The Science Behind Coloured Concrete

If the word concrete is mentioned, what do you think of? Do images of cold, grey stone appear in your mind? Is it overly sterile and kind of oppressive? A lot of the time, concrete is the utilitarian choice in building materials – to the point where aesthetics are often left behind. At A Better Driveway, we’re driven by excellence in concrete, so that means ensuring that it’s not only high quality in its function but also in its appearance.

However, when it comes to achieving the perfect colour in concrete, it’s not so much of an art as it is a science. For the overall appearance of a coloured concrete surface, there are a few factors at play, such as cement type, aggregate size and colour, water content, pigment selection, mixing technique and finishing methods. These all affect the final outcome of coloured concrete and that’s why in this week’s article we’re going to be explaining the science and process of it all in greater detail.


The cement

As you may suspect, the lighter the cement, the better it mixes with lighter pigments. That’s why white cement is best used with brighter and more vibrant colours. White cement also allows the colours to remain more consistent – meaning less variation from the original pigment when the final product is unveiled.

If you’re looking for some duller, earthy tones then grey cement is what you should go with. You should note, however, that the undertones of the grey cement can cause the colours you’re going with to alter slightly. So whatever colour you’re aiming for may be moderately offset due to the grey cement.


The aggregates

Aggregates generally come in two varieties – coarse and fine. Coarse aggregates – as the name suggests – include harsher materials such as gravel, limestone, crushed stone and expanded shale. Whereas fine aggregates are materials such as rock dust and silica sand.

Both types bring their own unique aesthetic to the table, but their effect is exclusively dictated by the volume of which is exposed on the surface of the final product. Though, the more aggregates that are heavily exposed on the surface, the more it starts to become the exposed aggregate style concrete.


The water

This may seem like an obvious point – as water is used to mix concrete – but it becomes a more precise science when colour is involved in the concrete. Water determined the durability, water tightness and strength of the concrete – depending on how much is mixed in to begin with.

These factors dictate the quantity of water that is used. Water is also key to controlling the colour of the concrete and ensuring consistent colouring between batches. The more water used in a mix – the lighter the colour will turn out. This is crucial to note when mixing in your pigments if you want to alter the tone of it – or avoid doing so.


The pigments

You might just think that pigments are simply defined as colours – and you’re not exactly wrong – but the science behind it goes much deeper than that. Pigments are actually defined as materials that either reflect or transmit light. This is an outcome of wavelength-selective absorption. It is this reaction that allows colours to be observed – because, at the end of the day, we only see colours because of light reflections.

The pigment particles themselves can actually come in different shapes, such as spheres, rods and other irregular shapes. Different shapes and forms will actually affect the final outcome of the mix differently, so, it’s vital that you test the pigments in smaller sample batches to make sure you perfect the mixture. This way, there’ll be no mistakes or heavy variations between the batches when it comes time for the real thing.


Inorganic and organic pigments

Pigments are split into two types. Inorganic pigments are the preferred pigment of choice for when it comes to the industry standard for integral colour in concrete – ASTM C979. Different inorganic pigments achieve different colours – though the majority of them are earthier tones. Some of the inorganic pigments you can use are:

  • Synthetic iron oxide – Will give you a variety of earthy tones.
  • Chromium oxide – Presents a stable green tone.
  • Titanium oxide – This is used for lighter colours such as white and – if used with grey cement – a light grey.
  • Cobalt oxide – Cobalt oxide will result in blue and teal tones.

Organic pigments are used in conjunction with inorganic pigments when you want to break the natural barrier and get a bit whimsical with your colours. They are cleaner, brighter and much stronger than oxides and thus allow for deeper colours to be achieved.

Whilst the use of organic pigments with inorganic pigments can allow the creation of colours such as bright violets, reds and yellows – there are some side-effects to using them such as curing time and the amount of water that is needed. This is another reason to test your mixtures in smaller samples before proceeding with large batches.


Using the colour in the cement

TCB stands for total cementitious binder. The TCB is made up of the combination of cement and pozzolans– which are mixed to form concrete. Loading rate, is the name given to the amount of pigment that is required to attain a particular colour. To determine the amount of pigment you’ll need to complete a specific job you’ll have to multiply the loading rate by the TCB. This will ensure that you have the correct amount of coloured concrete and that – more importantly – it will hold the same colour throughout with little to no tonal variation.


Interested in coloured concrete?

Whether you need your driveway redone or are looking to have something completely new paved – A Better Driveway is here to help. We specialise in coloured concrete and understand the finesse and mastery that comes with the territory. Our friendly and highly experienced contractors will work around your schedule to ensure that the job is done on time and to quality standards. Some of our other services also included exposed aggregate and textured concrete driveways.

If you would like to get in touch with us to know more about coloured concrete or how we can help you with your next driveway job, then please give us a call on (03) 9308 6112. Alternatively, you can also fill out the enquiry form on our website.