BACKGROUND: The increase in global plastic waste generation poses a threat to human, animal and plant life. As such, industries world-wide are encouraged to review waste management systems to prevent, minimise, recycle or recover plastic waste. There is a paucity of information on plastic waste generation by the local optical industry in South Africa, especially with respect to spectacle lens and contact lens recycling. AIM: The purpose of this review article was to provide a current outlook on spectacle lens and contact lens recycling in South Africa. METHODS: Literature review of scientific papers from online databases, websites and lens material patents. RESULTS: No studies regarding lens recycling in South Africa were found. However, data for this review were collated based on lens constituent materials. CONCLUSION: This review article provided an overview of lens recycling, identified the barriers and potential measures to advance plastic spectacle lens and contact lens recycling in South Africa, and suggested controlled energy recovery as an alternative pending implementation of lens recycling programmes. CONTRIBUTION: This paper contributes useful information on a previously unexplored aspect of recycling in South Africa. Ophthalmic lens recycling is currently not available in South Africa, and as such, this review focuses on the current outlook, barriers and considerations for implementation of such programmes.

Abstract: Deep eutectic solvents are characterized as natural, green, biodegradable, non-flammable, non-volatile, non-toxic, odorless, colorless, easy to prepare, and easy to recycle after use. They present an opportunity to introduce new techniques for the pulping process. This study investigated the possibility of using a green deep eutectic solvents from sorghum stalks for pulp and paper production. Choline chloride/ethylene glycol was used in the preparation of eutectic mixtures in molar ratios of 4/10, 5/10, and 6/10. These eutectic mixtures were then applied as cooking liquor to sorghum stalks at two different cooking times (140 and 160 minutes). In addition, the traditional pulping methods of soda and kraft cookings were carried out using sorghum stalks and the pulps were compared with the deep eutectic solvents pulps. The results showed that the pulp production using deep eutectic solvents was accomplished successfully. Some properties of deep eutectic solvents pulps were comparable to those of the soda and kraft pulps. deep eutectic solvents can play an essential role in cleaner pulp production.

Abstract The capability to recycle waste materials, such as steel slag, has appealed to the construction industry, as the cement industry faces a major challenge to reduce carbon dioxide (CO2) emissions into the atmosphere. This paper investigated the obtainment of cement pastes with Kanbara reactor desulfurization waste slag (KR slag) through alkaline activation using silicate and sodium hydroxide solutions. The mixtures were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), compressive strength, and physical property tests. The FTIR, XRD, and TGA results pointed to chemical activation, forming C-S-H and C-(A)-S-H gels. The formation of these compounds indicated the possibility of using KR slag in cementitious composites for civil construction.

Resumen Este artículo presenta los resultados de la investigación sobre reciclado de la cascarilla resultante de la laminación proveniente del proceso de conformado del acero en caliente, con el fin de explorar la posibilidad de obtener hierro esponjoso con un alto contenido metálico. La experimentación consistió en formar briquetas auto-reductoras mezclando óxido de hierro y grafito llevándolas a un proceso de auto-reducción variando la temperatura de 900 a 1050 ºC por el lapso mínimo de 30 min. extensible a 90 min., dependiendo del caso. La cascarilla y los productos reducidos obtenidos fueron caracterizados aplicando técnicas de análisis mineralógico mediante fluorescencia y difracción de rayos X, y de composición química mediante microscopía electrónica de barrido (SEM). En los productos reducidos, se determinó la cantidad de masa perdida y el cambio en la proporción de peso real. Adicionalmente, la determinación del grado de conversión metálica fue posible mediante la técnica analítica del análisis del Fe metálico y Fe total para cada muestra. Los resultados mostraron que en las condiciones: [90 min    1050 ºC - 13% de grafito, se alcanza un grado de conversión metálica igual al 99.9%], y para [30 min    1050 ºC - 20.7% de grafito, un 95% de conversión metálica se observa] y para [90 min    1050 ºC - 20.7% de grafito,   un 94.4% de conversión metálica se observa]. Para el caso del máximo grado de conversión metálica, se pudo observar la formación de hierro a partir del coalescimiento de puntos metálicos (whiskers) que conlleva a crear fases densas y compactas.

