Environmentally compatible construction with light-weight concrete

Ecology, environmental protection, environmental compatibility and holistic balancing are only a few of the buzzwords which have become indispensable in construction.

Ecological construction means building in an environmentally conscious or environmentally compatible manner in order to live environmentally friendly. Environmentally compatible construction means aligning building products and building processes such that our natural living space is preserved and the health of the person is not impacted. Environmental compatibility and health compatibility of construction are currently at the forefront. The light-weight concrete industry has signed on to this necessity regarding material and energy consumption as well as contaminant emission. When selecting construction products, the previously often one-sided assessment of the direct compatibility of substances must be replaced by a holistic approach.

All building materials, both natural and raw materials for industrially produced building materials, are taken from natural resources. Before removal it must be determined, which function the material to be mined has in the ecosystem and whether the purpose of its use justifies the removal. As the assessment has to be made both regionally and broadly, general rules cannot be established. The fact alone that a material grows back does not justify its preferred use. Building material production and processing must support frugal use of raw materials, through:

Thanks to appropriate raw material preparation of natural light-weight aggregates and the use of industrially manufactured ones in light-weight concrete production, resources are spared. Manufacturing errors are directly recycled and added to the production process. The energy consumption can be evaluated like the material consumption on the one hand in direct relation to the building material, its mining, use and recovery, on the other hand however e.g. also with regard to its insulation capacity, energy-storage capacity and its other suitability for energy-savings arrangements. The so-called energy content of a building product results from the values of the individual components of its constituents. The drying and hardening of the light-weight concrete products occurs without use of energy. Building products, the manufacture and use of which are connected with low external energy demand, should be preferred.

The technical performance and the price of a building material are no longer the only factors in today's assessment of building materials. The ecological evaluation of the building materials is included in the selection criteria by the building owners and decision-makers. The ecological balances available from the past, however, did not allow a comparison between them due to the different boundary conditions. Therefore the building material manufacturing and processing industries decided in 1994, in a first step to jointly work out a guideline for creating ecological balances in companies within the stone and earth industry.

The Institute for Plastic Testing and Plastic Studies (IKB) and the Institute for Materials in Construction (IWB) of the University of Stuttgart thus initiated examinations as part of the research project “Holistic Balancing of Building Materials and Buildings”, in which 50 companies and associations in the building industry from the areas stone and earth, insulation materials and thermal insulation bonding systems, roof, window and technical facade, heating and building services, including the Technical Union of the pumice and light-weight concrete industry, participated. The overall objective of this project was to protect the environment in connection with maintaining or improving the quality of life. In the project the impacts associated with the manufacture of light-weight concrete building materials on the environment were captured among others and a database created, which was also set up according to the same methodology and under comparable conditions for other building materials.

The research project and this brochure reflect that the light-weight concrete industry has been successful for years, and will be in the future, in combining economy and ecology with one another in a reasonable way. The light-weight concrete industry is aware of its responsibility towards the environment and has been acting accordingly for years.

In the last 25 years the ecology has moved increasingly into the centre of the social and political interest - with regard to construction measures as well. With a view towards the increasing influences on the environment it was recognised that prudent management is needed. The implementation is closely tied to emissions into the environment and the reasonable handling of resources. To be able to make a statement regarding the environmental impact of a building, an analysis of the entire life cycle of a building material or building product is necessary. Starting with the raw material mining and processing via the use and maintenance up to the disposal or recovery, all impacts on the environment such as emissions into the air and water, waste, energy and raw material consumption must be considered. A suitable instrument for this is “Holistic Balancing”. Based on technical and economic requirements the environmentally relevant impacts of products, systems or services must be analysed over the entire life cycle and evaluated.

The special requirements for environmentally compatible construction were specified in the past through legal regulations as well as national and international standards based on the latest insights from the environment, hygiene and health areas. At the same time numerous manufacturers of building materials and building materials have come together for years in the AUB, Working Association Environmentally Compatible Building Products e.V. Goal and task of the association was and is the support and development of environmentally and health-compatible building products as well as the appropriate environmentally-friendly and health compatible orientation of the production processes.

