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Mixed construction and demolition powder as a filler to Portland cement: study on packaged pastes

Pó misto de construção e demolição como fíler ao cimento Portland: estudo em pastas empacotadas

Abstract

The aim of this study is to explore more sustainable approaches by replacing Portland cement (OPC) with recycled mixed powder (RMP) derived from construction and demolition waste (CDW), with a focus on reducing carbon emissions. The CDW was subjected to grinding and sieving until a fraction <0.15 mm was obtained. The particles were then thermally activated at 800°C in a muffle for 0.5, 1, 2, and 3 hours. The OPC replacement levels by RMP were defined based on the particle packing method, ranging from 0 to 65%. The study was carried out on pastes with a water/fines ratio ranging from 0.07 to 0.14 and superplasticizer admixture (SP), evaluating the compressive strength at 28, 63, and 91 days. The mechanical and environmental performance of Portland cement pastes composed with RMP showed compressive strength higher than the reference, reaching 37 MPa for a 45% replacement content at 28 days, reducing the CO2 emissions per m³ of paste by up to 53%. This study suggested that the treatment and packaging RMP particles may potentially increase the mechanical and environmental performance, making it an alternative to promote the circular economy and low-carbon cement.

Keywords:
Eco-efficient Cement; Use of Construction and Demolition Waste; Particle Packing

Resumo

O objetivo deste estudo é explorar abordagens mais sustentáveis, substituindo o cimento Portland (OPC) por pó reciclado misto (RMP) derivado de resíduos de construção e demolição (RCD), focado na redução das emissões de carbono. O RCD foi submetido à moagem e peneiramento até a obtenção de uma fração < 0,15 mm. Em seguida, as partículas foram termicamente ativadas a 800°C em mufla por 0,5, 1, 2 e 3 horas. Os níveis de substituição de OPC por RMP foram definidos a partir do método de empacotamento de partículas, variando entre 0 e 65%. O estudo foi realizado em pastas com relação água/finos entre 0,07 e 0,14 e aditivo superplastificante (SP), com avaliação da resistência à compressão aos 28, 63 e 91 dias. Quanto ao desempenho mecânico e ambiental das pastas de cimento Portland compostas com RMP a resistência à compressão foi superior à referência, chegando a 37 MPa para um teor de substituição de 45% aos 28 dias, promovendo uma redução de 53% na emissão de CO 2 por m³ de pasta. O estudo indicou que tratar e empacotar as partículas de RMP aumenta o desempenho mecânico e ambiental, tornando-se alternativa para promover a economia circular e reduzir as emissões do cimento.

Palavras-chaves:
ecoeficiente; Aproveitamento de resíduo de construção e demolição; Empacotamento de partículas

Introduction

Carbon dioxide emissions from Portland cement production significantly impact the environment and contribute to climate change. Portland cement is the main component of concrete, which is widely used in civil construction. Portland cement production is responsible for about 7% of global CO2 emissions, of which 60% to 70% are caused by clinker production due to decarbonization and 30% to 40% are caused by burning fossil fuels (CNI, 2017CONFEDERAÇÃO NACIONAL DA INDÚSTRIA. A indústria brasileira de cimento base para a construção do desenvolvimento. Associação Brasileira de Cimento Portland, 2017.; WBCSD, 2023WORLD BUSINESS COUNCIL FOR SUSTAINABLE DEVELOPMENT. Getting the numbers right project: reporting CO2 - GNR Project. Available: https://www.wbcsdcement.org/GNR-2019. Access: 15 out. 2023.
https://www.wbcsdcement.org/GNR-2019...
). According to the World Business Council for Sustainable Development (WBCSD, 2023WORLD BUSINESS COUNCIL FOR SUSTAINABLE DEVELOPMENT. Getting the numbers right project: reporting CO2 - GNR Project. Available: https://www.wbcsdcement.org/GNR-2019. Access: 15 out. 2023.
https://www.wbcsdcement.org/GNR-2019...
), for each ton of clinker manufactured in 2019, 834 kg of CO2 were released into the environment. Global cement production was 4.2 billion tons in 2020 (GCCA, 2023GLOBAL CEMENT AND CONCRETE ASSOCIATION. Concrete Future: the GCCA 2050 cement and concrete industry roadmap for Net Zero Concrete. Available: https://gccassociation.org/concretefuture/wp-content/uploads/2021/10/GCCA-Concrete-Future-Roadmap-Document-AW.pdf. Access: 15 jul. 2023.
https://gccassociation.org/concretefutur...
), and it is estimated to reach 6 billion tons by 2050 (Scrivener; John; Gartner, 2018SCRIVENER, K. L.; JOHN, V. M.; GARTNER, E. M. Eco-efficient cements: potential economically viable solutions for a low-CO2 cement-based materials industry. Cement and Concrete Research , v. 114, p. 2-26, jun. 2018. ).

In this sense, the primary alternative for reducing CO2 emissions would be to reduce the clinker content of cement (Benhelal; Shamsaei; Rashid, 2021BENHELAL, E.; SHAMSAEI, E.; RASHID, M. I. Challenges against CO2 abatement strategies in cement industry: a review. Journal of Environmental Sciences, v. 104, p. 84-101, jun. 2021. ; Di Filippo; Karpman; Deshazo, 2019DI FILIPPO, J.; KARPMAN, J.; DESHAZO, J. R. The impacts of policies to reduce CO2 emissions within the concrete supply chain. Cement and Concrete Composites, v. 101, p. 67-82, ago. 2019. ). To this end, the powder is an alternative for developing cement with low clinker content and, consequently, lower associated emissions (He et al., 2022HE, Z. H. et al. A novel development of green UHPC containing waste concrete powder derived from construction and demolition waste. Powder Technology , v. 398, p. 117075, jan. 2022. ; Juenger; Snellings; Bernal, 2019JUENGER, M. C. G.; SNELLINGS, R.; BERNAL, S. A. Supplementary cementitious materials: new sources, characterization, and performance insights. Cement and Concrete Research, v. 122, p. 257-273, 1 ago. 2019. ; Panesar; Zhang, 2020PANESAR, D. K.; ZHANG, R. Performance comparison of cement replacing materials in concrete: Limestone fillers and supplementary cementing materials: a review. Construction and Building Materials, v. 251, p. 118866, ago. 2020. ; Di Salvo Barsi et al., 2020DI SALVO BARSI, A. et al. Carbonate rocks as fillers in blended cements: physical and mechanical properties. Construction and Building Materials , v. 248, p. 118697, jul. 2020. ; Scrivener; John; Gartner, 2018SCRIVENER, K. L.; JOHN, V. M.; GARTNER, E. M. Eco-efficient cements: potential economically viable solutions for a low-CO2 cement-based materials industry. Cement and Concrete Research , v. 114, p. 2-26, jun. 2018. ; WBCSD, 2023WORLD BUSINESS COUNCIL FOR SUSTAINABLE DEVELOPMENT. Getting the numbers right project: reporting CO2 - GNR Project. Available: https://www.wbcsdcement.org/GNR-2019. Access: 15 out. 2023.
https://www.wbcsdcement.org/GNR-2019...
).

