Yes / Nickel coated multi-walled carbon nanotubes (NiMCNTs) are favorable reinforcing nanofillers for modifying cementitious composites due to their preeminent mechanical properties, electrical conductivity, thermal properties and dispersibility. This paper investigates the mechanical properties and compatibility of NiMCNTs filled cementitious composites, having two different types of cement, two water to cement ratios, and two dosages of five types of NiMCNTs. The results show that 0.06 vol.% NiMCNTs with small aspect ratios can significantly enhance the mechanical properties of cementitious composites, while NiMCNTs with large aspect ratios play a better strengthening effect at 0.03 vol.%. The flexural strength/toughness of cementitious composites containing 0.06 vol.% NiMCNTs with an aspect ratio of 200 can be increased by 19.65%/116.78%. Adding 0.03 vol.% NiMCNTs with an aspect ratio of 1000 enhances the compressive strength/toughness of composites by 18.61%/47.44%. Besides, NiMCNTs have preferable compatibility to cementitious composites prepared by P·O 42.5R cement with a water to cement ratio of 0.3. The enhancement mechanism is related to the denser microstructure and effective suppression of microcracks in the cementitious matrix by NiMCNTs with filling, bridging and pull-out effects, as well as the high interface bond strength between NiMCNTs and matrix. A strength prediction model for NiMCNTs reinforced cementitious composites is also established to estimate the mechanical strength of cementitious composites containing NiMCNTs with different aspect ratios/contents, showing a small relative error within ±6%/±13% for predicted flexural/compressive strength values in comparison with the experimental results. / Funding supported from the National Science Foundation of China (51908103 and 51978127), and the Fundamental Research Funds for the Central Universities (DUT21RC(3)039).

Yes / The development of ultra-high performance cementitious composite (UHPCC) represents a significant advancement in the field of concrete science and technology, but insufficient hydration and high autogenous shrinkage relatively increase the pores inside UHPCC, in turn, affecting the macro-performance of UHPCC. This paper, initially, optimized the pore structure of UHPCC using different types and dimensions of nanofillers. Subsequently, the pore structure characteristics of nano-modified UHPCC were investigated by the mercury intrusion porosimeter method and fractal theory. Finally, the fluid permeability of nano-modified UHPCC was estimated by applying the Katz-Thompson equation. Experimental results showed that all incorporated nanofillers can refine the pore structure of UHPCC, but nanofillers with different types and dimensions have various effects on the pore structure of UHPCC. Specifically, CNTs, especially the thin-short one, can significantly reduce the porosity of UHPCC, whereas nanoparticles, especially nano-SiO2, are more conducive to refine the pore size. Among all nanofillers, nano-SiO2 has the most obvious effect on pore structure, reducing the porosity, specific pore volume and most probable pore radius of UHPCC by 31.9%, 35.1% and 40.9%, respectively. Additionally, the pore size distribution of nano-modified UHPCC ranges from 10-1nm to 105nm, and the gel pores and fine capillary pores in the range of 3-50nm account for more than 70% of the total pore content, confirming nanofillers incorporation can effectively weaken pore connectivity and induce pore distribution to concentrate at nanoscale. Fractal results indicated the provision of nanofillers reduces the structural heterogeneity of gel pores and fine capillary pores, and induces homogenization and densification of UHPCC matrix, in turn, decreasing the UHPCC fluid permeability by 15.7%-79.2%. / National Science Foundation of China (51978127, 52178188 and 51908103), the China Postdoctoral Science Foundation (2022M720648 and 2022M710973) and the Fundamental Research Funds for the Central Universities (DUT21RC(3)039).

Cementitious materials with strain-hardening property and high tensile ductility are promising materials on account of their mechanical and durability performances. These materials require special ingredients which make it costly to be used in conventional constructions. Hence, potential applications of Engineered Cementitious Composites (ECC) generally focus on layered systems or repairs which require the use of ECC together with another material. For it to be used especially as a repair material, it should have sufficient dimensional compatibility for preventing restrained shrinkage cracking. In this thesis, a strain-hardening fiberreinforced cementitious composite, named Engineered Cementitious Composites, was produced with local ingredients and their mechanical performance, dimensional stability properties were investigated. For investigating the effect of materials and mix proportions on mechanical properties, compressive strength, flexural strength with mid-span beam deflections and matrix fracture toughness tests were conducted. For determining the dimensional compatibility properties, autogenous, drying and restrained shrinkage tests were conducted along with tensile creep tests. As a result it was shown that, mechanical and dimensional stability properties are affected by the ingredients and mix proportions. It was shown that especially autogenous shrinkage of mixtures was relatively high which can cause early age cracking. In order to mitigate the adverse effect of autogenous shrinkage, the effect of pre-soaked expanded perlite aggregate replacement on mechanical, shrinkage and dimensional compatibility properties was investigated. As a result it was found out that autogenous shrinkage can be mitigated by the use of pre-soaked expanded perlite aggregate replacement.