Via the Federal Association Light-Weight Concrete e.V. manufacturers and sales companies of light-weight concrete products have been engaged in the working association since the founding of the AUB, have acquired the certificate of the AUB, and let their products be regularly assessed for environmental compatibility. Prerequisite for the assessment of the building products has been the description by the respective manufacturing or delivery company with detailed information on the form of trade of the building product, the processing and handling conditions in the various production phases from the material extraction up to the disposal, on basic materials, precursors, additives, residue and waste materials, on the ingredients in the use state and on possible emissions.

On the basis of these requirements the characteristics of building materials are made transparent not only in the use state but in the entire life cycle of a building product. Construction products that meet the requirements for hygiene, health and environmental protection in all phases of their life cycle have so far received an AUB certificate and were allowed to carry the certification mark. A construction product manufacturer thus discloses to the public all the properties of a construction product. For the user this brief “ecological balance” from the working association opened a glance behind the curtain that created trust and the opportunity for a factual and holistic assessment of environmental compatibility and lack of health concerns from building products.

The AUB, today the IBU, Institut für Bauen und Umwelt e. V., continues to endeavour to develop comprehensible criteria within the framework of technically prepared assessment guidelines, on the basis of which the environmental and health compatibility of construction products can be assessed. IBU views the latest insights and assigns them to a continuously developing description and assessment for building products. These are based on the Construction Products Act, national and international regulations, standards, etc. according to which construction products may not be placed on the market if the following effects may arise in the state of use of a construction product:

Building on these assessment guidelines, PCRs (product category rules) were created by corresponding expert product forums as binding guidelines for the determination of specific requirements for all product categories among the building products. Building products are materials, products, components, building kits or building systems which are manufactured for permanent installation in a building or building structure. Buildings (e.g. prefabricated houses) can be building products themselves. Product categories are products with comparable functional or declared units.

The PCRs orient themselves on the principles of the international standards ISO 14020; ISO 14040; ISO 14025 and ISO 21930, with inter alia the following being determined:

The PCRs of the AUB/IBU include:

The required information thus relates to the physical and chemical properties of the building product when used properly. The harmlessness of critical properties or with regard to compliance with guideline values shall be documented by appropriate verifications and measurement reports from recognised bodies.

The environmental declaration consists of a short version and a long version, which are checked and confirmed by the expert committee.

Product definition
The listed products are non-reinforced building blocks as well as reinforced components of different formats and sizes made out of porous aggregate or structurally dense light-weight concrete. The light-weight concrete is manufactured from natural or industrially produced stone grains (aggregates), water and hydraulic binding agents (cement).

Application
Unreinforced building blocks for bricked up, monolithic, load-bearing and non-load-bearing walls. Reinforced components for roof, ceiling and wall panels as well as other assembly components such as lintels, roller shutter boxes.
According to the regulations direct contact with groundwater is not possible. Only data for unreinforced masonry blocks are given below.

Product standards / Approvals
The applicable European or national standard or the general approval by the building authority or comparable national regulation must be listed.

Quality Assurance
For quality assurance (internal and third party monitoring according to test standards and approvals) a product-specific statement must be made. QMS, UMS must be listed.

Geometric data
Dimensions according to: DIN EN 771-3, DIN V 20000-403, DIN 18148, DIN 18162,
DIN V 18151-100, DIN V 15152-100, DIN V 18153-100

Building physics data
Gross density classes: 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.80, 0.90, 1.00, 1.20, 1.40, 1.60, 1.80, 2.00, 2.20

Strengths
Compressive stress classes: 2, 4, 6, 8, 10, 12, 20, 28, 36, 48
Tensile strength [N/mm2]: V2: βBZ = 0.13 * βD; otherwise (V, Vbl, Hbl): βBZ = 0.08 * βD
Bending tensile strength [N/mm2]: V2: βBZ = 0.45 * βD; otherwise (V, Vbl, Hbl): βBZ = 0.25 * βD
E-module [N/mm²]: all blocks: E = 750 * βD
Deformation parameters acc. to DIN 1053-1
Thermal conductivity according to DIN 4108-4, approvals in [W/mK]: ≥ 0.07
Water steam-diffusion resistance number μ according to DIN 4108-4: 5 - 10
Equilibrium moisture content at 23 °C, 80 % air humidity: ≤ 4.5 M.-%

Sound insulation
Listing of the assessed noise insulation dimension, according to the classification of the block gross density in the mass curve of DIN 4109. Possibly specification of the sound absorption degree.

