Channel Drain Material Properties

Trench drain and slotted drain products are only as good as their weakest link.  In order to make a wise product selection it is necessary to understand which product is best for your application.  You can do this by getting a basic understanding of how different trench drain materials perform under specific conditions.  Their material properties and construction determine this performance.  New trench drain and slotted drain products are emerging every day and not all of these will be discussed here, however, the same issues will plague all products and they should each be evaluated for their merit.  A channel drain product cannot simply be evaluated by it's material properties.  The installation ease and cost are always real life factors that also guide our buying decisions.  The more critical the need for a quality product the more weight that should be put on the evaluation of the channel drain material properties.

 

With that said there are several different properties that govern the longevity and performance of any trench drain.  The trench drain body, frame, grates, and grate locking devices need to be evaluated separately and weighed accordingly.  The following material properties should be studied:

 

Compressive strength

Tensile strength

Flexural strength

Impact resistance

Water absorption / freeze thaw

Thermal expansion

Bond strength

Bearing area

Fire resistance

Abrasion resistance

Chemical resistance

UV resistance

 

COMPRESSIVE STRENGTH

The compressive strength is technically defined as the ability of a material to withstand a force that is pushing the molecules together.  Typically, trench drains transfer loads from the grate through a frame, into a channel, and then into the concrete encapsulating the channel.  In this transfer if one of the trench drain materials is not capable of handling this load then the material will fail and the trench drain will be destroyed.  Grates made of iron, metals, and some plastics have high compressive strengths.  Avoid frames, grates, and channels made of soft plastics when loads will be transferred through them.

Material comparison based on typical trench drain construction (IE: material thickness, fabric orientation, resin content, etc).

MATERIAL RELATIVE COMPRESSIVE STRENGTH

Cast Iron                                                                           High (gauge dependent)

Ductile Iron                                                                       High (gauge dependent)

Steel                                                                                  Medium (gauge dependent)

FRP (Fiber Reinforced Plastic)                                       Medium (fabric orientation dependent)

Polyethylene                                                                      Low (resin content dependent)

Polymer concrete                                                             High (resin and aggregate content dependent)

GFRPC (Glass fiber reinforced polymer concrete)        High (resin, fiber, and aggregate content dependent)

Concrete                                                                            Medium (water / cement ratio dependent)

TENSILE STRENGTH

Tensile strength is defined as the ability of a material to withstand a force that is pulling the molecules apart.  Ex:  When you push down on a board the top of the board is being compressed as it bends but on the under side of the board the molecules are being stretched and pulled apart testing the tensile strength.  Tensile strength is especially important for trench drain grating materials as they can easily be flexed putting large tensile loads on the materials.  Trench drain or slotted drain bodies that receive loads may also experience tensile failure as buckling begins to occur.

Material comparisons based on typical trench drain construction (IE: material thickness, fabric orientation, resin content, etc).

MATERIAL RELATIVE TENSILE STRENGTH

Cast Iron                                                                            Medium (gauge dependent)

Ductile Iron                                                                        High (gauge dependent)

Steel                                                                                   High (gauge dependent)

FRP (Fiber Reinforced Plastic)                                        High (fabric orientation & fabric strength dependent)

Polyethylene                                                                      Medium (resin content and void dependent)

Polymer Concrete                                                             Low (resin/aggregate/void dependent)

GFRPC (Glass fiber reinforced polymer concrete)        High (glass fiber content dependent)

Concrete                                                                             Low (water/cement ratio dependent)

FLEXURAL STRENGTH

Flexural Strength is the amount that you can bend an object without it breaking.  Flexural strength varies with material type but is also very dependent on the thickness of the cross section.  This property is most important to trench drain grating materials as they take loads and span a distance allowing them to flex.  Trench drain and slotted drain bodies see high flexural loads during transport and job site installation.  Typically a channel should not be experiencing these stresses once installed, however, many channels improperly installed do see these stresses.  If a channel drain receives flexural loads the quality and thickness of the channel material can bridge these gaps when properly designed.  For gratings and frames, look to thicker materials and choose ductile irons over cast irons if this type of loading is expected to be severe.

Material comparisons based on typical trench drain construction (IE: material thickness, fabric orientation, resin, and aggregate content, etc).