<div> <p>The formation of the cracks in concrete materials can shorten the service life of the structure by exposing the steel rebar to the aggressive substances from the external environment. Self-healing concrete can eliminate the crack automatically, which has the potential to replace manual rehabilitation and repairing work. This thesis intends to develop a self-healing fiber-reinforced cementitious composite by the use of internal curing agents, such as lightweight aggregate, zeolite and superabsorbent polymer (SAP). This study has evaluated the crack width control ability of three different types of fiber, polyvinyl alcohol fiber (PVA), Masterfiber Mac Matrix and Strux 90/40 fiber. Mechanical performance and flexural stress-strain behavior of the fiber-reinforced cementitious composite were tested and compared. In order to investigate the feasibility of using internal curing aggregate to enhance autogenous healing performance, two types of porous aggregates, zeolite and lightweight aggregate (LWA), were used as internal curing agents to provide water for the autogenous healing. The pore structure of the zeolite and lightweight aggregate was examined by the scanning electron microscopy (SEM). Two replacement ratios of sand with internal curing aggregates were designed and the healing efficiency was evaluated by the resonant frequency measurement and the optical microscopic observation. To further understand the influence of the internal curing on the designed material, water retention behavior of the bulk sample and the internal curing aggregates was evaluated. Moreover, to study the self-sealing effect of the superabsorbent polymer (SAP), the robustness of the SAP under various environmental conditions was first evaluated. The influence of the superplasticizer, hydration accelerator and fly ash on the absorption behavior of the SAP was investigated by the filtration test and void size analysis. Afterward, the self-sealing performance of the SAP in cement paste was evaluated by a water flow test.</p> <p>The evaluation of three types of fiber indicated that the use of PVA fiber could produce a cementitious composite with stronger mechanical strength and crack width control ability. The result of the autogenous healing evaluation showed that the incorporation of the internal curing aggregates increased the self-healing recovery ratio from 12.6% to over 18%. The internal curing aggregate could absorb and store water during the wet curing and release it when the external water supply is unavailable. The comparison between the two types of internal curing aggregates indicated that finer pores in the internal curing aggregate can lead to a slower water release rate that is capable of continuously supplying water for the autogenous healing. In addition, the SAP was proved to be robust when various content of the additives and fly ash were used. And the self-sealing effect of the SAP is found to be effective in regaining the water tightness of cement paste. The result of this thesis can assist in the design of the fiber-reinforced cementitious composite with self-healing performance in civil engineering.</p> </div> <br>

In this study, the mechanical properties of a fiber-reinforced cementitious composite (FRCC) were derived for specimens fabricated using two different methods of casting: conventional cast construction and pump-driven extrusion. Through the extrusion process, fibers are more likely to be oriented along the length of the member being cast and will therefore be more efficient since they are aligned parallel to the tensile stresses produced in flexure testing. The FRCC employed 0.5% and 1% polyvinyl alcohol (PVA) fiber reinforcement by volume. The flexural properties of FRCC were determined using four-point bend tests according to a modified ASTM C1609. Calculations included the modulus of rupture (MOR) and flexural toughness based on load-deflection curves. The fracture properties of FRCC were determined by using three-point bend tests on the same design but having notched beams using the two-parameter fracture model (TPFM). Calculations included the Mode I critical stress intensity factor (KIC), the critical crack tip opening displacement (CTODc), the strain energy release rate (GIC), and the total fracture energy (GF). The results show that enhanced ductility and post-peak behavior are achieved in concrete to which fibers have been added, as has been demonstrated in other studies, although this study further demonstrated how preferential fiber alignment produced via an extrusion can enhance fracture and flexural properties of cementitious composites. / Master of Science / Fiber-reinforced cementitious composite (FRCC) is a type of cementitious composite that contains fibers that are added to the mixture to improve its strength, durability, and ductility. One of the key factors of FRCC that affects its mechanical properties is the fiber alignment. Extrusion can be used as a method to preferentially align the fibers in order to maximize the benefit of fibers. Extruded FRCC can be pumped through a nozzle, making fiber alignment a convenient option for construction projects where traditional concrete placement methods would be difficult. One of the main benefits of aligning fibers in pump-extruded FRCC is that it can improve cementitious composites' fracture and flexural toughness. Fracture toughness refers to the ability of a material to resist crack propagation, while flexural toughness refers to its ability to withstand bending. By adding fibers to the mixture, the fibers act as reinforcement and help to distribute stress more evenly throughout the material, leading to increased strength and ductility. Furthermore, the alignment of fibers within the mixture also plays a critical role in the fracture and flexural strength of the material. Research has shown that when fibers are aligned in a specific direction, they can improve the tensile strength of the concrete and decrease the likelihood of crack propagation. This can be especially useful in structures that are exposed to seismic activity or long-lasting heavy loads. Overall, the use of pump extrusion-based method as a fiber alignment for FRCC can significantly improve the fracture and flexural strength of concrete. This makes it an attractive option for construction projects that require strong and durable members.

