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Leaching issues in recycled aggregate concrete                    337


              On the other hand, the production of stainless steel is currently one of the boom-
           ing sectors of the manufacturing industry due to a large increase in the use of this
           material; Large amounts of waste are generated from these factories (Das et al.,
           2007); for every three tonnes of stainless steel produced, approximately one tonne
           of slag waste is generated.
              The stainless-steel slag is generated into powder. Powders are the most important
           by-product of stainless-steel manufacturing and refining operations.
              The use of this material may be conditioned by the content of Cr VI, according
           to the existing literature; the application of this slag in the production of cement for
           the manufacture of concrete is possible without exceeding the limits required by
           law (Rosales et al., 2017).

           12.2.2 Leaching behaviour of fine recycled materials

           In 2005, Sani et al. verified the possibility of using fine waste of CDW as substi-
           tutes for natural aggregate in the production of concrete. The results obtained
           showed that this substitution modifies the leaching behaviour. In general, the use of
           recycled aggregate as a total substitute for the natural aggregate causes an increase
           in total porosity, mainly due to the ceramic content, and this property influences the
           leaching behaviour of these recycled materials.
              Taking into account the effect of the matrix of concrete manufactured with fine
           recycled aggregate, the relationship that characterises the paths of fluid diffusion
           and conduction through porous media is 40% higher than that obtained in the pres-
           ence of natural aggregate, which confirms the greater leachability of its porous
           structure.
              On the other hand, the environmental concern related to the disposal of discarded
           cathode ray tube (CRT) glass has been increasing (Poon, 2008). Due to the high
           PbO content (approximately 20% 25%) it is classified as a hazardous waste, and
           its Pb content if leached into the environment can represent a threat to human
           health (Lee et al., 2004). Therefore, it is important to find a solution for this type of
           waste.
              CRT glass has a high silica content, making it a possible replacement for river
           sand in concrete. Romero et al. (2013) used CRT glass as a replacement for fine
           aggregates in concrete. They studied the physical, mechanical and environmental
           behaviour. The results indicated good mechanical behaviour with respect to conven-
           tional concrete. Environmental tests showed that for different percentages, the Pb
           content of the concrete could be below the drinking water limit. Walczak et al.
           (2015) observed that the use of CRT glass increased the compression and flexion
           strength of concrete mortar (16% and 14%, respectively).
              Sua-iam and Makul (2013) used CRT glass in self-compacting concrete fabrica-
           tion and Ling and Poon (2012) used acid-treated CRT glass to replace the fine
           aggregate in concrete blocks.
              In all studies, the most conflicting element is Pb. To limit the possible leaching
           of lead, it is recommended that the inclusion of CRT glass in concrete blocks is
           below 25%.
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