Abstract This paper shows the results of an investigation carried out to recycle the husk resulting from lamination coming from the (Mill Scale) forming process of steel in hot, in order to explore the possibility of obtaining sponge iron with a high metallic content. The experimentation consisted of forming self-reducing briquettes by mixing iron-oxide and graphite, and conducting them to a self-reducing process, varying the temperature from 900 to 1050 ºC for a minimum period of   30 min. expandable to 90 min, depending of the case. The husk and the reduced products obtained were characterized by applying mineralogical analysis techniques using fluorescence and X-ray diffraction, and chemical and mineralogical composition using scanning electron microscopy (SEM). In the reduced products the amount of mass loss and the change in the proportion of real weight were determined. Additionally, the determination of the degree of metallic conversion was possible by means of the analytical technique of the analysis of metallic Fe and total Fe for each sample. The results showed that at the conditions: [90 min    1050 ºC - 13% of graphite, the degree of metal conversion is equal to 99.9%], and for: [30 min    1050 ºC - 20.7% of graphite, a 95% of metal conversion is reached], and for: [90 min    1050 ºC - 20.7% of graphite, a 94.4% of metal conversion is reached]. In the case of the maximum degree of metal conversion, the formation of iron could be observed from the coalescing of metal points (whiskers) that leads to formation of dense and compact phases.

Resumen: El presente trabajo analiza los efectos de la pandemia Covid-19 en el Derecho de Contratos, específicamente el incumplimiento objetivo y los remedios contractuales en contexto de excepcionalidad. Este estudio es de carácter dogmático y se utiliza el método analítico y comparado. Se parte por verificar si la pandemia Covid-19 constituye caso fortuito, para lo cual se analiza si dicho fenómeno y sus consecuencias reúnen los requisitos de externalidad, imprevisibilidad e irresistibilidad. A partir de esta respuesta se exploran remedios contractuales como la teoría de la imprevisión o la frustración del fin del contrato, su relación con el principio de pacta sunt servanda y la manera en que han sido evocados en la legislación emanada en emergencia, para lo cual se desarrolla un análisis comparado de la regulación del contrato de arrendamiento de inmuebles. Posteriormente se analiza la naturaleza de los principios como fuentes del Derecho y su aplicación en el derecho privado. Se concluye que el derecho por contratos en la excepcionalidad recurre a los principios, entendidos como racionalización de las reglas, lo que permite flexibilizarlas en búsqueda de soluciones a la complejidad.

Abstract: This paper analyzes the effects of the Covid-19 pandemic on Contract Law, specifically objective non-compliance and contractual remedies in the context of exceptionality. This study is dogmatic using analytical and comparative methods. The starting point is to verify whether the Covid-19 pandemic constitutes an act of God, by analyzing whether this phenomenon and its consequences meet the requirements of externality, unpredictability and irresistibility. From this response, contractual remedies are explored, such as rebus sic stantibus or the frustration of purpose of contract, its relationship with the principle of Contract Law pacta sunt servanda, and how they have been evoked in the legislation issued in exceptionality, for which a comparative analysis of the regulation of the leasing contract is developed. The nature of the principles as sources of law and their application in private law is then analyzed. Finally, it is concluded that contract law in exceptionality resorts to principles, understood as the rationalization of the rules, which allows for flexibility in the search for solutions to complexity.

ABSTRACT Waste generation is increasing in many industries. Therefore, effective measures are required to secure an environmentally sustainable and economically viable waste destination. Co-processing in clinker kilns at high temperatures and incorporation into cement matrices may stabilize many types of industrial waste. This paper presents the results of a study that characterized pulp and paper mill waste and their recycling in clinker production. Chemical characterization and estimation of the hazardous potential of lime mud, biomass ash, and wastewater treatment plant (WWTP) sludge were performed in accordance with brazilian standard (NBR) 10004:2004. Biomass ash and WWTP sludge were classified as non-hazardous (class II), while lime mud was classified as hazardous (pH > 12.5, class I). These wastes were mixed (69 wt % lime mud, 29 wt % biomass ash, and 2 wt % WWTP sludge), and the resulting mixture was processed at 1455 ºC to generate ‘Ecoclinker’. The clinker was characterized, milled, and mixed with calcium sulphate for use as an ‘Ecocement’. Mortars were obtained and cured for periods of seven and twenty-eight days. The hardened product exhibited a mechanical strength of ~20 MPa. The leaching and pH tests indicated that these parameters were within the permitted limits, confirming that this waste-based cement was non-hazardous.

