Portal: General

Permanent modern shotcrete support in hard rock conditions is commonly based on achieving sufficient bond strength to the rock. A system with reinforced shotcrete with mesh reinforcement or fibers is dependent on the bond strength being able to carry loads from loose blocks. This is especially important where no, or very few, rock bolts are installed. Investi-gations1 show this behavior clearly. In Sweden, a common requirement for the bond strength between shotcrete and rock is a minimum of 73 psi (0.5 MPa). It is also essential to have full interaction between different shotcrete layers with a bond level of at least 145 psi (1.0 MPa). Also, in the repair of old concrete structures, Swedish bond strength requirements for the interaction between old concrete and new shotcrete are at least 218 psi (1.5 MPa).

Equipment Safety Quiz

At the beginning of the 20th century, signif-icant pieces in the foundation of America™s Industrial Revolution were established in the Lehigh Valley of Eastern Pennsylvania. Iron and steel, important products to the early development of our continent, were produced in Bethlehem, PA, and the first production of portland cement in North America took place in Coplay, PA. The Lehigh Portland Cement Company was founded in Allen-town in 1897, and cement production is still an important industry in the area. Several support businesses and professions, as well as Lehigh University, resided in the valley to provide engin-eering, design, testing, and manufacturing services for the production of cement and steel. Also early in the century, in 1904, the American Concrete Institute (ACI) was established, and the Portland Cement Association was formed in 1916.

For some, it may seem inconceivable, but a few equipment manufacturers produce machines capable of both wet-mix and dry-mix shotcrete spraying without converting the equipment. The method these machines use is known as the wet-thin stream method of conveyance.The design is based on the rotor-style dry process machine. The rotors, however, are designed for the wet process as well. This is achieved by equipping the machine with a low-profile rotor with large-diameter ports, which allows the wet-mix to drop into the ports and be pneumatically conveyed through the hose to the nozzle. The hoppers are fastened with rubber mounts and equipped with vibrators that assist the material in flowing into the rotor.

When it comes to pumping a typical concrete mixture, let™s face it”most pumps out there will work. When it comes to pumping a shotcrete mixture, however, your choice of pumps is critical.Shotcreting can be the most demanding job for a concrete pump. Basically, you are asking your pump to push a low-slump mixture, usually through a 2 in. (50 mm) diameter hose, as fast and as far as possible. Before you go and buy the largest, toughest pump you can find, you should ask your-self some questions.

This article touches on both wet- and dry-mix shotcrete equipment maintenance that is not typically in the owner™s manual. Equipment manuals for the dry- and wet-mix machines have a section on maintenance that tells you what to grease and check on a daily basis. Wet-mix shotcrete pump manuals will have a section on oil and filter changes needed at designated running hours.

Many factors affect the quality of shotcrete. The shotcrete process itself provides a unique and effective placement technique for portland cement concrete. For the shotcrete process to yield the highest possible quality product, however, many factors must be considered. The shotcrete process has both obvious and not-so-obvious factors that affect the quality of the end product.

Answer: Respiratory illness can take years to develop. As with smoking, the delayed but high-risk results sometimes make it diffi cult, crucial, to convince employees to wear respi-rators in certain environments, even if the air does not appear to be harmful. The key to convincing employees to protect themselves is to educate them on the hazards present in the workplace and the effects on the human respiratory system.

The American Shotcrete Association (ASA) and Hanley Wood teamed up to present a shotcrete extravaganza in Las Vegas, Nevada, during the 2005 World of Concrete. Encouraged by the successful Mega-Demo in 2001, the leadership

We all know job-site conditions can undergo constant changes. The best safety tip for these changing job-site conditions is to check all job sites before crews are dispatched. This inspection will take a little time and may be a little inconvenient, but after the inspection you will have an understanding of what potential hazards are present for your