Yes / This paper explores the development of the most suitable machine learning models for predicting the bending capacity of steel and FRP (Fiber Reinforced Ploymer) bars hybrid reinforced ECC (Engineered Cementitious Composites)-concrete composite beams. Five different machine learning models, namely Support Vector Regression (SVR), Extreme Gradient Boosting (XGBoost), Multilayer Perceptron (MLP), Random Forest (RF), and Extremely Randomized Trees (ERT), were employed. To train and evaluate these predictive models, the study utilized a database comprising 150 experimental data points from the literature on steel and FRP bars hybrid reinforced ECC-concrete composite beams. Additionally, Shapley Additive Explanations (SHAP) analysis was employed to assess the impact of input features on the prediction outcomes. Furthermore, based on the optimal model identified in the research, a graphical user interface (GUI) was designed to facilitate the analysis of the bending capacity of hybrid reinforced ECC-concrete composite beams in practical applications. The results indicate that the XGBoost algorithm exhibits high accuracy in predicting bending capacity, demonstrating the lowest root mean square error, mean absolute error, and mean absolute percentage error, as well as the highest coefficient of determination on the testing dataset among all models. SHAP analysis indicates that the equivalent reinforcement ratio, design strength of FRP bars, and height of beam cross-section are significant feature parameters, while the influence of the compressive strength of concrete is minimal. The predictive models and graphical user interface (GUI) developed can offer engineers and researchers with a reliable predictive method for the bending capacity of steel and FRP bars hybrid reinforced ECC-concrete composite beams.

O Engineered Cementitious Composite ou ECC é um compósito cimentício de elevada capacidade de deformação, concebido na Universidade de Michigan. Constituído por agregados miúdos, cimento e fibras, o compósito apresenta elevada ductilidade associada com a capacidade de gerar microfissuras quando submetido a carregamentos, num comportamento conhecido como strain-hardening. As pesquisas previamente desenvolvidas no Laboratório de Ensaios e Modelos Estruturais (LEME) da UFRGS objetivaram caracterizar um ECC adaptado aos materiais do Brasil, adicionando-se fibras de polipropileno na elaboração do compósito, e estudando-se alternativas para a substituição parcial de cimento. Na pesquisa aqui relatada, adotou-se o traço de referência definido previamente (ECCRef) e também foi utilizado um traço alternativo com 30% (em volume) de cinza de casca de arroz moída por 4 horas, em substituição parcial do cimento (ECCCCA). A pesquisa foi dividida em duas abordagens. A primeira consistiu na caracterização das propriedades mecânica dos traços em laboratório com a realização de ensaios de resistência à tração na flexão, à compressão simples, avaliação da aderência por cisalhamento direto e da trabalhabilidade, bem como ensaios de fadiga em viga quatro pontos. Em ensaios monotônicos o ECCCCA apresentou uma resistência à tração na flexão média (ft,f) de 8,2 MPa e resistência à compressão simples média (fc) de 50 MPa; já o ECCRef teve valores médios de 6,8 MPa e 36 MPa, respetivamente. Nos ensaios de aderência obtiveram-se resistências ao cisalhamento de 2050 kPa (ECCCCA) e 1900 kPa (ECCRef) A avaliação da trabalhabilidade permitiu estabelecer critérios para aprimorar o processo de mistura e manuseio do material em estado fresco, desta forma obteve-se adequada trabalhabilidade no ensaio de flow table, que aumentou de 44 para 90, possibilitando a utilização de betoneiras de tombo e obter os volumes de material necessários. Com os resultados dos ensaios dinâmicos foram estabelecidos modelos de fadiga em termos da deformação específica de extensão inicial (εti), deformação específica de extensão inicial normalizada (ti/εtP) e tração inicial (σti), assim como da energia dissipada (DE), igualmente foi possível estudar o processo de degradação dos compósitos. A segunda abordagem da pesquisa consistiu na realização de ensaios em verdadeira grandeza, com a utilização do simulador de tráfego do Laboratório de Pavimentação (LAPAV). Foram construídos dois recapeamentos (de 50 e 30 mm de espessura) sobre pavimentos flexíveis que apresentavam idêntico padrão de trincamento. Em cada recapeamento foram aplicados 100 mil ciclos da carga de semi-eixo de 5,5 toneladas. Foram acompanhados, visualmente, o surgimento e evolução de fissuras e outras manifestações patológicas, bem como o desgaste superficial, por meio dos ensaios de Pêndulo Britânico e Altura de Mancha de Areia. Após o fim do tráfego, foram serradas placas das seções trafegadas para verificar a propagação das fissuras e a aderência entre o compósito e o pavimento. Concluiu-se que o controle