RESUMEN La generación de residuos sólidos está aumentando en muchos sectores industriales; por lo tanto, se requieren medidas efectivas para garantizar un descarte de residuos que sea ambientalmente adecuado y económicamente viable. El coprocesamiento en hornos de producción de clínker a altas temperaturas, así como la incorporación en matrices de cemento, son estrategias utilizadas para estabilizar muchos tipos de residuos industriales. En este estudio se analizan los resultados de un estudio acerca de la caracterización de residuos de papel y celulosa y su reciclaje en la producción de clínker. La caracterización química y la estimación del potencial peligroso de lodo de carbonato, la ceniza de biomasa y el lodo de la estación depuradora de aguas residuales (EDAR) se realizaron de acuerdo con la norma NBR 10004: 2004. La ceniza de biomasa y los lodos de la EDAR se clasificaron como no peligrosos (clase II), mientras que el lodo de carbonato se clasificó como peligroso (pH > 12.5, clase I). Una mezcla de estos residuos (69 % en peso de lodo de carbonato, 29 % en peso de ceniza de biomasa y 2 % en peso de lodo de EDAR) fue procesada a 1455 ºC para generar el denominado Ecoclínker. El clínker fue caracterizado, molido y mezclado con sulfato de calcio para ser utilizado como Ecocement. Los morteros fueron obtenidos y curados por períodos de 7 y 28 días. El producto endurecido mostró una resistencia mecánica de ~ 20 MPa. Las pruebas de lixiviación y pH estuvieron dentro de los límites permitidos, lo que confirma el carácter no peligroso del cemento a base de residuos.

Abstract The problem studied in this paper is motivated by the recycling Directive on Waste Electrical and Electronic Equipment of the European Commission. The core of this law is that each company selling electrical or electronic equipment in a European country has the obligation to recollect and to recycle a number of returned items that is proportional to its market share. To assign collection stations to companies in Germany for one product type, a territory design approach is planned. However, in contrast to classical territory design, the territories should be as geographically dispersed as possible to avoid that a company, based on its logistics provider, responsible for the recollection, gains a monopoly in some regions. We present the application of a solution based on the Greedy Randomized Adaptive Search Procedure methodology. Extensive computational results assess the effectiveness of the heuristics.

Resumen En este artículo se presenta el estudio de un problema de diseño de territorios de máxima dispersión territorial, motivado por una aplicación real en el campo de recolección y reciclaje de aparatos eléctricos y electrónicos en desuso en Europa. El problema consiste en encontrar una asignación de los centros de recolección a las corporaciones recolectoras que maximice una medida de dispersión territorial. El contexto matemático incluye como criterios de planificación, equilibrar la distribución de los hogares entre las distintas corporaciones de acuerdo a sus porcentajes de venta de mercado, así como evitar monopolios regionales. Se aplica una metaheurística tipo Greedy Randomized Adaptative Search Procedures (GRASP) que incorpora tres mecanismos de construcción de soluciones y tres diferentes tipos de vecindarios para las estrategias de búsqueda, para la mejora de soluciones. El algoritmo se ha evaluado en varios conjuntos de instancias generados aleatoriamente a partir de datos reales proporcionados por la empresa en territorio alemán. Los resultados obtenidos indican la eficacia del método propuesto dado que en tiempos de cómputo relativamente rápidos, pudieron obtenerse soluciones de calidad muy superior a la de las obtenidas por la empresa, tanto respecto a la medida de compacidad como respecto a las restricciones de balanceado.

RESUMEN Una gran variedad de modificadores se han aplicado al betún para mejorar sus propiedades y rendimiento. Entre ellos, los polímeros han sido principalmente utilizados. El objetivo de este artículo es evaluar el uso del residuo de espuma de poliuretano como modificador de betún en mezclas bituminosas en caliente. La espuma de poliuretano es un residuo que se obtiene durante la fabricación del poliuretano para aislamiento térmico. A partir de un betún de penetración 50/70, se fabricaron y analizaron varias muestras con porcentajes de residuo en peso entre el 1 y el 5 %>. Las muestras con porcentajes del 5 % de residuo o superiores produjeron un material áspero y se descartaron debido a su poca trabajabilidad. Se fabricó una mezcla bituminosa con un 4 % de porcentaje de betún modificado con residuo de poliuretano y fue comparado con una muestra con los mismos áridos y el betún original. Los resultados en el test de Marshall mostraron que la mezcla con betún modificado provocaba un aumento en la estabilidad y una menor deformación. Estos resultados sugieren que el empleo de residuo de espuma de poliuretano es un prometedor modificador de betún, contribuyendo además al reciclado de materiales de desecho.