Fire protection
The corresponding fire behaviour must be listed, e.g. fire protection class A1, fire resistant walls F 30-A to F 180-A according to DIN 4102 T4, fire walls according to DIN 4102 T4.

Base materials / precursors

• Specification of all base materials in mass-% (average use volumes) separated by aggregates (pumice, lava, expanded clay, expanded shale, expanded glass, blast furnace slag and respective sands), cement and water.
• Aids / Additives
• Declaration of aids and additives e.g. mixed oil, mould oil, colour

Substance explanation
Explanation of precursors and additives, e. g.:
Pumice: The pumice used is a natural raw material of volcanic origin, which is mined in an open mine pit.
Cement: acc. to DIN EN 196; cement serves as a binding agent and is mainly produced out of limestone marl or a mix of limestone and clay. The natural raw materials are burned and subsequently ground.
Mould oil: Mould oil is used as separating means on the base boards between form and light-weight concrete. PAK-free mineral oils are used while adding long-chained additives for increasing viscosity. This prevents run-off in the mould and allows frugal use.

Raw material mining and material origin
Our earth needed 4.6 billion years to develop the way it is today. A small volcano, e.g. a cinder cone like the Wingertsberg on Lake Laach or the Plaidter Hummerich, is created in about 1 to 3 months. During the eruption of Lake Laach about 13,000 years ago about 5 km³ magma were released in a few days. That is about twice as much as from all 300 cinder cones of the East and West Eifel together. In this extreme short period of time powerful masses of ash and pumice were thrown up to 40 km high into the atmosphere and blown as far as Sweden and Italy. In today’s Neuwied basin approx. 16 km³ pumice was deposited on an area of 200 km² via natural falling deposits. They cover this region with a layer several metres thick. People already started using these ground treasures during the Bronze age. The pumice and light-weight concrete industry looks back at a long tradition in the area of raw material support. The mining of pumice outcroppings for manufacturing blocks has been going on since the middle of the 19th century. Despite its concentration on one location (Neuwieder Becken) and the associated disadvantages in terms of transport routes, the resulting lightweight concrete industry has maintained a nationwide market share of approx. 12% for the most important product group, masonry blocks. With around 1000 employees within this industry a broadly faceted product program made of natural pumice is manufactured today.
In order to guarantee controlled raw material extraction, the pumice law and the associated ordinances were enacted as early as 1949. For almost 60 years, this law has been ensuring the balance between economy and ecology by

• only approving suitable areas for mining,
• having planned in 1949 already the levying of security deposits to ensure recultivation,
• having the mining applications checked by a qualified committee and
• thus ensuring the subsequent use and an immediate return of the areas to the owners.

Practice has confirmed that this law was well thought-out back then already. It was possible to make the large-scale lowering of an entire landscape environmentally friendly. As a rule only experts recognise today where the pumice has already been mined. Via new design and recultivation a landscape can be created that has no disadvantages versus the original shape for the viewer in its aesthetic value and its shape. The gravel-shaped pumice is mined in open pit mines. After the mining via excavators or wheel loaders the pumice is driven to the manufacturing plant by truck. There it can be processed immediately depending on the quality requirement, or cleaned of foreign components by sieving, wind winnowing or washing. For mining and the procurement of pumice, 14 % of the total energy are needed. All additional base materials (except for small amounts of industrially manufactured aggregates) stem from factories in a region with a maximum 200 kilometres distance from the plant.