de qualidade na mistura é fundamental para garantir a qualidade da superfície. Além disso, percebeu-se que a aparição de fissuras está associada com possíveis problemas de aderência ECC-pavimento asfáltico, e em menor escala reflexão de fissuras. Globalmente, constatou-se que é possível produzir ECC’s com materiais disponíveis no estado e que este material pode ser aplicado na restauração de pavimentos. / Engineered Cementitious Composite or ECC is a material with a high deformation capacity, designed at the University of Michigan. Composed of fine aggregates, cement and fibres, the composite presents high ductility associated with the ability to generate microcracks when loaded, in a behavior known as strain-hardening. The research previously developed in the Laboratory of Structural Models and Tests (LEME) of UFRGS aimed to characterize an ECC adapted to the materials of Brazil, adding polypropylene fibres in the preparation of the composite, and studying alternatives for the partial replacement of cement. In the research reported here, the previously defined reference mix proportion (ECCRef) was adopted and an alternative mix proportion was used with 30% (by volume) of unprocessed rice-husk ash grinded for 4 hours, in partial replacement of the cement (ECCCCA). The research was divided into two approaches. The first one consisted in the characterization of the mechanical properties of the ECC’s in the laboratory with the execution of tests of flexural behavior and compressive strength, evaluation of adhesion by direct shear tests and the workability, as well as fatigue tests in four point configuration. In monotonic tests ECCCCA showed a resistance to flexural strength of 8.2 MPa and average compression strength of 50 MPa; ECCRef had mean values of 6.8 MPa and 36 MPa, respectively. In the adhesion tests, shear strengths of 2050 kPa (ECCCCA) and 1900 kPa (ECCRef) were obtained The evaluation of the workability allowed for the determination of criteria to improve the process of mixing and handling of the material in fresh state, in this way, adequate workability was obtained in the flow table test, which increased from 44 to 90, permitting the use of concrete mixer machines and to obtain the required volumes of material. With the results of the dynamic tests, fatigue models were stipulated in terms of initial tensile strain (εti), normalized initial tensile strain (ti/εtP) and initial traction (σti), as well as the dissipated energy (DE), it was also possible to study the process of degradation of the composites. The second approach of the research consisted in the accomplishment of tests in true greatness, with the use of the Accelerated Loading Facility of the Laboratory of Pavements (LAPAV). Two overlays (50 and 30 mm thick) were built over flexible pavements that had the same cracking pattern. At each overlay, 100 thousand cycles of the semi-axle load of 5.5 tons were applied. The appearance and evolution of cracks and other pathologies were monitored visually, as well as surface wear through the British Pendulum and Sand Patch tests. After the end of the traffic simulator, plates of the trafficked sections were sawn to verify the propagation of the cracks and the adhesion between the composite and the pavement. It was concluded that the quality control in the mixture is fundamental to guarantee the quality of the surface. In addition, it was noticed that the appearance of cracks is associated with possible problems of adhesion ECC-asphalt pavement, and to a lesser extent reflective cracking. Overall, it has been found that it is possible to produce ECC's with Brazilian materials and the ECC can be applied in the restoration of pavements. / El ECC (Engineered Cementitious Composites) es un compósito cementicio de elevada capacidad de deformación desarrollado en la Universidad de Michigan. Conformado por agregados finos, cemento y fibras poliméricas, presenta una alta ductilidad asociada con la capacidad de generar microfisuras durante la aplicación de cargas, comportamiento conocido como strain-hardening. Las investigaciones previamente desarrolladas en el Laboratório de Ensaios e Modelos Estruturais (LEME) de la UFRGS se direccionaron para caracterizar un ECC adaptado a los materiales brasileros, utilizando fibras de polipropileno y estudiando alternativas para la sustitución parcial del cemento. En la presente investigación se adoptó el trazo de referencia definido previamente (ECCRef), también fue utilizado un trazo alternativo con 30% (en volumen) de ceniza de cáscara de arroz molida por 4 horas como substituto parcial del cemento (ECCCCA). La investigación fue dividida en dos abordajes. La primera consistió en la caracterización de las propiedades mecánicas en laboratorio con la realización de ensayos de resistencia a tracción por flexión e compresión simple, evaluación de la adherencia por corte directo y