ABSTRACT A wide variety of modifiers have been applied to bitumen in order to enhance their properties and performance. Among them, polymers have been mainly used. The aim of this paper is to assess the use of polyurethane foam waste as a bitumen modifier for hot mix asphalts. The polyurethane foam is a by-product of the manufacturing of polyurethane for thermal insulation. From a bitumen with a penetration grade of 50/70, various samples with percentages of waste material in weight ranging from 1 % to 5 % were produced and tested. Samples with 5 % of waste material or more became rough and were refused due to their poor workability. A bituminous mixture with modified bitumen with a 4 % of polyurethane was manufactured and compared with a sample with the same aggregates and original bitumen. Results in Marshall test showed that a mix with polymer modified bitumen yielded improvements in stability and a lower deformability. This result suggests that the employment of polyurethane foam waste is a promising bitumen modifier, contributing also to recycle waste materials.

ABSTRACT Aramid fiber is an important polymer applied as reinforcement in high-performance composites, which, due its exceptional properties, becomes an excellent impact absorption material. It has been broadly utilized in aeronautic industry and ballistic protection. In aircrafts, it is mainly used in secondary structures, such as fairings, floor panels, and bullet proof structures in helicopters, whereas, in ballistic protection industry, it is applied in automotive armor and bullet proof vest. Under environmental perspective, it is worrying the development and application of composites, which generate proportional discards of these materials, whether originated from manufacturing process, spare parts or end of life cycle. High-performance composite materials like those using aramid fiber are generally difficult to recycle due to their properties and the difficulty for the separation of the components, making their recycling economically unviable. From the characteristics of composite materials and environmental viewpoint, this paper presents a new aramid fiber recycling process. The main objective of this research was to study different recycling methods in aramid fibers/Neoprene® composites. To promote the Neoprene® degradation, it was used a pyrolysis oven with controlled atmosphere and CO2 injection. For the degraded separation, it was designed a mechanical washing machine in which the most degraded separation occurred. To complete the materials separation, it was employed a manual cleaning process, and, at least to prove the efficacy of the process, it was applied a tensile test in the yarns.

RESUMO: O uso de efluentes na agricultura vem sendo praticado em escala crescente ao longo das últimas décadas em virtude de seu potencial fertilizante e da redução na demanda de águas superficiais e subterrâneas. No entanto, tal prática pode trazer prejuízos quando realizada sem planejamento, não respeitando a capacidade de suporte do solo para a reciclagem de resíduos orgânicos. Os problemas mais comuns são a contaminação de águas superficiais e subterrâneas, via lixiviação e escoamento superficial, bem como o acúmulo de nutrientes e elementos potencialmente poluentes que comprometem as características químicas, físicas e biológicas do solo. O compartimento biológico, representado pela micro, meso e macrofauna, desempenha importante papel na ciclagem de nutrientes, decomposição da matéria orgânica, movimentação das partículas e transporte de materiais em diferentes profundidades, contribuindo para a manutenção das características físicas e químicas do solo. Nesse sentido, o presente trabalho tem por objetivo discutir o efeito do uso de diferentes efluentes na agricultura sobre a biologia do solo, destacando aspectos positivos e negativos, bem como enfatizar a necessidade de conduzir investigações que potencializem os aspectos positivos do uso de efluentes associados aos processos edáficos.

ABSTRACT: The use of wastewater in agriculture has been practiced on an increasing scale over the past decades because of its fertilizing potential and the reduction in demand for surface water and groundwater. However, this practice may bring harm when performed without planning, not respecting the capacity of the soil to recycle organic waste. The most common problems are contamination of surface and groundwater via leaching and runoff, as well as accumulation of nutrients and potentially polluting elements that compromise chemical, physical and biological characteristics of the soil. The biological compartment, represented by the micro, meso and macrofauna, plays an important role in nutrient cycling, decomposition of organic matter, particle movement and transport of materials at different depths, helping to maintain soil physical and chemical characteristics. In this sense, this paper aims to discuss the effect of using different kinds of wastewater in agriculture on soil biology, highlighting strengths and weaknesses, as well as emphasizing the need to conduct investigations that enhance the positive aspects of wastewater use associated with edaphic processes.