In this context, studies in the literature showed that, based on mechanical (sieving and grinding) and chemical (calcination, CO2, among others) treatments, CDW particles smaller than 0.15 mm may be used as SCM or filler material in cement matrix compositions (Asensio et al., 2020ASENSIO, E. et al. Fired clay-based construction and demolition waste as pozzolanic addition in cements: design of new eco-efficient cements. Journal of Cleaner Production , v. 265, p. 121610, ago. 2020. ; He et al., 2022HE, Z. H. et al. A novel development of green UHPC containing waste concrete powder derived from construction and demolition waste. Powder Technology , v. 398, p. 117075, jan. 2022. ; Ma et al., 2020MA, Z. et al. Mechanical properties and water absorption of cement composites with various fineness and contents of waste brick powder from Construction waste. Cement and Concrete Composites , v. 114, p. 103758, nov. 2020. ; Meng et al., 2021MENG, T. et al. Comparison of technical properties of cement pastes with different activated recycled powder from construction and demolition waste. Cement and Concrete Composites , v. 120, p. 104065, jul. 2021. ; Oliveira, 2022OLIVEIRA, D. R. B. Aproveitamento da fração fina de resíduo de construção e demolição como alternativa para redução das emissões de CO2 associadas ao cimento Portland. Curitiba, 2022. Tese (Doutorado em Engenharia de Construção Civil) - Programa de Pós-Graduação em Engenharia Civil, Universidade Federal do Paraná, Curitiba, 2022.; Oliveira; Dezen; Possan, 2020OLIVEIRA, T. C. F.; DEZEN, B. G. S.; POSSAN, E. Use of concrete fine fraction waste as a replacement of Portland cement. Journal of Cleaner Production , v. 273, p. 123126, nov. 2020. ; Prošek et al., 2020PROŠEK, Z. et al. Recovery of residual anhydrous clinker in finely ground recycled concrete. Resources, Conservation and Recycling , v. 155, p. 104640, abr. 2020. ).

Considering the mixed clayey (ceramic) and cementitious origin material waste composition, reactivity increase with calcination occurs in the clayey fraction with the clay minerals dehydroxylation (Mohammed, 2017MOHAMMED, S. Processing, effect and reactivity assessment of artificial pozzolans obtained from clays and clay wastes: a review. Construction and Building Materials , v. 140, p. 10-19, jun. 2017. ; Msinjili et al., 2019MSINJILI, N. S. et al. Comparison of calcined illitic clays (brick clays) and low-grade kaolinitic clays as supplementary cementitious materials. Materials and Structures/Materiaux et Constructions, v. 52, n. 5, p. 1-14, out. 2019. ). For the origin fraction, cementitious calcination dehydrates the matrix decomposing the main C-S-H, portlandite, and calcium carbonates phase, forming calcium oxide (Kong; Ruan; Kurumisawa, 2022KONG, Y. K.; RUAN, S.; KURUMISAWA, K. Recycling of calcined carbonated cement pastes as cementitious materials: proposed CCUS technology for calcium looping. Journal of Environmental Chemical Engineering, v. 10, n. 5, p. 108247, out. 2022. ; Wu et al., 2021bWU, H. et al. Utilizing thermal activation treatment to improve the properties of waste cementitious powder and its newmade cementitious materials. Journal of Cleaner Production , v. 322, p. 129074, nov. 2021b. ), making CDW powder more reactive (Ma et al., 2022MA, Z. et al. Properties and activation modification of eco-friendly cementitious materials incorporating high-volume hydrated cement powder from construction waste. Construction and Building Materials , v. 316, p. 125788, jan. 2022. ). As the treatment involves thermal decomposition, depending on the number of carbonates, its viability must be evaluated, considering the decarbonization emissions. According to (ABRELPE, 2022ASSOCIAÇÃO BRASILEIRA DAS EMPRESAS DE LIMPEZA PÚBLICA E RESÍDUOS ESPECIAIS. Panorama dos resíduos sólidos no Brasil 2022. Rio de Janeiro, 2022. ), 48 million tons of CDW waste were collected in municipalities throughout Brazil in 2021, corresponding to 227 kg/person/year. 92% (Matias, 2020MATIAS, A. N. Resíduos de construção e demolição à luz da política nacional de resíduos sólidos. Foz do Iguaçu, 2020. Dissertação (Mestrado em Engenharia Civil) - Programa de Pós-Graduação em Engenharia Civil, Universidade Federal da Integração-Latino America, Foz do Iguaçu, 2020. ) of such CDW corresponds to class A waste (BRAZIL, 2002BRAZIL. Resolução CONAMA nº 307, estabelece diretrizes, critérios e procedimentos para a gestão dos resíduos da construção civil. Diário Oficial da República Federativa do Brasil , Brasília, DF, 2002.), of which more than 80% is concrete and brick waste (Xiao; Ma, 2022XIAO, J.; MA, Z. Utilization of recycled powder from construction and demolition waste. Low Carbon Stabilization and Solidification of Hazardous Wastes, p. 291-301, jan. 2022. ). This waste must be reused or recycled as aggregates, and reserved for future uses (BRAZIL, 2012BRAZIL. Resolução CONAMA nº 448, que altera os arts. 2º. 4º. 5º. 6º. 8º. 9º. 10º. 11º da Resolução nº 307, de 5 de julho de 2002, do Conselho Nacional do Meio Ambiente- CONAMA. Diário Oficial da República Federativa do Brasil, Brasília, DF, 19 de janeiro de 2012.). In Brazil, recycled aggregate is standardized by NBR 15116 (ABNT, 2021ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 15116: agregados reciclados para uso em argamassas e concretos de cimento Portland: requisitos e métodos de ensaios. Rio de Janeiro, 2021. ) and classified according to origin: recycled concrete aggregate - ARCO, recycled cement aggregate - ARCI, and mixed recycled aggregate - ARM. For aggregates processing, the revenue from the generated powder needs to be evaluated. For this purpose, this study used recycled mixed powder (RMP) from ARM, inserted as filler for the CP, as a Portland cement composite with CDW.

