Epoxy plastic application areas
» Construction and civil engineering works
» Electrical and electronics
» Marine constructions
» Packaging and strapping
Construction and civil engineering works
The largest amounts of epoxy plastic in the construction industry are used for coating of concrete floors. Untreated concrete floors are impractical for many reasons. They are difficult to clean and therefore unsanitary. Spill of, for example, oils are drawn into the concrete and cannot be removed. The chemical resistance of concrete is not especially high. From a purely wear perspective, it is often important to have a surface coating of some kind. An epoxy product intended for floor coating normally has a compression strength that is three to four times that of concrete.
The epoxy resins that are normally used for floor coating are the liquid low molecular resins. These resins normally contain no solvents, which entails that thick coatings can be applied on a single occasion. Furthermore, floor coating work presents no risk for fire.
Most epoxy coatings are applied to protect something. A special variant are the coatings in the pharmaceutical and foodstuffs industry, where the epoxy plastic’s freedom from pores make walls and floors easier to clean and thus protects operations from bacteria and contamination. Another variant is epoxy plastic as a moisture barrier to protect plastic mats and parquet from rising moisture and alkali.
Impregnation and sealing
The simplest coatings for concrete floors are for impregnation and sealing. These are achieved with low viscosity epoxy systems.
The impregnation is colourless and is intended to work its way into the concrete surface’s pores and seal them. At the same time, the loose cement and sand grains in the surface are bonded. The wear strength of the concrete surface is substantially increased, while the floor becomes more resistant to chemicals. Spilled oil can, for example, be easily wiped away because it does not force its way into the concrete. Sealing leaves a tougher surface film that further increases the resistance and the mechanical properties. It can be applied both pigmented and non-pigmented.
Thin layer coatings
The next category of coatings is thin layer coatings. Coatings of this type vary in thickness from about 0.3 mm to 1 mm. They normally contain hard filler to increase wear resistance.
This type of coating is primarily suitable for floors where loads are constituted by pedestrian traffic and light wheeled traffic in, for example, shops, warehouses, schools, hospitals, laboratories, etc.
A very common floor coating in industry is self-levelling flooring screeds.
These are applied in layer thickness’s from 3 to 5 mm. They withstand considerable mechanical and chemical stress. The binding agent content is relatively high (about 35%) and the remainder is made up of quartz sand of well-suited grain size and pigment. Self-levelling coatings provide completely level, seamless and poreless floors, which among other things, have shown to comply with the high demands of hovercraft traffic.
Coatings based on epoxy normally have a compression strength that significantly exceeds concrete’s. With heavy point loads, the underlying concrete can be pulverized, thus detaching the coating and resulting in damages. To avoid this, the thickness of the epoxy coating is increased so that the load is distributed over a somewhat larger concrete surface. Experience has shown that 3 mm is the thinnest coating for which one can expect load distribution. This is why coatings of 2 mm hardly ever occur. See “Necessary layer thickness”.
When it comes to very large mechanical stress, coating is performed using so-called epoxy concrete. This is a high-fill epoxy mortar that is applied like concrete in layers of about 10 mm and above. The binding agent content is low, normally about 15%, and the filler consists of quartz sand with carefully determined grain distribution.
The low binding agent content entails that the linear coefficient of thermal expansion approaches that of concrete. This is important in the avoidance of stresses in the boundary layer to the concrete during temperature changes.
To achieve the highest possible strength, this type of coating is lightly vibrated. This is achieved by rendering with subsequent smoothing.
Epoxy concrete is used for many types of castings, for example, underpinning of rails and heavy machinery bedding, transitions between bridge decks and roadways, gravel courses, loading docks, truck-ways and ramps.
Concrete that is subjected to moisture, frost and air pollution is eventually damaged. The damage process is usually relatively slow, but on bridges the process most often occurs significantly faster. This can be explained by a bridge being subjected to several degrading forces, such as settling, drying, heat, cold, vertical movements because of traffic, and not the least, chemical stresses in the form of acid rain (pH value of rain can in some cases be as low as 2) and salting. See the chapter “Concrete and air pollutants”. Damages that arise from salting are evident by de-scaling of thin layers of concrete. The risk for damage is greatest when the concrete contains water, as shown by damages being greatest where water drainage is worse. The reason for the salt’s degradation capacity is probably of a physical nature. When salt melts ice, a substantial temperature drop occurs. For example, it can be mentioned that 33 grams of sodium chloride (common salt) that is spread over 100 grams of snow produce a temperature of -20°C, and a mixture of 140 grams of calcium chloride and 100 grams of snow produces a temperature of -55°C. Additionally, it is well known that a salt solution has a lower freezing point than regular water.
Of these known facts, one can draw the conclusion that the following two factors are degrading:
Hydraulic pressure and formation of ice crystals
Hydraulic pressure occurs when the ice crystals in the capillaries expand and force away unfrozen water so that it pushes a flow through the part of the concrete that is not frozen. High porosity and fast freezing can produce very high pressure.
The other factor is the formation of ice crystals. When ice is formed in a cavity, it has the property of attracting water from non-frozen areas as soon as the temperature in the cavity falls beneath the freezing point. In this way, the ice crystals grow and expansion and bursting effects occur, especially in concrete with low porosity. The forces of the two mentioned factors can easily exceed the concrete’s tensile strength, thus resulting in damages. To counteract or prevent damages of the above-mentioned type, the concrete must be sealed against the entry of water, and additionally, free water in the concrete must be permitted to drain. This means that the sealer should be watertight and open to diffusion.
