Properties of Geopolymer Concrete

The properties and durability of geopolymer concrete made using flyash have been extensively explored by various universities in Western Australia, as well as around the world.

Published scientific findings have repeatedly concluded that the performance of concrete made from geopolymer cement (GPC) is comparable to that of concrete made from Ordinary Portland cement (OPC).

The most important characteristics that affect the properties of the GPC and resulting geopolymer concrete, are the type, amount and reactivity of the amorphous alumino-silicate pozzolanic particles in materials such as flyash.

The flyash is activated with alkaline reagents such as caustic soda or lye, one of the common names for sodium hydroxide (NaOH), combined with soluble sodium or potassium silicate chemicals, to cause an ambient temperature polymerisation reaction resulting in the formation of cementitious material.

Water-to-geopolymer solids ratio

Work done by Rangan & Hardjito devised the Water-to-Geopolymer Solids Ratio (W/GPS) for Class F flyash.

It was found that as this ratio increases, the workability of the mixture also increased as it contained more water; but this results in a decrease in the compressive strength of the geopolymer concrete.

With a fixed W/GPS ratio, Hassan found that the slump value is dependent on the ratio of sodium silicate (Na2SiO3) to sodium hydroxide (NaOH), as well as the concentration of NaOH used.

Optimal workability was achieved when the W/GPS ratio was more than 0.22, in addition to the use of a low water absorption grade of aggregates. It was found that workability can be improved by using a naphthalene-based superplasticizer additive.

Silicate-to-flyash ratio

Work done by van Riessen found that the compressive strength of geopolymer concrete increases as the ratio of Na2SiO3/flyash is increased, but also decreases as the binder/sand ratio approaches more than 0.5.

Applying the findings of this study, he was successful in creating GPC concrete which achieved a compressive strength of 100 MPa.

It was also found that a 20–30% increase in the compressive strength was achieved by first sieving the flyash and only using the smallest particles.

Shrinkage and heat of hydration

GPC concrete has a much lower shrinkage and heat of hydration when compared to OPC concrete.

Additionally, the chemistry of GPC concrete can provide a better resistance to both heat and to chloride attack, making it very suitable for concrete products designed for fire rings, or saline or marine environments, for example.

The Colliecrete project will address the findings of such prior research and use it to build a specific understanding and optimisation of geopolymer cements and geopolymer concretes manufactured from Collie flyashes and other local industrial waste materials.

Ultimately, the project aims to create geopolymer products with unique Intellectual Property (IP) that meet all the required specifications for targeted specific applications.