Portal: General

Shotcrete has been an important part of the construction industry for more than 90 years. As a specialty concrete technique, it is basically another means for the placement of concrete with its own peculiarities and characteristics. In the early years after its introduction by the Cement Gun Company of Allentown, Pa., in 1910, relatively little testing was done, prima-rily because the technique had limited use. What testing was performed was done to pro-mote the technique”to show its efficacy for specific applica-tions or to exhibit its superior-ity over other existing concrete technologies. The tests in-cluded were for material and design criteria and properties such as compressive, tensile, and flexural strengths, bond, permeability, shrinkage, and soundness. These tests were based on American Society for Testing and Materials (ASTM) concrete tests adapted for the shotcrete process. When inter-est in concrete durability began to heighten after World War II, freeze-thaw tests were also in-troduced. As in conventional concrete, compressive strength has been the defining property of shotcrete testing. However, if other properties are required for a particular application, they can be arranged at the time of specification. The main dif-ference in the tests is in the preparation of samples, which is usually different because of the unique nature of the shotcrete process.
While interest in shotcrete was limited prior to the 1940s, an upsurge developed, espe-cially in the wet-mix process, in the 1950s. In 1990, ASTM decided that the technology had grown sufficiently enough that a new ASTM subcommittee on shotcrete, ASTM C09.46, should be organized. This would complement the existing American Concrete Institute Committee 506 on Shotcreting. ASTM Subcommittee C09.46, Shotcreting, would absorb the

A crane operator, carpenter, baseball player or a shotcrete crew? Probably everyone listed should use them. On a scale of 1 to 10, the shotcrete crew would rate a 10 with need. œWho on the crew should wear them? I asked one of my superintendents, she said, œThat™s easy, everyone on the crew. The nozzleman and air lance man for obvious reasons, but also the pump operator and potman to protect themselves from dust and shotcrete overspray and rebound. The finishers also need eye protection from constantly working vertical concrete surfaces. The laborers also need protection from rebound, dust and overspray, and the occa-sional burst hose or coupling!
A shotcrete operation requires several high-pressure pieces of equipment, all of which, unfortunately, can burst. The dry-mix

Shrinkage is a potential problem in shotcrete construction that can lead to restrained shrinkage cracking.

Cheap Insurance: Most of us in the shotcrete industry have had a plugged hose creating either a dust storm with the dry process or concrete over-spray everywhere with the wet process. When a hose is plugged, it has been my experience that everybody on the crew starts yelling and running toward the operator. Communication between the nozzleman and the gun/pump operator is one of the most important and critical links on the job for productivity, and most of all, safety for everyone. Unfortunately, because of different job site layouts, continual rotation of people, and equipment movement on and around the job site, good communication is often diffi cult to achieve or maintain.

Shotcrete has been widely used by the Ministere de Transports du Quebec for restoration and rehabilitation. Shotcrete has been widely used by the Ministere de Transports du Quebec for restoration and rehabilitation.

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