Sugar factories do achieve an efficient use of process water, but this process should be self-sufficient for consumption because these sugar factories have the special characteristic of having as its main raw material, sugar cane, which consists in approximately 70% of water.Those condensed recovered will be the first option to recover process water and are aimed to the feeding of boilers. The quantities of the condensate types are dependent of the evaporator’s configuration, also the grade in that show up the vapor extractions.In this paper the fundamental aspects are described as for the use and handling of water in the process of sugar production. Also, important considerations are shown on the treatment systems of residual that are generated in these factories. The evaporation system is shown as the most important area for the handling of water in the process, in it, vegetable vapor takes place and it is used in other technological equipment. A major surplus of steam will be produced in this area if the process is more energetically efficient.It is shown through a balance of water that the process is self-sufficient for water consumption.

En las fábricas de azúcar si se logra un uso eficiente del agua de proceso, el mismo deber autosostenerse en cuanto a su consumo ya que estas fábricas tienen la característica especial de que la materia prima principal que procesan, la caña, consiste en aproximadamente 70% de agua. Los condensados recuperados constituyen la primera opción para recuperar agua de proceso y son destinados para la alimentación a calderas. Las cantidades de los diferentes tipos de condensados son dependientes de la configuración de evaporadores y del grado en que se presenten las extracciones de vapor en los mismos.En este artículo, se describen los aspectos fundamentales en cuanto al uso y manejo de agua en el proceso de fabricación de azúcar. También se presentan consideraciones importantes sobre los sistemas de tratamientos de residuales que en estas fábricas se generan. Se muestra como el área más importante en cuanto al manejo del agua en el proceso es el sistema de evaporación, en el mismo se produce vapor vegetal, que es utilizado en otros equipos tecnológicos del proceso y cuanto más eficiente energéticamente sea ésta área, mayor será el excedente producido.Se muestra a través de un balance de agua que el proceso tiene posibilidades de autosostenerse en cuanto a consumo de agua.

El objetivo de este artículo es mostrar los resultados del análisis de la gestión de los Residuos Sólidos Municipales (RSM), en la Municipalidad de Guácimo, localizada en Limón, Costa Rica. Esta Municipalidad no dispone de suficiente cantidad de información básica, para implementar su sistema de gestión integral de residuos sólidos (GIR), por esta razón, esta investigación provee los insumos necesarios para poder iniciar este proceso de construcción del GIR. Para esto, se recopiló la información bibliográfica disponible de la zona, se desarrollaron los instrumentos de captura de información, se entrevistaron los principales actores sociales, se realizaron visitas de campo y se analizó toda esta información, de forma que se logró sistematizar y organizar en los siguientes tópicos: Gestión administrativa de los residuos sólidos (porcentajes de cobertura de recolección, planes de gestión, camiones recolectores y rutas, limpieza de parques y vías, botadero que utiliza la municipalidad), Actores Sociales (centros de recuperación de residuos sólidos y acciones municipales). La Municipalidad de Guácimo maneja sus residuos sólidos con poca planificación, atendiendo más bien las urgencias que se presentan el día a día, con un presupuesto insuficiente para garantizar un servicio de calidad que proteja el ambiente, por lo que genera grandes impactos ambientales tanto en los procesos de recolección, transporte y disposición, siendo este último el de mayor impacto, ya que los RSM son enterrados en una finca sin ningún tipo de protección ambiental. Este artículo, analiza la interacción entre los factores políticos, organizacionales, culturales, la administración de los residuos sólidos municipales y su impacto en el ambiente, con el fin de proveer algunas alternativas para mejorar la GIR. Se espera que este esfuerzo sirva para poder mejorar e implementar el sistema de gestión integral de residuos sólidos para la Municipalidad de Guácimo.

