Traditional construction grade concrete was the original trench drain channel material. Concrete is a mixer of coarse aggregate, fine sand and Portland cement in a 3:2:1 composition: 3 parts aggregate, 2 parts sand and 1 part Portland cement. (Add water until you reach a proper consistency.) Today, it is more common to buy pre-mixed bags of concrete or have a ready-mix truck bring concrete to your site. A large number of trench drains are still made with concrete as the “working” lining material. This is especially true of trench drain systems with channels that are 12” and wider.
Concrete is a good material for using as a trench channel because it is strong, easy to form into custom shapes and relatively inexpensive. Smaller trench drain systems use concrete as the backing material, which anchors the drain into the ground. For wide, high volume storm water applications, concrete is still the main working lining for trench drain. Three trench drain systems that use standard construction grade concrete as the trough material are:
- Pre-cast concrete trench drains – These trench drains are large, reinforced trench drains that are made in a concrete shape manufacturing facility. One section of drain can weigh tons and will require a crane to set in place. There is no national manufacturer and no standard size of pre-cast trench drains. However, many regional manufacturers are spread across North America.
- Formed-in-place systems (also known as frame and grates) – Just like the name states, these trench drains are built at the site. Installation requires building a wooden form that is suspended in the trench and affixing the grate frame to the form. Grates are installed after the concrete is poured and the form removed.
- Former Systems – These systems are basically formed-in-place systems with pre-made channel forming molds. Molds are made of cardboard or expanded polystyrene (EPS). The framing system allows for easy suspension in the trench and quick installation.
Polymer concrete is a blend of mineral aggregates and polymer resin. Just as Portland cement is used as a binding agent when making traditional construction grade concrete, liquid polymer resins (polyester and vinyl ester) are used as the binder when making polymer concrete. The polymer concrete components are blended in a mixer with a resin hardener which accelerates the speed of the concrete set time. After thorough blending, the “still wet” concrete is poured into rubber molds in the form of trench drain channels. When the concrete has set, the molds are stripped and the channel is put into a drying oven to complete the curing process.
Polymer concrete is an ideal material for making trench drain channels for several reasons:
- Low Porosity - Because of the resin bonding process, polymer concretes have a rate of water absorption around 1% and are considered “watertight”. This low absorption rate is great for drainage applications because it helps reduce the coefficient of friction and allows fluids to flow more efficiently.
- High Compressive Strength: One of the basic appeals of polymer concrete is its compressive strength and durability under loads. With compressive strengths of 11,000 PSI or higher, polymer concrete is 3 to 4 times stronger than standard concretes. Since higher strength can be achieved, smaller channel designs can be used.
- Corrosion Resistance: Like most polymers, polymer concrete is resistant to a number of harmful chemicals that are corrosive to traditional concrete. The resin in polymer concrete wraps a protective coating around the aggregate material to keep alkalis and acids from eating through the product.
- Freeze-thaw Resistance: Freeze-thaw happens when water seeps into the pores of concrete and expands as the temperature drops below freezing. The expansion and contraction of water within concrete causes tensile strength properties to be exceeded, which results in the breakdown of concrete. The low porosity of polymer concrete stops water penetrations and reduces the likelihood of freeze-thaw occurring.
Fiberglass channels are made with the pultrusion process. In this process, fiberglass matting is pulled through a series of forming chambers and heated dies to manufacture a continuous shape in the form of a channel. The rigorous process toughens fiberglass and makes it a good choice for construction contractors because of the following factors:
- Chemical Resistance – fiberglass is extremely resistant to caustic materials and is used in paper/pulp manufacturing and chemical processing applications.
- Lightweight – Compared to polymer concrete and other trench forming shapes, fiberglass is lightweight. Channel sections of 8’ to 10’ long can be handled easily during installation.
- Temperature Resistance – The polymers used during the manufacturing of fiberglass enable the material to withstand a wide range of extreme temperatures without damaging its strength.
Polyethylene (PE) and High Density Polyethylene (HDPE)
PE and HDPE are used for making trench drain channels. Dense polyethylene (plastic) is heated and either extruded or injection molded into water cooled dies in the shape of the final product. Polyethylene is a major component used in making plastic containers. HDPE also represents a significant part of the construction industry because of its unique properties:
- HDPE plastics are impact resistant and sturdier than other plastics because of the chemical process which creates a compacted polymer.
- A low water absorption rate keeps HDPE from cracking when the temperature fluctuates, which makes it useful as both a container and as a drainage product.
- Effective sterilization with gamma irradiation, chemical disinfection and gas make HDPE a win for laboratory settings and preventing contamination.
- HDPE products are highly chemical resistant and able to withstand acids, alcohols and bases easily.
- PE and HDPE are lightweight and inexpensive relative to metals.
Other plastic products and composites are used to make trench drain channels and grates.Polyvinyl Chloride (PVC) is a popular thermoplastic used for making many extruded and injection molded channel shapes. UV inhibitors can be added to PVC to help reduce the effects of weathering by the sun. Polypropylene is another plastic material used in making some of the less expensive and less durable products.
Stainless steel is a common channel and grating material used in applications that need corrosion and chemical resistance. It is the high chromium content of stainless steel that separates it from carbon steel. When exposed to oxygen, the chromium in stainless steel creates a boundary against rust that halts surface erosion and prevents rust from moving into the interior structure of the steel. It is a large player in specialized construction projects for that reason and more:
- Corrosion resistant – Stainless steel not only stains less than carbon steel, but it resists the corrosion of chemicals, too. It is used in laboratories and food preparation areas to catch spills and runoff. It is able to withstand strong chemicals that are used to kill bacteria, making it an ideal product for these applications.
- Sterilization – Stainless steel can be sterilized by steam cleaning and, because it is manufactured to be rust-resistant, does not require any painting or coating before use in a sterilized environment.
Cast iron contains iron, carbon, silica and various other inoculating elements. Ductile Iron (or nodular iron) is a type of cast iron that contains a manganese component which changes the structure of the carbon from flake to nodular. Ductile iron has better impact resistance than standard gray iron. However, both products are strong and are used for the channel bodies and grating of some trench drains.