Name: Nicholas Trussell

Project title: Sprayed concrete application, porosity and permeability

Project description:

Sprayed concrete is concrete that is applied by pumping through a nozzle and is consolidated by the impact of subsequent sprayed particles. This is different to conventional concrete, which is applied manually or by pumping through a pipe, and consolidated under gravity and often mechanically by vibration or other forms of compaction. The sprayed application enables sprayed concrete to be placed in vertical or overhead locations, in irregular geometry, and with little or no formwork.

Sprayed concrete makes up 5 – 10 % of the annual consumption of ready mixed concrete in Norway and is mainly used for immediate rock support and linings in tunnels. Tunnel linings made of sprayed concrete are a core method of tunnel support in Norway, acting as immediate support during excavation to enable high productivity and allowing a cost efficient tunnel support.

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This PhD investigates:

• The effect of adding set accelerator at the nozzle on the porosity of sprayed concrete. The porosity is investigated by capillary suction, PF test and image analysis. Full scale sprayed concrete experiments have been conducted to produce the sprayed concrete samples with the set accelerator dose varied. Furthermore cast samples have been cast in the laboratory to compare with the samples sprayed in the full-scale spraying experiments.
• Water transport in cracks in sprayed concrete. Crack free and well compacted sprayed concrete can have a very low water permeability of less than 5 x 10-14 ms-1 (Holter, 2015). But sprayed concrete experiences cracks at joints between consecutive applications of sprayed concrete and due to shrinkage. Sprayed concrete discs were cracked, with the crack width controlled and measured by digital image correlation. Capillary suction and water permeation tests were undertaken on cracked and uncracked discs. Both a “standard” mix and a mix containing polymer were tested, to also investigate the effect of the polymer on the water transport.

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Funding: This PhD project is part of a joint project between SINTEF, Norwegian Geotechnical Institute, NTNU and several industrial partners: SUPERCON (Sprayed sUstainable PErmanent Robotmade CONcrete tunnel linings). 80 % of the funding is provided by the Research Council of Norway and 20 % by a group of industrial partners. The project was initiated to investigate sprayed concrete sustainability and durability.

Start date of PhD: November 2019