GREEN CAST-Demonstration of innovative lightweight construction components made of recycled ashes for sustainable buildings

The GREEN CAST project has been funded by the European Commission within the CIP Eco-Innovation-First Application and market replication projects framework. It started in September 2011 and is being carried out in collaboration with CETMA and Mostostal.

The GREEN CAST project consists on the fabrication of lightweight construction elements by using fly ash obtained as by-products in combustion processes in thermal plants. These fly ash are activated with an alkaline solution and a foaming agent, added to the mixture, generates the cellular structure of the material. Its characteristics are similar to those for conventional autoclaved aerated concrete, but in the total absence of Portland cement, therefore the CO2 footprint is minimized and the use of natural resources reduced. Also, the high pressures and temperatures that conventional autoclaved aerated concrete requires are minimized, making this process more efficient from the energetic point of view.

GREEN CAST has been thought to be an alternative for cement-based insulating construction elements that already exist in the construction sector, but offering a very interesting alternative from the economic and environmental perspectives, maintaining the required mechanical, thermal and acoustic properties.

The main outcome is the development of an innovative construction product with good thermal, mechanical and acoustic properties, economically competitive and a minimized environmental footprint. The production process has been optimized and the GREEN CAST pre-casts are being produced at relatively low temperature with no need of high pressure. The mechanical, acoustic and thermal properties of the obtained product are similar to those for the commercial, well settled products.

A design of a pilot plant is being design as well as a life cycle analysis that will be very useful to compare the environmental impact of GREEN CAST with the commercial products. GREEN CAST elements are going to be used to build two first application huts that will be exposed to different climatic conditions. A series of dissemination activities have been successfully carried out to show GREEN CAST and make it attractive to promoters and constructors. A preliminary market analysis has been performed and will be extended in order to target potential consumers.

The two first applications have been built in Madrid and Warsaw and identical mockups made of AAC blocks have been built in order to compare GREEN CAST to a commercial material. The insulation behavior of the materials are being measured and compared

The Material

The GREEN CAST material has been ideated to be an alternative to traditional autoclaved aerated concrete (AAC).

The AAC is a material composed of cement, sand, calcium oxide and a foaming agent that gives the cellular structure to the material during the fabrication process. The AAC can be manufactured with different foaming agent concentrations in order to offer a variety of densities, typically between 300 and 1000 kg/m3, whereas the conventional concrete possesses a density around 2500 kg/m3.

Moreover, the cellular structure confers to the AAC good thermal and acoustic insulation behavior and a lightweight at the same time.

The GREEN CAST material has been developed in form of blocks (62.5x25x7cm) and compared to its main commercial competitor. In sight of the results it is possible to observe that the GREEN CAST material possesses similar properties to those of a commercial AAC, but with much lower energy consumption.

Density (kg/m3)Flexural strength (MPa)Compression strength (MPa)Thermal Conductivity (W/mK)Ra Insulation index
GREEN CAST6600.53.140.1436
Curing time (h)Curing temperature (°C)Curing pressure (atm)


Fly ash is a byproduct generated in the combustion of fossil fuels in power plants. In Europe, 2 million tons are generated yearly. Industrial fly ashes are commonly landfilled but this presents disadvantages: the presence of chemical species such as heavy metals and the large amount of this material causes serious environmental issues.

Fly ashes are mainly composed of aluminosilicates that can be activated by an alkaline solution generating reactive species capable of generating bonds with each other and yield a reaction denominated geopolymerization.

Fly ashes are commonly added into cementitious matrixes, substituting partially Portland cement, as an additive or in order to improve durability and chemical resistance.

In the production of 1 ton of Portland cement, approximately 900 kg of CO2 are generated and released to the atmosphere. In 2010, 3.3 billion tons of cement were consumed worldwide, therefore, the replacement of traditional cement is a paramount challenge.


As it has been evidenced, the GREEN CAST product offers a series of advantages with respect to its commercial competitors.

EnvironmentalGREEN CAST is a material made exclusively with recycled fly ash, without traditional Portland cement.
GREEN CAST helps to improve the environment and manage the large amount of fly ash that goes to landfill.
PerfomanceGREEN CAST is a lightweight cellular material, alternative to AAC.
It possesses good thermal and acoustic insulation properties, and at the same time keeping similar mechanical properties to those of its commercial homologous.
Cost savingThe production of GREEN CAST is carried out at lower temperature and pressure than the conventional AAC, which leads to a reduction of Energy consumption.
The main material used in the production of GREEN CAST is a recycled byproduct, much cheaper than the materials used in traditional AAC.
OpportunityGREEN CAST represents a great opportunity for AAC manufacturers to produce and sell an alternative product with a low environmental impact, good properties, reduced associated costs and easy to install.