Availability of the raw materials
Mineral building products like light-weight concrete consist mostly of mineral raw materials. There is no significant scarceness of resources.

Product manufacturing with pumice as the example

Cement (DIN EN 196) is added as a binding agent to the natural lightweight aggregate pumice. Additionally, aggregates for light-weight concrete can be added (see base materials). At the light-weight concrete plant the aggregates are stored depending on the type of aggregate, bulk density and grain size in several silos or temporarily stored at open-air sites. The binding agent is also stored in silos. The dosed aggregates are withdrawn from the silos and premixed dry with the binding agent (8 - 12 % of the total mixture). Then the mixture is mixed with water into a plastic malleable concrete. This mixture enters the filling box of the stone forming machine, which feeds the filling car. Stone moulds made of steel, which are filled from above by the filling car, stand on a support board. Depending on the requirements, the stone moulds contain cores for slots or chambers. Then the blocks are compressed using load and vibration by imbalance motors and freed from the mould. The now unshelled blocks are transported on the support boards into a dry high-bay warehouse. During drying, without use of energy, the light-weight concrete blocks harden and after 24 to 36 hours reach a strength that allows the blocks to be mechanically palletised, bound and piled. The individual block packages are packaged with a shrink cover and thereby protected from the effects of weather. For at least 28 days, the packages, turned and packaged ready for processing, are stored in a storage area for complete curing until they are delivered to the construction site.

Material demand
The recipes used are adjusted to the respective raw material properties and building physics requirements and vary within the area listed under “base materials”.

• Health protection during manufacturing
• Representation of measures for health protection in the manufacturing process that extends beyond national regulations (production country).
• Dust: Dust extraction system for cement silos, paving or asphalting of the storage locations or watering

A fine dust contamination of the fabrication hall is not expected as the fine dust contents of the product are clearly below the permitted limit of 6 mg/m³ air.

Environmental protection during manufacturing
Representation of measures for environmental protection in the manufacturing process that extends beyond national or local regulations:

• Declaration of direct emissions in air, water and ground: The production process occurs free of waste water.
• Noise: Special measures can be listed. Due to noise protection measures the measurement values are 15 % below the limit values.
• Energy: The primary energy requirement for the production of lightweight concrete blocks is very low compared to other wall-building materials, as no energy is required for firing processes or drying during production.

Processing recommendations
The processing of light-weight concrete blocks is done manually, and for components with a mass over 25 kg lifting gear is required. Dividing components is done with masonry saws or by hand using hard metal saws. Quickly operating tools such as angle grinders must only be used while operating in a water bath, due to their dust generation.The connection of the lightweight concrete components with each other as well as with other standardised building materials is carried out with normal and lightweight mortar according to DIN 1053-1 and with thin-bed mortar or as dry masonry according to approval. The light-weight concrete components can be plastered, layered or covered with paint. Cladding with small parts or the attachment of facing shells in accordance with DIN 1053 is also possible.

Work and Environmental Protection
During the processing of the light-weight concrete building products no special measures need to be taken for protecting the environment.
When selecting constructively necessary additional products, attention must be paid that these do not negatively impact the described properties of the environmental compatibility of the listed building products.

Residue material and packaging
The recovery of the residue materials must be declared, e.g. handling the residues, sorting, use, disposal. The packaging used must be declared by type and composition.

Packaging, pallets and light-weight concrete remains that accumulate at the construction site must be collected separately. INTERSEROH takes on the disposal of polyethylene shrink covers and sacks of mortar and sends them to recycling. The returnable wood pallets are taken back by the manufacturer or the building material business (returnable palettes for refund in the deposit system) and returned to the production process.

Light-weight concrete residue can also be taken back by the manufacturing factories and recycled, used as raw material or disposed of in landfills of class I. For possible redemption the economic efficiency should be considered depending on the distance between the construction site and the manufacturing plant.

