Page 438 - New Trends in Eco efficient and Recycled Concrete
P. 438

390                               New Trends in Eco-efficient and Recycled Concrete


         mortars, the strength was superior, being 14 18 MPa for plain BFA systems and
         36 39 MPa for 60% BFA/40% MK system. Biomass ashes from combustion of
         rice husk and eucalyptus bark yielded rice husk-bark ash (RHBA) ashes. Some
         reports described the characteristics of these ashes and geopolymers behaviour.
         Songpiriyakij et al. (2010) studied FA/RHBA systems in which 30% in the RHBA
         was eucalyptus bark ash. The best behaviour in terms of compressive strength was
         40% FA/60% RHBA, which had more than 60 MPa after 90 days of curing at room
         temperature. Nazari et al. (2012, 2011) also studied this type of mixes.
           POFA was alkali activated without any additional mineral admixture. Salih et al.
         (2014, 2015) studied POFA activated systems and showed that 20 MPa in compres-
         sion was reached after 7 days and more than 35 MPa after 180 days. Salami et al.
         (2017) demonstrated that POFA-based geopolymers had better durability in MgSO 4
         environment than in Na 2 SO 4 . Also, Salami et al. (2016) showed that the use of
         naphthalene-based superplasticizer did not improved properties of geopolymer in
         both fresh and hardened states. POFA also was tested by blending with additional
         mineral admixtures. POFA/FA blends (Ariffin et al., 2011, 2013; Ranjbar and
         Kuenzel, 2017) were studied. Ariffin et al. (2013) demonstrated that 70:30 blend
         had the best performance in workability and yielded 25 MPa in compression. This
         geopolymer showed a better behaviour than OPC system when exposed to sulphuric
         acid attack (Ariffin et al., 2013). Several studies were carried out with alternative
         binary, ternary and quaternary POFA systems: MK (Ismail et al., 2013; Tippayasam
         et al., 2010), blast furnace slag (Yusuf et al., 2014), slag and FA (Huseien et al.,
         2016), RHA and slag (Karim et al., 2013, 2017) and calcium hydroxide, aluminium
         hydroxide and SF (Mijarsh et al., 2015).
           Castaldelli et al. (2013, 2014) studied the binary blends of blast furnace slag
         (BFS) and SCBA. SCBA contained a large proportion of organic matter (32.20%
         LOI) and CaO (16.05%) It was blended with BFS and it was activated by means
         5 mol/kg of sodium cation, a SiO 2 /Na 2 O molar ratio of 1.46 and a water/precursor
         ratio of 0.45. BFS/SCBA systems (85/15, 75/25, 60/40) yielded more than 50 MPa

         at 28 days and more than 65 MPa at 270 days for mortars cured at 20 C. Pereira
         et al. (2015) studied a SCBA sample with low organic content (LOI 4.4%). The
         BFS/SCBA blend with 75/25 mass ratio showed higher strength than plain BFS
         NaOH activated. Same for KOH activated samples and sodium silicate/NaOH acti-
         vated samples. Thus, a good synergic behaviour was found for this binary blended
         precursor. Fig. 13.23 shows the strength ratio for several curing times in the 3 90
         days range. Deepika et al. (2017) prepared BFS alkali activated mortars replacing
         0%, 10% and 20% by SCBA. They found a decreasing of strength with the replace-
         ment of BFS by SCBA. Spent CG, the beverage waste derived from drinking cof-
         fee, were mixed with SCBA and SCBA/BFS and activated by means NaOH
         (Arulrajah et al., 2017). Synthetised geopolymers were low grade compressive
         strength although they meet the minimum specified requirements for subgrade
         pavement materials in various countries (e.g., Thailand and Malaysia).
           Binary SCBA/FA blends were activated by means KOH/K 2 SiO 3 activating solu-
         tions (Castaldelli et al., 2016). The partial replacement of FA by original SCBA

         (with high organic matter fraction) did not set. Calcination of SCBA at 650 C was
   433   434   435   436   437   438   439   440   441   442   443