A significant number of studies focusing on the use of recycled aggregates could be found in the literature (Ahimoghadam et al., 2020AHIMOGHADAM, F. et al. Influence of the recycled concrete aggregate features on the behavior of eco-efficient mixtures. Journal of Materials in Civil Engineering, v. 32, n. 9, set. 2020. ; Arun; Chekravarty; Murali, 2021ARUN, A.; CHEKRAVARTY, D.; MURALI, K. Comparative analysis on natural and recycled coarse aggregate concrete. Materials Today: Proceedings, v. 46, p. 8837-8841, jan. 2021. ; Cominato et al., 2022COMINATO, V. et al. The effect of granulometry of natural and recycled coarse aggregate on permeable concrete properties. Materials Today: Proceedings , v. 65, p. 1711-1718, jan. 2022. ; De Souza et al., 2022DE SOUZA, D. J. et al. Influence of the mix proportion and aggregate features on the performance of eco-efficient fine recycled concrete aggregate mixtures. Materials, v. 15, n. 4, fev. 2022. ; Gupta; Chaudhary, 2022GUPTA, S.; CHAUDHARY, S. State of the art review on supplementary cementitious materials in India: II: characteristics of SCMs, effect on concrete and environmental impact. Journal of Cleaner Production , v. 357, jul. 2022. ; Hassan; Faroun; Mohammed, 2021HASSAN, R. Y.; FAROUN, G. A.; MOHAMMED, S. K. WITHDRAWN: Mechanical properties of concrete made with coarse and fine recycled aggregates. Materials Today: Proceedings , v. 1, p. 1-8, abr. 2021. ; Kumar et al., 2022KUMAR, S. et al. A review on the properties of natural and recycled coarse aggregates concrete made with different coal ashes. Cleaner Materials , v. 5, p. 100109, set. 2022. ; Liu et al., 2022LIU, H. et al. Hardened properties of 3D printed concrete with recycled coarse aggregate. Cement and Concrete Research , v. 159, set. 2022. ; Moulya; Chandrashekhar, 2022MOULYA, H. V.; CHANDRASHEKHAR, A. Experimental investigation of effect of recycled coarse aggregate properties on the mechanical and durability characteristics of geopolymer concrete. Materials Today: Proceedings , v. 59, p. 1700-1707, jan. 2022. ; Prasad Dash et al., 2022PRASAD DASH, A. et al. Experimental study on the effect of superplasticizer on workability and strength characteristics of recycled coarse aggregate concrete. Materials Today: Proceedings , v. 60, p. 488-493, jan. 2022. ; Rahul et al., 2022RAHUL, A. V. et al. 3D printable concrete with natural and recycled coarse aggregates: rheological, mechanical and shrinkage behaviour. Cement and Concrete Composites , v. 125, jan. 2022. ; Shi et al., 2016SHI, C. et al. Performance enhancement of recycled concrete aggregate: a review. Journal of Cleaner Production , v. 112, p. 466-472, jan. 2016. ; Ye; Chen; Su, 2022YE, P.; CHEN, Z.; SU, W. Mechanical properties of fully recycled coarse aggregate concrete with polypropylene fiber. Case Studies in Construction Materials , v. 17, p. e01352, dez. 2022. ; Zhouet al., 2021ZHOU, H. et al. Static size effect of recycled coarse aggregate concrete: experimental study, meso-scale simulation, and theoretical analysis. Structures, v. 34, p. 2996-3012, dez. 2021. ; Zhu et al., 2022ZHU, L. et al. Compressive strength and microstructural analysis of recycled coarse aggregate concrete treated with silica fume. Construction and Building Materials, v. 334, p. 127453, jun. 2022. ). The market for powder fraction is still small, and it is usually discarded (Vázquez, 2013VÁZQUEZ, E. Progress of recycling in the built environment: final report of the RILEM Technical Committee 217-PRE. Germany: Springer, 2013.; Xiao et al., 2018XIAO, J. et al. Mechanical properties of concrete mixed with recycled powder produced from construction and demolition waste. Journal of Cleaner Production , v. 188, p. 720-731, jul. 2018. ). Due to the environmental problems caused by incorrect processing and/or disposal and the amount of waste generated, sustainable development strategies should prioritize promoting CDW’s circular economy (Lederer et al., 2020LEDERER, J. et al. Potentials for a circular economy of mineral construction materials and demolition waste in urban areas: a case study from Vienna. Resources, Conservation and Recycling, v. 161, p. 104942, out. 2020. ; López Ruiz; Roca Ramón; Gassó Domingo, 2020LÓPEZ RUIZ, L. A.; ROCA RAMÓN, X.; GASSÓ DOMINGO, S. The circular economy in the construction and demolition waste sector: a review and an integrative model approach. Journal of Cleaner Production , v. 248, mar. 2020. ), providing the correct handling and use of all granulometric fractions to return them to the production chain.

Overall, most researches focus on using concrete and mortar waste powder to harness the potential of residual anhydrous clinker (He et al., 2020HE, X. et al. New treatment technology: the use of wet-milling concrete slurry waste to substitute cement. Journal of Cleaner Production , v. 242, p. 118347, 2020. ; Oliveira, 2022OLIVEIRA, D. R. B. Aproveitamento da fração fina de resíduo de construção e demolição como alternativa para redução das emissões de CO2 associadas ao cimento Portland. Curitiba, 2022. Tese (Doutorado em Engenharia de Construção Civil) - Programa de Pós-Graduação em Engenharia Civil, Universidade Federal do Paraná, Curitiba, 2022.; Oliveira; Dezen; Possan, 2020OLIVEIRA, T. C. F.; DEZEN, B. G. S.; POSSAN, E. Use of concrete fine fraction waste as a replacement of Portland cement. Journal of Cleaner Production , v. 273, p. 123126, nov. 2020. ; Prošek et al., 2020PROŠEK, Z. et al. Recovery of residual anhydrous clinker in finely ground recycled concrete. Resources, Conservation and Recycling , v. 155, p. 104640, abr. 2020. ) and recycled ceramic waste powder due to its pozzolanic property (El-Dieb; Kanaan, 2018EL-DIEB, A. S.; KANAAN, D. M. Ceramic waste powder an alternative cement replacement: characterization and evaluation. Sustainable Materials and Technologies, v. 17, p. e00063, set. 2018. ; Li et al., 2020LI, L. et al. Waste ceramic powder as a pozzolanic supplementary filler of cement for developing sustainable building materials. Journal of Cleaner Production , v. 259, p. 120853, jun. 2020. ; Xu et al., 2021XU, K. et al. Mechanical properties of low-carbon ultrahigh-performance concrete with ceramic tile waste powder. Construction and Building Materials, v. 287, p. 123036, jun. 2021. ), increasing the mechanical performance. However, the disadvantage of using SCM-composed cement is the low rate of compressive strength gain due to reduced binder content. The use of particle packing techniques could be a potential alternative to compensate such effect. The packing concept involves arranging larger particles filled by smaller ones to promote granular closure and consequently reduce the number of voids (Chu et al., 2021CHU, S. H. et al. Roles of packing density and slurry film thickness in synergistic effects of metakaolin and silica fume. Powder Technology , v. 387, p. 575-583, jul. 2021. ). Although in small amounts, Portland clinker hydration, with the high packing density and water/fines (w/f) ratio reduction, produces enough to fill the intergranular spaces and promotes increments in the mixtures (Zheng et al., 2020ZHENG, K. et al. Reverse filling cementitious materials based on dense packing: the concept and application. Powder Technology , v. 359, p. 152-160, jan. 2020. ).

