Is recycled concrete better than gravel?

Cómo preparar el hormigón reciclado

La generación de residuos sólidos de hormigón hidráulico, también considerados residuos, se está convirtiendo en un problema medioambiental. El material de construcción que se fabrica principalmente es el cemento Portland, pero uno de los principales problemas es su alta temperatura de fabricación que genera contaminantes. El uso de agregados molidos que provienen de la demolición del concreto hidráulico se utiliza para generar concreto hidráulico reciclado, un material que podría disminuir los costos, disminuir la contaminación y abaratar la construcción. Sin embargo, la elaboración de hormigones reciclados se enfrenta a la búsqueda de diseños óptimos para conseguir las mayores prestaciones mecánicas bajo requerimientos estáticos y dinámicos. Este trabajo revisa los avances internacionales en este campo.

Lo anterior pensando en hacer mezclas asfálticas con emulsiones aniónicas o catiónicas, donde es de capital importancia saber si habrá afinidad. También se ha elaborado concreto reciclado con residuos de neumáticos como en los pavimentos asfálticos (Kardos et al, 2015) La intensidad de la carga de la superficie del agregado, en combinación con la intensidad de la carga del agente emulsivo, puede influir marcadamente en la velocidad de rotura, en particular en el caso de emulsiones catiónicas. Los iones de calcio y de magnesio presentes en la superficie del agregado pueden reaccionar con -y desestabilizar a- ciertos emulsivos aniónicos, acelerando la rotura de la emulsión (Carrasco, 2004). Este problema de la afinidad eléctrica superficial no ocurre en los casos de concretos hidráulicos reciclados con matrices cerámicas.

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Recycled concrete with rubble

Used massively since the Roman era in buildings of the most diverse scales, it is almost impossible to think of a building that does not have at least one concrete element. In fact, it is the most widely used building material in the world, due to its versatility, strength, ease of handling, affordable value, aesthetics, among other factors. At the same time, however, its manufacture is a major polluter of the atmosphere, mainly because the cement industry emits about 8% of all global carbon dioxide (CO2) emissions.

Beyond its intensive production, being such a rigid, heavy material composed of cement, water, stone, and sand, is it possible to continue using concrete sustainably after its demolition, eliminating its waste and landfill overload?

The answer is yes. Although it is not that simple, it is possible to use concrete waste to make new structural parts, with good resistance to loads, and for noble uses. First of all, it is important to understand that the intense extraction of sand and gravel -medium and large aggregates of concrete, respectively- has a great environmental impact, although they are generally exploited locally. Although cement is the material that releases the most carbon dioxide during its production, seeking to conserve natural resources by reducing the need for gravel and sand mining is already a major environmental gain, especially if we think about the amount of concrete produced daily in the world.

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Disadvantages of recycled concrete

The quality of the recycled aggregate influences the quality of the concrete, with the modulus of elasticity, shrinkage and creep being the properties that are most affected, the higher the strength of the recycled concrete. For this reason, it is desirable to limit the maximum allowable strength of recycled concrete. The results obtained indicate that the loss of mechanical capacity of recycled concrete up to 50 N/mm2 is lower, especially if percentages of recycled aggregate not exceeding 20% are used. Recycled aggregates should therefore not be used in the manufacture of high-strength concrete.

Recycled concrete thesis

The key to achieve this recycling of materials such as gravel and sand lies in an adequate final disposal of the waste, i.e., a hauling and collection (from the truck) that avoids the mixing of the materials.

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It is a priority that the rubble or concrete residues are not mixed with other types of soils, thus reducing the undesirable content. Linked to this, it is advisable to separate the masonry and concrete rubble throughout the demolition process, thus avoiding the need for further or more complex treatment of the waste.

The gravel obtained from a recycling process is classified according to the nature of its original waste, thus there are three types: gravel from concrete, ceramic gravel and mixed gravel (a mixture of waste of different nature).

It is worth emphasizing that all the material resulting from a recycling process, in this case gravel, must be processed in an authorized plant specialized in the treatment of demolition and construction waste.