Durability development in sprayed concrete for rock support;
Is it possible to establish a basis for modelling?
Norwegian Public Roads Administration, Norway
Road Department, Tunnel and Concrete Division
The Norwegian Public Roads Administration has investigated durability of sprayed concrete for rock reinforcement for almost three decades. The work involved core extraction, standard concrete testing, concrete petrography and water chemical analysis. The durability challenges are mainly related to a complex sulfate attack in sprayed concrete on sulfide-bearing Alum Shale and a combined biofilm- and abiotic attack in subsea sprayed concrete within the subsea environment. Both deterioration schemes have caused transformation of the cement paste matrix and localised destructive steel fiber corrosion where conditions are unfavourable. This paper investigates the possibility of establishing a basis for computer modelling in view of accumulated data from four main exposure situations. The emphasis was laid on the complex interactions of water loads, geological loads and design parameters such as concrete mixes and spray thicknesses. Due to the typical complex and uneven distribution of both exposure conditions and degradation phenomena, being very dependent on site-specific characteristics, durability modelling of sprayed concrete for rock support seems to be an extremely difficult task. Collection of empirical data over several years is a prerequisite for building a fundamental basis for computer modelling.
Key words: Sprayed concrete, durability development, water environment, geological context, design, modelling versus empirical approach