de la trabajabilidad, además de ensayos de fatiga en viga cuatro puntos. En ensayos monotónicos el ECCCCA presentó una resistencia a la tracción por flexión media (ft,f) de 8,2 MPa y resistencia a la compresión simple media (fc) de 50 MPa; ya el ECCRef tuvo valores medios de 6,8 MPa y 36 MPa, respectivamente. En los ensayos de adherencia se obtuvieron resistencias al corte de 2050 kPa (ECCCCA) y 1900 kPa (ECCRef). La evaluación de la trabajabilidad permitió establecer criterios para mejorar el proceso de mezcla y manipulación del material en estado fresco, de esa forma se obtuvo una adecuada trabajabilidad en el ensayo de flow table, que aumentó de 44 para 90, posibilitando la utilización de mezcladoras de tambor y la obtención de los volúmenes de material necesarios. Con los resultados de los ensayos dinámicos fueron establecidos modelos de fatiga en términos de la deformación específica de extensión inicial (εti), de la deformación específica de extensión inicial normalizada (ti/εtP), de la tracción inicial (σti) y de la energía disipada (DE), igualmente fue posible estudiar el proceso de degradación de los compósitos El segundo abordaje de la investigación consistió en la realización de ensayos en verdadera grandeza con la utilización del simulador de tráfico del Laboratório de Pavimentação (LAPAV). Fueron construidos dos recapeamentos (de 50 y 30 mm de altura) sobre pavimentos flexibles que presentaban idéntico patrón de fisuración. En cada recapeamento fueron aplicados 100 mil ciclos da carga de semi-eje de 5,5 toneladas. Fueron acompañados, visualmente, la aparición y evolución de fisuras y otras patologías, así como el desgaste superficial por medio de los ensayos de Péndulo Británico y Altura de Mancha de Arena. Una vez terminados los ciclos de carga, fueron extraídas placas de las secciones ensayadas para verificar la propagación de las fisuras y la adherencia entre el compósito y el pavimento. Se concluyó que el control de calidad durante el proceso de mezcla es fundamental para garantizar la calidad superficial. Además, fue percibido que la aparición de fisuras está asociada con posibles problemas de adherencia ECC-pavimento asfáltico y en menor escala reflexión de fisuras. Globalmente, se constató que es posible producir ECC’s con materiales disponibles a nivel local y que este material puede ser aplicado en la restauración de pavimentos.

abstract: Being a remarkably versatile and inexpensive building material, concrete has found tremendous use in development of modern infrastructure and is the most widely used material in the world. Extensive research in the field of concrete has led to the development of a wide array of concretes with applications ranging from building of skyscrapers to paving of highways. These varied applications require special cementitious composites which can satisfy the demand for enhanced functionalities such as high strength, high durability and improved thermal characteristics among others. The current study focuses on the fundamental understanding of such functional composites, from their microstructural design to macro-scale application. More specifically, this study investigates three different categories of functional cementitious composites. First, it discusses the differences between cementitious systems containing interground and blended limestone with and without alumina. The interground systems are found to outperform the blended systems due to differential grinding of limestone. A novel approach to deduce the particle size distribution of limestone and cement in the interground systems is proposed. Secondly, the study delves into the realm of ultra-high performance concrete, a novel material which possesses extremely high compressive-, tensile- and flexural-strength and service life as compared to regular concrete. The study presents a novel first principles-based paradigm to design economical ultra-high performance concretes using locally available materials. In the final part, the study addresses the thermal benefits of a novel type of concrete containing phase change materials. A software package was designed to perform numerical simulations to analyze temperature profiles and thermal stresses in concrete structures containing PCMs. The design of these materials is accompanied by material characterization of cementitious binders. This has been accomplished using techniques that involve measurement of heat evolution (isothermal calorimetry), determination and quantification of reaction products (thermo-gravimetric analysis, x-ray diffraction, micro-indentation, scanning electron microscopy, energy-dispersive x-ray spectroscopy) and evaluation of pore-size distribution (mercury intrusion porosimetry). In addition, macro-scale testing has been carried out to determine compression, flexure and durability response. Numerical simulations have been carried out to understand hydration of cementitious composites, determine optimum particle packing and determine the thermal performance of these composites. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2018