Ingredients
As described under the product manufacturing section, light-weight concrete consists mainly of natural aggregates (natural pumice as pit or wash pumice, lava, sand, grit) or industrially manufactured aggregates (expanded clay, expanded glass, expanded slate or other expanded granules). Plasticisers, colour additives and highly hydraulic lime can be additives for the light-weight concrete blocks. Cement as a binding agent and water are parts of light-weight concrete blocks. The raw materials are moist from the soil depending on the storage or wet due to the effects of weather so water consumption during production is relatively low. The natural and industrially manufactured raw materials do not contain additional chemicals and are therefore emission-free.

Interactions – environment / health
Indication of the interactions between product, environment and health and of possible levels or emissions of pollutants.

• Light-weight concrete emits no hazardous substances such as VOC.
• The natural ionising radiation of the light-weight concrete products is extremely low and of no concern with respect to health (see radioactivity).

Resistance
Notes regarding application experiences, possibly recommended measures for avoiding building damage

Use condition
Light-weight concrete changes after leaving the plant according to the deformation parameters pursuant to DIN 1053-1: 1996-11. When used as intended, it has unlimited stability.

Fire
Information on the fire behaviour
In case of fire no toxic gases or steam can occur. The listed products comply according to DIN 4102 with the requirements of the building material class A1, “non-combustible”. Fire resistance classes from F 30-A to F 180-A are reached by the block types.

High water
Specification of the behaviour in case of water effects
With water effects (e.g. high water) light-weight concrete reacts neutrally. No substances that could be hazardous to water are washed out. (cf. leaching behaviour).

Post-utilisation phase
Buildings made of light-weight concrete are generally built without additional thermal insulation. They can therefore be removed in a simple manner. In the event of demolition, the lightweight concrete blocks do not have to be treated as hazardous waste. However, care must be taken to ensure that the dismantling is carried out as unmixed as possible.

Reuse and subsequent use
Light-weight concrete lasts longer than the useful life of the building built from it. After the removal of such buildings the materials can therefore be prepared, classified, assessed (environmental compatibility, building material parameters, uniformity) and used again.
Type-pure light-weight concrete residues can be taken back by light-weight concrete manufacturers and reused or used subsequently. This has been practiced for breakage during production for decades already. This material is used as aggregate or stone grains in production.

Building rubble and production rejects should be prepared mixed, so uniform characteristics of the light-weight concrete blocks from recycling material are achieved. The recycling material should comply with the natural requirements of the material standards of the raw material to be replaced. Recycling material made of light-weight concrete is used for road and path construction.
Disposal

The ability to deposit light-weight concrete in landfills acc. to class I pursuant to the TA Residential Waste is guaranteed. The waste key according to the waste recycling index must be listed.

The following diagram shows the entire “life cycle” of a product from raw material extraction via use to removal and the associated recycling. In all building phases the possible stresses must be reduced to a minimum. That is during extraction of base materials for the building products, during their manufacture and during the building process itself. Later at the finished building in all phases of use, but also in case of danger, e.g. during a fire. Finally, during the removal and the then required disposal.

This is called “holistic balancing”, which considers material, energy and contaminants at all times. The material cycle of light-weight concrete products encompasses the three phases production, use and removal, which are subject to constant monitoring.

Production includes: natural raw material, environmentally friendly extraction, close-to-nature recultivation, standard conforming binding agent, pure water, environmentally friendly manufacture and low primary energy consumption.

The limits of the system for a product, which provides the desired function or specification, must be defined.
Emissions

Substances occurring in nature have different compatibilities for living beings like humans, animals and plants. These range from poisons, substances that endanger health and disturb well-being, to substances that are extremely well-tolerated and essential to life, and promote our well-being. Tolerable living conditions can be impacted by different influences:

• Hazards from gases, dusts, steams and liquids,
• Stresses from noise, vibrations, impact, electric and magnetic fields as well as radiation,
• damaging effects from changes of the landscape, soil, water, air, climate and light,
• unfavourable building design.

