Portal: General

I remember doing a job in San Francisco, CA, about nine or ten years ago. The job consisted of building a basement in an existing commercial area. There were buildings on both sides of the new proposed basement. The construction called for the new basement walls to be built on the property line with a 2-in. foam spacer”the perfect shotcrete job!

In 2000, ACI, in cooperation with ASA, estab-lished a formal certification program for certifying shotcrete nozzlemen. Prior to that date, ACI had a guideline document for certifying nozzlemen, but it was not being uniformly applied, it contained outdated features and appli-cations, and it was not being universally accepted nor endorsed.

Where a section of shotcrete is left incom-plete at the end of a shooting shift, some provision must be made to ensure that the joint will not develop a plane of weakness at this point. According to the American Concrete Institute™s œGuide to Shotcrete1 and the œUnified Facilities Guide Specifications,2 construction joints should be tapered to a shallow edge form, about 25 mm thick. (1 in.) Therefore, in North America, contract specifications will typically require that shotcrete construction joints be tapered to a 45-degree edge and be thoroughly cleaned and wetted prior to the application of additional shotcrete. When welded wire mesh re-inforcement is used, some contractors will also overlap two layers of mesh at the expected location of construction joints in the antici-pation that the shotcrete at the joint may be weaker than the unjointed portions of the shotcrete.

The use of calcium aluminate cement as the binder in refractory systems in general, and refractory shotcretes in particular, is widely approach to high-performance refractory shotcrete involves the use of calcium aluminate aggregates along with the calcium aluminate cement. The addition of this unique aggregate imparts enhanced properties to shotcretes, enabling them to endure the toughest of industrial environments.

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.