Page 429 - New Trends in Eco efficient and Recycled Concrete

382 New Trends in Eco-efficient and Recycled Concrete

Figure 13.16 SEM micrographs for MWSI/FA samples: (A) 0/100; (B) 20/80; (C) 40/60;
and (D) 100/0 (Wongsa et al., 2017).

carbonation conditions of the hydrated Portland cement paste also were tested
(Paya ´ et al., 2012). The carbonated powders were activated using alkaline solutions
of 7 and 9 M NaOH and SiO 2 /Na 2 O molar ratios of 1.22 and 1.56. Geopolymer

mortars cured at 20 C for 28 days yielded 10 14 MPa, while curing in a thermal

bath (65 C, 7 days) yielded 14 20 MPa. Fig. 13.17 shows the SEM micrographs
for activated pastes.
Hydrated cement paste was reactivated by calcination in the 700 800 C range

and this reactivated cementitious material (RCB) was blended with OPC, SF and
NaOH (0% 6% by mass) for yielding new binders (Serpell and Lopez, 2013).
RCB showed substantial pozzolanic capacity and high NaOH dosage increased the
early age strength, but diminished in the longer term. High calcining temperature
allowed obtain good long term mechanical behaviour: 32 38 MPa were achieved
for the best contents.
Concrete waste powder (CWP) was blended with FA for obtaining geopolymer
binder activated with NaOH/waterglass (Ahmari et al., 2012). Good mechanical
behaviour (15 35 MPa) was reached for 50:50 CWP/FA blends after 7 days of cur-
ing at room temperature (Fig. 13.18). A mix with 60% from demolished walls
(DW) and 40% waste concrete (WC) was studied by Khater (2012). The mix was
ground and fraction passing a 90 μm sieve was took for geopolymerisation. In some
cases, part of DW powder was replaced by hydrated lime (HL) and part of the WC
by MK. The best behaviour was found for 50:10:20:20 DW/HL/WC/MK system,

reaching 15 MPa for water saturated specimen and more than 25 MPa after 80 C