Page 380 - New Trends in Eco efficient and Recycled Concrete
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Leaching issues in recycled aggregate concrete                    335





















           Figure 12.3 Schematic flow of contaminants in the field and extrapolation to a laboratory
           test.

           of real scenarios is extremely expensive, laboratory tests were performed in condi-
           tions that closely mimic the actual situation.
              As previously stated, the most extensively researched material used in the pro-
           duction of RCA is recycled aggregates from CDW. However nowadays, due to the
           efforts of the scientific community, a wide variety of waste materials are suscepti-
           ble to be incorporated in the concrete mixture, such as glass, different ashes (volca-
           nic, coal and biomass bottom ashes), plastic, tyres, foundry sand or iron and steel
           slags.
              In order to perform an environmental risk assessment of these materials, numer-
           ous leaching tests are available, but in general the most commonly used methods
           are percolation tests for granular materials and diffusion tests for monolithic pro-
           ducts. The daily operation of CDW plants includes the environmental evaluation of
           materials. Plant managers predominately use procedures that are easy to perform
           and yield results that are comparable to the actual legal limits imposed.
              The construction industry is putting greater emphasis than ever before on
           increasing recycling and promoting more sustainable waste management practices.
           In keeping with this approach, many sectors of the industry have actively sought to
           encourage the use of recycled materials as an alternative to natural aggregates in
           concrete production.
              Considering this boom in the use of recycled materials, many wastes can be used
           as new raw materials in the manufacture of concrete, for example, recycled arid, fly
           ash and bottom ash, glass waste, steel slag, tyres and plastics, etc.
              In the case of recycling and reusing industrial co-products as recycled aggregate,
           the main aspect is the evaluation of the environmental compatibility of RA as new
           construction material. The convenience of its utilisation is not determined by the
           total content of potential contaminants in the solid material, but by the potential
           leaching behaviour.
              Size and shape are factors that determine the surface area of a particle. The reac-
           tions involved in the dissolution are heterogeneous, in which the reaction rate is
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