Considering that the mixed CDW waste is most found due to construction techniques, especially in Brazil, and studies with less heterogeneous materials (concrete and ceramic waste) are observed in the literature, this study brings an opportunity to enhance the mixed recycled powder, associated with the particle packing technique. Such motivation comes from the potential use of waste generated by the civil construction sector, entering the cement industry with a reduced carbon footprint (Akhtar; Sarmah, 2018AKHTAR, A.; SARMAH, A. K. Construction and demolition waste generation and properties of recycled aggregate concrete: a global perspective. Journal of Cleaner Production, v. 186, p. 262-281, jun. 2018. ; Kisku et al., 2017KISKU, N. et al. A critical review and assessment for usage of recycled aggregate as sustainable construction material. Construction and Building Materials , 30 jan. 2017.). In this context, the pioneering research by Oliveira (2022)OLIVEIRA, D. R. B. Aproveitamento da fração fina de resíduo de construção e demolição como alternativa para redução das emissões de CO2 associadas ao cimento Portland. Curitiba, 2022. Tese (Doutorado em Engenharia de Construção Civil) - Programa de Pós-Graduação em Engenharia Civil, Universidade Federal do Paraná, Curitiba, 2022. was used as a parameter for developing this study.

Therefore, this study’s differential is to reduce CP content in the mixtures using mixed CDW (RMP) powders treated with different calcination times as a replacement, and by arranging the fines (OPC and RMP) and particle packing techniques (Larrard, 1989LARRARD, F. de. Ultrafine particles for the making of very high strength concretes. Cement and Concrete Research , v. 19, n. 2, p. 161-172, mar. 1989. ; Wong; Kwan, 2008WONG, H. H. C.; KWAN, A. K. H. Packing density of cementitious materials: part 1-measurement using a wet packing method. Materials and Structures/Materiaux et Constructions v. 41, n. 4, p. 689-701, may 2008. ). That is to obtain the highest granular closure and improve the mechanical performance for compressive strength and environmental performance (CI and BI) in these matrices.

Materials and methods

Materials

Ordinary Portland cement (CP I - S 40, called OPC) was used in CDW powder compositions production. Portland cement composed with up to 25% filler (CP II - F 32, named FPC) was used as a reference (ABNT, 2018ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 16697: Portland cement: requirements. Rio de Janeiro, 2018. ). A superplasticizer admixture, a third-generation product based on modified carboxylic ethers polymers with a specific mass between 1.080 and 1.120 g/cm³ and CDW powder, were also used.

The CDW powder was obtained from processing the “Class A” fine aggregate according to Resolution no. 307 (BRAZIL, 2002BRAZIL. Resolução CONAMA nº 307, estabelece diretrizes, critérios e procedimentos para a gestão dos resíduos da construção civil. Diário Oficial da República Federativa do Brasil , Brasília, DF, 2002.) produced in a CDW recycling center, consisting mainly of ceramic materials, mortars, and concrete. The material was crushed in a jaw mill, originating an ARM (4.75 mm) that was oven-dried at 40°C for 24 hours, then sieved until a <0.15 mm fraction was obtained, called RMP0h. The waste obtained from sieving was thermally activated (calcination) at 800°C in a muffle for 0.5, 1, 2, and 3 hours, originating the RMP0.5c; RMP1c; RMP2c and RMP3c, respectively (Figure 1). Thermogravimetric analysis determined the calcination temperature (Figure 6).

Such temperature was applied considering the composition of the waste containing clayey and cementitious origin material. The temperature ranging 800 °C is ideal for increasing reactivity the clayey recipe, fostering dehydroxylation and generating amorphous phases (Ayati et al., 2022AYATI, B. et al. Low-carbon cements: potential for low-grade calcined clays to form supplementary cementitious materials. Cleaner Materials, v. 5, p. 100099, set. 2022. ). Reactive phases are also formed in the cementitious origin, with dehydration (Zhang et al., 2022ZHANG, D. et al. Comparison of mechanical, chemical, and thermal activation methods on the utilisation of recycled concrete powder from construction and demolition waste. Journal of Building Engineering , v. 61, p. 105295, dez. 2022. ), as presented in the results section.

Figure 1
RMP mechanical and thermal treatment processes

Materials characterization

The reference cement and RMP underwent specific gravity determination as per NBR 16605 standard (ABNT, 2017ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 16605: Portland cement and other powdered material: determination of the specific gravity. Rio de Janeiro, 2017. ). The granulometry analysis by laser diffraction was carried out using a Cilas 1190 granulometer, with grain reading ranging from 0.04 to 2500 µm, using ethyl alcohol as a dispersing agent using the Fraunhofer analysis method, with approximately 25% obscuration. The BET test was carried out to determine the specific surface area using the Nova 3200e - Quantachrome equipment in a nitrogen atmosphere. The degassing process followed the recommendations by Scrivener, Snellings, and Lothenbach (2016)SCRIVENER, K.; SNELLINGS, R.; LOTHENBACH, B. A Practical Guide to Microstructural Analysis of Cementitious Materials . 1. Ed. Boca Raton: CRC Press, 2016. 560 p., where 200 mg of cementitious sample was inserted into a quartz sample holder, using vacuums at 40ºC for 16 hours. X-ray fluorescence spectrometry (FRX) on a Panalytical Axios Max spectrometer characterized the semi-quantitative chemical composition with no fire loss correction. Mineralogical analysis by X-ray diffraction (XRD) was performed using a Panalytical diffractometer, with Cu Kα radiation and λ = 1.5418 Å, 40 mA current, 40 kV voltage, 96.390 s collection time, 0.026° 2θ angular collection step, and angular range from 5° to 70° in 2θ scanning, using the High Score Plus software. Thermogravimetric analyses were conducted using a Percking Elmer - STA 8000 equipment in an open alumina crucible, using approximately 50 mg of sample mass, pre-treated in the equipment in an isothermal process at 30°C for one hour, avoiding the influence of water unreacted waste. A 30ml.min-1 nitrogen flow was applied in the 30°C to 1000°C heating interval and 10°C.min-1 equipment heating rate. The pozzolanic activity index (PAI) of finely mixed waste was determined by evaluating the pozzolanic activity with lime at seven days (ABNT, 2015ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 5751: materiais pozolânicos: determinação da atividade pozolânica com cal aos sete dias. Rio de Janeiro, 2015. ) and the performance index with Portland cement at 28 days (ABNT, 2014aASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 12653: pozzolanic materials: requirements. Rio de Janeiro, 2014a).

SP admixture optimization and w/f ratio

The SP saturation point analysis was carried out separately for each material (OPC, RMP0h, RMP0.5c; RMP1c, RMP2c, and RMP3c), producing pastes with a fixed 0:4 w/f ratio and varying SP levels for dry material mass: 0.0%, 0.3%, 0.6%, 0.9%, 1.2%, 1.5%, 1 .8%, and 2.1% (manufacturer's recommendation ranging from 0.3% to 2%).

All pastes were produced with manual mixing for 60 seconds as standard, followed by mechanical mixing for 120 seconds in an automatic mixer (Fisatom 713D) at 1600 rpm. The type of mixer may influence the interaction between fines and admixture. Therefore, the same equipment and rotation must be used for all analyses.

