Page 214 - New Trends in Eco efficient and Recycled Concrete

184 New Trends in Eco-efficient and Recycled Concrete

SiO 2 Al 2 O 3 CaO, as in the case for systems in which metakaolin or BF slags are
applied (Scientific Research Institute on Binders and Materials Kiev State
Technical University, 1994). The mechanical behaviour of each type of geopolymer
depends on several factors, such as the type of waste or by-product used as a pre-
cursor, the concentration of the alkaline solution, the curing conditions used (either
by temperature or time of application) or the specific surface of the precursors
(Ravikumar et al., 2010). The alkaline activator presents a very important function
since it is designed to activate polymers of the nature of aluminium silicate or cal-
cium silicate. The commonly used alkali activators include sodium silicate, sodium
carbonate and NaOH (Ravikumar et al., 2010).
Different geopolymers have been developed from fly ash, metakaolin, palm oil
fuel ash and rice bark, etc., each applying different curing conditions (Karthik
et al., 2017). In a specific way, coal fly ash, metakaolin and BF slag have been
very effective as precursors for the development of geopolymers because they facil-
itate geopolymerisation processes and provide excellent strength and mechanical
stability in the mixtures obtained (Karthik et al., 2017). In this section the possibil-
ity of applying SSs in geopolymer manufacturing is presented.
The application of SSs in geopolymer formation is complicated because these
waste materials contain heavy metals and an alkali-activated precursor is required
in the process. There are mainly four types of SSs: ground granulated blast furnace
slag (GGBFS), EAFS, LFS and SSSs.
Several studies have been undertaken to assess the application of these slags in
geopolymer production.
1. Application of GGBFS in geopolymer production: Although there have been several stud-
ies, perhaps the most interesting one for the present purpose is that by Saha and
Rajasekaran (2017).
These authors studied the properties of geopolymer pastes by applying GGBFS in the
mixtures. They studied different mixtures applying different slag percentages and with
variable concentrations of the alkaline activator, sodium hidroxide solution. It was demon-
strated that the high content of CaO in the applied slags helped to form a C S H gel
along with the 3D stable silico-aluminate structure through the geopolymeric reaction
very quickly. Besides this, the setting time was reduced considerably as higher doses of
GGBFS were applied; also the compressive strength increased significantly with the
increase in the concentration of the activator.
On the other hand, it was observed that the compressive strength of those formed poly-
mers was improved by increasing the concentration of the Sodium hydroxide solution and
the results were used when applying more than 50% of BF slag point were obtained to
obtain resistances of 78.2 MPa with a solution of sodium hydroxide 16 M. On the other
hand, it was observed that the use of high slag granulated oven with activators present a
few mechanical functions. It is possible to use fly ash and GGBFS to produce geopoly-
mers which has the potential to reduce environmental degradation problems. GGBFS are
used in cement production as mineral additions, but another possibility would be to
include this industrial waste in the production chain of geopolymers.
2. Use of EAFS in geopolymer production: Niklio´ c et al. (2016) studied the modification of
the mechanical and thermal properties of fly ash-based geopolymer by the incorporation
of SSs. It is common to use the fly-based geopolymer as a precursor in the production of