Híbridos orgânico-inorgânicos para aplicações anticorrosivas na construção civil
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Data
2020-03-06
Autores
Uvida, Mayara Carla
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
A corrosão do aço de reforço é a principal causa de falha de estruturas de concreto armado e, na ausência de manutenção preventiva, resulta em tragédias e implicações financeiras, sociais e ambientais. O alto valor de pH da solução de poro do concreto (pH ± 14) contribui para a formação de uma fina camada de óxido passivo na superfície do vergalhão de aço, no entanto, íons agressivos como cloretos podem permear essa barreira. Para superar esses problemas, novos materiais nanocompósitos à base de híbridos orgânico-inorgânicos, combinando polímeros e materiais cerâmicos em uma única fase, mostraram-se promissores como revestimentos anticorrosivos. Nesse contexto, os revestimentos à base de PMMA (polimetacrilato de metila)-sílica e epóxi-sílica foram preparados combinando a metodologia sol-gel (policondensação hidrolítica de organosilanos) e polimerização radicalar de monômeros/ reação de cura da fase orgânica. A influência das diferentes proporções de iniciador térmico (BPO, peróxido de benzoíla/MMA, metacrilato de metila) e do agente de cura (DETA, dietiltriamina/DGEBA, poli (bisfenol-A-co-epicloridrina)) nas propriedades estruturais e de barreira de longo prazo foram investigadas para os dois sistemas híbridos. Os resultados da análise estrutural confirmaram a formação do híbrido PMMA-sílica, depositado em substratos aço de reforço no formato de disco por dip-coating. Os revestimentos com espessura entre 13-15 μm, possuem uma estabilidade térmica de até 260 ° C, elevada adesão a superfície metálica (>13 MPa), e morfologia homogênea e ausente de poros. As medidas de espectroscopia de impedância eletroquímica (EIS) em solução de NaCl 3,5% mostraram uma excelente resistência à corrosão com módulo de impedância a baixa frequência de até 100 GΩ cm2, com uma durabilidade superior a 250 dias, enquanto resistência à corrosão semelhante, mas com vida útil inferior foram obtidas em solução de poros de concreto simulado alcalina (SCPS1) e carbonatada (SCPS2). O revestimento preparado com razão intermediária de BPO/MMA = 0,05 depositado por dip-coating na superfície tridimensional das barras de aço de reforço apresentou uma excelente resistência à corrosão e módulo de impedância a baixa frequência, após 4 h de imersão, de ~3 GΩ cm2 em solução de NaCl 3,5% e SCPS2 com durabilidade de 14 dias, e ~90 MΩ cm2 em solução SCPS1 e durabilidade de 7 dias. Híbridos epóxi-sílica resultaram em revestimentos homogêneos, transparentes, ligeiramente hidrofóbicos, com boa adesão (>8 MPa), espessuras entre 8-12 μm, estabilidade térmica de até 328° C, e alta resistência à corrosão. Para a melhor formulação, valores de módulo de impedância de ~ 1 GΩ cm2 e durabilidade de várias semanas foram obtidas nas soluções estudadas.
