Paving and road marking paint - The truth revealed
Why Concrete Pavers?
During the last five years, concrete bricks, also known as “cement bricks” have been gaining rapid market share. As a masonry unit, clay has always been favoured above concrete. However, new designs and colour ranges, higher standards, a consumer mindset change, an increase in concrete brick specifications by architects and the relative ease and exactness of producing these bricks have resulted in a concrete brick boom.
The Features and Benefits of Concrete Pavers:
Concrete pavers are cheaper than clay bricks
You can have concrete pavers in the shapes of circles, squares, rectangles, triangles, or just about any other shape one can imagine. With clay you really only have one choice. Concrete units are exact in dimension. Because of the materials a concrete paver is made from, it is more dye-friendly than clay, which means it will accommodate a greater variation of size and shape than clay.
• Extremely hard wearing
• Textured blocks available
• Highly accurate sizes
• Wide choice of block depths, from 50mm to 80mm
• Longevity - can last up to 50 years with very little maintenance
• Not prone to mosses
• Easier to cut than the clay paver
Concrete has no such ‘grain’, and as such is a better choice structurally when considering pavements that will receive vehicle traffic, like driveways or streets.
Durability is the ability to last a long time without significant deterioration. A durable material helps the environment by conserving resources and reducing wastes and the environmental impacts of repair and replacement. Construction and demolition waste contribute to solid waste going to landfills. The production of new building materials depletes natural resources and can produce air and water pollution. Durability of concrete is also defined as the ability of concrete to resist weathering action, chemical attack, and abrasion while maintaining its desired engineering properties.
• High Humidity and Wind-Driven Rain - Concrete is resistant to wind-driven rain and moist outdoor air in hot and humid climates because it is impermeable to air infiltration and wind-driven rain.
• Resistance to weathering, including freezing and thawing
• Ultraviolet Resistance
The ultraviolet portion of solar radiation does not harm concrete. Using coloured pigments in concrete retains the colour in concrete long after paints have faded due to the sun’s effects.
• Chemical Resistance
Concrete is resistant to most natural environments and many chemicals. Concrete is virtually the only material used for the construction of wastewater transportation and treatment facilities because of its ability to resist corrosion caused by the highly aggressive contaminants in the wastewater stream as well as the chemicals added to treat these waste products.
• Abrasion Resistance
Concrete is resistant to the abrasive affects of ordinary weather. Examples of severe abrasion and erosion are particles in rapidly moving water, floating ice, or areas where steel studs are allowed on tires. Abrasion resistance is directly related to the strength of the concrete. For areas with severe abrasion, studies show that concrete with compressive strengths of 12,000 to 19,000 psi work well.
• Fire Resistance
Concrete is almost unique in being an inexpensive, readily available building material which is intrinsically fire resistant, needing no additional application of fire protection, and at the same time have structural and aesthetic qualities.
When choosing a layout for an estate or property, all the above mentioned characteristics make it sound appealing enough for a contractor or architect not to think twice to make use of concrete pavers in parking areas, entrances and sometimes even roads in private estates. The above mentioned “pro’s” are always considered, leaving out the “cons” for later when the problems actually become realities - one of these cons being the problem of road marking and the durability thereof.
For years contractors believed that Road Marking Paint could be used on both tar and concrete, delivering durability and low maintenance, exactly because of the fact that it was manufactured specifically for road marking. Not that anyone can be blamed – After all, it does indicate on the data sheet of road marking paint that it is “suitable for use on concrete and bituminous road and runway surfaces.” Still the problem remains that Road Marking Paint does not last on concrete pavers and we have looked into the problem to find out why and how to solve the problem.
The following factors were looked into:
• Interlocking paving bricks – The Manufacturing Process
• What is paint and what chemicals are used in the manufacturing process?
• Road Marking Paint – why it doesn’t work
• Exploring other options
• The Ultimate Solution
Interlocking paving bricks – The Manufacturing Process
The manufacturing process, just to get a piece of concrete used for paving, is not as simple as the end product at all. According to Billy J.Wauhop Jr.of the Interlocking Concrete Pavement Institute (ICPI), Interlocking Concrete Paving Bricks (ICPB) are made from two different types of mixtures called the face mix and the base mix.
