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Quebec city possesses a historic arc.a in which many concrete structures need repair. For economic as well as practka] reasons. since some of these structures are curved. shotcrete is the logical solution when a repair is considered. In order to provide attractive looking finishes for the re­ paired structures, ii was decided to see if it was possible to obtain a better finish ap­pearance than the usual wood trowel shotcrete finish.

The placement of high strength wet-mix shotcrete is sometimes complicated by the compromise required between obtaining suitable pumpability and shootability.

There is probably nothing as frustrating to even the most tolerant wet-mix shotcrete placing contractor or crew as problems related to pumping. While the following comments are spe-cifically related to shotcrete placement, many of them are also applicable to normal concrete pumping applications. The rheology of shotcrete mixtures is affected by the pumping pro-cess, which typically involves repetitively compressing a shotcrete mixture and forcing the mixture to the point of final placement under pressure.

Most architects, design engineers and design-build contractors are familiar with preparing and producing specifications for various types of concrete construction. There are projects where the use of shotcrete, rather than cast concrete, may be more technically and economically advantageous, but the designer is reluctant to specify shotcrete because of a lack of familiarity in preparing shotcrete specifications. This article provides owners and designers con-sidering the use of shotcrete with information on guidelines and specifications for shotcrete in a variety of different applications. This information should assist designers in preparing project-specific specifications.

I was asked by the ASA Executive Com­mittee to prepare a bibliography of shotcrete reference publications that would provide owners, designers/specifiers, sup­pliers, contractors and testing companies with useful information concerning the various aspects of shotcrete technology. I started by going to the ACI CD-ROM Con­crete Abstracts Quick Search and obtained over 300 hits with the word shotcrete in the search index. It became readily appar­ent that assembling a detailed compilation of all the shotcrete papers published would be a very onerous task and probably not that useful. So I decided to take another tack: I simply went to my personal library and pulled out those shotcrete publications

In prescription-based specifications the engineer will typically set out in detail all requirements for the materials and shotcrete mixture proportioning as well as the type of equipment required for batching, mixing, supply, and application of shotcrete. In performance-based specifications the engineer will specify the required performance characteristics for the shotcrete and let the contractor select the materials, mixture proportions, type of equip­ment and application procedures to be used. In general, perfor­mance-based specifications are preferred to prescription-based specifications in that they encourage innovation and introduction of new technology and generally result in lowest cost to the owner. Let us examine in some detail the differences

Shotcrete is a unique procedure for placing concrete or mortar. Because of its substantial advantages, it has found use in a wide variety of very different applications. This has unfortunately led to much misunderstanding and few, if any, practitioners that have experience in all of the different types of applications.

“Giving structural steel a protective rust­proof and fireproof coating, without the use of forms … Lining tunnels, dry earth walls, irrigation ditches, etc. with a waterproof protective coating … Coating wood piles to protect them from destructive sea insects … Waterproofing concrete dams and reservoirs … Repairing defective concrete sea walls … And, coating frame houses, fac-tory curtain and inclosing walls, waterproof­ing, etc.”

Streetsboro, Ohio, a small town just southeast of Cleveland, recently became the site for a landmark occasion in the shotcrete industry. For six days in Septem­ber, 1999, the back lot of the Master Build­ers’ manufacturing plant and a local hotel in Streetsboro became the venues for the first shotcrete nozzleman certification held by an industry association in North America.

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