There are many fantastic tunnel constructions all around the world. The Tunnel Emisor Oriente is a 62 km long underground wastewater treatment tunnel being built in Mexico City, Mexico and is set to be one of the largest wastewater tunnels in the world. The Guangzhou Metro Line 3 in China is the longest metro and rapid transit tunnel with 60 km of length worldwide. The extraordinary Gotthard railway tunnel in the Swiss Lepontine Alps has two tubes and each of them is about 57 km long.
Stabilise and secure working areas during the construction of tunnels
But as with all these architectural masterpieces, many steps have to be taken during construction works. For underground construction works in tunnels, hydroelectric power plants and also in mining, it is essential for progress and safety reasons to stabilise and secure the working areas at the face as quickly and effectively as possible. This is generally achieved using sprayed concrete, whereby pumpable concrete is mixed with Sika admixtures and accelerated during the spraying process so that it bonds to the walls and roof, then hardens immediately.
Pre-analysing of concrete is possible for the first time
It has not previously been possible to model and pre-analyse this very specific concrete application reliably in the laboratory, because the distinct physical conditions of the spraying process always have a significant effect on the setting and hardening of the material. With the new Sika MiniShot Laboratory System it is now possible for the first time to simulate both the composition of the concrete components and their mixing process at the nozzle realistically in miniature, as the name Sika MiniShot suggests.
The concrete spraying machine generate mechanical conditions which correspond to the ones on site
This is effectively a static miniaturized concrete spraying machine, which is designed so that, even on this small scale, as the test materials and mix designs are sprayed, the discharge quantities and the machine dimensions generate mechanical conditions which correspond precisely to those occurring on the construction site. The Sika MiniShot results also give a reliable indication of the complex interaction of different cements, additives and Sika admixtures, which allows us to make targeted product developments, also opening up opportunities that did not previously exist to optimize specifically for major projects.
Subsequent strength measurement of sprayed concrete samples
In addition to the realistic application of sprayed concrete test mixes and materials, the Sika MiniShot system also breaks new ground for subsequent strength measurement of the sprayed concrete samples. An ultrasound spectrometer is included, the Pulsment, which has been developed to automatically carry out non-destructive measurement and recording of strength developments over 24 hours.
Very good correlation between Sika MiniShot measurements and sprayed concrete on site
Comparison between Sika MiniShot measurements and ‘real’ sprayed concrete shows very good correlation of the test results. This means that even simple laboratory tests with small samples will give a good idea of the sprayed concrete performance to be expected on site. The Sika MiniShot system has already been successfully used in Sweden, Finland, Portugal, Turkey and Australia, where it has been particularly helpful for large mining customers as well as construction professionals.
Sika MiniShot Laboratory now carries out laboratory scale tests on sprayed concrete and mortar systems
The Sika MiniShot Laboratory system is a development made entirely in-house by Sika, i.e. all of the different components of the system such as the spray machine (MiniShot), ultrasound measurement system (Pulsment) and all of the support electronics and software were developed, built and tested to production stage in the Central Research Centre facilities in Zurich. As a result, only Sika is capable of carrying out such realistic laboratory scale tests on sprayed concrete and mortar systems.
Watch the video about Sika MiniShot.