ENEA

BAAC: autoclaved bio-aerated concrete

Innovative system in the aeration process and in the mix design of the components that make up Bio-Aerated Autoclavated Concrete (BAAC), a bio-cement for construction that is innovative in terms of energy saving and environmental sustainability. The innovation concerns the production process and consists mainly of the technology used to create the aerating agent, and in particular the use of micro-organisms (yeasts), which together with hydrogen peroxide generate the oxygen necessary for the formation of porosity and the reduction of the density of the block, obtaining values of mechanical resistance to compression and thermal conductivity that are fully in line with the values of similar commercial products.

Patent Status

PENDING

Priority Number

102017000101039

Priority Date

08/09/2017

License

ITALY

Market

Thermal insulation and the anti-seismic stability of a building are undoubtedly the qualifying aspects that promote the use of materials with strong thermal insulation power that are light, resistant and durable. AAC cements (aerated autoclaved cements) meet these requirements and therefore their use is expected to increase in new construction as well as in the redevelopment of existing buildings, also in order to meet the obligations of European Union directives. In Italy alone, more than 50% of the heritage is inadequate in terms of energy efficiency and therefore needs to be upgraded in terms of energy performance and seismic resistance according to current regulations. Abroad, the Chinese and Northern European markets are very active, both as users and producers of AAC, so it is possible to hypothesise that if BAAC (Bio-Aerated Autoclaved Concrete) becomes established as an alternative product, its diffusion on the global market could be considered:

2019: $17,7 B
2027: $28,3 B (+7,2% / year)

Problem

EU Directive 31/2010 requires that all new buildings constructed in the European Union must be ‘energy neutral’. The technological innovation introduced by the BAAC can contribute substantially to the technological requirements needed to meet these obligations. In Italy alone, more than 50 per cent of the building stock was built in the forty years between the 1950s and the 1990s and is inadequate in terms of energy efficiency, and must therefore be upgraded in terms of energy performance and seismic resistance according to current regulations. Thermal insulation and seismic stability of the building are undoubtedly the qualifying aspects that promote the use of materials, such as AAC cements, with strong thermal insulation power, light, resistant and durable.The AAC concretes now on the market have an unfavourable economic impact on building construction costs compared to other construction solutions and this currently limits their use. Furthermore, aluminium metal, depending on the conditions of storage and use, has flammability and explosibility risk classes varying from St1 (weak) to St3 (maximum) and therefore requires the adoption of specific prevention regulations against accidental incidents.

Current Technology Limits

Conventional aerated autoclaved concrete (AAC) is produced from a mixture of various components: Portland cement, lime, water, gypsum and sand, called grout. To these reagents, metallic aluminium powder is added, the reaction of which with calcium hydroxide results in the formation of hydrogen, which causes the final product to decrease in density. The final curing process takes place within autoclaves operating at temperatures between 160°C and 200°C, which will determine the final consolidation and increase in mechanical properties. Conventional AAC cements are mainly marketed with densities varying between 300 and 800 kg/m3 depending on the type of application they are intended for: load-bearing and infill masonry, thermal and acoustic insulation coats, fire barriers and in anti-seismic applications. The production process of commercial AAC concretes presents some critical aspects both in terms of the increased safety requirements of the working environment (fire and explosion risks due to the handling of aluminium metal), and the energy required in the grout rising process (temperature of 60°C). Furthermore, the AAC concretes now on the market have an unfavourable economic impact on building construction costs compared to other construction solutions, and this currently limits their use.

Killer Application

The technology makes it possible to produce a series of innovative autoclaved bio-cements (BAAC) with different target densities (300, 500, and 800 Kg/m3 ) endowed with mechanical resistance, thermal insulation, acoustic insulation, fire resistance, thermal inertia, transpiring capacity, antiseptic effect, and reduced environmental impact in terms of energy saving and recycling of materials to be used as innovative construction elements for the production of bio-building products. With a view to the circular economy and ‘green economy’, new mix designs based on components derived from by-products of other industrial processes have also been studied with the aim of improving their economic and environmental sustainability. In addition, possible solutions have been studied to give the material antiseptic properties that eliminate or reduce the development of pathogenic microorganisms to improve the healthiness of living and working environments.

Our Technology and Solutions

One of the peculiarities offered by the innovation of the BAAC concrete preparation process is the fact that the aeration principle is independent of the materials used in the product mix design, a feature that allows, combined with other features of the proposed technology, to increase the types of applications and reduce production costs, in particular through:

the simplification of the mix design by reducing the materials used in commercial AACs, in particular gypsum and lime;
the reduction of energy requirements in the aeration phase of the grout (at room temperature, whereas the conventional process requires a temperature of 60°C);
simplification of occupational safety requirements: the absence of aluminium powder in the grout aeration process leads to a reduction in the safety risks associated with handling this material, which has a certain degree of inherent fire hazard in the presence of air or the generation of flammable gases if in contact with oxidising compounds;
the possibility of using recycled materials derived from other industrial processes such as fly ash from thermal plants or waste from the food industry in the mix design of BAAC;
the improved mechanical performance, combined with the inherent lightness of the material, would favour its use as a building material in seismic areas.

Advantages

The proposed technology is focused on reducing the production costs of currently marketed BAAC blocks and increasing their energy and sustainability performance.

The BAAC aerating system is applicable to a wide range of mix designs as an autonomous reaction system, independent of the composite material in which it acts
Simplified mix design.

No lime
No gypsum
No aluminium powder

3. Indirect environmental benefit and direct economic benefit, in terms of lower raw material costs and simplification of the production cycle compared to conventional.

4. Lower consumption of Al and the energy required for its production process with a direct impact on the reduction of greenhouse gases released into the atmosphere. Al production is increasingly concentrated in certain areas of the globe (e.g. Asia) and therefore its supply is potentially exposed to geopolitical assessments.

Roadmap

The PoC BIOCEM project has made it possible to confirm, even on a pre-industrial scale and with much larger volumes of component materials, the goodness of the formulated recipe and the compliance of the products with the technical regulations in force regarding aerated autoclaved concretes. The growth of the cement mix takes place in rapid times, completely similar to those of the commercial product, in which aluminium paste is used as the aerating agent.

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