Resumo A corrosão é um dos principais fenômenos que geram manifestações patológicas nas estruturas de concreto armado em ambientes agressivos, sendo o íon cloro o maior responsável por sua ocorrência. Desta forma, entender os mecanismos de transporte deste íon através da microestrutura do concreto é de fundamental importância para impedir ou retardar a penetração destes agentes agressivos, visando garantir uma estrutura durável. Na literatura são vastos os estudos referentes à difusão de cloretos em concreto e a influência das adições pozolânicas neste mecanismo, entretanto, poucos correlacionam os diferentes métodos de análise. Assim, este trabalho visa determinar os coeficientes de difusão do íon cloro em concretos contendo diversos teores de adição de sílica ativa (5%, 10% e 15%) ou com variação do teor de argamassa (54%, 80% e 100%), comparando os resultados obtidos por meio dos ensaios de migração iônica e de coluna. Observou-se que, apesar das técnicas utilizadas serem bastante distintas, os valores de coeficientes de difusão obtidos foram semelhantes, colaborando para a validação de ambas as técnicas. Além disso, a variação no teor de argamassa acarreta uma redução na zona de transição interfacial agregado graúdo/argamassas e um aumento no teor de aluminatos, o que promove efeito semelhante ao uso de sílica ativa.

Abstract Corrosion is one of the main phenomena that lead to pathological manifestations in reinforced concrete structures under aggressive environments. with the chloride ion being the most responsible for its occurrence. In this way, understanding the transport mechanisms of this ion through the microstructure of the concrete is of fundamental importance to prevent or delay the penetration of these aggressive agents to guarantee a durable structure. In the literature, there are extensive studies concerning the diffusion of chlorides in concrete and the influence of pozzolanic additions in this mechanism. However, only a few correlate the different methods of analysis. This work aims to determine the chloride ion diffusion coefficients in concrete containing various levels of silica fume (5%, 10%, and 15%) or varying the mortar content (54%, 80%, and 100%), and compares the results obtained through column tests and chloride migration tests. It was observed that, although the techniques used were quite distinct, the diffusion values obtained were similar, contributing to the validation of both techniques. Furthermore, the variation in the mortar ratio causes a reduction in the interfacial transition zone of coarse aggregate/mortars and an increase in the content of aluminates, which promotes a similar effect to the use of silica fume.

Resumo Segundo estudos anteriores, materiais finos provenientes de um agregado reativo podem agir como mitigadores da reação álcali-agregado (RAA), contudo, a efetividade da ação desses finos depende do seu grau de reatividade, finura e teor adicionado. Assim, o presente trabalho visa estudar se finos de rochas graníticas reativas (FRG), passante na peneira #200, podem mitigar ou reduzir a RAA e como a finura do material influencia na sua capacidade de mitigação. Para isso, foram utilizados FRG provenientes de 2 diferentes jazidas, obtidos após moagem. Cada adição foi utilizada em três finuras diferentes e adicionadas à argamassa nos teores de 10% e 20%, em relação à massa de cimento. Observou-se que a presença dos FRG não prejudicou as propriedades físico-mecânicas da argamassa, e ainda possibilitou redução da RAA, sendo mais acentuada à medida que se aumentou a superfície específica do material.

Abstract According to previous studies, fine materials originated from reactive aggregates can act as a Alkali-Aggregate Reaction mitigator, having its effectiveness dependent on their reactivity, fineness and added content. Thus, the present work aims to study if reactive granitic rock fines can mitigate or reduce the AAR and how the fineness of the material influences its mitigation capacity. For this purpose, granitic rock fines (GRF) from 2 different deposits and Pyrex glass fines (PGF) were tested as concrete addition. Each one of these fines were used in two different finesses and added to the concrete in the contents of 20% by mass of cement. It was observed that the addition of GRF did not affect the physical-mechanical properties of concrete and allowed the reduction in the AAR, being more accentuated with the increase of its specific surface.

