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Shotcrete is placed and compacted/consolidated at the same time, due to the force with which it is ejected from the nozzle. It can be sprayed onto any type or shape of surface, including vertical or overhead areas. Shotcrete has the characteristics of high compressive strength, good durability, water tightness and frost resistance. [2]
Traditional rebars are generally used to improve the tensile strength of the concrete in a particular direction, whereas steel fibers are useful for multidirectional reinforcement. This is one of the reasons why steel fiber reinforced (shotcrete form) concrete successfully replaced weldmesh in lining tunnels. Less labour is required.
The excavation is protected by a layer of sprayed concrete, commonly referred to as shotcrete. Other support measures can include steel arches, rock bolts, and mesh. Technological developments in sprayed concrete technology have resulted in steel and polypropylene fibers being added to the concrete mix to improve lining strength.
High-strength concrete has a compressive strength greater than 40 MPa (6000 psi). In the UK, BS EN 206-1 [3] defines High strength concrete as concrete with a compressive strength class higher than C50/60. High-strength concrete is made by lowering the water-cement (W/C) ratio to 0.35 or lower.
Twenty eight days is a long wait to determine if desired strengths are going to be obtained, so three-day and seven-day strengths can be useful to predict the ultimate 28-day compressive strength of the concrete. A 25% strength gain between 7 and 28 days is often observed with 100% OPC (ordinary Portland cement) mixtures, and between 25% and 40 ...
The early strength of the concrete can be increased if it is kept damp during the curing process. Minimizing stress prior to curing minimizes cracking. High-early-strength concrete is designed to hydrate faster, often by increased use of cement that increases shrinkage and cracking. The strength of concrete changes (increases) for up to three ...
A normal-size fiber for European shotcrete (1 mm diameter, 45 mm length—steel or plastic) will increase the concrete's tensile strength. Fiber reinforcement is most often used to supplement or partially replace primary rebar, and in some cases it can be designed to fully replace rebar.
Improve concrete strength at low cost. Adds tensile reinforcement in all directions, unlike rebar. Add a decorative look as they are visible in the finished concrete surface. Polypropylene [18] and nylon fibers can: Improve mix cohesion, improving pumpability over long distances; Improve freeze-thaw resistance