The SP saturation content was analyzed according to the pastes’ consistency, using the Kantro cone on a glass surface, a conical acrylic mold with a 40 mm diameter base, top with 20 mm diameter, and 60 mm height (Kantro, 1980KANTRO, D. Influence of water-reducing admixtures on properties of cement paste: a miniature slump test. Cement, Concrete and Aggregates, v. 2, p. 95-102, 1980.). SP levels were tested after paste production (Figure 2a), and the conical mold was filled up to the surface and smoothed (Figure 2b). The mold was removed vertically in approximately 3 seconds (Figure 2c). After stabilizing the paste on the glass surface, two pastes’ spread sizes were measured at 0, 30, and 60 minutes (Figure 2d).

The a/f ratio determination was based on the thermal density experimental method (Wong; Kwan, 2008WONG, H. H. C.; KWAN, A. K. H. Packing density of cementitious materials: part 1-measurement using a wet packing method. Materials and Structures/Materiaux et Constructions v. 41, n. 4, p. 689-701, may 2008. ), which consists of making pastes with different w/f ratios until reaching the optimal balance that provides the maximum mass density of the mixture with a damp aspect. The method was adapted considering the pastes’ production, as described above, and the reduced cylindrical container with a 40 cm³ volume. The technique considered a 400 cm³ container; such adaptation optimizes the analysis using less material.

The procedure consists in producing the paste (Figures 3a and 3b), using the the SP saturation content (0.6% OPC, 0.3% FPC, and 1.5% RMP), deducting the total water in the mixture from the admixture water. The paste is poured into a mold (Figure 3c) and compacted on a consistency table with 10 drops, taking the set mass (Figure 3d). The analyses were carried out separately for each fine, ranging the ratios until finding the lowest limit, where the paste no longer presents cohesion between the particles exhibiting a dry aspect (Figure 3e). From this point on, 1% of w/f ratio increments were performed until the highest solids concentration was reached (Figure 3f).

Particle packing optimization

After determining the maximum solids concentration (β i ) using the experimental wet density method by Wong and Kwan (2008)WONG, H. H. C.; KWAN, A. K. H. Packing density of cementitious materials: part 1-measurement using a wet packing method. Materials and Structures/Materiaux et Constructions v. 41, n. 4, p. 689-701, may 2008. , the CPM analytical packing analysis by De Larrard (1999)DE LARRARD, F. Concrete mixture proportioning: a scientific approach. In: CONCRETE Mixture Proportioning. London: CRC Press, 1999. was carried out.

Figure 2
Fines’ SP saturation point

Figure 3
Materials’ w/f ratio optimization

The mass replacement contents were converted into volume (yi) using the specific mass of the materials (ρ). The average particle diameter (d50) was defined as the largest diameter among the classes involved in the mixture (d i ) and the spacing effect (a ij ) and wall (b ij ) was determined using Equations 2 and 3. This way, the virtual packing density (γ i ) was determined (Equation 1). The real density (Φ) was obtained by the compression criterion k = 12 proposed by Fennis (2011)FENNIS, S. Design of ecological concrete by particle packing optimization. Thesis- Delft University of Technology, Netherlands, 2011. , using Equation 4.

The analytical determination was based on the combinations of three fine materials (OPC + R1 + R2), containing in all analyses OPC, RMP0h as R1 and calcinated fines as R2 (RMP0.5c; RMP1c; RMP2c and RMP3c). Portland cement FPC was used as a comparison parameter as it is composed of filler.

The analytically tested RMP content (R1 + R2) t replacing OPC ranged from 0% to 65%. Interactions between the three types of RPM were analyzed. 140 mixtures were calculated and 22 were selected based on the highest densities among the replacement ranges of 7%, 15%, 25%, 35%, 45%, 55%, and 65% of RMP by OPC.

γ i = β i 1 - j = 1 i - 1 1 - β i + b ij β i 1 - 1 β j y i - j = i + 1 n 1 - a ij β i β j y j Eq. 1

a ij = 1 - ( 1 - d j di ) 1.02 Eq. 2

b ij = 1 - ( 1 - d i dj ) 1.50 Eq. 3

k = i = 1 n y i β i 1 Φ + 1 γ i Eq. 4

Compressive strength and environmental performance

Aiming at an experimental design of greater scope and contributing to the reduction of material consumption, the compressive strength analysis was conducted on 25x50 mm cylindrical specimens. The admixture content and the paste w/f ratio were proportional to the content of each powder type in the mixture. All specimens were covered with PVC film for the initial curing (24 hours), then molded and placed in lime-saturated submerged curing (3g/l) until test ages. Compressive strength was determined in a servo-controlled hydraulic press (Model Intermetric CT 201. C) with a 0,15 ± 0,05 MPa/s loading speed, adapted from NBR 7215 standard (ABNT, 2019ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 7215: Portland cement: determination of compressive strength of cylindrical test specimens. Rio de Janeiro, 2019.). The specimens’ upper surface was ground using equipment adapted for small-sized specimens. Compressive strength was determined on pastes at 28, 63, and 91 days, taking the average of 4 samples.

All cementitious compositions were analyzed considering cement consumption and CO2 emissions in terms of environmental performance. The binder index (BI) and the carbon index (CI) of pastes were calculated based on the average compressive strength, the CO2 emissions associated with raw materials production (from cradle to gate), and the cement used to produce one m³ of material. The binder index (BI) in kg.C/m³/MPa (Damineli, 2014DAMINELI, B. L. Conceitos para formulação de concretos com baixo consumo de ligantes: controle reológico, empacotamento e dispersão de partículas. São Paulo, 2014. Tese (Doutorado em Engenharia) -Escola Politécnica, Universidade de São Paulo, São Paulo, 2014.) indicates the amount of cement in kg (clinker, calcium sulfate, and limestone filler) used to obtain 1 MPa, as per Equation 5.

BI = PortlandCementconsumption ( kg m 3 ) Compressivestrengt h ( MPa ) Eq. 5

The Carbon Index (CI) in kg.CO2/MPa indicates how many kilograms of carbon dioxide were emitted to produce 1 MPa, according to Equation 6.

CI = Pastecarbondioxideemisions ( kg . CO 2 m 3 ) Compressivestrengt h ( MPa ) Eq. 6

For CO2 emissions analysis, Equations 7 to 11 were used.

E R 1 = C R 1 * E t 1 Eq. 7

E R 2 = C R 2 * E t 1 + C R 2 * E t 2 Eq. 8

E R = E R 1 + E R 2 Eq. 9

E C . comp = E c . Portland * C c . Portland + E R Eq. 10

E paste = E c . comp + E SP * C SP Eq. 11

Where:

ER1 = waste 1 emissions (kg.CO2/kg);

CR1 = waste 1 content (kg/m³);

Et1 = grinding emissions (kg.CO2/kg);

ER2 = waste 2 emissions (kg.CO2/kg);

CR2 = waste 2 content (kg/m³);

Et2 = calcination emissions (kg.CO2/kg);

E1 = waste emissions (kg.CO2/kg);

EC.comp = composite cement emissions (kg.CO2/kg);

Ec.Portland = Portland cement emissions (kg.CO2/kg);

Cc.Portland = Portland cement content (kg/m³);

Epaste = paste emissions (kg.CO2/kg);

ESP = SP emissions (kg.CO2/kg); e

CSP = SP content (kg/m³).