Made available in DSpace on 2014-12-17T14:07:20Z (GMT). No. of bitstreams: 1 ElvioAG_TESE.pdf: 3444604 bytes, checksum: d60cf497e4c263de969e02bb2eefe56f (MD5) Previous issue date: 2013-12-20 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This research was motivated by the requirement of asbestos s replacement in building systems and the need to generate jobs and income in the country side of the state of Bahia, Brazil. The project aimed at using fibers from licuri leaves (syagrus coronata), an abundant palm in the region, to produce composites appropriate for the sustainable production of cement fibre reinforced products in small plants. The composites were produced in laboratory using Portland cement CP-II-F32, sand, water, licuri palm fiber contents of 1.0, 1.5 and 2.0% by weight of binder (two different fiber length) and metakaolin. The latter was chosen as an additional binder for its efficiency to reduce the alkalinity of cementitious matrixes therefore preventing the degradation of vegetable fibers. The characterization of the composite components was carried out by sieving and laser particle size analyses, thermal analysis, fluorescence and X-ray diffraction. The composites performance was evaluated by 3- point-bending tests, compressive strength, ultrasound module of elasticity, free and restrained shrinkage, water capillarity absorption and apparent specific gravity. It has been found that the addition of fibers increased the time to onset of cracking over 200.00% and a 25% reduction in cracks opening in the restrained shrinkage test. The capillary absorption reduced about 25% when compared to fiber-free composites. It was also observed with regard to flexural strength, compressive strength and specific gravity, that the addiction of fibers did not affect the composite performance presenting similar results for compounds with and without fibers. In general it can be stated that the reinforced composite fibers of palm licuri presents physical and mechanical characteristics which enable them to be used in the intended proposals of this research / A exig?ncia da substitui??o do amianto em sistemas construtivos em conjunto com a necessidade de gera??o de renda no sert?o da Bahia fez nascer o projeto do aproveitamento da fibra da palma do licuri (syagrus coronata), palmeira abundante na regi?o, na produ??o de comp?sitos para a fabrica??o artefatos de cimento refor?ados com fibras para a constru??o civil de maneira sustent?vel, em pequenas unidades fabris. Os comp?sitos foram produzidos em laborat?rio utilizando cimento Portland CP II-F32, areia, ?gua, metacaulinita e fibra da palma do licuri. As fibras foram adicionadas em teores de 1,0, 1,5 e 2,0% da massa do aglomerante e com dois comprimentos de fibra diferentes. A metacaulinita foi selecionada como aglomerante suplementar de forma a agir na redu??o da alcalinidade da matriz ciment?cia na perspectiva de diminuir ou at? mesmo eliminar a degrada??o das fibras vegetais em meio alcalino. Foram realizados ensaios de caracteriza??o dos componentes do comp?sito, incluindo granulometria, an?lise t?rmica, fluoresc?ncia e difratometria de Raios-X. A verifica??o do desempenho dos comp?sitos foi feita com ensaios de flex?o em tr?s pontos, resist?ncia ? compress?o axial, m?dulo de elasticidade por ultrassom, retra??o livre e restringida, absor??o de ?gua por capilaridade e massa espec?fica aparente. Verificou-se que a presen?a das fibras de licuri aumentou o tempo para o surgimento da fissura??o acima de 200,00% e redu??o de 25% na abertura das fissuras no ensaio de retra??o restringida. Com rela??o ? absor??o capilar ocorreu uma redu??o de 25%, quando comparados com os materiais sem fibras. Observou-se que, com rela??o ? resist?ncia a flex?o, compress?o axial e massa espec?fica aparente, a adi??o de fibras n?o afeta o desempenho dos materiais, apresentando resultados similares para materiais com e sem fibras. De uma maneira geral pode-se afirmar que os comp?sitos refor?ados com fibras da palma do licuri apresentam caracter?sticas f?sicas e mec?nicas que viabilizam sua aplica??o dentro das condi??es estabelecidas neste trabalho