Corrosion of reinforcing steel is the principal cause of failure of reinforced concrete structures and, in the absence of preventive maintenance, results in tragedies and financial, social and environmental implications. The high pH value of the concrete pore solution (pH≈14) contributes to the formation of a thin passive oxide layer on the surface of steel rebar, however, aggressive ions such as chlorides can permeate this barrier. To overcome these problems novel nanocomposite materials based on organic-inorganic hybrids have been developed to protect effectively reinforcing steel, combining polymers and ceramic materials in a single phase. In this context, coatings based on PMMA (methyl polymethacrylate)-silica and epoxy-silica were prepared by combining the sol-gel methodology (hydrolytic polycondensation of organosilanes) and radical monomer polymerization/curing reaction of the organic phase. The influence of different proportions of the thermal initiator (BPO, benzoyl peroxide / MMA, methyl methacrylate) and the curing agent (DETA, diethyltriamine / DGEBA, poly (bisphenol-A-co-epichlorohydrin)) in the structural and long-term barrier properties was investigated for the both hybrid systems. The results of the structural analysis confirmed the formation of the PMMA-silica hybrids, deposited by dip-coating on reinforcing steel substrates in form of discs. The coatings have a thickness between 13-15 μm, thermal stability up to 260 °C, high adhesion to the surface metallic (> 13 MPa), and homogeneous morphology without defects or pores. Electrochemical impedance spectroscopy (EIS) measurements in 3.5% NaCl solution showed excellent corrosion resistance to with a low-frequency impedance modulus of up to 100 GΩ cm2 and a durability greater than 250 days, while similar corrosion resistance but somewhat lower lifetime was obtained in simulated alkaline (SCPS1) and carbonated (SCPS2) concrete pore solution. Coatings with the intermediate ratio BPO/MMA = 0,05 deposited by dip-coating on the three-dimensional surface of the reinforcing steel bars showed excellent corrosion resistance with a low-frequency impedance modulus after 4 h of immersion of ~ 3 GΩ cm2 in 3.5% NaCl and SCPS2 solution with durability 14 days, and ~ 90 MΩ cm2 in SCPS1 solution, and durability of 7 days. Epoxy-silica hybrids resulted homogeneous, transparent, slightly hydrophobic coatings, with good adhesion (> 8 MPa), thicknesses between 8-12 μm, thermal stability up to 328 °C and high resistance to corrosion. For the best formulation impedance modulus values of ~ 1 GΩ cm2 and several weeks of durability were achieved for the studied solutions.
Corrosion of reinforcing steel is the principal cause of failure of reinforced concrete structures and, in the absence of preventive maintenance, results in tragedies and financial, social and environmental implications. The high pH value of the concrete pore solution (pH≈14) contributes to the formation of a thin passive oxide layer on the surface of steel rebar, however, aggressive ions such as chlorides can permeate this barrier. To overcome these problems novel nanocomposite materials based on organic-inorganic hybrids have been developed to protect effectively reinforcing steel, combining polymers and ceramic materials in a single phase. In this context, coatings based on PMMA (methyl polymethacrylate)-silica and epoxy-silica were prepared by combining the sol-gel methodology (hydrolytic polycondensation of organosilanes) and radical monomer polymerization/curing reaction of the organic phase. The influence of different proportions of the thermal initiator (BPO, benzoyl peroxide / MMA, methyl methacrylate) and the curing agent (DETA, diethyltriamine / DGEBA, poly (bisphenol-A-co-epichlorohydrin)) in the structural and long-term barrier properties was investigated for the both hybrid systems. The results of the structural analysis confirmed the formation of the PMMA-silica hybrids, deposited by dip-coating on reinforcing steel substrates in form of discs. The coatings have a thickness between 13-15 μm, thermal stability up to 260 °C, high adhesion to the surface metallic (> 13 MPa), and homogeneous morphology without defects or pores. Electrochemical impedance spectroscopy (EIS) measurements in 3.5% NaCl solution showed excellent corrosion resistance to with a low-frequency impedance modulus of up to 100 GΩ cm2 and a durability greater than 250 days, while similar corrosion resistance but somewhat lower lifetime was obtained in simulated alkaline (SCPS1) and carbonated (SCPS2) concrete pore solution. Coatings with the intermediate ratio BPO/MMA = 0,05 deposited by dip-coating on the three-dimensional surface of the reinforcing steel bars showed excellent corrosion resistance with a low-frequency impedance modulus after 4 h of immersion of ~ 3 GΩ cm2 in 3.5% NaCl and SCPS2 solution with durability 14 days, and ~ 90 MΩ cm2 in SCPS1 solution, and durability of 7 days. Epoxy-silica hybrids resulted homogeneous, transparent, slightly hydrophobic coatings, with good adhesion (> 8 MPa), thicknesses between 8-12 μm, thermal stability up to 328 °C and high resistance to corrosion. For the best formulation impedance modulus values of ~ 1 GΩ cm2 and several weeks of durability were achieved for the studied solutions.
Descrição
Palavras-chave
Nanocompósitos, Processo sol-gel, Concreto armado, Revestimentos protetores, Aço carbono, Nanocomposites, Sol-gel process, Steel-reinforced concrete, Protective coatings, Carbon steel