Researchers from three European institutions have collaborated on a project to determine how different formulations of shotcrete, or sprayed concrete, interacts with the environment, which formulations are best suited to varied environmental influences, and the effects additives have on durability and workability.
Known as Advanced and Sustainable Sprayed Concrete (ASSpC), this shotcrete research project was initiated by Florian Mittermayr, researcher at the Institute of Technology and Testing of Construction Materials at Graz University of Technology (TU Graz) (Graz, Austria), along with Wolfgang Kusterle from the Concrete Laboratory of OTH Regensburg (Regensburg, Germany) and the Austrian Society for Construction Technology (ÖBV) (Vienna, Austria).
ASSpC researchers discovered how shotcrete should be processed under ideal conditions and how binders must be constituted to achieve particularly high durability. “For four years, we investigated the process in its entirety in many laboratory and large-scale tests and provided scientific support at various tunnel construction sites,” says Mittermayr.
When it comes to durable and sustainable shotcrete, the ASSpC team considered important issues such as constituent materials and mixtures and their interaction with the surrounding media. Once those issues were clarified and deciphered, the project partners were then ready to prepare the detailed results for practical application.
One of the team’s main findings is that shotcrete can be made more durable when cements, supplementary cementitious materials, admixtures, and aggregates are better matched to the requirements. They discovered that granulated blast furnace slag, in combination with other supplementary cementitious materials such as metakaolin and siderite, is an effective way of increasing resistance against sulphate attack. In addition, they found that even a small addition of ultrafine limestone powder can significantly increase the early strength of shotcrete.
The use of shotcrete is one of the most important support measures in tunnel construction. While many tunnels are assumed to have a 100-year-long service life, there are factors that complicate this. “The service life is currently calculated on the basis of theoretical key figures and empirical values,” explains Mittermayr. “Environmental conditions such as chemically aggressive groundwater, for example, can possibly lead to cost-intensive maintenance measures earlier than expected.”
“Another milestone in terms of sustainability; we are particularly pleased about that,” adds Sebastian Spaun, managing director of the Association of the Austrian Cement Industry (VÖZ) (Vienna, Austria), another important partner in the consortium. “The extended service life means that tunnels can now be maintained at longer intervals, the maintenance effort is reduced for the operator and for motorists this means less congestion. Also impressive is the research zeal of the universities, which is helping to position our building material more and more as an environmentally friendly material with precise and tailor-made formulations.”
Source: TU Graz, www.tugraz.at.