O Engineered Cementitious Composite ou ECC é um compósito cimentício de elevada capacidade de deformação, concebido na Universidade de Michigan. Constituído por agregados miúdos, cimento e fibras, o compósito apresenta elevada ductilidade associada com a capacidade de gerar microfissuras quando submetido a carregamentos, num comportamento conhecido como strain-hardening. As pesquisas previamente desenvolvidas no Laboratório de Ensaios e Modelos Estruturais (LEME) da UFRGS objetivaram caracterizar um ECC adaptado aos materiais do Brasil, adicionando-se fibras de polipropileno na elaboração do compósito, e estudando-se alternativas para a substituição parcial de cimento. Na pesquisa aqui relatada, adotou-se o traço de referência definido previamente (ECCRef) e também foi utilizado um traço alternativo com 30% (em volume) de cinza de casca de arroz moída por 4 horas, em substituição parcial do cimento (ECCCCA). A pesquisa foi dividida em duas abordagens. A primeira consistiu na caracterização das propriedades mecânica dos traços em laboratório com a realização de ensaios de resistência à tração na flexão, à compressão simples, avaliação da aderência por cisalhamento direto e da trabalhabilidade, bem como ensaios de fadiga em viga quatro pontos. Em ensaios monotônicos o ECCCCA apresentou uma resistência à tração na flexão média (ft,f) de 8,2 MPa e resistência à compressão simples média (fc) de 50 MPa; já o ECCRef teve valores médios de 6,8 MPa e 36 MPa, respetivamente. Nos ensaios de aderência obtiveram-se resistências ao cisalhamento de 2050 kPa (ECCCCA) e 1900 kPa (ECCRef) A avaliação da trabalhabilidade permitiu estabelecer critérios para aprimorar o processo de mistura e manuseio do material em estado fresco, desta forma obteve-se adequada trabalhabilidade no ensaio de flow table, que aumentou de 44 para 90, possibilitando a utilização de betoneiras de tombo e obter os volumes de material necessários. Com os resultados dos ensaios dinâmicos foram estabelecidos modelos de fadiga em termos da deformação específica de extensão inicial (εti), deformação específica de extensão inicial normalizada (ti/εtP) e tração inicial (σti), assim como da energia dissipada (DE), igualmente foi possível estudar o processo de degradação dos compósitos. A segunda abordagem da pesquisa consistiu na realização de ensaios em verdadeira grandeza, com a utilização do simulador de tráfego do Laboratório de Pavimentação (LAPAV). Foram construídos dois recapeamentos (de 50 e 30 mm de espessura) sobre pavimentos flexíveis que apresentavam idêntico padrão de trincamento. Em cada recapeamento foram aplicados 100 mil ciclos da carga de semi-eixo de 5,5 toneladas. Foram acompanhados, visualmente, o surgimento e evolução de fissuras e outras manifestações patológicas, bem como o desgaste superficial, por meio dos ensaios de Pêndulo Britânico e Altura de Mancha de Areia. Após o fim do tráfego, foram serradas placas das seções trafegadas para verificar a propagação das fissuras e a aderência entre o compósito e o pavimento. Concluiu-se que o controle de qualidade na mistura é fundamental para garantir a qualidade da superfície. Além disso, percebeu-se que a aparição de fissuras está associada com possíveis problemas de aderência ECC-pavimento asfáltico, e em menor escala reflexão de fissuras. Globalmente, constatou-se que é possível produzir ECC’s com materiais disponíveis no estado e que este material pode ser aplicado na restauração de pavimentos. / Engineered Cementitious Composite or ECC is a material with a high deformation capacity, designed at the University of Michigan. Composed of fine aggregates, cement and fibres, the composite presents high ductility associated with the ability to generate microcracks when loaded, in a behavior known as strain-hardening. The research previously developed in the Laboratory of Structural Models and Tests (LEME) of UFRGS aimed to characterize an ECC adapted to the materials of Brazil, adding polypropylene fibres in the preparation of the composite, and studying alternatives for the partial replacement of cement. In the research reported here, the previously defined reference mix proportion (ECCRef) was adopted and an alternative mix proportion was used with 30% (by volume) of unprocessed rice-husk ash grinded for 4 hours, in partial replacement of the cement (ECCCCA). The research was divided into two approaches. The first one consisted in the characterization of the mechanical properties of the ECC’s in the laboratory with the execution of tests of flexural behavior and compressive strength, evaluation of adhesion by direct shear tests and the workability, as well as fatigue tests in four point configuration. In monotonic tests ECCCCA showed a resistance to flexural strength of 8.2 MPa and average compression strength of 50 MPa; ECCRef had mean values of 6.8 MPa and 36 MPa, respectively. In the adhesion tests, shear strengths of 2050 kPa (ECCCCA) and 1900 kPa (ECCRef) were obtained The evaluation of the workability allowed for the determination of criteria to improve the process of mixing and handling of the material in fresh state, in this way, adequate workability was obtained in the flow table test, which increased from 44 to 90, permitting the use of concrete mixer machines and to obtain the required volumes of material. With the results of the dynamic tests, fatigue models were stipulated in terms of initial tensile strain (εti), normalized initial