As glue, the epoxy plastics have many application areas. Wood, metal and stone materials can be successfully glued to one another or to concrete. The epoxy plastics’ high tensile strength and adhesion make them suitable for anchoring bolts and cables in concrete and rock. Glue based on epoxy is solvent-free and therefore has very little shrinkage. Based on the materials that will be glued and the glue location, one should select glue with the right elasticity, viscosity and hardening time. If the glue joint is subjected to chemicals, consideration should be taken to this. For more information, see the chapter “Gluing”.
Reinforcement of concrete constructions
Thanks to the epoxy glues’ capacity to absorb considerable tensile and shearing stresses, it is possible to reinforce concrete constructions, for example, a bridge deck, so that they can withstand heavier loads.
The method involves gluing steel plate or carbon fibre to the concrete to increase the reinforcement area. It is possible to reinforce for both bending forces and shear forces.
The epoxy glue must have the right properties both in regards to consistency and strength for the glue joint to be able to transfer the forces to the applied reinforcement. The method of strengthening bridges has been adopted by the Swedish National Road Administration and is generally used to increase the bearing capacity of a large part of the bridge structure.
Gluing of new concrete to old
A very interesting application area is the gluing of fresh concrete to hardened old and new concrete. It is a known fact that the adhesion of concrete to concrete, and concrete to rock is relatively poor; breakaway often occurs.
To avoid this, especially composed epoxy glues can be applied to the hard concrete that is to be covered; directly after gluing, the fresh concrete is cast.
The epoxy glue is designed so that the hardening time is longer than the concrete’s, causing a gluing-together of the concrete surfaces to occur. Glue of the latter type shall contain filler that prevents an all too powerful penetration of the glue; moreover, it may not contain solvents.
Concrete that is cast to a glued surface shall be kept dryer than normally because no water may be drawn into the underlying concrete.
As repair material, the epoxy plastics are used for repairing holes and damages in the form of putty, repair paste and epoxy concrete. Examples of damages include pot-holes, impact damages, salt damages, damages from component production and concrete pile damages. Another application example is as sealing material around fixtures, such as around railing posts.
Another special variant of gluing with epoxy plastic is injection into cracks and breakaways in concrete and rock. The method involves pumping in low-viscosity epoxy plastic in the cracks. The plastic thus glues together the separated surfaces. There is much that speaks for a cracked construction being repaired, namely:
- Cracked concrete cannot distribute the load it was designed for.
- Cracked concrete easily further degrades when subjected to freezing.
- Corrosion to reinforcement occurs.
- Pure leakage considerations.
Injection is addressed in detail in the chapter “Application and function”.
In construction and civil engineering works, lamination with epoxy and various fibres, primarily fibreglass also occurs. Examples of use are interior coatings in chemical tanks and renovation of sewer pipes.
Electrical and electronics
As shown in the figure, the largest application area for epoxy is electrical and electronics. Epoxy’s electrical insulation capability in combination with low moisture effect makes it suitable for the manufacture of circuit boards that are found in most devices, such as TVs, computers, cameras, etc. Epoxy is also used for components such as capacitors, diodes and transistors.
Epoxy is even used for embedding devices to protect against moisture or other aggressive environments.
In the aircraft industry, epoxy is primarily used as a laminate. The strength of carbon fibre epoxy laminate, in relation to weight, is very high in comparison to steel and aluminium alloys. The weight savings gained entail substantial benefits.
Model air planes used in competition are often manufactured in epoxy laminate, and details such as propellers, in carbon fibre and epoxy.
In the automotive industry, epoxy is primarily used as structural glue and thus replaces welding. These epoxy glues are of the single-component type, i.e. the hardener is mixed in the glue. Hardening subsequently occurs in a few seconds at high temperature. In the automotive industry, epoxy is also used for manufacturing press tools for sheet metal in the production of new car models. Extreme racing cars are as a rule, manufactured in epoxy and carbon fibre.
Once again, it is strength and low weight that is important.
As marine constructions, all types of boats are naturally included. By tradition, most fibreglass boats are manufactured in polyester resin. When if comes to boats with high performance, for example racing boats, epoxy is a better alternative. The epoxy’s strength and lower water absorption enables the laminate in the hull to be made thinner and consequently lighter.
Epoxy is used to a large extent to prevent water absorption in boats made of polyester resin. Water absorption in polyester plastic can lead to hydrolysis, i.e. degradation. A layer of just 0.3 mm epoxy prevents water from forcing its way into the polyester plastic.
On oil platforms, epoxy is used as protective coating on steel, both as a strong floor coating and as advanced corrosion protection.
Powder in this context refers to high molecular epoxy resin and hardener that are ground together. This powder can then be sprayed on a heated surface, where it melts and hardens to a coloured film. Examples are washing machines and corrosion shielded reinforcement bars.
Packaging and strapping
The interior lacquer in, for example, tin cans, is often epoxy lacquer. Freedom from pores and chemical resistance characterise such lacquers.
Under this heading, many things can be included. A very rapidly growing area of application is in the manufacture of propeller blades for wind power plants.
Epoxy is used to a relatively high degree in the manufacture of moulding tools. Examples of such manufacture can be sheet metal pressing, polyurethane casting, RTM, vacuum forming, injection moulding and blow moulding.
Such tools are used both in mass production of parts and for quick production of prototypes.