Portal: General

After a brief history of different installation modifications, this paper introduces a novel installation technique, which enables form-free placement of low cement and fully dispersed castable compositions. The method does not require the typical wet pumping equipment, as is needed for shotcreting, but delivers similar lining properties.

Whenever possible, try to pre-site all construc-tion projects before scheduling personnel and equipment. A little extra planning ahead of the actual work can save a lot of headaches later on.

I only recently joined the American Shotcrete Association. But, in reading through the issues of Shotcrete and ASA™s excellent brochure, I was struck by how little seems to be known about Carl E. Akeley, the man to whom we all owe our livelihoods. What™s more, I™m told by the litera-ture that he invented the cement gun œto apply mortar over skeletal matrices to form the shapes of prehistoric animals (not true); that he was a Doctor (his schooling was limited to three or four years of grade school); and that the œdevelopment of the original cement gun started in 1895 (it actually started twelve years later).

About fifteen years ago, we had a project that involved doing some extensive shotcrete (dry process) window infills. The job required shooting from the inside of the building onto plywood forms and involved about 5 stories of window.

The proper encasement of reinforcement in shotcrete is a criti-cal issue with respect to the quality and the durability of a shotcrete application. One simply has to refer to the Shotcrete Nozzleman Training Course offered by the ASA (see Shotcrete Magazine, Vol. 1, No. 4) or the recently available Nozzleman Certification Program of ACI to confirm this statement. Although many concerns have been raised, mostly by owners, regarding the presence of voids around reinforcement and their potential effects on structural per-formance, there is, unfortunately, little technical data available to back up the shotcrete industry on this problem.
Several years of experience with a certification program for shotcrete nozzlemen, as well as early research (Studebaker, 1939) suggest that the best approach is to apply dry-mix shotcrete1 at its wettest stable consistency, which is defined as œthe consistency at which the moisture content is the maximum, the maximum being determined by the stability of the fresh gunite (shotcrete). How-ever, observations on many job sites and training of nozzlemen show that many apply shotcrete with a relatively dry (stiff) shooting con-sistency, which may adversely affect rebar encapsulation as well as increase rebound.
The Industrial Chair on Shotcrete and Concrete Repairs of Laval University (City of Quebec, Canada) has initiated a thorough inves-tigation into the Evaluation of reinforcement encasement quality and its effect on shotcrete quality. This research program is financed by the partners of the Industrial Chair, the Concrete Research Council of ACI, as well as by the American Shotcrete Association (ASA). It has several objectives, including:

Scaffolding, in my opinion, could be listed as the #1 item on a top ten safety checklist. I believe it becomes 50% more diffi cult to work safely and properly on scaffolding than on the ground. Shotcreting using the dry-mix process is much easier to handle because of the weight of the hose, and

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