Environmentally Friendly Construction Technology
Interaction between Construction and Environment

Peter Grübl

Introduction
Interaction between Construction and Environment in this context means that everything we do in connection with building constructions, has an influence on the environment. In general we can say this is die ecological aspect of building activities. In addition there is the social aspect we have to consider. This compromises the interaction between die building and the human being with all its facets. A keyword here is sick building syndrome.

In this paper 1 will concentrate my explanation mainly on the ecological aspects.

Parameters
We can characterise the influences on environment in this respect with three main affects as following:
-consumption of resources,
-consumption of energy and
-emission of harmful substances.

• Consumption of resources means mainly the exploitation of raw materials which are used to produce the building materials. In addition to this we have also to take into account die stocks of mineral oil and gas. And as a third factor we have to consider the use of land.
• The consumption of energy comprises the energy necessary to maintain the construction process and the production and delivery of the building materials as well as the equipment needed for the construction. Also important is the energy necessary for running the building during its lifetime.
• The energy consumption is associated whit the output of emissions, chiefly the emission of carbon dioxide and sulphur dioxide. Carbon dioxide is responsible for the global warming up of the atmosphere.

Sustainability
When we regard these impacts in connection with the challenge of the sustainability of our doings, there is a common consensus, that we have to take care, that all these impacts should be reduced to a minimum.

To reach this goal, at first we have to get information, in which way and with what quantity the different actions necessary to build and use constructions generate substances, which pollute the environment. One source to get more information about the emission and the consumption of resources and energy are live cycle assessment studies.

In a following step we have to analyse, what we can do to avoid or to reduce harmful effects on environment. The answer can be simple - or very difficult. Probably new technologies or new materials or new processes for constructions, or all of them, have to be developed to come to environmentally friendly solutions. In this context the questions about feasibility and costs are of high importance. The solutions we have to offer must be affordable.

When we evaluate the harmfulness of emissions, we have to consider the elements water, air and soil. One principle is that the concentration of harmful substances compared with the actual situation should not be increased as consequence of any action. In this context we have to define which substances in what quantities are harmful for the environment and the living nature. This question is very difficult to answer. This problem can only be solved by means of a general social consensus. For instance, there is a region in our world, where arsenic occurs in a concentration which is fatal for any live at all. This rnay point out the dimension of the problem of this undertaking.

Recycling
With all producing processes a main goal must be to avoid waste. In some fields new technologies are needed. To design constructions which we can disassamble or which are suitable for a changing use without changing the structure are two contributions in this respect.

But avoiding waste is not possible in all cases. Therefore we also have to concentrate our efforts on recycling. This is an important aspect on the way to come to an environmentally-friendly construction technology.

Regarding recycling we can distinguish two cases. In one case the recycling is a substantial part of the production process. Substances, which are not the aim of the production process are in general declared as waste. These substances must be, if possible, completely reintegrated into the production process. We can call this the "narrow material circle". lt takes place inside of the production unit. Also the recycling of cars after they are given back to the producer belongs to this case of material cycle.

Other conditions exist when we consider a construction either at the end of its lifetime or in case of changing the use. lt cannot be given back to the contractor. There will be undertaken a complete or a partial demolition. Some elements, for example windows, rooftiles, bricks, and so on, can flow back to production plants and can be recycled for new products of the same kind. This can also be classed as the "narrow material cycle". In all other cases die result of the demolition is rubble, mainly consisting of old mineral building materials such as concrete, masonry, mortar, glass, tiles, and so on, but also organic materials such as plastics, asphalt etc.

Approximately 40 % of the whole amount of waste is generated by the construction industry. The main part of the waste from die building activities is soil. The building rubble amounts from 20 to 25 %. In Europe the amount of building rubble is estimated about 300 Million Tons per year. With this quantity we can cover an area of about 200 km² with a layer of 1 m thickness. From this we can deduce the urgent necessity for developing suitable methods for recycling the rubble, that means processing the rubble and using it as a secondary raw material for construction purposes, for instance concrete.

As a matter of reason the aim should be the reuse on the highest possible quality level. In all other cases we practice downcycling.

Exchangeability
When we use recycled materials as raw material to produce building components, we should take into account, that the product, produced with recycled material as a secondary raw material, should have the same quality and the same properties as the product, produced with primary raw material. Primary and secondary raw material must be exchangeable without loss of quality of the product for which it is used. This exchangeability of the materials is very important with regard of economical aspects, mainly concerning the price. When the product can only be produced using secondary raw material and it is not or not in sufficient amount available, the production can not take place or the market price will go up.

Industrial By-products
Another case is the use of industrial by-products for the production of building materials. This is a special kind of recycling. Examples are fly ash, blast furnace slag, gypsum from flu gas desulfurization and so on. The technologies for using these materials are nowadays for many substances well advanced. Some ranges of application are already standardised, for example for fly ash and powdered blast furnace slag as additions for cement. Despite of this we have to look for further applications, because not the whole amount of these materials is suitable for the above mentioned use.