Abstract: This paper describes how under-graduate students at Laval University managed to develop and use a shotcrete technique for a small construction application. This technique was developed especially for an engineering competition. The students had to build a canoe made out of concrete. It had to be as light as possible and strong enough to survive a race with four paddlers aboard. So, a pumpable light-weight concrete and a shotcrete technique were developed to construct the canoe.
Every year since 1988 in the USA, Master Builders Technologies has sponsored a civil engineering competition. Undergraduate students are chal-lenged to design a concrete mix to build a canoe. In the USA, there are 20 regional competitions. The winners of these regional competitions are invited to the national competition. The winning team from the Canadian competition is also invited to the national competition as an interna-tional entry. To evaluate teams, they must race the canoe, have a display in which technical information is presented, and give an oral presen-tation. The final product is evaluated at the beginning of the races, and at the middle day of the competition for durability. Each team must also produce a design paper in which they explain how they designed and built the canoe, and also how they developed their concrete mix design.
Scaffolding, in my opinion, could be listed as the #1 item on a top ten safety checklist. I believe it becomes 50% more difï¬ 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
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 difï¬ 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 apÂpearance 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.
