**2. Materials and methods**

### **2.1 Materials**

*Geopolymers and Other Geosynthetics*

sodium silicate or potassium silicate.

a.100% natural local resource

b.Very low carbon footprint

c.Good for indoor climate

d.Low life cycle cost

e.Detoxifying effect

f. Moisture control

g.Fire resistance

h.Noise control

i. Affordable

j. Zero waste

changing weather conditions.

these binders.

this case is a polymerization process, he coined the term 'Geopolymer' to represent

There are two main constituents of geopolymers, namely the source materials and the alkaline liquids. The source materials for geopolymers should be rich in silicon (Si) and aluminum (Al). These could be natural minerals such as kaolinite and natural clays. By-product materials such as fly ash, ground granulated blast furnace slag (GGBS), silica fume, slag, rice-husk ash, and red mud can also be used as source materials. The alkaline liquids are from soluble alkali metals that are usually sodium or potassium based. The alkaline liquid used in geopolymerization is a combination of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and

Geopolymers are used to manufacture construction products like, geopolymer bricks [4], tiles and concrete. In geopolymer bricks and in geopolymer concretes, geopolymers do not form C-S-H gel (calcium-silicate-hydrates) unlike the Ordinary Portland Cements (OPC), for matrix formation and strength in a geopolymer concrete, but it utilizes the polycondensation of silica and alumina and high alkali content. Earth is the oldest building material used by man for millennia. All over the world there are thousands of earth buildings which are over 500 years old. All these structures are still in sound condition and are well occupied. Even if earth is an ancient building material [1], the earth building tradition has been kept blooming in many countries and the technology is constantly being adapted to the requirements of modern civilization. In terms of sustainability, un-stabilized earth outdoes any other building material, including timber, owing to its low carbon footprint, its durability and its unlimited recyclability. The advantages of earth buildings are as follows [1]:

The earth as a construction material has the following disadvantages:

c.Low resistance to abrasion requiring frequent repairs and maintenance.

a.Low resistance to water penetration resulting in structural failure due to crumbling.

b.High shrinkage and swelling resulting in structural cracks when exposed to

**40**

A good brick earth, which is available as a natural resource, usually consist of 50–60% of silica, 20–30% of alumina, 5% of lime and 5–6% of oxide of iron [7].

However, for non-fired green bricks which can be made by using industrial wastes, materials to be used includes iron ore tailings (IOT), slag sand, fly ash and ground granulated blast furnace slag (GGBS), which can replace good brick earth of similar constituents [4]. Geopolymer is synthesized by using fly ash, GGBS, sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and water. These bricks can be manufactured without firing, but using geopolymer as binder.

#### *2.1.1 Iron ore tailings*

Iron ore tailings (IOT) [6, 8] are the waste materials obtained during the process of separating the valuable fraction of iron from the iron ore. The different steps involved in this process are crushing, screening, grinding, washing, jigging, cyclizing etc. The Iron ore tailing usually contains about 20–30% of iron. Further extraction of iron is too expensive. The composition of the ore and the process of mineral extraction adopted have a direct influence over the composition of the tailings. The iron ore tailings are obtained from Bellary, Karnataka, India, where steel companies are located (Please refer to **Table 1** for the chemical composition and **Table 2** for the physical properties of the iron ore tailings used).

Similar iron ore tailings are available in other parts of India and world too which have different percentage of iron in the tailings.
