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2013SumShotcreteEMag

Shotcrete Contractor Qualification By Marcus H. von der Hofen iprograms, which many individuals within the degrees of difficulty as exists in the field. Thereis not a guarantee that this nozzleman is thenable to place shotcrete in all applications andt’s been over a decade since the inception ofthe ACI Shotcrete Nozzleman certification American Shotcrete Association (ASA) and the is no substitute for documented experience in American Concrete Institute (ACI) worked the shotcrete application at hand. extremely hard to create. Many thought that cer- What has been left out of the ACI Shotcrete tification should have been done at the contractor Nozzleman certification programs is the fact that level. Through hours of debate and consensus the nozzleman did not gain shotcrete nozzling building, however, ASA moved forward in form- experience and get certifiedon his or her own. The alizing the shotcrete nozzleman programs. fact is that much of the field operation needed for The ACI Shotcrete Nozzleman certification nozzling success is not necessarily under the programs were designed to be at a “baseline” nozzleman’s direct control. The diligent work of a level. The nozzleman receives a certificate for qualified shotcrete contractor, who provides the each shotcrete process (dry- and/or wet-mix) and right mixture design, properly sized and maintained orientation (vertical with or without overhead) if equipment, the guidance of an experienced noz- successful in both the written and the performance zleman, and additional shotcrete crew members exam(s). They were not intended to be the most (for example, gunman, pump operators, finishers, rigorous exams possible. The shotcrete industry and hose tenders), is essential because it gives the has a wide spectrum of applications, practices, nozzleman trainee the opportunity to learn quality shotcrete processes, performance requirements, shotcrete placement before being certified.Specific site constraints, and geographic differences. Cor- project qualificationsare achieved if the con- respondingly, a wide range of project needs tractor, key personnel, material, equipment, and exists, from lightly reinforced basic shotcrete to placement methods are either known to meet the heavily reinforced concrete sections with complex requirements (that is, previous successful work geometry and limited access requiring much more experience/contractor prequalification) of the sophisticated workmanship. No single shotcrete project or proven through preconstruction testing. certification program can address all the variables It cannot be stressed enough that satisfactorily one may encounter on a project. meeting any one of the elements alone cannot The ACI certification programs focus on guarantee success; however, failing any one of certain and specific key elements (knowledge, them can cause a substandard finished product. skills, and abilities) deemed by knowledgeable Currently, the owner or specifier of a specific committee and industry members to be the most project must consider the experience of the shot- essential for general applications. They consist crete contractor, nozzlemen, and field shotcrete of a general-knowledge written examination crew before deciding when to require a compre- and a performance examination that includes hensive preconstruction qualification program. shooting an actual test panel containing rein- When considering prequalifying the shotcrete forcing steel. The test panel is 30 x 30 x 3.5 in. contractor, it is vital that sufficiently documented (800 x 800 x 90 mm) deep and contains a single projects that involved similar challenging applica- layer of reinforcing steel of different sizes and tions using the proposed nozzlemen, crew, and spacing. Thus, they are basic—they neither procedures be provided and verified. The criteria simulate deep sections, multiple layers of rein- for waiving preconstruction testing procedures forcing, or obstructions, nor do they address for highly experienced shotcrete contractors bonding and surface preparation. After hard- should be detailed in the project specifications ening, the panel is cored for evaluation in accor- and should clearly establish the highest level of dance with prescribed procedures. Evaluation is previous experience required. When contractor primarily based on the degree of encapsulation of prequalification is not used, applicable, or avail- the reinforcing steel. The certification programs able, project preconstruction testing with mockups verify the certified nozzleman knows the basics should be considered. There is a significant cost of both general knowledge and performance associated with a preconstruction testing program, technique and has the potential for satisfactorily and this should be considered in developing the placing shotcrete. Again, this certification alone contract requirements (refer to Fig. 1). 34 Shotcrete • Summer 2013


2013SumShotcreteEMag
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