New development of sprayed concrete with improved waterproofing, durability and sustainability performance

Abstract

Sprayed concrete in combination with rock bolts is successfully being used for permanent rock support in tunnels. The main shortcoming is that sprayed concrete alone is unable to function as the permanent waterproofing with strict requirements on a dry interior tunnel surface. Final linings with precast or cast-in-place concrete with sheet membrane waterproofing represent an excessive structural design in hard rock conditions. The SUPERCON research project (Sprayed sUstainable PErmanent Robotized CONcrete) is currently aiming to improve the sprayed concrete technology to enable a permanent waterproof tunnel lining, based entirely on sprayed concrete.

Laboratory and full scale spray application testing include innovative mix designs with significantly reduced cement content. The effects of the use of fly ash and limestone powder binder replacement, hydration accelerators and high-performance shrinkage reducing agents as well as adding of polymer modification to the concrete mix and special steel fibres for the distribution of cracks in the hardened concrete were studied. A significant reduction of the autogenous shrinkage potential, and a reduction in the water transport (capillary suction and permeation) through cracks in the concrete using polymeric modification of the concrete was achieved. The use of shrinkage reducing measures in the mix, combined with anti-dryout measures on the sprayed concrete surface significantly reduce cracking risk. The research results so far indicate the feasibility of a waterproof sprayed concrete without a waterproofing membrane.