MATERIAL RELATIVE FLEXURAL STRENGTH

Cast Iron                                                                            Low (gauge dependent)

Ductile Iron                                                                        Medium (gauge dependent)

Steel                                                                                   High (gauge dependent)

FRP (Fiber Reinforced Plastic)                                        High (fabric orientation dependent)

Polyethylene                                                                      High (resin content dependent)

Polymer Concrete                                                             Low (resin and aggregate dependent)

GFRPC (Glass fiber reinforced polymer concrete)        High (glass fiber content dependent)

Concrete                                                                             Low (water/cement ratio dependent)

IMPACT RESISTANCE

This property is important for the trench drain grating material and the frames as they are constantly in contact with hard items such as carts, fork truck tires, and items being dropped.  This is also critical to the trench drain and slotted drain channel bodies during the installation process.  Plastic and fiber reinforced materials will not easily break while being transported or in the installation process.  The cyclic nature of these dynamic forces can instantaneously or over time cause cracks to propagate until the material fails.  During the design process it should be determined if this is a concern.  If there will be a high frequency of impact or very heavy impact loads then heavier gauge materials should be chosen and ductile irons should be selected over cast irons.  Steel typically has high impact resistance but be ware that if welding is done improperly that the failure may come at the welds even thought the gauge and material are sufficient to handle the impact loads.  Select polymers and plastics that have fiber reinforcing to combat impact loading.

WATER ABSORPTION / FREEZE THAW

Trench bodies (the channel material) should be made of a material that does not absorb large amounts of fluids.  When materials go through a freeze thaw cycle any water absorbed inside the material it can cause failure from within.  Joints should be sealed between channels if freeze thaw is considered to be a problem in your climate.  

 

MATERIAL RELATIVE ABSORPTION RESISTANCE

Cast Iron                                                                            High (non porous material)

Ductile Iron                                                                        High (non porous material)

Steel                                                                                   High (non porous material)

FRP (Fiber Reinforced Plastic)                                        High (non porous material)

Polyethylene                                                                      High (non porous material)

Polymer Concrete                                                             High (non porous material)

GFRPC (Glass fiber reinforced polymer concrete)        High (non porous material)

Concrete                                                                             Medium (porous material)

THERMAL EXPANSION

Many regions of the world can experience temperature differences of 20 to 40 degrees in a single day from the heat of the day to the coolest part of the night.  Seasonal changes can cause temperatures to have a difference of 100+ degrees.  During cool temperatures the trench drain materials shrink and during warmer temperatures materials expand.  The rate and amount of expansion and contraction can cause channel drain materials to fail especially if they are mechanically fastened to other materials that are expanding and contracting at different rates.  These rigid connections can cause problems when the concrete expands and contracts.  Temperature dependent materials such as thermoplastics can warp and grow significant amounts when temperatures change.  Trench bodies can literally pull themselves apart when encased in concrete moving at different rates.  Thermal expansion is a very serious issue that cause numerous failures each season.  Choose materials wisely when you are looking for products that will perform over wide temperature differentials.

 

The final problem with thermal cycling for trench drain materials is with thermal plastic materials.  Thermal plastics are heated to be formed into a shape.  They can also be heated and bent into a new shape at any time.  In processes where high temperature fluids are used thermal plastic materials such as Polyethylene should be avoided as they can lose their shape and strength.  Other resins like themal set polymers such as FRP, Polymer concrete, GFRPC, and epoxies are thermal set resins that have a chemical reaction to take their shape and are not generally affected by higher temperatures.

 

BOND STRENGTH

Bond strength is a load transfer mechanism that occurs when a material chemically bonds to the surrounding concrete allowing for a transfer of  stress to the surrounding material.  Unfortunately there is no chemical bonding of materials currently in the trench drain business unless a poured in place material is used and the surface is properly prepared.  This means that loads must be transferred through mechanical (geometric) means or keyways.  When choosing a trench drain channel or frame make sure that it has sufficient concrete anchors and keyways to properly transfer any loading that the system may experience.

BEARING AREA

Bearing area is the cross sectional area under the edge of the trench drain grate that mechanically transfers the load from the grate to the trench drain frame or body and finally to the surrounding concrete.  If the area is insufficient to carry or transfer the load or the material that the load is transferred through is weak a system failure will occur.  There are two common problems.  The first is that the area is too small usually caused by a system with a small frame design and few or no concrete anchors.  This type frame provides little bearing area or load transfer means.  The other problem commonly seen is that plastics or other weak (in compression) materials are placed between a the trench drain frame and the concrete.  If the sandwiched material has low compressive strength it allows a rigid trench drain frame assembly to flex and causes concrete to fail around the anchors and edges.  If the loading is simply too severe for the bearing area then the concrete will sheer off leaving the rail to rock or twist causing the same type of failure.  This is a very important issue for heavy loads and where high speed traffic is likely.  High speed traffic, even if technically considered light, can put much higher dynamic loads on a system than a much heavier force at slower speeds.  Dynamic loads can be as much a 10X the static loading.

