GEOPOLYMER CONCRETE

GEOPOLYMER CONCRETE

General Introduction

Concrete usage around the world is second only to water. For the production of concrete Ordinary Portland Cement (OPC) is a major material for binding purpose. Some environmental issues are there during production of OPC. One ton of cement production approximately liberates 0.80 – 1 ton of carbon dioxide to the environment. In addition, more energy are required to produce the cement next to steel.

Portland cement manufacture can cause environmental impacts at all stages of the process. This includes emissions of air pollution in the form of dust, gases, noise and vibration when operating machinery and during blasting in quarries, consumption of large quantity of fossil fuel during manufacture and release of CO₂ from the raw materials during manufacture.

The CO₂ associated with Portland cement manufacture falls in to three categories:

Source 1: CO₂ emission from decarbonation of lime stone.It is fairly constant, minimum around 0.47kg CO₂ per kg of cement, maximum 0.54kg CO₂ per kg of cement.

Source 2: CO₂ from kiln fuel combustion, it varies with plant efficiency: efficient precalciner         plant 0.24kg CO₂ per kg of cement, low efficiency wet process as high as 0.65kg CO₂ per kg of cement, typical modern practices (e.g. UK)  averaging around 0.30kg CO₂ per kg of cement.

Source 3: CO₂ produced by vehicles in cement plants and distribution. It is almost insignificant at 0.002 – 0.005 CO₂ per kg of cement.

Total CO₂ emission around the world is 0.80kg CO₂ per kg of cement. Electrical energy consumption is of the order of 90 – 150 kWh per ton of cement.

Emission of carbon di oxide causes greenhouse effect and it is consider to an increases of global temperature that may result in climate change. In an article scientist John Hooke, Queensland University, Australia. He told that every day there will be an increases of CO₂ in our earth, this temperature was 4 times bigger than the temperature produced during bomb blast in Hiroshima and Nagasaki at Japan. 90% of global temperature goes to inside the sea.  The amount of greenhouse gas emission due to cement production is estimated to be about 1.35billion tons annually or 7% of total greenhouse gas emission to the environment.

On the other hand, abundant availability of fly ash worldwide creates opportunity to utilize this by product of burning coal, as a substitute for manufacturing of concrete. When used as a partial replacement of OPC, in the presence of water in ambient temperature, the fly ash reacts with calcium hydroxide during hydration process of OPC and form the calcium silicate gel (CSH).

Geo polymer

Geo polymer are material based on pure aluminosilicate materials such as fly ash, granulated blast furnace slag obtained from industrial waste or calcined clays like metakoline, activated with an alkali metal hydroxide and silicate solution. The term “Geo polymer” was proposed by Davidovits(1980)  due to their setting mechanism, a polycondensation process under alkaline conditions, similar to organic polymers.

Geo polymerization is a complex multiphase exothermic process, involving a series of dissolution – reorientation – solidification reaction analogous to those observed in zeolite synthesis. According to T.F.Yen(Year ) geo polymers can be classified in to two major groups: pure inorganic geo polymers and organic containing geo polymers.

Benefits of Geo polymer                                                                                               

The geo polymer does not create a greenhouse gas emission since there is no calcination step in the synthesis, thus avoiding the release of CO₂ and because of this energy efficiency, inorganic polymer have become increasingly attractive. Additionally it is possible to produce these products using recycled materials. In addition these alumino silicate materials possess comparatively higher strength and are much more resistance to chemical attack, e.g. by acids.

                                     

Figure 1 Comparison of Conventional Cement and Geo polymer binder.                                                                                                                    

Fly ash based geo polymer concrete:

The geo polymer concrete can be formed by binding the fine and coarse aggregate with geo polymers (Fly ash and alkaline solution). It can be used in structures instead of OPC concrete. The manufacture of geo polymer concrete is carried out using usual concrete technology methods. 

As in case of OPC concrete, the aggregate occupy about 75 – 80% by mass in geo polymer concrete. The silicon and aluminium in the low calcium fly ash react with alkaline liquid that is combination of sodium or potassium hydroxide and sodium or potassium silicate to form the geo polymer that binds the fine, coarse aggregate and other unreacted materials.