Abstract This study investigates the effect of hydrothermal aging on the properties of glass fiber reinforced polymer (GFRP) rebars manufactured with isophthalic polyester or vinylester resin and glass fiber type E. The GFRP rebars were immersed in an alkaline solution (pH 12.6) for 1000 h at different temperatures (23 and 60 ºC), and their deterioration was evaluated based on microstructural and chemical changes (using SEM, DSC, XRF, and FTIR techniques), moisture absorption, and variation in mechanical properties. The results indicated an increase in the presence of voids and water absorption of the rebars with accelerated aging, with a reduction in the glass transition temperature of the resin and alteration of the chemical composition of the glass fiber. The comparison between the experimental results indicates that the rebars with matrix in vinylester resin present greater chemical resistance than the rebars with a polyester matrix. The degradation of the rebar also resulted in a reduction of approximately 6% in the tensile strength of the rebar and 2% in the modulus of elasticity. Using the damage model, it was possible to identify that the reduction in mechanical strength was associated with the simultaneous degradation of the resin and glass fiber due to the alkaline attack.

Resumo Intensificaram-se os esforços para a redução das emissões de gases do efeito estufa no contexto do desenvolvimento sustentável, com o desenvolvimento de pesquisas, visando a produção de novos materiais e ligantes para a construção. Esse artigo analisa a influência da geometria dos pellets, na produção de clínqueres, com a incorporação de resíduo da construção civil (RCC). Foram adotados procedimentos adaptados da metodologia proposta pela ABCP e adotada em estudos de clínqueres laboratoriais, na tentativa de simular etapas do processo industrial. Pellets foram preparados com a mesma formulação, porém, com quarto diferentes geometrias: esféricos, com diâmetros de 1 cm, de 2 cm e de 3 cm, com modelagem manual, e semi-esféricos, com diâmetro de 2 cm, empregando-se moldes de PLA (ácido polilático) impressos em impressora 3D, que facilitaram a moldagem dos clínqueres de forma padronizada. Os clínqueres foram caracterizados mineralogicamente por difração de raios x (DRX) e o método de Rietveld foi empregado na quantificação das fases. Observaram-se variações nas quantidades das fases alita e belita em função da geometria dos pellets, embora tenham sido utilizadas as mesmas condições de calcinação, provavelmente devido à variação da área superficial (área de exposição) e a gradientes da taxa de resfriamento.

Abstract Efforts to reduce greenhouse gas emissions in the context of sustainable development have intensified, with the development of research aimed at the production of new materials and binders for construction. This article analyzes the influence of pellet geometry in the production of clinkers, with the incorporation of construction waste (CCW). Procedures adapted from the method proposed by Brazilian Portland Cement Association were adopted in studies of laboratory clinkers, in an attempt to simulate the stages of the industrial process. Pellets were prepared with the same formulation, however, with four different geometries: spherical, with diameters of 1 cm, 2 cm and 3 cm, with manual molding, and semi-spherical, with a diameter of 2 cm, using molds of PLA (polylactic acid) printed on a 3D printer to facilitate the molding of the clinkers in a standardized way. Clinkers were characterized mineralogically by x-ray diffraction (XRD) and the Rietveld method was used to quantify the phases. Variations in the quantities of the alite and belite phases were observed depending on the geometry of the pellets, although the same calcination conditions were used. This is probably due to the variation in the surface area (exposure area) and the gradients of the cooling rate.

Abstract Materials such as magnesium phosphate cement (MPC) have attracted significant attention of researchers, therefore, understanding the effects of dosage parameters, such as water content and MgO/NH4H2PO4 ratio on phase formation is essential for obtaining cementitious matrices with improved performance. In the present work MgO was sintered at 900 °C and 1110 °C in a conventional oven, and the effect of water concentration and MgO/NH4H2PO4 (or ADP) ratio on the properties of MPC was evaluated in terms of phase formation by X-ray diffraction, pore size distribution, mechanical properties, and microstructure. For less-reactive MgO (calcined at 1100 °C) with a high MgO/ADP ratio, increased water content did not cause additional solubilization of ADP or formation of more hydrated phases, although the cement porosity increased. Compositions with more reactive MgO (calcined up to 900 °C) formed dittmarite (NH4MgPO4.H2O) independent of water content. Higher water content and MgO calcination temperature were associated with increased MPC setting time and decreased mechanical strength due to higher porosity.