The 3.5% calcium sulfate found in Portland cement was applied. Data for calculating CO2 emissions were based in the literature (Table 1).

Table 1
CO2 emission data

Results and discussions

Materials characterization

The granulometric analysis indicated a slight reduction in the mean diameter of RMP particles as the calcination time increased (Figure 4), whose particles are larger than those of Portland cement.

Table 2 showed that the calcination period increased the density and reduced the mean particle diameter and the BET surface area.

Mixed construction waste powder calcination caused organic and compositional changes, such as particle breaking, resulting in smaller particles, which increased the material’s density and fineness of the material. These changes affected the surface area measured by the BET method.

The mixed waste is composed of various materials (Table 3). During calcination, such materials may undergo reactions and be eliminated as per time and temperature variations.

This implies a reduction in volume and, consequently, an increase in the material’s density. In addition, the loss of volatile materials, such as water and other organic compounds, may also contribute to lower BET values. These changes due to the powders’ thermal treatment were studied by He et al. (2023)HE, Z. et al. Reusing thermoactivated construction waste spoil as sustainable binder for durable concrete: Microstructure and chloride transport. Construction and Building Materials , v. 398, p. 132553, set. 2023. , Tokareva, Kaassamani and Waldmann (2023TOKAREVA, A.; KAASSAMANI, S.; WALDMANN, D. Fine demolition wastes as supplementary cementitious materials for CO2 reduced cement production. Construction and Building Materials , v. 392, p. 131991, ago. 2023. ), Wu et al. (2021b)WU, H. et al. Utilizing thermal activation treatment to improve the properties of waste cementitious powder and its newmade cementitious materials. Journal of Cleaner Production , v. 322, p. 129074, nov. 2021b. , and Zhang et al. (2022)ZHANG, D. et al. Comparison of mechanical, chemical, and thermal activation methods on the utilisation of recycled concrete powder from construction and demolition waste. Journal of Building Engineering , v. 61, p. 105295, dez. 2022. .

RMP presented a large surface area before calcination, characteristic of porous particles with cavities. Its particles collapsed when subjected to high temperatures, significantly reducing its surface area.

For the X-Ray fluorescence spectrometry (FRX) (Table 3), the RMP composition showed a high presence of silica and calcium oxide and to a lesser extent, iron oxides, aluminum, magnesium, and sulfur trioxide. The RMP’s paste fractions (SiO2+ Al2O3+ Fe2O3) did not conform to NBR 12653 standard (ABNT, 2014bASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 5752: materiais pozolânicos: determinação do índice de desempenho com cimento Portland aos 28 dias, 2014b.) for natural pozzolana (>70%), indicating that they do not have pozzolanic activity.

Figure 4
Portland cement and CDW powders’ particle size curves

Table 2
Physical characterization results of materials

X-ray diffraction (Figure 5) corroborate the FRX results, showing characteristic silica (quartz) and calcium carbonate peaks due to the mixed origin of the recycled powder from ceramic materials and cementitious matrices (concrete and mortar). Such pattern was also observed by (Tokareva; Kaassamani; Waldmann, 2023TOKAREVA, A.; KAASSAMANI, S.; WALDMANN, D. Fine demolition wastes as supplementary cementitious materials for CO2 reduced cement production. Construction and Building Materials , v. 392, p. 131991, ago. 2023. ), who stated that the absence of portlandite and ettringite is possibly due to carbonation processes overtime.

The thermogravimetric profiles (Figure 6a) showed the fines’ residual mass percentages. It was noted that the longer the calcination period, the lower the mass loss obtained in the test, with mass losses greater than 10% for RMP0h, RMP0.5c, and RMP1c and less than 10% for RMP2c and RMP3c. In the derivative thermogravimetric (Figure 6b), four mass variation peaks were identified based on the methodology by Neves Junior (2014)NEVES JUNIOR, A. Captura de CO2 em materiais cimentícios através de carbonatação acelerada. Rio de Janeiro, 2014. Tese (Doutorado em Engenharia Civil) - Programa de Pós-Graduação em Engenharia Civil, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 2014..

Table 3
X-ray fluorescence - Chemical composition

Figure 5
XRD analysis of materials - Mineralogical composition

Figure 6
Thermogravimetric and derivative curves of materials

Peak 1 (up to about 250°C) correspond to the gypsum, ettringite, tobermorite, C-S-H, and hydrated silicates dehydration. Peak 2 is attributed to Ca(OH)2 dehydroxylation (380°C to 500°C) for cement. In the waste, peaks 2 and 3 showed loss characteristic of kaolinite, illite, and smectite dehydroxylation in partially overlapping temperature ranges (Msinjili et al., 2019MSINJILI, N. S. et al. Comparison of calcined illitic clays (brick clays) and low-grade kaolinitic clays as supplementary cementitious materials. Materials and Structures/Materiaux et Constructions, v. 52, n. 5, p. 1-14, out. 2019. ; PTÁČEK et al., 2013PTÁČEK, P. et al. The influence of structure order on the kinetics of dehydroxylation of kaolinite. Journal of the European Ceramic Society, v. 33, n. 13-14, p. 2793-2799, nov. 2013. ). Peak 4 (600 °C to 800°C), the most intense, corresponds to CaCO3 decomposition and oxide formation. The level reached at peak 4 occurred at 800°C. Such temperature was applied for the powders’ thermal treatment. Vasconcelos and Rêgo (2016)VASCONCELOS, G. A.; RÊGO, J. H. da S. Efeito do processo de calcinação na atividade pozolânica da argila calcinada efeito do processo de calcinação na atividade pozolânica da argila calcinada. In: CONGRESSO BRASILEIRO DE CIMENTO, 7., São Paulo, 2016. Anais […] São Paulo, 2016. analyzed the effects of calcination temperature of clays used as MCS and obtained the highest reactivity at 800°C.

The IAP analysis showed no results that would classify the material as pozzolanic. Therefore, its use may be more associated with a filling effect (packaging) than with chemical reactivity in the matrix.

The waste’s chemical composition (ABNT, 2014bASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 5752: materiais pozolânicos: determinação do índice de desempenho com cimento Portland aos 28 dias, 2014b.) and the powder particles size are the main factors contributing to the pozzolanic activity and mechanical performance as per NBR 5751 (ABNT, 2015ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 5751: materiais pozolânicos: determinação da atividade pozolânica com cal aos sete dias. Rio de Janeiro, 2015. ) and NBR 5752 (ABNT, 2014aASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 12653: pozzolanic materials: requirements. Rio de Janeiro, 2014a) standards. Fine particles improved particle packing and pozzolanic effect, according to El-Dieb and Kanaan (2018)EL-DIEB, A. S.; KANAAN, D. M. Ceramic waste powder an alternative cement replacement: characterization and evaluation. Sustainable Materials and Technologies, v. 17, p. e00063, set. 2018. , Li et al. (2021)LI, S. et al. Investigation of using recycled powder from the preparation of recycled aggregate as a supplementary cementitious material. Construction and Building Materials, v. 267, p. 120976, jan. 2021. , Tang et al. (2020)TANG, Q. et al. The utilization of eco-friendly recycled powder from concrete and brick waste in new concrete: a critical review. Cement and Concrete Composites , v. 114, nov. 2020., and Wu et al. (2021a)WU, H. et al. Water transport and resistance improvement for the cementitious composites with eco-friendly powder from various concrete wastes. Construction and Building Materials, v. 290, p. 123247, jul. 2021a. . In addition, these effects enhance the microstructure by granular closure, affecting water transport, which is crucial to assess the matrix’s durability.

