Page 77 - New Trends in Eco efficient and Recycled Concrete

52 New Trends in Eco-efficient and Recycled Concrete

concrete which presents a high open voids ratio will have a greater sound absorp-
tion coefficient than less-porous concrete (Kim et al., 2012). Nevertheless, no study
has been found in the literature regarding to the use of biomass ash in geopolymers
with the purpose of enhancing its acoustic properties. The development and applica-
tion of geopolymers manufactured with biomass ashes as insulated materials can
contribute to the environmental impact on buildings reducing the energy demand
both during the construction and use.

2.5 Concluding remarks

Renewable resources such as biomass are used for heating and electricity genera-
tion, etc., and generate large amounts of ashes. Due to their pozzolanic or filler
capacity, it is possible to determine these specific conclusions, related to the recy-
cling of BA in cement-based materials:

Biomass for energy can include a wide range of materials such as natural biomass, resid-
ual biomass and energy crops.
Currently, the performance and technology of systems to produce energy with biomass
are highly advanced and have the potential to be used for many applications due to differ-
ent energy conversion technologies: transport, heat and electricity production, etc. As a
result, a reduction of pollution emissions such as CO, HC and NO and protecting the envi-
ronment would be achieved.
The use of ashes from biomass combustion in cement-based materials are strongly condi-
tioned by their physico-mechanical properties.
The rapidly increasing amount of biomass ash generated implies the necessity of recy-

cling, with their application in cement-based materials being a highly appropriate use.
Two types of biomass ash are obtained, BBA and BFA. BBA is the portion of non-

combustible residue found in the furnace or incinerator and it looks like artificial sand.
BFA is the portion of ash that escapes through the chimney and is retained to prevent
it from being released into the atmosphere, and it presents a dusty appearance such as
coal FA.
BBA presents high contents in CaO (17% 30%) and in some cases in SiO 2 (until 72%),
which could allow for its application in the manufacture of concrete and mortar, although
it is recommended to apply some type of processing to reduce the organic matter content.
Moreover, partial substitutions of cementitious materials by biomass ashes are frequently
required due to their excess content in K 2 O and MgO.
BFA can be effective in the development of the strength of recycled concrete, and its
behaviour depends mainly on the level of SiO 2 in the ashes, thus, it can be applied in
substituting up to 50% of cement. On the other hand, substitutions of less than 20% of
sand by BBA do not produce significant decreases in the mechanical properties of
concrete.
In general, the use of biomass ashes in the manufacture of alternative cement-
based materials is positive, however, it is necessary to continue carrying out spe-
cific studies regarding to the application of BBA and BFA, and legal adaptations
should be made.