Resumo O reaproveitamento de resíduos industriais para o setor da construção civil tem se mostrado uma alternativa ambiental e economicamente atrativa, principalmente para a indústria do cimento, que por muito tempo tem procurado procedimentos que efetivamente reduzam a alta energia e emissões de CO2 gerados durante a produção de clínquer. Nesse sentido, destaca-se a necessidade de utilização de materiais alternativos na produção de clínquer como substitutos parciais às matérias-primas. Dessa forma, o objetivo da presente pesquisa é avaliar a produção de clínquer Portland com baixa emissão de dióxido de carbono a partir da incorporação de minério não reagido (MNR), resíduo gerado durante a produção de dióxido de titânio (TiO2). As emissões de dióxido de carbono geradas durante a produção desse material foram verificadas através de análises térmicas (TG/DTG), e a influência do resíduo na formação de fases dos clínqueres foi verificada por análise mineralógica (DRX), por microscopia óptica (MO) e por microscopia eletrônica de varredura (MEV). A partir dos resultados obtidos, determinou-se o teor de incorporação ideal de TiO2 para produção de clínquer, sendo constatado que o MNR, até um teor limite de incorporação, atua como mineralizante, sendo, assim, benéfico para a formação de alita.

Abstract The reuse of industrial waste in the construction industry has proven to be an environmentally and economically attractive alternative, especially for the cement industry, which has long sought after procedures that effectively reduce the high use of energy and CO2 emissions generated during clinker production. In this sense, it is necessary to use alternative materials as partial substitutes for raw materials in clinker production. Thus, the objective of this research study is to produce Portland clinker with low carbon dioxide emissions from the incorporation of unreacted ore (UOW), a waste generated during the production of titanium dioxide (TiO2). The carbon dioxide emissions generated during the production of this material were verified by thermal analysis (TG/DTG), and the influence of the waste on the formation of clinker phases was verified by mineralogical analysis (XRD), optical microscopy (MO) and scanning electron microscopy (SEM). The results obtained led to the determination of the ideal incorporation content of TiO2 for clinker production, and they also showed that the UOW - up to a limit content of incorporation - acts like a mineraliser and is, therefore, beneficial for the formation of alite.

Reinforced concrete is the main structural material used in the world in the construction of bridges, roads and commercial and residential buildings. One effective method for preventing corrosion of steel reinforcement is the application of galvanic coatings to the reinforcement itself. The present study evaluated the performance of three groups of reinforcing steel bars (black steel, used as a reference and rebars electroplated with Zinc and Zinc-Nickel alloys) to corrosion and adherence to the concrete matrix. For the analysis of corrosion, the specimens were subjected to two different accelerated corrosion tests: salt spray exposure and wet and dry semi-cycles. The corrosion potential was measured for the qualitative monitoring of the corrosion process and the corrosion rate was estimated. In order to evaluate the steel-concrete adherence, the pullout test was used, in accordance with RILEM-CEB-FIP. The results showed that Zinc and Zinc-Nickel coatings increased the durability of the reinforcing bars and the accelerated corrosion test of wetting and drying cycles proved to be more aggressive compared to the salt spray method to evaluate the corrosion process in the reinforced concrete specimens. Additionally, galvanized reinforcement reduced adherence to the concrete matrix.