Some methods have been developed to enhance the recycled CDW powder properties and make it more reactive, including powder comminution, consequently, the particle size (Chen et al., 2022CHEN, X. et al. Sustainable reuse of ceramic waste powder as a supplementary cementitious material in recycled aggregate concrete: Mechanical properties, durability and microstructure assessment. Journal of Building Engineering, v. 52, p. 104418, jul. 2022. ; Kim; Jang, 2022KIM, J.; JANG, H. Closed-loop recycling of C&D waste: mechanical properties of concrete with the repeatedly recycled C&D powder as partial cement replacement. Journal of Cleaner Production , v. 343, p. 130977, abr. 2022. ; Li et al., 2021LI, S. et al. Investigation of using recycled powder from the preparation of recycled aggregate as a supplementary cementitious material. Construction and Building Materials, v. 267, p. 120976, jan. 2021. ; Prošek et al., 2020PROŠEK, Z. et al. Recovery of residual anhydrous clinker in finely ground recycled concrete. Resources, Conservation and Recycling , v. 155, p. 104640, abr. 2020. ; Tang et al., 2020TANG, Q. et al. The utilization of eco-friendly recycled powder from concrete and brick waste in new concrete: a critical review. Cement and Concrete Composites , v. 114, nov. 2020.), thermoactivation (Florea; Ning; Brouwers, 2014FLOREA, M. V. A.; NING, Z.; BROUWERS, H. J. H. Activation of liberated concrete fines and their application in mortars. Construction and Building Materials , v. 50, p. 1-12, jan. 2014. ; He et al., 2019HE, Z. et al. Comparison of CO2 emissions from OPC and recycled cement production. Construction and Building Materials , v. 211, p. 965-973, jun. 2019. ; Ma et al., 2022MA, Z. et al. Properties and activation modification of eco-friendly cementitious materials incorporating high-volume hydrated cement powder from construction waste. Construction and Building Materials , v. 316, p. 125788, jan. 2022. ; Wang; Mu; Liu, 2018WANG, J.; MU, M.; LIU, Y. Recycled cement. Construction and Building Materials , v. 190, p. 1124-1132, nov. 2018. ) and chemical activation (Kaliyavaradhan; Ling; Mo, 2020KALIYAVARADHAN, S. K.; LING, T. C.; MO, K. H. Valorization of waste powders from cement-concrete life cycle: a pathway to circular future. Journal of Cleaner Production , v. 268, p. 122358, set. 2020.; Luet al., 2018LU, B. et al. Effects of carbonated hardened cement paste powder on hydration and microstructure of Portland cement. Construction and Building Materials , v. 186, p. 699-708, out. 2018. ; Tang et al., 2020TANG, Q. et al. The utilization of eco-friendly recycled powder from concrete and brick waste in new concrete: a critical review. Cement and Concrete Composites , v. 114, nov. 2020.; Wang et al., 2020WANG, L. et al. Tea stain-inspired treatment for fine recycled concrete aggregates. Construction and Building Materials , v. 262, p. 120027, nov. 2020. ; Xiao; Ma, 2022XIAO, J.; MA, Z. Utilization of recycled powder from construction and demolition waste. Low Carbon Stabilization and Solidification of Hazardous Wastes, p. 291-301, jan. 2022. ; Zajac et al., 2020ZAJAC, M. et al. Effect of carbonated cement paste on composite cement hydration and performance. Cement and Concrete Research , v. 134, p. 106090, ago. 2020. ). Furthermore, other studies have evaluated the potential of these techniques (Carriço; Bogas; Guedes, 2020CARRIÇO, A.; BOGAS, J. A.; GUEDES, M. Thermoactivated cementitious materials: a review. Construction and Building Materials, v. 250, p. 118873, jul. 2020. ; Meng et al., 2021MENG, T. et al. Comparison of technical properties of cement pastes with different activated recycled powder from construction and demolition waste. Cement and Concrete Composites , v. 120, p. 104065, jul. 2021. ; Sousa; Bogas, 2021SOUSA, V.; BOGAS, J. A. Comparison of energy consumption and carbon emissions from clinker and recycled cement production. Journal of Cleaner Production , v. 306, p. 127277, jul. 2021. ).

Each method of modifying waste cement powder poses advantages and disadvantages. Further studies with recycled powders as a Portland cement replacement to improve CI and BI indicators are essential to develop less emissive cement. For He et al. (2023)HE, Z. et al. Reusing thermoactivated construction waste spoil as sustainable binder for durable concrete: Microstructure and chloride transport. Construction and Building Materials , v. 398, p. 132553, set. 2023. , behavior evaluation of matrices with long-term waste is crucial as prolonged curing times improve pozzolanic reactions between the thermoactivated construction waste particles and the Ca(OH)2 in the matrix. Also, temperature optimization and replacement rate are significant factors in this process.

Paste’s packing density analysis

The maximum wet solids concentration results established by Wong and Kwan (2008)WONG, H. H. C.; KWAN, A. K. H. Packing density of cementitious materials: part 1-measurement using a wet packing method. Materials and Structures/Materiaux et Constructions v. 41, n. 4, p. 689-701, may 2008. for OPC and FPC were 0.648 and 0.689 and 0.23 and 0.21 for w/f ratios, respectively. All materials were tested from the dry mass density to the highest wet mass density. RMP results are shown in Figure 7.

The virtual and real packing obtained from the fines optimized compositions analysis by the CPM method (De Larrard, 1999DE LARRARD, F. Concrete mixture proportioning: a scientific approach. In: CONCRETE Mixture Proportioning. London: CRC Press, 1999.) are shown in Table 4. Among the analyzed compositions, it was verified that the mixtures with RMP0.5c presented lower packing and those with RMP3c presented the maximum densities within the same replacement range.

In this study, it was observed that overall, the higher the compressive strength, the lower the w/f ratio (Figure 8a), the lower the replacement content (Figure 8b), and the lower effect of the packing density of the mixtures (Figure 8c).

According to the literature, when fines are larger than cement particles, compressive strength reduction proportional to the replaced rate occurs (Ma et al., 2020MA, Z. et al. Mechanical properties and water absorption of cement composites with various fineness and contents of waste brick powder from Construction waste. Cement and Concrete Composites , v. 114, p. 103758, nov. 2020. ). In addition to dilution, the hydration products formation is reduced and the water demand increases (He et al., 2020HE, X. et al. New treatment technology: the use of wet-milling concrete slurry waste to substitute cement. Journal of Cleaner Production , v. 242, p. 118347, 2020. ).