The aim of this paper its shows the results about the analysis of the solid waste management in the “Municipalidad of Guacimo” located in Limón, Costa Rica. The Municipalidad of Guacimo doesn’t have the basic records and enough information that is necessary for improve the management of the solid waste. Because of that, this investigation provides the inputs for begin to design the solid waste management for the Municipalidad of Guacimo. We search quotes bibliographic about the situation and characteristics of the management of solid waste in Guácimo, we develop the methodology for research and obtain primary information, interview the principal people that work with the solid waste in the Municipalidad of Guacimo and gathering the most important information. We sort and systematize the information about the administration for cleaning the streets and municipal parks, the administration of the collect the solid waste from the streets, schedule and routes of collection, operation of the landfill and the state of the recycle centers. The Guacimo Municipality doesn’t handle appropriately their solid waste, the administration doesn’t have proposals for the adequate management of the solid waste, the budget isn’t enough for collect, transport and disposable the solid waste considering the optimal methods for secure environmental protection, instead, the Municipality contributes to increase the environmental contamination in the area, because the solid waste are dumping in inappropriate site. In this paper, we analyze the interaction among of the politics, organizational culture, management and municipal administration, it’s our wish to provides different alternatives and solutions for improve the waste management in the Municipalidad of Guacimo.

Na região norte do Brasil são encontradas grandes reservas minerais, as quais tem sido exploradas nas últimas décadas gerando normalmente grande volume de rejeito para o meio ambiente. No caso específico do caulim, o principal produto exportado é para cobertura de papel (commodity) que apresenta baixo valor agregado. Sua produção, também gera um rejeito volumoso composto essencialmente de caulinita, de elevada pureza, porem fora de especificação para cobertura de papel que é descartado e ou utilizado em outras aplicações menos nobre. Como as zeólitas são materiais mais nobres e apresentam na sua estrutura cristalina sílica e alumina este trabalho teve como um dos objetivos o desenvolvimento de processo de produção da zeólita analcima a partir de um rejeito de caulim menos nobre, diatomito e solução de hidróxido de sódio. Por outo lado, os métodos descritos na literatura para obtenção de zeólitas são desenvolvidos em meio alcalino e utilizam normalmente um excesso de hidróxido de sódio no meio reacional ocasionado problema econômico e ambiental. Assim este trabalho descreve o processo de síntese da zeólita analcima semi-contínuo, no qual o excesso de hidróxido utilizado foi recuperado e reutilizado em um novo ciclo de processo. O processo foi desenvolvido em cinco ciclos consecutivos em autoclave através da reação de caulim calcinado, diatomito como fonte de sílica adicional, solução aquosa de hidróxido de sódio fresco e solução de hidróxido de sódio reciclada. A reação do processo foi desenvolvida a 210 °C por 24 h. O produto obtido no final de cada ciclo foi a zeólita analcima caracterizada por fluorescência de raios X, difração de raios, análise termogravimétrica-térmica diferencial, e microscopia eletrônica de varredura. O processo de produção de analcima apresentou elevado rendimento e o reaproveitamento do hidróxido de sódio por meio de reciclo mostrou-se tecnicamente viável.

In the north of Brazil large mineral reserves are found, which have been exploited in recent decades typically generating large volumes of waste to the environment. In the specific case of the kaolin is the main product exported is for paper coating (commodity) with low value. Its production also generates a massive waste composed mainly of high purity kaolinite, but with no specification to cover paper, being discarded or used in other less noble application. As zeolites are more noble materials and present silica and alumina, one of the goals of this work was the development of the production process of the zeolite analcime from kaolin waste, diatomite and sodium hydroxide solution. In the other hand, the methods described for obtaining zeolites are developed in an alkaline medium, typically using an excess of sodium hydroxide in the reaction, causing environmental and economic problems. The synthesis process of zeolite analcime semi-continuous is described, using excess of sodium hydroxide to be recovered and reused in a new process cycle. The process consisted in five consecutive cycles in an autoclave by reaction of calcined kaolin, diatomaceous earth as a source of additional silica, aqueous solution of sodium hydroxide, and fresh sodium hydroxide solution, and recycled. The reaction process was developed at 210 °C for 24 h. The product obtained at the end of each cycle was analcime zeolite characterized by XRF, XRD, DTA / TG, SEM. The production process of analcime showed high yield and reuse of sodium hydroxide through recycle to be technically feasible.

