La vivienda social en Nicaragua: análisis desde la sostenibilidad

En Nicaragua el déficit de vivienda es una cifra que crece incesantemente. De acuerdo a Hábitat para la Humanidad (2008), la demanda de vivienda nueva en Nicaragua supera el medio millón de unidades, cifra que se incrementa en veintidós mil viviendas cada año, mientras otro medio millón de viviendas ameritan reparación. Los esfuerzos realizados por las diferentes organizaciones y entidades involucradas en el tema de la vivienda social en Nicaragua han generado una variedad de soluciones habitacionales que se tratan de adecuar a las necesidades de los pobladores, jugando un papel importante ante la reducción cuantitativa del déficit habitacional. Sin embargo, estas soluciones manifiestan deficiencias en el aspecto cualitativo, específicamente respecto a aquellos estándares que inciden en el bienestar habitacional y el desarrollo de la vida humana -de diseño, de calidad ambiental y calidad constructiva. La ausencia de criterios y lineamientos en Nicaragua que orienten los proyectos de viviendas de interés social hacia la búsqueda de la sostenibilidad ha dado como resultado la proyección de viviendas que no satisfacen las necesidades de sus habitantes, sus expectativas, relaciones sociales, la posibilidad de convivir y de tener derecho a la ciudad. El presente trabajo define un sistema de indicadores de elaboración propia que ha sido adaptado al contexto urbano, socioeconómico y ambiental de Nicaragua para poder evaluar de forma cualitativa los proyectos “Desarrollo Integral de Acahualinca” y “Casas para el Pueblo”, como modelos representativos de vivienda social en Nicaragua, cuyos resultados permiten identificar las carencias y puntos fuertes de los proyectos objeto de estudio, con el fin de retomar los aspectos positivos de los mismos y de evitar repetir aquellos que tengan repercusiones negativas e incidan de forma directa o indirecta en el desarrollo sostenible de las viviendas.In Nicaragua, the housing scarcity is a fact that grows continuously. According to Habitat for humankind (2008), the demand for new housing in Nicaragua overs half a million units, which increases in twenty thousand homes each year, while another half million homes require to be repaired. The efforts that have been done by various organizations and entities involved in the social housing issue in Nicaragua have generated a variety of housing solutions that try adequate to the needs of people, playing an important role toward the quantitative reduction of the housing deficit. However, these solution show deficiencies in terms of quality, specifically regarding the standards that affect the welfare housing and development of human life, design, environmental quality, and construction quality. The absence of criteria and lineaments in Nicaragua that guide housing projects of social interest toward the search of sustainability has resulted in the projection of homes that neither satisfy their inhabitants needs nor satisfy their expectations, social relationships, possibility of coexistence, and the right of being part of a city. This paper defines an own elaboration indicators system that has been adapted to the urban, socioeconomic, and environmental context of Nicaragua in order to assess in a qualitative way the projects “Desarrollo Integral de Acahualinca” and “Casas para el Pueblo” as representative models of social housing in Nicaragua, whose results allow to identify weaknesses and strengths of the projects surveyed, in order to regain the positive aspects of them and to avoid repeating those with negative implications that affect directly or indirectly the sustainable development of housing

Effect of a Crystalline Admixture on the Permeability Properties of Concrete and the Resistance to Corrosion of Embedded Steel

Reinforced concrete structure durability hinges on concrete permeability, which relies on the characteristics of the inner porous network. Harmful ions and gases can accelerate steel corrosion. Permeability-reducing admixtures (PRA), including crystalline admixtures (CA), are commonly used to mitigate this. This study examines a commercial CA’s impact on durability-related aspects in concrete specimens. Two concrete mixtures with matching proportions were prepared: a reference mix and another mix with a commercial crystalline admixture. Several properties were studied, such as compressive strength, density, porosity, electrical resistivity, water absorption capacity, chloride diffusion, air permeability, and corrosion resistance. The studied admixture in concrete yields several positive outcomes such as a slight reduction in mixing water, a potential 6% increase in concrete’s compressive strength and the development of a denser and less permeable structure with 3% lower porosity and water absorption than the reference mix. Electrical resistivity improves by 10%. Unidirectional chloride diffusion tests show no differences. Air permeability decreases by from 36% to 55%, and the water absorption rate diminishes by 23%. The admixture potentially reduces the scatter in corrosion initiation periods for steel reinforcements, delaying corrosion onset by around 60 days, although more extensive experiments are needed for definitive conclusions.This research was funded by the Spanish Agencia Estatal de Investigación (grant code BIA2016-80982-R) and by the European Regional Development Fund (grant code BIA2016-80982-R)

