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336                               New Trends in Eco-efficient and Recycled Concrete


         dependent on the interfacial area. It is for this reason that leaching kinetics are
         affected by the particle size of the material; a smaller particle size produces rapid
         dissolution since the finer particles have larger specific surfaces. According to parti-
         cle size, the recycled materials can be classified into powder, fine and coarse.



         12.2.1 Leaching behaviour of powdered recycled materials

         Several powder waste and by-products applied in sustainable construction applica-
         tions, have to be studied from a leaching point of view. Various research projects
         have been undertaken on the leaching behaviour of steel waste, powdered glass
         waste, fly ash and granulated blast-furnace slag, etc.
           For example, electric arc furnace slag (EAFD), which is a residual by-product of
         steel plants in production, and typically contains between 12 and 20 kg of EAFD
         produced per tonne of steel that is recycled. The EAFD is formed of around 50%
         iron oxide and approximately 21% zinc oxide, and smaller proportions of magne-
         sium, chromium, nickel, silicon and oxide of calcium, etc. Due to the leachability
         of heavy metals, for example nickel, chromium and zinc, this material is classified
         as hazardous material by the EPA (Maslehuddin et al., 2011).
           In 1998, Xu and Tian studied the physical properties and chemical composition
         of EAFD for possible use in cements. It was concluded that cement made with
         EAFD complies with the Chinese specifications for cement. In addition, the use of
         EAFD for the manufacture of cement is more economical than the use of iron ore
         (Xu and Tian, 1998).
           Numerous studies evaluated the use of EAFD in concrete using ordinary
         Portland cement (OPC) (Al-Zaid et al., 1997; Xu and Tian, 1998; Sikalidis and
         Mitrakas, 2006).
           The concentrations of metals in the leachate of EAFD are mainly Fe, Zn and Pb
         and, depending on the regulations used to catalogue the waste, can be considered as
         non-hazardous and even inert within a cementing matrix.
           Jony et al. (2011) studied the use of glass powder (more than 90% lower
         0.075 mm) as a filler in asphalt concrete compared to the use of traditional lime-
         stone powder and OPC in hot mixed asphalt concrete.
           During the past few decades, the use of recycled glass in concrete and OPC has
         gained increasing interest mainly due to the high disposal costs and environmental
         concerns. Recycled glass has an amorphous structure and is formed by silica and
         calcium, in theory, it is pozzolanic or even of a cementitious nature when it is
         finely ground. Many studies have focused on the use of glass in cement waste
         (Meyer et al., 1996; Meyer and Baxter, 1998; Polley et al., 1998; Baˇ zant et al.,
         2000; Byars et al., 2004; Topcu and Canbaz, 2004; Shao et al., 2000; Dhir et al.,
                                  ¸
         2004; Shayan and Xu, 2004; Shayan and Xu, 2006).
           From an environmental point of view, glass powder has a high content of silica,
         aluminium and calcium. For this reason, glass powder can react quickly and dis-
         solves easily in the cement matrix. This reaction causes concentrations of non-
         hazardous leachates in adherence with environmental requirements.
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