Figure 7
RMP’s solids concentration and void ratio

Table 4
Paste material content and packing density

Figure 8
Compressive strength, w/f ratio, replacement content, and packing density

The particle packing technique reorganizes the fines' granular skeleton and optimizes the w/f ratio, controlling the available water precipitated by the matrix dissolution. The waste tends to fill the voids between the cement particles, which would be filled by water through the waste’s filling potential (filler) (Chu et al., 2022CHU, S. H. et al. Packing density of ternary cementitious particles based on wet packing method. Powder Technology, v. 405, p. 117493, jun. 2022. ; Tang et al., 2020TANG, Q. et al. The utilization of eco-friendly recycled powder from concrete and brick waste in new concrete: a critical review. Cement and Concrete Composites , v. 114, nov. 2020.). The packed matrices showed a higher mass density (Figure 9a) and a higher mechanical performance (Figure 9b) than the unpacked matrices. Figure 9c showed that a higher level of replacement demands a higher w/f ratio providing a higher packing density.

The compressive strength results (Figure 10a) demonstrated that the pastes packed with 7% RMP reached strengths of up to 49 MPa and 60 MPa, at 28 and 91 days, respectively. For 25% replacement levels, the compressive strength at 28 and 91 days were 42 MPa and 59 MPa, respectivey, up to 31% higher than the reference. RMP contents of up to 45% provided greater results to FPC, which is composed of up to 25% of carbonate material as per the normative parameter (ABNT, 2018ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. NBR 16697: Portland cement: requirements. Rio de Janeiro, 2018. ).

Pastes packed with recycled powders (OPC + R1 + R2) achieved a 56% higher mechanical performance than the pastes without particle packing (OPC + R1), showing the applied techniques potential (Figure 10b).

According to Zheng et al. (2020)ZHENG, K. et al. Reverse filling cementitious materials based on dense packing: the concept and application. Powder Technology , v. 359, p. 152-160, jan. 2020. , the porosity of matrices based on additional cementitious materials may be reduced by increasing the packing density with particles optimization and the use of SP, directly influencing the composites’ mechanical strength and durability.

Meng et al. (2021)MENG, T. et al. Comparison of technical properties of cement pastes with different activated recycled powder from construction and demolition waste. Cement and Concrete Composites , v. 120, p. 104065, jul. 2021. stated that the performance improvement by mechanical and thermal activation may be related to chemical and physical changes in the waste. Such as, changes in crystalline structure, size, density, and surface area. According to Xiao et al. (2018)XIAO, J. et al. Mechanical properties of concrete mixed with recycled powder produced from construction and demolition waste. Journal of Cleaner Production , v. 188, p. 720-731, jul. 2018. , recycled powder produced from CDW crushing has low reactivity and large particle size, contributing only slightly to compressive strength. In this way, the different sizes material proportion offers a more significant granular closure. Consequently, the compressive strength is incremented by the mixture’s packaging.

The results showed that the highest compressive strength increments obtained at 28 days and 91 days for the packaged pastes were 42 MPa and 59 MPa, respectively.

Analysis of variance (ANOVA) for compressive strength at 28, 63, and 91 days, at the 5% significance level (p<0.05), showed a significant difference between the compositions. The isolated effect of compressive strength on replacement content and thermal activation (Figure 11a) demonstrated that the 7% and 15% replacement contents were statistically similar at 28 days, and the 7%, 15 %, and 25% replacement contents at 91 days, indicating the potential for the highest replacement content. For the thermal activation effects (Figure 11b), RMP0.5c presented the most significant contribution, statistically equivalent to the other activated waste.

All compositions were analyzed considering cement consumption and CO2 emissions for environmental performance. Figure 12 shows CO2 emissions of the materials found in the paste: Portland cement (OPC), RMP powder, and SP. The pastes’ total emissions carbon index at 28 days is also shown. The research reduced CO2 emissions (kg.CO2/m³ of pulp) by up to 53% for OPC and FPC.

CO2 emissions, carbon index (CI), and binder index (BL) results for all analyzed pastes are shown in Figure 13. The correlation of total emission, BI, and CI with the compressive strength for the pastes showed that all mixtures favored the reference's mechanical and environmental performance. It also showed that the longer the curing time, the lower the CO2 emissions, the binder, and carbon indexes.

Furthermore, Tang et al. (2020)TANG, Q. et al. The utilization of eco-friendly recycled powder from concrete and brick waste in new concrete: a critical review. Cement and Concrete Composites , v. 114, nov. 2020. stated that the waste’s porous particles absorb free water, and with increasing curing age, the absorbed free water may be released into the surrounding cementitious material, improving the hydration reaction and, consequently, the mechanical performance.

Figure 14a showed that at 91 days the best carbon (27 kg.CO2/m³/MPa) and binder (28 kg.C/m³/MPa) indexes were obtained. BI and CI reduction rates (Figure 14b) to the FPC at 28 days were 56% and 50%, respectively, and the BI and CI reduction rates at 91 days were 47%, and 38%, respectively.

Conclusions

The results of this study showed that, despite not classified as pozzolanic, fine mixed CDW (RMP) favored compressive strength and reduced CO2 emissions. Particle packing technique application increased the mechanical performance of the matrices with RMP by 55%, reaching 42 MPa against 27 MPa at 28 days.

The 0.5 hours calcination time had the most significant contribution to the study, statistically equivalent to the other activated waste.

RMP replacements of up to 45% showed higher compressive strength than the reference with statistical significance. All analyzed pastes presented superior environmental performance compared to the reference, reducing the CI by 50%, and the IL by 56% for the pastes analyzed. This study may enable CO2 emissions reduction by up to 53% (kg.CO2/m³ of paste) compared to the reference, reaching 27 kg.CO2/m³/MPa and 28 kg.C/m³/MPa levels after 91 days.

Figure 9
Packing density potential

Figure 10
Compressive strength and cement replacement content

Figure 11
Isolate effect of compressive strength, replacement content, and processing

Figure 12
Studied paste’s CO2emissions

Figure 13
CO2 emissions, BI, and CI correlation with compressive strength

Figure 14
Environmental performance analysis (BI and CI)

Replacement content, w/f ratio, and particle packing were found to have a significant effect on compressive strength and environmental performance. Considering that the calcination temperature applied (800°C) is lower than clinkerization temperature (1450°C), further studies of the physical, mechanical, and durability properties in Portland cement-based matrices composed of CDW ought to be conducted to evaluate the performance in various applications.

Acknowledgements

The authors would like to thank the Federal University of Latin American Integration, UNILA for Performance Laboratory and Structures and Materials - LADEMA and the Interdisciplinary Laboratory in Physical Sciences (LICF) for their support in the experimental project.To PRPPG/UNILA for supporting the research.

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Edited by

Editor do artigo:

Marcelo Henrique Farias de Medeiros

Publication Dates

  • Publication in this collection
    08 Jan 2024
  • Date of issue
    2024

History

  • Received
    18 Apr 2023
  • Accepted
    18 Aug 2023
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