Geopolymer Concrete

Geopolymer Concrete The Concrete of Next Decade

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Introduction • The name Geopolymer was formed by a French Professor Davidovits in 1978. • It is broad range of materials characterized by networks of inorganic molecules. • Geopolymer Cement is a binder whereas Geopolymer concrete is the composite material resulting from the addition of cement to stone aggregates. • Geopolymer cement is a binding system that hardens at room temperature, like regular Portland cement.

• Geopolymer cement is an innovative material and a real alternative to conventional Portland cement for use in transportation infrastructure, construction and offshore applications. • Geopolymer depend on thermally activated natural materials like Meta kaolinite or industrial byproducts like fly ash or slag to provide a source of silicon (Si) and aluminum (Al). • Silicon and Aluminum is dissolved in an alkaline activating solution and subsequently polymerizes into molecular chains and become the binder.

• The ultimate structure of the geopolymer depends largely on the ratio of Si to Al (Si:Al), with the materials most often considered typically having an Si:Al between 2 and 3.5. • The reaction of Fly Ash with an aqueous solution containing Sodium Hydroxide and Sodium Silicate in their mass ratio, results in a material with three dimensional polymeric chain and ring structure consisting of Si-O-Al-O bonds

The schematic formation of geopolymer material can be shown as described by Equations (A) and (B)

• Water is not involved in the chemical reaction of Geopolymer concrete and preventing from hydration reactions that occur in Portland cement when mixed with water. • Unlike OPC/PPC, geopolymer do not form calciumsilicate-hydrates (CSHs) and calcium hydroxide for matrix formation and strength, but utilize the polycondensation of silica and alumina precursors and a high alkali content to attain structural strength.

• This difference has a significant impact on the mechanical and chemical properties of the resulting geopolymer concrete, and also renders it more resistant to heat, water ingress, alkali – aggregate reactivity, and other types of chemical attack. • The temperature during curing is very important, and depending upon the source materials and activating solution, heat often must be applied to facilitate polymerization, although some systems have been developed that are designed to be cured at room temperature

General • Production of one ton of cement emits approximately one ton of carbon dioxide to the atmosphere and also consumes significant amount of natural resources. • At present more than 2.6B tones of cement is required every year and this quantity is likely to increase by 25% within the span of 10 years. • About 860M tones of coal ash is produced every year worldwide.

Production of GPC • Thermal Industry produces a waste coal ash which is simply dumped on the earth, occupies larges areas. • Waste(e.g. Red Mud) from the Chemical Industries is discharged into the ground which contaminates ground water. • Waste Coal Ash from Thermal Industry + Waste from Chemical Refineries = Geo polymer concrete.

Category of Geopolymer Cement • Slag-based Geopolymer cement • Rock-based Geopolymer cement • Fly ash-based Geopolymer cement – type 1: Alkali-activated fly ash Geopolymer – type 2: Slag/fly ash-based Geopolymer cement

• Ferro-Sialate-based Geopolymer cement

Constituents of Geopolymer Concrete Coal Ash- rich in Silica and Aluminium Sodium Hydroxide or Potassium Hydroxide Sodium Silicate or Potassium Silicate

Properties of Geopolymer Cement • • • • •

Shrinkage during setting: < 0.05% Compressive strength: > 90 MPa at 28 days Flexural strength: 10–15 MPa at 28 days Young’s Modulus: > 2 Gpa Freeze-thaw: mass loss < 0.1, strength loss