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Concrete Spraying Technology : Shotcrete

PART 1

Given the reduced usage of this technology in Romania, through this article series we intend to present the main advantages and applications of the concrete spraying technology, whether dry or wet.

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Shotcrete has often been described not as a material but as a process. Both dry and wet processes produce a material that exhibits superior hardened properties compared to high quality conventional concrete: higher strength and durability and much lower permeability.

The properties of both wet and dry-process shotcrete can be further enhanced through the addition of many different additives or admixtures such as: Air-Entraining Admixtures — Improve pumpability and adhesion in wet-process shotcrete and freeze-thaw durability in both wet and dry processes; Fibers — Control cracking, increase toughness values, improve impact resistance and energy absorption; Accelerators — Improve placement characteristics in adverse conditions, allow for thicker single pass applications, increase production capabilities, and reduce the occurrence of fallouts on structures subjected to vibration.

Advantages of the shotcrete technology:

  1. Formwork savings of 50 to 100% over conventional cast-in-place construction, even for complex shapes,
  2. No need for vibration,
  3. Crane and other equipment savings or elimination,
  4. Labor savings of at least 50% in repair applications and of 35%-40% in new construction applications.

Dry Mix or Wet Mix Process?

Utilaj marca Ocmer folosit de catre Matei Construct

Although both wet and dry shotcrete have specific pros and cons, chosing one is mainly a factor of the equipment available, the contractor’s know-how and the availability of dry or wet concrete at the construction site. Generally speaking, dry shotcrete is preffered given the lower cost of the dry concrete, increased working speed and superior bonding to the substrate.  However, Romania offers limited possibilities in obtaining dry-mix concrete due to the fact that very few concrete stations are equipped with aggregates dryer. Wet-mix shotcrete also requires specialised equipment and very knowledgeable  workers.

As of today, Matei Construct is among very few Romanian contractors that possess the equipment for large scale wet-mix projects.

In the next newsletter we will detail each of the main applications of the shotcrete process: Repair and Restoration; Ground support and rock anchoring; Reservoirs; Tunnels; Refractory concrete.

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