The construction industry must meet current environmental requirements, mostly those pertaining to the reduction in construction and demolition waste and the consumption of raw materials. The use of recycled concrete aggregates can be part of the solution, but one question that arises is how many times recyclables can be recycled. This unknown involves other related queries regarding the properties and possible uses of repeated recycled concrete aggregates. This research is derived from the precast concrete industry, where multi-recycling is a pressing need. From good-quality parent concretes, three cycles of recycled concrete aggregates were produced and analysed. The final results are promising due to the good quality of the recycled and multi-recycled concrete aggregates obtained. Not only can they be used in low-level applications (backfilling) as usual, but they can also be used for more demanding purposes, such as graded aggregates, cement-treated road bases and concrete pavements. Their use in structural concrete is feasible, but it will be dependent on the water absorption level and the amount of recycled aggregate substitution. This research proves the viability of multi-recycled concrete aggregates with all of the associated environmental benefits.
The treatment of wastewater from small towns supposes problems of economic efficiency, leading to very high environmental costs in areas with low population density. Constructed wetlands (CW) seems to be the more suitable solution for this kind of situation, but further investigations are needed regarding their efficiency under different climatic conditions. This work presents the results concerning urban wastewater treatment by means of two different constructed wetlands using macrophytes: horizontal subsurface flow (HSSF) and free water surface (FWS). The systems are located in a Mediterranean continental climate area and are fed by a by-pass at the entrance of a wastewater treatment plant. A four-year sampling campaign at the outlet of the CW allowed verifying their relative effectiveness in removing pollutants in the different seasons of the year. BOD5, COD, and TSS were significantly removed (with average reductions of 55%, 60%, and 57%, respectively) by these natural phytodepuration systems, with HSSF being more efficient during plants’ dormancy than FWS, but the concentrations of nutrients indicated that cumulative effects occur in CW with the need of adequate annual maintenance. It was found that the main factors controlling the efficiency of such systems throughout the year are the period of vegetative development, the presence/absence of a solid substrate, and the pollutant load of the wastewater inlet.
In the present study, the recycling of modified bitumen soundproofing membranes, known as automotive type membranes (ATR), was carried out. The ATR sheet waste was incorporated in the mixing stage of the asphalt mastic, which is part of the manufacturing process of new sheets. The selection of the best asphalt mastic formulation was carried out at laboratory scale, where the ATR sheet cutting waste was added to the original asphalt mastic in percentages of 2.5, 5.0, 5.0, 7.5, 10.0 and 15.0 % w/w. The formulations were evaluated for six parameters of interest associated with softening point, rotational viscosity, density, weight per area, thickness and creep. It was determined that the properties of all the formulations studied met the minimum requirements stipulated for the commercialization of the product. The recycling process was carried out on an industrial scale using the formulation with 5% w/w of ATR residues, which presented a viscosity close to that of the original mastic. The results at industrial scale were favorable, since the six parameters of interest were within the ranges established in the regulations. Translated with www.DeepL.com/Translator (free version)
At present, there is no harmonized test standard to determine the contribution of tensioned solid steel braces protected by intumescent paints on fire resistance. For this reason, the adaptation of the Bridge Pavilion built in Zaragoza for the International Exposition (2008) and its adaptation to a new use made it necessary to design a test protocol that allowed determining the time equivalent to Standard Fire Resistance for those metallic structural elements. This paper presents both the methodological design and the results obtained in this specific case. The experimental scheme allowed us to verify that a thickness of 4 mm of intumescent paint guarantees a fire resistance R60, and a thickness of 5 mm guarantees the resistance R90, both cases for loaded braces. The applied protocol allowed us to check the difficulties to apply the paint on elements of reduced dimensions, concluding that the most appropriate solution was application by brush and subsequent sanding to avoid irregularities and excess paint. This information was essential when planning the subsequent application to the real case.
El deterioro ocasionado en el patrimonio histórico a consecuencia de las sales procedentes de deyecciones de palomas debe ser adecuadamente identificado y localizado. La realización de mapas de conductividad superficial en los paramentos, la extracción de sales mediante apósitos de celulosa y su análisis químico, y la posterior evaluación geoquímica constituyen la mejor combinación metodológica disponible para identificar la procedencia de este tipo de sales. A partir de un caso práctico se ha podido concluir que, en las zonas donde son patentes estas concentraciones salinas y sus consecuencias, predominan las sales de KNO3, pero donde los precipitados están en una fase incipiente de acumulación, es posible identificar dicho proceso activo por el predominio de Na+, K+, NO3- y Cl- en las extracciones salinas obtenidas mediante apósitos de celulosa. La correcta identificación del origen de las sales en los paramentos permite diseñar de forma eficiente las actuaciones de limpieza y mantenimiento.
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