The Base concrete mix normally contains at least 16% Type I Portland cement based on dry weight. Nominal maximum aggregate size is generally 3/8 inch, with a common aggregate ratio of about 60% to 70% sand with the remainder being gravel. The Face mix however, consists of cement and fine sand and is only part of the top 0.6 – 1 cm of the paver and makes the paver more durable, with a smooth, non-slip texture.
Admixtures are often used to increase concrete strength, reduce mould wear, and reduce efflorescence. Water-repelling admixtures such as calcium stearate may be added to reduce water absorption by the paver.
Superplasticizers, added at the rate of about 0.4% of cement by weight, disperse cement grains, permitting water reductions that produce high early strengths. The extra fluidity gained by the use of superplasticizers also reduces the effort required to remove the pavers from the mould, thus reducing mould wear. Colouring pigments also disperse more uniformly in superplasticized mixes. The concrete mix is fed into the appropriate mould and is then subjected to intense vibration. This process results in a dense, high-strength product.
Regardless of the type of paver production machine used, the concrete pavers are normally cured for 24 hours. In most multilayer operations the green cubes are stored on the factory floor or in open storage racks that use only the natural heat of hydration for curing. Free water evaporating from the concrete is the source of moisture. However, in some single-layer operations, the curing storage racks are enclosed in a curing room to help confine the heat of hydration. Sometimes recirculating fans help provide a uniform temperature distribution from top to bottom of this room. As long as the products are properly stored and insulated such that the heat from hydration is retained and the free water isn’t lost, no external heat or moisture is needed. The finished cube is wrapped with steel banding after the product has cured, and in some cases, wrapped with plastic sheeting for yard storage and transportation to the jobsite.
?What sort of chemicals are inside paint?
You might think paint is just a colour chemical dissolved in a liquid to make it spread, but it's a bit more than that. Most paints actually have three main components called the pigment, the binder, and the solvent. (The binder and solvent are sometimes collectively called the vehicle.) There are also typically a number of additives to improve the paint's properties in various ways, depending on where and how it's going to be used.
The pigment is the colour chemical in paint. It looks a certain colour because it reflects some wavelengths of light and absorbs others (see our article on light for an explanation of how colours work). Traditionally, metal compounds (salts) are used to create different colours so, for example, titanium dioxide (a bright white chemical often found in sand) is used to make white paint, iron oxide makes yellow, red, brown, or orange paint (think of how iron turns rusty red), and chromium oxide makes paint that's green. Black (arguably not a colour) comes from particles of carbon (think what your burned toast looks like and you're getting close to a colour chemical known as "carbon black"). Different pigments are mixed together to make paint of any colour you can imagine.
Pigments are typically solids, so you couldn't use them to paint by themselves. They'd be difficult to apply, they wouldn't spread evenly, they wouldn't stick to paper or a wall, and they'd wash straight off if they got wet. That's why paints also contain substances called binders. Their job is to glue the pigment particles to one another, but also to make them stick to the surface you're painting. Some binders are made from natural oils such as linseed oil, but most are now made from synthetic plastics. Visualize the binder as an invisible skin of plastic with a colourful pigment dispersed through it and you can see just how paint gives a layer of protection.
Mix a pigment and a binder and you get a thick substance that's difficult to spread. Ever tried painting a wall with syrup? That's what using a pigment and a binder is like. It's the reason why paints have a third major chemical component called the solvent. As its name suggests, a solvent is something that dissolves something else. The solvent's job is to make the pigment and binder into a thinner and less viscous (more easily flowing) liquid that will spread evenly (that's why paint solvents are sometimes called thinners). Once the paint has spread out, the solvent evaporates into the air, leaving the paint evenly applied and dry beneath it. When you apply a really nasty paint and there's a smell lingering for days while it dries, that's the solvent evaporating into the air.
Water is the best-known and most versatile solvent we have and it's widely used in water-based paints, including emulsions (for walls) and watercolour paints (for paintings). When you paint a picture with watercolours, you're using water as a solvent to dissolve some pigment on your brush that you can easily spread on the paper.
Other paints (including oil and gloss paints) use solvents made from strong organic (carbon-based) chemicals extracted from petroleum. If you leave paints sitting in tins and jars, gravity gradually separates them into their different chemical components. Typically you find the solvent sitting on top as a reasonably clear, thin fluid with the binder and pigment making up a thick, opaque sludge underneath. That's why it's always important to stir tins of paint before you use them.