O objetivo deste trabalho é refletir e compreender como catadores de lixo ex-detentos de Fortaleza reconstituem a identidade de trabalhador com base no trabalho precarizado e estigmatizado socialmente. Foram realizados pesquisa bibliográfico-documental e estudo de inspiração etnográfica, tendo como ferramentas a observação direta e entrevistas semiestruturadas. Os resultados apontam para condições precárias de trabalho e conflitos com o "deposeiro" (dono do depósito) que explora os catadores em todos os âmbitos. Vistos pela população como vagabundos, perigosos e sujos, a sua condição de trabalho e de vida é permeada por exploração, conflito e preconceito. As narrativas desses reciclados pela justiça indicam forte identificação com o refugo que coletam. Na busca da reinserção social e reconstrução de identidades, alguns admitiram práticas ilícitas ou recaídas, demonstrando a fragilidade do sistema, tentando reciclá-los e incluí-los precariamente.

The goal of this paper is to reflect on and understand how ex-con trash pickers in the city of Fortaleza established a new worker identity through socially stigmatized unstable employment. Both bibliographical-documentary research and an ethnographical inspiration study were carried out, using direct observation and semi-structured interviews as tools. The results indicate unstable working conditions and conflicts with the "deposeiros" (recycling center owners), who exploit the trash pickers in every way possible. People regard these workers as dangerous, dirty bums, and their working and living conditions are riddled with exploitation, conflict and prejudice. The narratives of these recycled people for justice reveal a strong identity with the refuse that they collect. In their quest for reentry to society and reconstruction of identity, some of them admitted to illicit practices or recidivism, thereby demonstrating the fragility of the system, which attempts to recycle them and include them in a precarious manner.

L'objectif de ce travail est de mener une réflexion qui permette de comprendre comment les personnes qui font les poubelles, ex-prisonniers de Fortaleza, retrouvent une identité de travailleurs en se basant sur une activité précarisée et stigmatisante socialement. Une recherche bibliographique et documentaire ainsi qu'une étude d'inspiration ethnographique par l'observation directe et par des interviews semi-structurées a été réalisée. Les résultats indiquent des conditions précaires de travail et des conflits avec les propriétaires de dépôts qui exploitent les personnes qui font les poubelles à tous les niveaux. Perçu par la population comme des marginaux, dangereux et sales, leurs conditions de travail et de vie sont marquées par l'exploitation, les conflits et les préjugés. Les narrations de ces recyclés par la justice montrent une forte identification avec les déchets qu'ils ramassent. A la recherche d'une réinsertion sociale et de la reconstruction d'une identité, certains admettent pratiquer des actes illicites ou faire des rechutes,signes d'une fragilité du système qui essaie de les recycler et de les insérer de manière précaire.

Residues generation at Ready-Mixed Concrete Plants (CPs) occurs due to concrete leavings in the drum mixer of concrete delivery trucks; waste in piping and pumps agitators; on truck’s cleaning; and on the plant itself. The aim of this paper is to analyze technical and economic viability of employment of hydration control admixture (HCA) to permit reusing these residues. Technical viability was verified though setting times of samples with several HCA/cement ratios added to the concrete at the time of mixing, and also by setting times when HCA was added in time lag intervals of 1h and 3h after the admixture with a HCA/cement ratio of 0.30% by mass. There was verified axial compressive strength of the samples. Results showed that setting time increased progressively as long as it was increased rates of HCA. It was possible to reuse 88% of concrete leaving. Economic analysis permits to conclude that there are economic gains to the CPs. It can be concluded that hydration control admixture technique is an efficient way to recycle ready-mixed concrete residues.

La generación de residuos de hormigón en las Centrales Dosificadoras (CD) se produce debido a la devolución de los residuos de los camiones hormigoneras/mezcladores, pérdidas en la tubería y en el agitador de bombas de hormigón, limpieza de los camiones y en la propia Central. El objeto de este trabajo es evaluar la viabilidad técnica y económica de utilización del aditivo estabilizador de hidratación (AEH) para la reutilización del hormigón retornado. La viabilidad técnica se evaluó midiendo el tiempo de fraguado en muestras de hormigón con diversas concentraciones de AEH añadidas en el momento de la mezcla y también la medición del tiempo de fraguado cuando se añadió AEH a intervalos de tiempo de 1h y 3h después de mezclar con una misma tasa de AEH/cemento (0.30% en masa). Se observó la resistencia a compresión. Los resultados mostraron que los tiempos de fraguado aumentaran al incrementar los niveles de AEH. Fue posible reutilizar 88% del hormigón retornado a la CD. La viabilidad económica demostró la posibilidad de beneficios económicos. Se concluyó que el aditivo estabilizador de hidratación (AEH) es un apoyo eficaz para el reciclaje de residuos de hormigón.