Cement is an important binding agent for construction industry and is produced world-wide in large amounts. A central process step during the manufacturing of cement is the production of the intermediate product clinker. For this production, inorganic raw materials are burnt at temperatures in the range of 1,500°C. In order to reduce the costs of this energy-intensive process which has a high share in the manufacturing costs of cement, regular fuels are increasingly substituted by secondary fuels. In cement manufacture, use of waste is not restricted to the use as an energy carrier in the burning process of clinker production. Waste is also used as an alternative inorganic raw material as well as an interground additive in the cement grinding process. All types of waste contain trace elements. With exception of the share which is emitted and which is very small for most elements, these elements are transferred into the product cement.
Aim of this project was to investigate the impact of the use of secondary fuels, secondary raw materials and blending agents on trace element concentrations in cement and concrete. Furthermore, the aim was to investigate under which conditions and to which extent the incorporated trace elements can be released into the environment. Additionally, it should be proofed, whether regulations, standards, directives, etc. for the production of cement and corresponding construction products contain specific requirements for pollutant loads.
The study has shown, that presently used secondary raw materials and fuels result in some cases in a slight increase in trace element concentrations in cement. However, a general assessment of the use of wastes in cement production and of its impact on trace element input can not be performed. Furthermore, future developments can hardly be estimated.
The release of trace elements from concrete elements is negligible small during the phase of use. An increased release of trace elements is possible under special assumptions after demolition. However, the present knowledge is not sufficient for a definite assessment.
Existing regulations concerning the production and use of cement do not presently contain defaults for allowed concentrations of pollutants. However, changes can be expected in future due to demands which are presently worked out for the EU.