Rotary-vacuum-filter mud (RVFM) is waste generated during the manufacturing process of titanium dioxide. In this work, RVFM and ceramic bricks containing different ratios of this waste are investigated. The mud samples were characterized using thermal analysis (TG/DTG). The aim of the present work was to determine the effect of adding RVFM on the ceramic properties of clay, such as apparent porosity, water absorption, linear shrinkage and flexural strength, used to produce red ceramics (bricks and roofing tiles). Samples were dried out at 110°C and fired at 800°C, 950°C and 1100°C. The addition of RVFM tends to increase the apparent porosity and water absorption and to decrease the flexural strength of the ceramic specimens. Based on the results, ceramic specimens with 20% RVFM content that are burned at 800ºC can not be used as bricks, and ceramic specimens with 20% RVFM content that are fired at 800ºC and 950°C can not used as roofing tiles, according to Brazilian standards.

This study evaluated the feasibility of using sugar cane bagasse ash (SCBA), a by-product of the sugar cane ethanol industry, obtained under controlled calcination as a partial replacement for Portland cement in mortars. Materials with pozzolanic characteristics may be used to partially replace cement in mortars or concrete and are known to provide durability to the products. Initially, TG/DTA curves of the sugar cane bagasse were conducted to define suitable calcination temperatures (500ºC, 600ºC and 700ºC), and tests were conducted to characterize the physical-chemical parameters of the SCBA and the pozzolanic activity according to NP EN 196-5. The results showed the technical feasibility of using the SCBA as a pozzolanic material in construction, which would provide an alternative to proper disposal for this waste while providing products with high technical performance.

Red mud, the main waste generated in aluminum and alumina production by the Bayer process, is considered hazardous due to its high pH, according to the Brazilian standard NBR 10004/2004, and worldwide generation of this waste exceeds 117 million tons/year. In this work, non-calcined red mud was used, thus requiring less energy and time and reducing costs, which is the ideal condition for reusing wastes. Mortars containing 30 wt. (%) of cement substituted by red mud showed higher strength of hardened products. The pozzolanic activity index was evaluated based on physical and mechanical parameters (Brazilian NBR 5751 and NBR 5752 standards) and on a chemical analysis (European EN 196-5 standard). A comparison of the reference mixture (without red mud) and the results obtained with red mud confirm the potential of non-calcined red mud for use a as pozzolanic additive in cementitious materials. The setting time (according to the MERCOSUL NM 65 standard) tends to increase but workability remains almost unchanged.

Red mud, which is a solid waste produced in the alumina production process, is classified as dangerous due to its high pH. In this work, the concentration of chlorides was monitored by measuring the conductivity of the anolyte, which initially was distilled water. The steady and nonsteady-state chloride diffusion coefficients were estimated from the "time lag"� and "equivalent time" between diffusion and migration experiments. The capillary water absorption, apparent porosity and pore size distribution of concretes were also analyzed. The addition of red mud apparently ensured lower chloride diffusion in the tested mixtures due to its superfine particle-size distribution and its "filler"� effect. Red mud lengthened the service life of the concrete to 35 years (double that of the reference concrete). This finding is very positive since it indicates a delay in the onset of the rebar corrosion process caused by the migration of chloride ions.

The sheave leather was subjected to chemical treatment in an attempt to immobilize chromium ion in a matrix of cement. Cementitious pastes were obtained by adding different proportions of waste treated solutions (5 and 10% compared to the cement mass) and the pH and setting time (hardening) were measured. Aiming to check the leather influence in Portland cement pastes, the phases formation were observed by X-ray diffraction (XRD). The results showed that the pretreatment was effective for the waste dissolution and the pH of treated waste chemical solutions did not influence significantly the characteristics of cement paste, with a slight increase in setting time results.

Magnesium phosphate cement materials are formed by reacting magnesium oxide with water-soluble phosphates such as monoammonium dihydrogen phosphate (ADP), which solidifies at ambient temperature through the formation of hydrated phases in the material. Cylindrical specimens of magnesium phosphate cement were molded and varying amounts (0 to 30% weight) of grinding dust were added to the ceramic matrices. The influence of the addition of grinding dust on the characteristics of the mortars in terms of microstructure (SEM), mechanical strength and capillary water absorption was verified. The results obtained proved very satisfactory for the use of this waste as an additive in magnesium phosphate mortars.