The public discussion focuses on pollutants and emissions in relation to their direct compatibility with humans. According to today's state of knowledge, all influences which have a direct or indirect effect on the habitat through breathing, skin contact, mouth contact (including oral ingestion), sensory perception and radiation must be controlled. Here, ecologically oriented examinations must above all assess the stresses on the living space. Base material extraction, manufacture, processing, use and waste from the building product can result in contaminant stresses for the living space, which can jeopardise health indirectly via air, water and soil. These indirect hazards are particularly critical. Contaminants or emissions are mainly to be traced to:

• natural contaminations of the substances from which the building product is manufactured,
• the manufacturing process itself (flue gas emissions, waste heat, waste water etc.),
• substance changes and residue accumulation during manufacturing, processing and handling,
• the addition of substances which are used as aids during manufacture, processing and handling,
• manufacturing processes, processing and handling procedures that haven’t been totally completed,
• handling of building products (dust development during sawing, grinding etc.),
• substances that are used for preservation and for care.

The above-mentioned emissions do not apply to lightweight concrete products or apply only to a negligible extent.

Light-weight concrete masonry blocks
Before block production comes the extraction of raw materials and possibly the industrial preparation of porous light-weight additives. Aggregates and raw materials are mined close to the plant and fed to manufacturing. The significance of the transports is therefore relatively low. In the plant there are mainly processes for mixing, logistics and moulding. Emissions from diesel and heating oil combustion are the only relevant emissions in this context that are emitted directly at the plant. In addition to the porous aggregates, primary products (cement, PE film, raw material additives, etc.) are mainly used, so that most of the environmental impact is caused in the upstream processes and energy supply. Due to the moisture in the raw material itself the water demand is low, so there is no waste water.

The exact production process is described under “Product manufacturing with pumice as the example”.

Upkeep, care and repairs are part of the use phase. The professional product forum specifies the aspects, which must be considered during the use phase, for solidly created apartment buildings 80 to 100 years.

The protection of residents is primarily concerned with avoiding possible emissions during the service life of a building, but also during certain manufacturing processes and in the event of fire. Light-weight concrete products are free of contaminants and do not emit.

A major part of environmental stresses results from energy consumption during the use phase of the building. Energy saving construction therefore considers not only optimal thermal insulation of all exterior components of the house and other building physics requirements, but also the interdependencies between topography, orientation, vegetation and regional climate of a location. Heat-insulating lightweight concrete masonry meets the requirements for thermal insulation even without additional insulation.

The priority task for the future is, from an ecological and economic point of view, the reuse of the recovered masonry. Through environmentally compatible reuse of recycling materials the building material costs are lowered in the form of raw material and energy savings. At the same time the valuable landfill space is spared and dumping costs are avoided. The most important prerequisite for future use of masonry construction residues is, however, that they do not negatively impact the environment or people during later use. According to current knowledge, this is the case with products made of lightweight concrete, i.e. the recyclability of unmixed building materials made of lightweight concrete generally poses no problems. The light concrete industry has already ensured 100% recycling within the plant production process.

In the evaluation, indicators are to be stated as aggregation values of the life cycle inventory and the impact assessment as a minimum rate of the life cycle assessment to be declared. This includes the input of material flows (primary energy from non-renewable resources or from renewable sources, secondary fuels, non-renewable material resources, water use and land use), the output of material flows (overburden and processing residues, commercial and hazardous waste) and ultimately an impact assessment (e.g. global warming potential, acidification potential, etc.). Optionally statements regarding human and ecological toxicity potential can be made.

Due to the environmentally friendly raw material extraction, the almost energy free manufacture including drying and hardening as well as relatively short freight pathways light-weight concrete building materials are only affected to a very low degree by negative influences.

Building material analyses must be carried out with a view to the later use of the building. If components (e.g. exterior walls) are considered, their later use in the building must be clearly specified. For example, two exterior wall constructions can be compared to one another if they fulfil the same requirements regarding heat protection, statics etc. (see the examples on the side). The exterior walls can be analysed with regard to their parts. Comparisons of production or comparisons of production and use phase must be meaningful to show optimisation approaches.

