The tunnelling industry relies heavily on the use of concrete, and most of all shotcrete. The ingredients in shotcrete and concrete are very similar, both relies on the use of cement. Cement production is one of the most energy consuming, if not the most energy consuming, industry in the business. One way of reducing the emissions of shotcrete production is to replace parts of the ingredients. Both cement and aggregates can be replaced by materials that are reused and thereby reducing emissions. Recycled aggregates are already used in construction to some extent. These recycled aggregated are usually from the demolition industry. The most effective way of reducing the carbon footprint of shotcrete is by decreasing cement levels. Fly ash and steel slag are two materials that are a suitable replacement for parts of the cement. It’s obvious that there is room for improvement, and improvement must be done. However, the reliability and consistency of many new alternative materials to cement isn’t quite there yet. It is hard to get sufficient data for these alternatives, since few big scale tests have been conducted. The life cycles of tunnels are usually very long, which makes it hard to get long time statistics for constructions with new techniques. Reducing the use of shotcrete is also something that will make a big difference on the carbon footprint. Applying shotcrete and achieving perfect results is hard, but some techniques has been developed to help the operator with the application process. Scanning is a very effective way of calibrating the operators to spray the correct thickness. Since the scanning method is still somewhat slow, scanning every single cycle is not an option today. The logistics behind shotcrete spraying is also an area that could be improved and thereby reducing the over usage of shotcrete. Replacing the current steel fibers used as reinforcement with a more sustainable material will also help reducing the carbon footprint. However, the emissions from the cement production are significantly larger. There are however other benefits with switching to synthetic fibers, mostly to do with safety of workers and machinery since synthetic fibers aren’t as sharp. These fibers are also resistant to corrosion, which makes them suitable for wet conditions. In the field tests, four different shotcrete mixes were compared and sprayed in test boxes. These mixes replaced 0, 10, 19 and 30% of the cement with steel slag. Early compressive strength was measured on all mixes and all of them achieved 10 MPa after 10 hours. At 10 hours the shotcrete mix with no steel slag, the reference concrete, accelerated its compressive strength growth. And achieved a compressive strength of 28 MPa after 17 hours. The other mixes had around 15% less compressive strength at 17 hours, but they all achieved 50% of the maximum strength within 20 hours.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-105109 |
| Date | January 2024 |
| Creators | Keijser, Olle, Segerstedt, Nils |
| Publisher | Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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