FIRE RESISTANCE

Fire resistance of trench drain materials is important in industrial applications where welding occurs, hangars where fuels can ignite, and many other places where added flammability has the potential to spread fire to areas where the problem can become more severe.  

MATERIAL FLAMMABILITY

Cast Iron                                                                            Low (not flammable)

Ductile Iron                                                                        Low (not flammable)

Steel                                                                                   Low (not flammable)

FRP (Fiber Reinforced Plastic)                                        Medium (does not sustain a flame)

Polyethylene                                                                      High (flammable material)

Polymer Concrete                                                             Medium (does not sustain a flame)

GFRPC (Glass fiber reinforced polymer concrete)        Medium (does not sustain a flame)

Concrete                                                                             Low (not flammable)

ABRASION RESISTANCE

Trench drain bodies are subjected to a large amount of grit that over time can cause the trench liner to be abraded away.  Grit in the bottom of the trench drain acts as sand paper removing material from the trench body over time.  The thicker the material the longer it will last, but more importantly the hardness or resistance to being worn away will ensure a long life.

Below is a relative scale of the abrasion resistance of typical trench body materials.  It is based off the material type and thickness of typical cross sections of trench bodies.

MATERIAL ABRASION RESISTANCE

Cast Iron                                                                            High (thick cross section with hard/dense material)

Ductile Iron                                                                        High (thick cross section with hard/dense material)

Steel                                                                                   Medium (hard material but typically thin cross section)

FRP (Fiber Reinforced Plastic)                                        Medium (hard material but typically thin cross section)

Polyethylene                                                                      Low (soft material)

Polymer Concrete                                                             High (good cross section with hard material)

GFRPC (Glass fiber reinforced polymer concrete)        High (good cross section with hard material)

Concrete                                                                            High (thick cross section)

 

CHEMICAL RESISTANCE

Many manufacturing plants need to consider chemical resistance before choosing a material.  For specific chemicals and how they affect different materials see the chemical resistance charts.  The biggest problem in the industry is that a good trench drain material is selected, but the joints in the materials and concrete encapsulation & reinforcing are not treated properly.  All drain connections must be properly sealed.  If chemicals are severe a test should be done before concrete is poured around the trenches to ensure water tightness of the trench drain system.  Plug the outlet pipe, fill the trench with water, and then check for leaks.  Make sure all are repaired before concrete is poured.  Sealant with proper chemical resistance must be used.  Standard caulks and glues do not have good chemical resistance.  Steel trench drain joints should be welded water tight.  Fiberglass, polymer concrete, and GFRPC should be roughed up and a proper chemical resistant epoxy should be used to bond the joints together.  Thermal plastic materials such as HDPE or polypropylene joints should be welded (sealants do not stick to thermal plastics for long periods of time).  If using a formed concrete trench drain it will need to be coated with an epoxy system.  

Finally, care must be taken to ensure that the concrete encapsulation does not move and crack.  Any movement in the surrounding concrete will pull the drain apart and cause leaking of the trench drain channel.  Significant reinforcement in the concrete, dowels, and proper compaction of the subsoil are mandatory.

MATERIAL CHEMICAL RESISTANCE

Cast Iron                                                                            Medium (strong acids and hard to seal joints)

Ductile Iron                                                                        Medium (strong acids and hard to seal joints)

Steel                                                                                   Low/High (varies with steel type)

FRP (Fiber Reinforced Plastic)                                        High (Resistant to broad range of chemicals)

Polyethylene                                                                      High (Resistant to broad range of chemicals)

Polymer Concrete                                                             Low (Good resistance but short channels difficult to seal)

GFRPC (Glass fiber reinforced polymer concrete)        High (Resistant to broad range of chemicals & long sections)

Concrete                                                                            Medium (reacts with acids & sugars)

 

UV (ULTRAVIOLET LIGHT) RESISTANCE

Trench drain grating and trench bodies exposed to the sunlight should be made of UV resistant materials.  The best UV inhibitor is carbon black which you can generally tell when the plastic is black.  Many colored plastics also have a UV inhibiting feature.  Beware of materials that have little or no color as they likely do not have a UV package incorporated.  Ask the manufacturer to certify that their product is UV stable for all materials exposed to sunlight.  In exterior applications we have seen plastics turn brittle from UV and fail under much smaller loads than they were designed to handle.

 
 
 
 
 
 
 
 
 
 
 
 
 

Watch the effects of weld spatter on trench bodies video to watch for yourself.