The production of lightweight concrete masonry, e.g. from natural pumice, has the lowest primary energy consumption of all compared to other masonry industries. It is 805 MJ/m³. This applies to monolithic masonry as well as to slim constructions with a thermal insulation bonding system. The lightweight concrete spectrum provides suitable blocks and elements for many applications.
In view of the Energy Savings Ordinance it must be ensured that exterior walls are combined with good thermal insulation properties, good windows and environmentally friendly, energy efficient heating systems, as the environmental impact depends to a high degree on the quality of the entire building. From an ecological point of view, the walls must meet the requirements (ecological balance of manufacture, good U-value and stability) in order to be combined with windows, heating systems etc. in a sensible way. Walls made of light-weight concrete can fulfil these requirements within the examined framework. The results allow architects and designers to assess the ecological aspects more objectively, comparable to the economic and technical ones. They are thus called upon to incorporate environmental protection into their planning.

Our earth's interior consists of a liquid core surrounded by a thick earth crust. The earth's crust contains uranium and thorium as well as a whole range of other chemical substances. These substances are radioactive, which means they can transform into other substances and thereby emit radiation. Through the use of mineral raw materials for manufacturing building materials the natural radioactive substances contained in these materials or released from them can lead to an additional radiation exposure of the residents of houses.
Basically today we distinguish between artificial radiation exposure (x-ray diagnostics and nuclear medicine examinations, radiation from nuclear power plants and from malfunctions such as radiation expositions from atomic tests) and natural radiation exposure (cosmic radiation, terrestrial environmental radiation, natural radionuclides in the ground, intake of radionuclides through food, water and inhalation of air). Another area is the radiation exposure changed by humans due to the use of building materials.

Due to their concentration of naturally occurring radionuclides, various building materials can lead to an increase in natural radiation exposure in buildings. All mineral base substances, so also the building materials manufactured from them, contain small quantities of radioactive substances, mostly radium, thorium and potassium isotope.

The radium, thorium and potassium content can be measured and the specific radiation activity is listed in becquerel per kg. The average for light-weight concrete blocks from today’s production in Germany is for radium226 = 50 Bq/kg, thorium232 = 40 Bq/kg and potassium40 = 700 Bq/kg. Comparisons of the concentration values in lightweight concrete building materials with other building materials show that even bricks with pumice aggregate may by no means be regarded as building materials with increased activity compared with other comparable building materials. The assessment of the radiation exposure of building materials with regard to their concentration of natural radioactive substances, which is still practised, is no longer justifiable due to many test results. However, the inhalation of the short-lived radioactive by-products of radon is regarded as essential.

The radioactive inert gas radon222 is non-combustible, colourless, odourless and tasteless, and can dissolve in water and spreads through stones and dirt. Radon can leave the stone matrix to a certain percentage and reach the atmosphere if it finds an open pore system for this. This so-called emanation ability is only possible for pores connected to each other that are open to the outside air. A part of the radon atoms then reaches the boundary surface to the free atmosphere through diffusion in the pore system and is released into the air (exhalation).

It is not so much the radon gas itself that is harmful to humans, but the radioactive secondary products that result from the further transformation of radon. Polonium, lead and bismuth, all heavy metals, attach to dust particles and aerosols and can lead through inhalation to a selective radiation of the bronchial epithelium.

Radon enters residential houses through 4 pathways: through the air, from building materials, via the drinking water and mostly from the ground, in this case particularly through cracks in the masonry and the foundation slab, via cable and pipe penetrations, through light shafts and waste water pipes as well as exhausts. Light-weight concrete building materials are only rarely the cause of high concentrations of radon in interior rooms because the aggregates, in particular pumice, are stone grains made of an amorphous glass, in which the air pores are embedded in the so-called glass melt. As an average radon222 exhalation rate for light-weight concrete products, a value of 0.50 mBq m²-2s-1 should be specified.

