Equipment considerations for new facilities and a look at new versus used equipment.
By Mel Marshall and Richard Isaacson
Regardless of whether you are considering entering the precast concrete industry, entering a new marketing area or expanding an existing facility, many factors will be a part of your decision-making process. One of the most important is money. The amount of money you want to spend and the amount you can afford are not always the same.
One of your first decisions concerns the products that you intend to manufacture. You will want to conduct a market survey of the proposed location for your new facility to determine how many other precast concrete manufacturers, if any, are active in the market that you wish to enter. Keep in mind that, even though there may be no producers in the area, that region may be serviced by precasters from remote locations. Several horror stories exist about folks who invested a great deal of money without doing a proper market survey to determine whether there was a need for the products they planned to manufacture.
Another early decision that you must make is the size and configuration of the property as well as the size and shape of the building (if one is required). The building’s size should include suitable clearances around machinery and production areas to provide a safe environment and efficient operation. The building’s location on the property is important to minimize product handling, maximize yard storage, and ensure the efficient flow of trucks hauling raw materials onto the property and finished product away to the job site.
Having determined a market requirement for specific products, one of the initial points you will want to consider is how you will precast those products: Will you wet-cast or dry-cast? These two basic methods of manufacturing precast products involve different types of manufacturing equipment.
The term “wet-cast” generally refers to those products that are manufactured from concrete with a water/cement ratio greater than 0.40 or a lower water/cement ratio concrete that uses a superplasticizer to make it flow. Because wet-cast concrete is very fluid and flows easily, one form set is required to contain each piece of precast product. After the concrete has set and sufficiently cured, the forms are stripped from the product and reused.
Although the investment in form equipment can be substantial, the cost is directly proportional to the number of pieces that you want to produce each day. Many concrete manufacturers start out with just a few forms and add to their form inventory as market demands increase.
One advantage of wet-casting is that it is not necessary for the precaster to invest in a concrete batch plant. Quality ready-mixed concrete is available from a large number of suppliers, so utilizing this concrete source can be very effective, particularly during your formative years. As sales increase and your concrete requirement increases, there may be financial justification to construct your own concrete batch plant. With regards to ready-mixed concrete, you will want to consider constructing your production facility as close to a ready-mixed operation as possible. In fact, some wet-cast precasters have set up their production facilities on the properties of their concrete supplier, when space is available. In these situations, the supplier will frequently offer free rent to secure the supply of ready-mixed concrete to the precaster.
Depending on the climatic conditions, it may or may not be necessary to construct a building to house the production process. Many wet-casters pour their products outdoors, while others erect a structure that has a roof but no walls (this offers some protection from the elements). If you are going to produce outside, however, it is important to protect the freshly poured product from elements such as rain, direct sunshine and wind.
Another major consideration is the method of pouring concrete into the forms, as well as handling the forms and finished product. Concrete that is poured directly from a ready-mixed truck or concrete batch plant into a concrete bucket can be distributed to the forms by forklifts or by utilizing an overhead crane. Larger production facilities frequently use flying buckets to carry the concrete from the mixer to concrete-holding hoppers located at the respective production stations.
You also will want to consider how you are going to vibrate the product. Vibrators are powered with electricity, pneumatics or hydraulics, and are available in a number of different sizes and shapes. A common method of internal vibration is to utilize pencil vibrators (stinger vibrators) that are inserted into the concrete between the inner and outer forms. This can be an effective method, but it requires a significant labor cost in order to achieve consolidation.
Form vibration is less labor intensive than pencil vibration, but requires the mounting of vibrators on the forms. Although there is an investment in vibrators, labor is reduced and productivity is increased. It is important to mount the vibrators on brackets welded to the form stiffeners, rather than mounting them directly onto the skin of the form. Precasters using this vibration method must work closely with their form and vibrator suppliers to ensure that the forms are of sufficient strength and that the vibrators are located in the right positions on the form.
