What's wrong with cement which is a highly used material in the construction industry. cement has good binding properties than other binding materials like if we compare with lime. so let's go to know two major regions which insist us to find out other alternatives.
CO2 Emission :
About
1.35 billion tons made per year Ordinary Portland cement (OPC) is typically
used in the production of concrete as a binder. In
the production of OPC carbon dioxide (CO2) is also produced. OPC is responsible for approximately 7% of
the total CO2 emissions released into the atmosphere per year worldwide. so due
to many environmental concerns, the need to develop a new, sustainable
alternative for OPC is needed.
Workability :
Another
problem faced by OPC concrete is related to its durability issues. OPC has a
relatively high permeability, thus allowing water and other harmful media to
penetrate concrete, causing corrosion and carbonation problems.
So what would be Alternative?
In this blog, I am gonna explain about Alkali Activated Binder
Why: Alkali
Activated binders have shown to be a potential solution to OPC concrete
concerns. Alkali – activated binders are seen to be a more sustainable choice
due to its use of waste by-products, such as slag from the production of iron
or fly ash from the burning of coal.
HOW TO GET alkali-activated binder
Davidovits, when he used to work in the industry, proposed that an alkaline liquid that can react with the silicon (Si ) and
aluminum (Al) in a source material of geological origin or in by-product
material can be used to produce binders.
Exp. Fly
ash, when combined with an alkaline activator such as sodium hydroxide (NaOH)
or sodium silicate has been seen to produce not only a strong concrete binder
but also more durable, in comparison to OPC when exposed to harsh environments
Source
material + Alkaline liquid
Alkali
activated cement constitutes of two main compounds namely source materials and
alkaline liquids.
What could be the source material?
Generally, we take those waste materials having aluminum content more to minimize the CO2
emissions.
&
Depending on aluminum and calcium contents we can classify GEO-POLYMER, SOIL CEMENT, INORGANIC-POLYMER CALCIUM SULFO-ALUMINATE, and ORDINARY PORTLAND CEMENT
So, we are gonna use waste material having a low content of calcium and high content of aluminum. for example: fly
ash, granulated blast furnace slag, rice husk ash, silica fume, red mud, municipal
solid waste, metakaolin, or other alumina-rich materials
What could be Alkaline liquid?
The
alkaline liquids are from soluble alkali metals which are sodium or potassium-based.
Sodium hydroxide (NaOH) or Potassium Hydroxide (KOH) and Sodium silicate
or Potassium
silicate are most widely used alkaline liquid.
Alkali-activated
cement (AAC), also broadly termed as geopolymers (mainly for those systems
with low content of calcium).
the
application of inorganic polymers as construction materials is unfavorable due
to the high price of commercially available raw materials. For example, the
price of metakaolin has risen during the last years due to its high demand.
Therefore, in recent years, there is a trend to investigate alternative
prime materials to be revalorized for the development of alkali-activated binders.
In recent literature, other raw materials than metakaolin, mainly waste
products from different industrial origins, are increasingly studied to be
processed to synthesis an alkali-activated binder or geopolymer binder, and very
promising results have been found, but also indicate that further research is
needed. the synthesis of geopolymers out of waste ceramics which were activated
by alkali hydroxides and/or sodium/potassium silicate solutions. compressive
strength measured after 28 days was 71.1 MPa
and favorable thermodynamically stable properties were observed. The results
approve the approach of recycling ceramic wastes for the production of value-added
alkali-activated composites.
The greatest effect on
strength characteristics is made by soluble sodium silicates. The
alkali-activated cement concretes made using sodium silicates have high
compressive strength reaching 120–140 MPa.
Producing
binders using low basic calcium or calcium-free aluminosilicates (clays) and
solutions containing alkali metals. the binders called "soil cement"
and the corresponding concretes "soil silicates".
Composition of Waste material or source material
In the below table, we have taken compositions of fly ash and ground granulated blast-furnace slag
GRADE OF ALKALI-ACTIVATED FLY ASH CONCRETE AND RATIO
CORRESPONDING COMPRESSIVE STRENGHT
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