In tunnelling construction, fast setting shotcrete is applied as a security lining before the load bearing lining of cast-in-place concrete is inserted. This economical construction method has a number of serious drawbacks. The aim of the scientific research is to develop a shotcrete without these drawbacks but with greater efficiency. The research will lead to safer, more frequent and less expensive use of this construction method in the development of transport and traffic infrastructure in Europe. This will be achieved by:
- cements which show the required setting qualities without the use of alkaline accelerators
- non-polluting, non-alkaline additives to control the shotcrete's setting behaviour as well as the application of damp aggregate
- effective decrease of rebound to reduce material loss during application and to increase the safety of the heading team
- new process engineering producing an exceptionally homogeneous shotcrete.
1 Special cements
During the project, three different binders and an non-alkaline accelerator have been developed.
HEIDELBERGER ZEMENT has developed a special binder on basis of clinker with an high sulphate resistance and by use of non-sulphatic compound. This cement called CHRONOLITHS, meets the highest requirements for shotcrete (according to the Austrian Guidelines on Shotcrete). As this binder shows a repose phase before the start of setting, its special suitable for the use of damp aggregates. But of course, the use of dry aggregates is possible. For changing conditions (temperature, water content of aggregates), the repose phase can be regulated. The general certification is applied for this new binder in Germany, even a patent.
WIETERSDORFER & PEGGAUER developed a binder similar to the binder of HEIDELBERGER ZEMENT on basis of a comparable W&P-clinker and so a very satisfying binder was produced too.
CEMENTI BUZZI developed a different type of cement on basis of a normal pouzzolanic cement, called ECOSPRITZ. This binder also shows the required properties concerning strength development and durability. A variable repose phase and the suitability with damp aggregates also characterize this cement.
Another important property, which is also achieved by CHRONOLITHS, is a high sulphate resistance. This allows the application of these cements also in areas with a high sulphate content in ground water in soil.
2 Non-alkaline accelerators
A new alkali-free accelerator was developed by HEIDELBERGER BAUSTOFFTECHNIK. This new product in pulverous form is available for the production of environmentally compatible shotcrete with ordinary cement, either in the dry-mix and in the wet-mix process. This accelerator is in use and application not hazardous to health and environment. The quality of the shotcrete with the new accelerator is decisively increased in comparison to usual alkali-bearing accelerators.
3 Process engineering
A suitable process engineering was developed by the consortium in order to allow the employment of damp aggregates in combination with the new shotcrete cements. This extends the application possibilities of the shotcrete construction method and increases its economical efficiency by the renunciation of oven dried aggregates.
The investigations, developments and results achieved in the project, showed that the production of a high-quality shotcrete is possible without addition of alkaline setting accelerators, nevertheless meeting the highest demands concerning strength development. The higher density also improves the elution behaviour.
The improvement of working conditions on site is of decisive importance. The clear reduction of the development of dust and toxic agents reduces the health risks of the working team considerably.
Funding SchemeCSC - Cost-sharing contracts
15033 Casale Monferrato Alessandria