Process dependence of shotcrete for repairs: Fid-Bau Portal

Process dependence of shotcrete for repairs

Bindiganavile, Vivek / Banthia, Nemkumar

In the study presented here, the authors illustrate that the properties of steel fibre reinforced shotcrete are a function of the manufacturing process. The paper examines the causes for the higher penetration resistance in dry-mix shotcrete, while highlighting the differences in composition and rebound during the fresh state. A strong influence of the spray process is witnessed on the hardened properties under both compression and flexure. For an identical fibre content, the toughness of shotcrete is noticeably different from that of the corresponding cast concrete. The principal source of penetration resistance for dry-process shotcrete is thought to be the early products of cement hydration, which are formed in the immediate aftermath of spraying, upon the first contact with water. While these initial products offer high resistance to penetration, in wet-process shotcrete, these products are repeatedly sheared during the mixing process. As a result, any resistance offered by the wet-process shotcrete is most likely due to the thixotropic behaviour of the hydrating cement paste. Both the overall material rebound and the rebound of fibres were lower than what is usually seen with the dry-process shotcrete. Although the water/binder ratios for the dry and the wet processes were essentially identical, compressive strength for the dry-process shotcrete mixes were significantly higher than those recorded for the wet-process shotcrete. Doubling the fibre dosage (from 30 kg/m3 to 60 kg/m3) resulted in a mere 38% increase in the flexural toughness factor for the dry-process shotcrete, while the corresponding increase in the wet-process was over 50%.