 2017. doi: http://dx.doi.org/10.1016/j.conbuildmat.2017.05.119.
https://doi.org/10.1016/j.conbuildmat.20...
] achieved around 27 MPa with 10% resin, but using more expensive techniques such as vacuum vibrocompression (VVC).

Also, the results are close to the flexural strength values of natural stones, according to the Catalog of Ornamental Rocks of São Paulo [3[3] INSTITUTO DE PESQUISAS TECNOLÓGICAS, Catálogo das rochas ornamentais de São Paulo, São Paulo, IPT, 1990.] and the study of RIBEIRO et al. [34[34] RIBEIRO, C.E.G., RODRIGUEZ, R.J.S., CARVALHO, E.A., “Microstructure and mechanical ­properties of artificial marble”, Construction & Building Materials, v. 149, pp. 149–155, 2017. doi: http://dx.doi.org/10.1016/j.conbuildmat.2017.05.119.
https://doi.org/10.1016/j.conbuildmat.20...
], which presents granites and marbles with flexural strength in the range of 10–15 MPa.

For both mixtures, it can be observed that from 10%, the values achieved are already approaching the commercially used value for natural stones. For 15% or more resin, the values attained surpass those of commercial natural stones. The mixtures with 20% resin reach values in the range of double that of natural stones.

It can be observed that group B, with slightly smaller aggregates, performed better at almost all resin contents, except for the 20% resin content, which experienced a decrease in performance compared to group A. This is explained by the previous section, where density is improved for the A combination, corroborating the studies of LOVO et al. [2[2] LOVO, J.F.P., PEDROSO, M.P.G., ERBERELI, R., et al., “Synthetic granite composite for precision equipment structures”, Matéria (Rio de Janeiro), v. 23, n. 4, pp. e-12229, 2018. http://dx.doi.org/10.1590/s1517-707620180004.0563.
https://doi.org/10.1590/s1517-7076201800...
], which presented a good combination with 19% resin for the size ranges of group A. Nevertheless, group B shows very similar strength, demonstrating good performance and the feasibility of using this size range of residues as well.

In conclusion, both mixtures show satisfactory performance for the desired application. As discussed in previous sections, even if there is a need for smaller particle size for a smoother surface, it is expected that the same mixture with smaller diameter proportions could achieve even better strength, utilizing all size ranges of the residues. This is because the combination of different aggregate sizes can be the same, even for larger or smaller sizes, as long as both sizes of each type of aggregate change in the same proportion.

Analyzing images of the specimen fracture, it is possible to observe some behavior of the material in its breakage.

In Figure 8, we observe the fracture of specimen A5, where it is possible to see that some aggregate particles are broken in half (example circled in blue), while others remain intact (circled in yellow). This indicates that the fracture occurred both intergranularly and intragranularly [19[19] CALLISTER, W.D., Materials science and engineering: a introduction, 7th ed., USA, John Wiley & Sons, Inc., 2007.].

Figure 8:
Transverse fracture of resin-infused granite sample A5.

Characterizing a ductile fracture, where the fracture can travel through the resin, bypassing some of the aggregates, thus increasing its path and requiring more energy for rupture, as sometimes it fractures and crosses the aggregate, showing that its resistance also contributed to the specimen’s strength, as much as the resin.

It is also visualized that the grains of the specimen were broken and not crushed, characterizing failure by flexural tension. This explains the gain in strength for the resin-infused granite compared to natural granite, as the former has higher tensile strength than granite, which performs better in compression, similar to concrete and various rocks. It also emphasizes the importance of the flexural test for its characterization, as in its applications for kitchen countertops and sinks, it functions as bent plates.

Other studies, such as CABRAL [17[17] CABRAL, T.B., “Estudo acerca da viabilidade de confecção de granitos e mármores sintéticos de baixo custo na construção civil a partir de resíduos de pedras ornamentais”, Trabalho de Conclusão de Curso, Caraguatatuba, 2022.], where samples of white and beige marble were tested, show broken or contoured grains more prominently, as seen in Figure 9.

Figure 9:
Image of the fracture of resin-infused marble [17[17] CABRAL, T.B., “Estudo acerca da viabilidade de confecção de granitos e mármores sintéticos de baixo custo na construção civil a partir de resíduos de pedras ornamentais”, Trabalho de Conclusão de Curso, Caraguatatuba, 2022.].

4. CONCLUSIONS

Natural and resin-coated granites and marbles are commercialized and found in construction materials and artifacts; nevertheless, a considerable amount of waste is generated and improperly discarded.

The article presented an experimental study, supported by the literature, aiming to contribute to a more economical application of these materials. Some noteworthy contributions of this work are detailed below:
  • The influence of resin content of 5%, 10%, 15%, and 20% resulted in flexural strength of up to 7, 11, 24, and 28 MPa. Up to a limit for each composite, the more resin, the better it will bind the material and fill the voids, ensuring greater resistance. The study allows the selection of an economical resin content for specific desired resistances. It also influences the finish and porosity of the material, which can be further studied in future work.

  • Experimentally, it was observed the possibility of using almost the entire waste by combining them in different ratios to generate materials with flexural strength suitable for the intended application.

  • Although the use of granite waste as raw material can cause a reduction in environmental impact. Work focused on studying the life cycle (LCA) of the composite with resins and reverse engineering is suggested for future work.

  • The observed materials exhibit anisotropic characteristics, which can be further studied in the future to optimize their processing and application even more.

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Publication Dates

  • Publication in this collection
    04 Mar 2024
  • Date of issue
    2024

History

  • Received
    07 Dec 2023
  • Accepted
    30 Jan 2024
Laboratório de Hidrogênio, Coppe - Universidade Federal do Rio de Janeiro, em cooperação com a Associação Brasileira do Hidrogênio, ABH2 Av. Moniz Aragão, 207, 21941-594, Rio de Janeiro, RJ, Brasil, Tel: +55 (21) 3938-8791 - Rio de Janeiro - RJ - Brazil
E-mail: revmateria@gmail.com