Gloss paint uses oil-based solvents so it spreads evenly. It's usually much thicker and more opaque than water-based emulsion and the oily solvents have a powerful smell that can linger for days afterward.
Apart from the pigment, binder, and solvent, most paints also have chemical additives of various kinds. For example, ceramic substances can be added to paints to improve their strength and durability. Fluorescent pigments added to paints make them glow in the dark. Additives in paint designed for outdoor use can help to make things waterproof and rustproof, protect against frost or sunlight, and keep them free of mould and mildew.
How paint is made
Although there are many different types of paint, they are broadly all made the same way. First, the pigment is prepared. If it's made from a metal salt such as titanium dioxide, it'll be dug from the ground as mineral ore, so it will need to be refined in various ways to remove impurities. (Having pure pigment chemical is essential to ensure the final paint has a uniform colour.) The pigment chemical might start off as a lump of rock, so it needs to be ground into a very fine powder. It may also need to be physically or chemically treated to change its colour in subtle (or not so subtle ways). It might be roasted, for example, to make it darker. Once it's been ground to a powder, the pigment is mixed with the binder by a huge, industrial machine that works a bit like a giant food mixer and solvent and additives are added as necessary. That's not the end of the process, however. Because it's vital that each sample of a particular paint looks exactly the same colour as every other sample, the mixed paint has to be sampled and compared with previous batches. If the colour isn't exactly right, the factory workers add extra pigments. Extra solvents are added if the paint is too thick. Once the paint is the right colour and consistency, it can put into cans, bottles, tubes, or other containers and shipped to the stores.
Road Marking Paint – why it doesn’t work
Because of the solid, smooth textured Face layer on concrete pavers (other than the rough absorbent surface of a tar road) and Road Marking paint being a water-based paint the paint does not penetrate the solid Face layer of the brick, causing a lack of ability to “stick” to the surface. Damage caused by constant traffic on the paint as well as the harsh weather conditions we face in South Africa, contribute to the paint fading even quicker. According to a Technical Consultant of ICI Dulux (Pty) Limited, “road marking paint is considered a maintenance item”, indicating that road markings constantly need to be maintained and redone for so-called “long-lasting” results. This of course, also explains why Plascon clearly states that there is absolutely no guarantee on road marking paint
Exploring Other Options
Taking all above mentioned factors into consideration, other options were explored to find a solution for road markings that last longer.
Because roof paint is UV-resistant, and manufactured to last long on cementuous roofs, one would surely consider roof paint as a solution to fading road markings. According to the Technical Data Sheet no. L-9-P of Plascon Nuroof paint, roof paint is an acrylic type of paint and is extremely durable against the harshness of the weather.
When concrete roof tiles are manufactured a much finer aggregate is added to conform to national standards for specific properties, causing the cement to have fewer surfaces to “cling” to, resulting in a rough surfaced and porous tile, other than the smooth surface of a concrete paver. That is why acrylic paint would rather stick to roof tiles than concrete pavers, as roof tiles are more absorbent.
The Ultimate Solution – an answer to Paved Road Marking
Extensive research and studies by Acme paving in Singapore and Bosun Brick in Midrand Southern Africa found that reflective surface topping found on reflective interlocking pavers, could in fact reduce the number of accidents caused by poor road demarcation. This is due to the luminosity of the reflective beads that make up the product’s topping.
Performance trials conducted in Singapore also demonstrated that under similar traffic conditions, reflective pavers continued to perform after seven years, while painted road markings started to disappear within a month of application. In fact, the wear and tear exposed the reflective beads in the top layer of the reflective surface topping to such an extent that the product’s light reflecting capability improved, making it more cost effective, “roadworthy” and slip resistant than painted road markings in the long run.
Garth McMillan of Bosun Brick explains: “While traditional road marking is done by means of road marking paint and glass beads [lines are painted with road marking paint where after glass beads are sprinkled into the applied painted line], reflective pavers are manufactured with Acme’s unique reflective top mix.” Once installed, the reflective pavers never need to be resurfaced and last as long as the brick holds its structure, which can be over 30 years. Traditional painted road applications need to be repainted at least once or twice per year.
Another advantage of reflective pavers is that the pattern can be uplifted and reused or redesigned at any given time, and then relayed again.
Submitted by PJVANS Construction, your construction, building, painting, road marking, paving and water feature expert - You are the center of our attention.
For more info, visit http://www.pjvans.com