AlSiment

Concrete is the most produced material on Earth and is essential to the continued development of human civilization. The amazing strength and properties of concrete are thanks to cement, and its reactions with water. However, cement production has a gigantic carbon footprint. The CO₂ emissions are caused both by the unavoidable release of CO₂ from the calcination of limestone, as well as the large amount of fossil fuels that are combusted to power this extremely energy intensive process. In total, the production of cement accounts for 7-8% of anthropogenic greenhouse gas emissions.

The present project demonstrates the viability of using geopolymers (AlSiment) as a binding material for the production of cement-free concrete. The chemical composition of the geopolymer is in some ways similar to cement, but it is richer in Al- and Si-oxides. The AlSiment is mixed with water, as well as activators such as strong alkali and alkali silicate solutions. The result is a binder material that can be mixed with the same aggregate materials that are used for conventional concrete.

The material used for the production of the geopolymer can be waste products from other industries such as steel and aluminium production, but can also be from natural sources such as volcanic ash and geothermal silica, which are especially abundant in Iceland. During the project, a mix design for paving stones using the same aggregates that are currently used by Steypustöðin was developed and mechanically tested. The results proved that cement-free paving stones are viable.

Part of the project revolved around the development of a new technology that can help decrease the carbon emissions from the construction industry by sequestrating CO₂ using the AlSiment technology. During the three months of the project many series of samples were developed in order to find out what were the main variables influencing the compressive strength of carbon sequestered AlSiment composites as well as if they would be able to meet the requirements of a typical Portland cement specifications (35 MPa at 28 days). Our main observations were that the concentration of the alkaline materials used in the fabrication of the binder as well as the concentration of CO₂ were the main contributors to the final compressive strength, workability and physical properties of the samples. The sequestration range studied was from 3.7 kg to 26 kg of CO₂ per cubic meter of composite, developing compressive strengths of 80 MPa and 60 MPa respectively. We concluded that carbon sequestration using the AlSiment technology could contribute significantly to the reduction of carbon emissions from the construction industry by providing an alternative to ordinary Portland cement that is able to perform at the same standards and even outperforming it in some instances.