In a current examination (Sept. 2007) Professor Dr. Gert Keller, radioactivity measurement office of the University of Saarland, Homburg, provides the following statement: “The present examinations and assessments show that the natural radioactivity of light-weight concrete blocks from a radiological point of view allow unrestricted use of the building material. Light-weight concrete blocks do not contribute to a relative increase in radon concentration in rooms, and their contribution to the inhalation dose is insignificantly low compared to the share in radon from the ground.”

The methodology for impact estimation of the toxicity potentials, i.e. to estimate a possible influence e.g. of a process on humans and to describe the damage impact, is still partially in the development phase. The toxicity of a substance depends on different parameters, where the distribution of the contaminants always occurs into the distribution paths atmosphere, water or ground.

Light-weight concrete blocks consist of firmly bound ingredients. Pumice is chemically neutral. The proportion of elutriable solids lies at approx. 3 - 8 weight% and the proportion of water-soluble salts lies under 0.1 weight%. Due to the complete waterproof binding of the ingredients, emissions of solutions or emulsions are not possible. Hazards for water, air and ground cannot occur.
In accordance with the IBU product declarations, the lightweight concrete industry has had investigations of leaching behaviour carried out by the state-approved Neuwied Materials Testing and Research Institute with regard to various chemical characteristic values on solids and eluate on lightweight concrete blocks. The examination of the eluate was done among others with regard to compliance with the insignificance threshold values according to “LAWA, Derivation of Insignificance Threshold Values for Groundwater”.

Typically for the determination of metal content in the eluate in environmental analysis atom absorption spectroscopy or atom emission spectroscopy with visual detection are used as methods. As a rule the natural background contamination of the environment with such substances (e.g. metals) lies above the verification limits of these visual verification methods by a factor of 10 to 100.

The abovementioned procedures are therefore sufficient as a rule for assessing the environmental relevance. To be able to compare the contents of the chemical parameters determined on the eluate with the threshold values specified in LAWA, however, procedures are required which implement detection limits that are significantly below this natural background load. This can be done, for example, by measuring using argon plasma coupled with a mass-specific detector. Such methods, however, are usually used more in research (isotope determination) than in environmental analysis, since for the usual environmental analysis methods with detection limits that are sometimes significantly higher than the minority-thresholds mentioned in LAWA are sufficient.

The following results show a small selection of materials, their actual content and the extremely low LAWA de minimis thresholds that lightweight concrete fell below overall. The test report can be requested from the federal association.

The product variety of the lightweight concrete industry is shown opposite. In addition to most large components made of structurally dense light-weight concrete this industry manufactures mostly porous aggregate light-weight concrete into masonry or components for structural engineering. The focus here is on porous, industrially produced lightweight aggregates such as natural pumice.

Pumice grains themselves consist of approx. 85 % air and 15 % mass. The individual pumice grains are mixed with cement lime. This creates the so-called aggregate porosity, which creates additional air-filled hollow spaces in the light-weight concrete. Through targeted moulding (chambers and slots) in combination with the porosity of the pumice grains and the aggregate porosity a highly thermally insulating masonry building material is achieved. Here λR-values up to 0.07 W/mK are reached, which then, in combination with different masonry thicknesses, result in U-values up to 0.18 W/m²K. Here it can be seen that the monolithic wall is able today and in the future to guarantee top thermal insulation properties that are possible without adding additional insulating materials to the wall structure. These favourable thermal insulation characteristics stand out not only in lightweight concrete products for masonry, but are also achieved in wall elements, roof panels (as hollow core slabs) and the solid roof of lightweight concrete. At the same time, prefabricated elements made of lightweight concrete have the property of balancing the temperature in the room air so that a pleasant natural climate prevails in the rooms. The entire product palette of the light-weight concrete industry reflects that today’s shell construction can be manufactured from one cast. With their diversity, the light-weight concrete products allow a broad spectrum, which reflects the requirements for high thermal protection as well as a high degree of noise protection and high load-bearing capacities and sufficient fire protection. A carefully selected supplementary range allows fast, economical construction of the building at the construction site. This also reflects the high share of masonry building materials in apartment construction because approx. 85 % of todays apartments are built in masonry.