Table vibration is very effective for flat products and is increasing in popularity for smaller products as well. This system involves vibrators mounted below a table to impart vibratory forces to the product on the table’s top surface.
SCC (self-consolidating concrete) is a material that all wet-casters will want to investigate. SCC is a relatively new development that is proving to be very effective for wet-cast production. This material utilizes fourth generation superplasticizers (referred to as polycarboxylate admixes) and VMAs (Viscosity Modifying Agents) to produce a concrete that is almost as fluid as water but does not segregate. SCC is so liquid that it is measured by slump flow (spread) rather than slump. The spread can vary from about 20 to 32 inches, depending on the product. Because SCC is self-leveling and consolidates under its own weight, it pours easily and quickly without the need for vibration. The finished product will have virtually no bugholes.
Dry-cast concrete is a zero slump concrete with a water/cement ratio below 0.40, but commonly in the range of 0.30 to 0.36. Because this concrete is very stiff, it is possible to utilize production methods that permit the product to be immediately stripped from the form. Dry-cast production equipment consolidates these products sufficiently so that the concrete can support its own weight when placed in the curing area.
A number of companies manufacture dry-cast systems for the production of concrete pipe, manholes, box culverts, grade rings and several other products. Because it is not possible to pour dry-cast concrete from a ready-mixed truck, a concrete batch plant is a necessity for this type of production. Also, a building structure is required for dry-cast production, although there are a few exceptions in warm climates.
The major advantage with dry-casting is that, although investment is required in a dry-cast machine, only one form set is required for the whole day’s production of a specific product. This is, as mentioned above, because of the concrete stiffness and effective consolidation. The labor cost of dry-cast products can be significantly lower than that of comparable wet-cast production, and the output rate can be higher.
Dry-cast systems are available with different degrees of labor input, varying from manual to fully automated systems. Generally, investment is made in a dry-cast facility only when there is a large demand for the items being manufactured.
Depending on the type of machinery, off-bearing and stripping of the product will be handled with overhead cranes, forklifts or automated handling equipment.
If you plan to batch your own concrete, you will need to consider the size and types of aggregates that you will be using and suitably size the aggregate bins to match the requirements of your mixer. Also think about the number of cement silos you will need to hold cement, fly ash, slag and blended cements. Be sure to size the mixer properly. The size of the mixer depends on the quantity of concrete you pour per hour or the size of the pouring bucket (for wet-cast products) that you plan to use. The larger the pouring bucket, the more concrete you can pour at one time. For example, if you are going to pour large utility boxes, you would likely consider a larger pouring bucket than you would if you are going to pour concrete into smaller forms such as small meter boxes.
Curing is an important part of concrete production that is all too frequently overlooked. Keep in mind that curing (the hydration reaction between the cementitious materials and water) is essential to the formation of concrete. It is, therefore, imperative that the moisture not escape from the concrete product during the curing process so that sufficient moisture will hydrate virtually every particle of cement. If adequate curing does not occur, it will not be possible to achieve the mix design strengths. Concrete products must be protected from wind and direct sunlight during the curing process.
Although not necessary, the inclusion of a QC testing facility at your new plant is strongly recommended. It is possible to arrange for testing at independent laboratories, but this can be costly and not nearly as convenient as conducting your own tests. By doing your own testing, you will find it much easier to modify your mix designs in order to achieve the most efficient and effective mix designs that will enable you to produce the strongest, highest-quality products.
If financial resources are limited, you may want to consider purchasing used equipment. This can be a very cost-effective way to start out, but you will want to ensure that the equipment you are purchasing is in good working order. There are frequently good buys on used equipment, but there is also a lot of dysfunctional used equipment.
Investing in a new facility is a major undertaking, so take the time to carefully study your requirements. Always keep in mind that it is far less costly to make mistakes on paper than at the building site. Consult with experienced suppliers, who are very knowledgeable in their respective fields. With proper planning and intelligent equipment selection, there is every reason to expect your new plant to be efficient, safe and productive.
Best wishes for a very successful installation.