Portal: General

E-mails are often sent to the ASA website from engineers, contractors, builders/owners, and home owners asking for information on proper methods for curing shotcreted structures.

This article presents a procedure for up-dating your environmental knowledge and keen awareness for a deeper appreciation of our surroundings. It discusses the new regulations for implementing the procedural provisions of the National Enormental Policy Act.

It is virtually impossible to hold a discussion at a trade or technical organization meeting without the topic of sustain-ability being raised. Skeptics might describe the intense interest in this subject as one more attempt to burden society, particularly the construction industry, with little or no discernable benefit. Conversely, there are fringe groups with radical political agendas that attempt to use sustainability discussions for their own purposes. There is, however, an important central issue”the need to analyze the long-term impact of how things are designed and constructed to minimize environmental change and maximize resources as the world™s population grows. Building œgreen (constructing buildings that make efficient use of energy, water, and materials; limit impact on the outdoor environment; and provide a healthier indoor environment) is being supported by both public and private entities in recognition of the finite resources available to support a growing population and higher levels of economic activity. This is where mainstream thinking is focused and where reasonable thought resides.
To begin to understand a bit more about sustainability, it is important to answer a few basic questions.
Question: What makes concrete a œgreen building material? Answer: Concrete is a responsible choice for sustainable development. Purely as a material characteristic, durability is a significant sustainable attribute of concrete because it will not rust, rot, or burn, requiring less energy and fewer resources over time to repair or replace it. Structures built with insulated concrete have optimal energy performance. Additionally, concrete is easy to use, incurs little waste, and can be readily recycled.
Question: What is energy efficient about concrete?Answer: Concrete on its own is not a very good insulator. Recent developments in building systems, however, have combined concrete with insulation, creating highly efficient, strong, and easy-to-build assemblies. Homes and buildings constructed with insulated concrete walls use the comparative great weight of concrete to moderate daily temperature swings, as did the pueblo dwellers of centuries past. This means home or building owners can lower heating and cooling bills up to 25%. Also, heating, ventilating, and air-conditioning can be designed with smaller-capacity equipment. Along with thermal mass, high-performance insulated concrete wall systems offer high R-value and low air infiltration to provide superior thermal efficiency.
Question: How does concrete relate to recycling?
Answer: Recycling is part of concrete™s life cycle from the beginning. Several common industrial byproducts like fly ash and slag that would otherwise add to landfills are incorporated into concrete mixes. Use of these byproducts also reduces

It is inevitable that every firm will have to verify its work at some point in time. No matter how the process gets started, each contractor and supplier should be prepared to methodically respond in a timely manner. This article will offer some important concepts and suggestions for creating your own œdisaster plan. It would be foolish to think that such a plan will never be needed. The only thing more foolish is not to have created a plan in advance.
Step One: Recognition and
Timely Response
Once a report is received, action should be taken to define and acknowledge the concern. Request clarification of the concern and its source: Is it coming from the owner, architect, engineer, consultant, general contractor, or construction manager? Is the concern a serious issue? Some-times a casual comment develops into a major problem (a cut on a finger turns into an amputated arm in the rumor mill). Let all concerned parties know your position immediately. If an investi-gation is required, request a meeting as soon as possible to discuss the problem and the investi-gation process. This gets you on the record as being responsive and begins to give you some control of the process.
Step Two: Fact Finding
Let™s use a simple example of how important it is to collect facts before diving into an inves-tigation. A number of years ago, while working for a ready mixed concrete supplier, I was called by a customer who was constructing a high-rise condominium project and told that we had low compressive strengths for concrete used for a slab pour from the previous month. This was a very large project that was closely monitored by our Technical Services Department. We had not even a hint of any low compressive strengths on any phase of the project prior to receiving this report.

I am frequently asked by contractors to aid in the selection of shotcrete equipment and acces-sories for many types of shotcrete applications, both wet-mix and dry-mix processes, including concrete repair and restoration, pool construction, mining, tunneling, soil nailing, slope stabilization, and refractory applications. There are many choices of equipment and acces-sories for shotcrete contractors today. Various types of equipment include concrete pumps, gunite (dry-mix shotcrete) machines, mixers, and predampeners. There are many more types of ancillary equipment and accessories that go along with the primary shotcrete equipment used today. Let™s take a look at some of these other tools used to apply shotcrete and why they are important.

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.