tensile strain (ti/εtP) and initial traction (σti), as well as the dissipated energy (DE), it was also possible to study the process of degradation of the composites. The second approach of the research consisted in the accomplishment of tests in true greatness, with the use of the Accelerated Loading Facility of the Laboratory of Pavements (LAPAV). Two overlays (50 and 30 mm thick) were built over flexible pavements that had the same cracking pattern. At each overlay, 100 thousand cycles of the semi-axle load of 5.5 tons were applied. The appearance and evolution of cracks and other pathologies were monitored visually, as well as surface wear through the British Pendulum and Sand Patch tests. After the end of the traffic simulator, plates of the trafficked sections were sawn to verify the propagation of the cracks and the adhesion between the composite and the pavement. It was concluded that the quality control in the mixture is fundamental to guarantee the quality of the surface. In addition, it was noticed that the appearance of cracks is associated with possible problems of adhesion ECC-asphalt pavement, and to a lesser extent reflective cracking. Overall, it has been found that it is possible to produce ECC's with Brazilian materials and the ECC can be applied in the restoration of pavements. / El ECC (Engineered Cementitious Composites) es un compósito cementicio de elevada capacidad de deformación desarrollado en la Universidad de Michigan. Conformado por agregados finos, cemento y fibras poliméricas, presenta una alta ductilidad asociada con la capacidad de generar microfisuras durante la aplicación de cargas, comportamiento conocido como strain-hardening. Las investigaciones previamente desarrolladas en el Laboratório de Ensaios e Modelos Estruturais (LEME) de la UFRGS se direccionaron para caracterizar un ECC adaptado a los materiales brasileros, utilizando fibras de polipropileno y estudiando alternativas para la sustitución parcial del cemento. En la presente investigación se adoptó el trazo de referencia definido previamente (ECCRef), también fue utilizado un trazo alternativo con 30% (en volumen) de ceniza de cáscara de arroz molida por 4 horas como substituto parcial del cemento (ECCCCA). La investigación fue dividida en dos abordajes. La primera consistió en la caracterización de las propiedades mecánicas en laboratorio con la realización de ensayos de resistencia a tracción por flexión e compresión simple, evaluación de la adherencia por corte directo y de la trabajabilidad, además de ensayos de fatiga en viga cuatro puntos. En ensayos monotónicos el ECCCCA presentó una resistencia a la tracción por flexión media (ft,f) de 8,2 MPa y resistencia a la compresión simple media (fc) de 50 MPa; ya el ECCRef tuvo valores medios de 6,8 MPa y 36 MPa, respectivamente. En los ensayos de adherencia se obtuvieron resistencias al corte de 2050 kPa (ECCCCA) y 1900 kPa (ECCRef). La evaluación de la trabajabilidad permitió establecer criterios para mejorar el proceso de mezcla y manipulación del material en estado fresco, de esa forma se obtuvo una adecuada trabajabilidad en el ensayo de flow table, que aumentó de 44 para 90, posibilitando la utilización de mezcladoras de tambor y la obtención de los volúmenes de material necesarios. Con los resultados de los ensayos dinámicos fueron establecidos modelos de fatiga en términos de la deformación específica de extensión inicial (εti), de la deformación específica de extensión inicial normalizada (ti/εtP), de la tracción inicial (σti) y de la energía disipada (DE), igualmente fue posible estudiar el proceso de degradación de los compósitos El segundo abordaje de la investigación consistió en la realización de ensayos en verdadera grandeza con la utilización del simulador de tráfico del Laboratório de Pavimentação (LAPAV). Fueron construidos dos recapeamentos (de 50 y 30 mm de altura) sobre pavimentos flexibles que presentaban idéntico patrón de fisuración. En cada recapeamento fueron aplicados 100 mil ciclos da carga de semi-eje de 5,5 toneladas. Fueron acompañados, visualmente, la aparición y evolución de fisuras y otras patologías, así como el desgaste superficial por medio de los ensayos de Péndulo Británico y Altura de Mancha de Arena. Una vez terminados los ciclos de carga, fueron extraídas placas de las secciones ensayadas para verificar la propagación de las fisuras y la adherencia entre el compósito y el pavimento. Se concluyó que el control de calidad durante el proceso de mezcla es fundamental para garantizar la calidad superficial. Además, fue percibido que la aparición de fisuras está asociada con posibles problemas de adherencia ECC-pavimento asfáltico y en menor escala reflexión de fisuras. Globalmente, se constató que es posible producir ECC’s con materiales disponibles a nivel local y que este material puede ser aplicado en la restauración de pavimentos.