Corrosion Behavior of Steel Reinforcement in Concrete with Recycled Aggregates, Fly Ash and Spent Cracking Catalyst

The main strategy to reduce the environmental impact of the concrete industry is to reuse the waste materials. This research has considered the combination of cement replacement by industrial by-products, and natural coarse aggregate substitution by recycled aggregate. The aim is to evaluate the behavior of concretes with a reduced impact on the environment by replacing a 50% of cement by industrial by-products (15% of spent fluid catalytic cracking catalyst and 35% of fly ash) and a 100% of natural coarse aggregate by recycled aggregate. The concretes prepared according to these considerations have been tested in terms of mechanical strengths and the protection offered against steel reinforcement corrosion under carbonation attack and chloride-contaminated environments. The proposed concrete combinations reduced the mechanical performance of concretes in terms of elastic modulus, compressive strength, and flexural strength. In addition, an increase in open porosity due to the presence of recycled aggregate was observed, which is coherent with the changes observed in mechanical tests. Regarding corrosion tests, no significant differences were observed in the case of the resistance of these types of concretes under a natural chloride attack. In the case of carbonation attack, although all concretes did not stand the highly aggressive conditions, those concretes with cement replacement behaved worse than Portland cement concretes.Authors thank to University of Alicante and Generalitat Valenciana the financial support given to this research through projects GRE11-27 and GV/2013/021

Caracterización de hormigones ecológicos con adiciones puzolánicas y árido reciclado, y su protección frente a la corrosión de armaduras

Ministerio de Educación, Cultura y Deporte. Beca FPU 12/0324

Desempenho do concreto com adições pozolânicas e agregado reciclado

Se evalúan las propiedades mecánicas y de durabilidad de hormigones de bajo impacto ambiental con sustituciones de cemento por subproductos industriales (35% cenizas volantes y 15% catalizador de craqueo catalítico) y de áridos gruesos por áridos reciclados (20% y 100%). Los hormigones estudiados se han sometido a ensayos de caracterización mecánica, porosidad, permeabilidad al aire y nivel de penetración del ion cloruro. Los resultados obtenidos muestran que las propiedades mecánicas se ven reducidas con el incremento en las proporciones de árido reciclado y de los residuos utilizados como sustitución en la matriz cementante, mientras que las propiedades de durabilidad se ven únicamente afectadas por el aumento en el porcentaje de áridos reciclados. Todos los hormigones estudiados son aptos para ser utilizados como hormigón estructural.Mechanical and durability properties of concrete with a reduced environmental impact have been evaluated. This approach consist of replacing 50% of Portland cement by fly ash (35%) and spent catalytic cracking catalyst (15%), and also substituting a 20% and 100% of natural coarse aggregates by recycled aggregates. The performance of the prepared concrete consisted of mechanical tests, porosity, air permeability and chloride penetration. The obtained results show that the mechanical performance are significantly reduced in concretes with recycled aggregates and the pozzolanic binder, but durability-related properties are only affected by the use of recycled aggregates. Nevertheless, all the tested formulations are suitable for their use as structural concretes.As propriedades mecânicas e de durabilidade de concreto com baixo impacto ambiental são avaliadas com substituições de cimento por subprodutos industriais (35% cinzas volantes e 15% catalisador de craqueamento catalítico) e de agregados graúdos por agregados reciclados (20% e 100%). Os concretos estudados foram submetidos a ensaios de caracterização mecânica, porosidade, permeabilidade ao ar e nível de penetração do íon cloreto. Os resultados obtidos mostram que as propriedades mecânicas são reduzidas com o aumento das proporções de agregado reciclado e de resíduos usados como substituição na matriz cimentícia, enquanto as propriedades de durabilidade são afetadas apenas pelo aumento na porcentagem de agregados reciclados. Todos os concretos estudados são adequados para uso como concreto estrutural