Page 71 - New Trends in Eco efficient and Recycled Concrete

46 New Trends in Eco-efficient and Recycled Concrete

acoustic absorption behaviour of recycled concrete, as long as the size distribution
is similar.
The use of BA depends on their physical and chemical properties. The ashes
coming from the rice husk which, among its varied chemical composition, has a
high content of amorphous silica. This mineral is known to be one of the minerals
that intervenes in cementing reactions and, therefore, are susceptible to developing
pozzolanic activity if combined with the appropriate alkaline activator additive
(Behak and Peres, 2008).
This high silicon content provides the ash, mixed with other additives, with good
pozzolanic properties. In Bangladesh, researchers at the University of Dhaka have
examined BA as a possible profitable ingredient in the development of a variety of
building materials, such as bricks, low cost thermal insulators and pozzolanic
cement (Farooque et al., 2009).

2.4 Biomass ash-based geopolymer: clean production,
properties and applications

In recent years BA have been used in the manufacture of geopolymer products
allowing opportunities for their application in construction. In the following subsec-
tions the use of biomass ashes in the production of sustainable concrete, besides the
different applications and benefits achieved, are presented.

2.4.1 Geopolymer concrete. A green concrete

The demand of ordinary Portland cement (OPC) to manufacture conventional con-
crete has been constantly increasing due to the increment of infrastructural activities
in the world. In order to produce OPC, the cement industry demands large amounts
of energy, in addition to high quantities of limestone and clay as natural raw materi-
als, with the consequent environmental impact due to the depletion of raw materi-
als, the economic cost and the emissions to the atmosphere (Suksiripattanapong
et al., 2017). The development of green concrete as an alternative to Portland
cement concrete has the aim of reducing the environmental impact of construction
sector, both increasing the use of industrial waste or by-products and reducing the
negative impacts of cement production industry (Ramujee and PothaRaju, 2017). In
this sense, the use of waste ashes as a precursor instead of the traditional pozzolanic
coal ashes also allows for improving concrete performance (Islam et al., 2017).
Geopolymers are one of the most promising alternative cementitious materials,
which are obtained by mixing several source materials with a high content in silica
and alumina, as FA, ground granulated blast furnace slags (GGBFS) or MK, with a
solution of potassium or sodium hydroxides and soluble silicates, which is strongly
alkaline (Part et al., 2015). In this system, the alumina and silica dissolved into the
solution experiment geopolymerisation by means of thermal curing at temperatures

below 100 C and lower times of curing up to two days to form an amorphous