Once you have established a basic understanding of a simple concrete mix you can begin to learn more about new concrete technologies and the true limitations of this incredible building material – hint, there are not many!
By changing the volume and type of aggregates that you use in your cement mix you can create many different types of concrete suited to different applications. In general the goal of substituting aggregates is to have the concrete remain consistently strong as a finished product. Some examples of concrete advanced techniques are:
1) Color or dye in the concrete
2) Lightweight concrete
3) High strength concrete
4) Decorative concrete
Even all of these options are just the tip of the iceberg for what concrete is capable of. The extreme limitations of current concrete technology being researched and developed are transparent (translucent actually) concrete which will show a silhouette through concrete that is meters thick! Limitations of concrete strength is self supporting concrete which does not require the mechanical assistance of steel grid work. Concrete strength used to be measure is PSI however mPa or mega Pascals is the current unit of compressive concrete strength referring to the amount of force the concrete can ensure before failure.
You can add powder or liquid pigments to your concrete to achieve interesting and dynamic colors. Common colors would be brown, red, dark grey, tan and other similar earth tones. To get more vibrant concrete colors you can use pure white Portland cement in place of regular cement, as well as pure white sand instead of regular sand. This white mortar mix will react well to more vibrant colors and pigments. The amount of pigment or dye that you use will depend entirely on the brand that you choose. The best method is to purchase from a specialty concrete supply store which will have a far better selection of quality concrete color additives than your local hardware supply store.
You can replace all or part of the sand in a 3:1 mortar mix with aggregate materials that are much lighter in nature than sand. The result will be a concrete that is much lighter, but also vastly weaker than a 3:1 sand mortar. There are many applications for lightweight concrete with many of them being decorative such as planter pots or garden statues. The most common lightweight aggregate material substitutions for making concrete are:
Vermiculite – which is a mineral and often sold as “pool base” in larger quantities from pool stores which will make a relatively strong, but compressible concrete. The insulation value of vermiculite is very high, more than ten times as high as sand, so vermiculite concrete mixes are often used for sound dampening and insulating.
Peat Moss – Using peat partially in place of sand will result in a concrete that is much weaker than traditional 3:1 mortar and even much weaker than vermiculite concrete. The texture of the concrete is somewhat earthy and finishing and detail work con be slightly difficult by comparison with other mixes.
Saw Dust – This is another readily available and cheap aggregate substitutions used to achieve a lightweight concrete. In addition to providing a rough and inconsistent texture to the concrete, the wood ingrained will often stain and discolour creating an interesting and unique pattern. Too much sawdust can make the concrete unacceptably weak very quickly – more so than vermiculite and peat moss.
Perlite – This is commonly used for gardening and is recognisable in that it is completely white and very similar in texture to styrofoam beads. The main advantage of this aggregate choice is the fact that it is white. It has a similar overall feel as vermiculite however the concrete produced with vermiculite is much easier to work and finish than concrete made with perlite.
Usually you can replace up to two of your three buckets of sand with an alternative aggregate. Vermiculite can be mixed with straight cement without sand and still remain strong enough to suit several tasks such as swimming pool floors. The other aggregates will yield a concrete that will break under its own weight.
High Strength Concrete
The current strength for concrete is measured in mPa with the average sidewalk concrete being 10-15 mPa where as foundations for homes usually start at 20-25 mPa. High rise commercial concrete is closer to 35 mPa as is swimming pool construction concrete.
The strengthening of concrete over and above what a 3:1 mortar mix will yield requires engineering and testing. If you order concrete from a ready mix or bath plant you can specify precisely how strong you want the concrete to be. If you are mixing it yourself and want to make the concrete as strong as reasonably possible there are a few things that you can do.
Glass Fibres – Glass fibres and fibreglass are two different additives which you can put into your concrete to help make it cohesively stronger as well as minimize hairline cracking in the concrete during the curing process.
Water Reducer – is a liquid that you can put into the concrete in place of water. The water reducer will increase the viscosity and workability of the cement dramatically without affecting the finished strength negatively. The more water that you put in concrete the weaker the finished product will be. In place of water reducer you can also use the absolute minimum water possible to get the concrete workable to make it as strong as possible.
Powder Additives – Combinations of highly dense powders such as silica fume and fly ash can potentially help to make concrete stronger by filling in some of the microscopic spaces left in regular concrete by the larger sized aggregates. These tiny aggregates are dangerous to work with because the airborne particles are small enough to damage your lungs should you breathe them. Most of these powder additives will be hard to locate for the average DIY enthusiast.
In place of sand you can also add just about any other substance such as glass or coloured beads, pieces of plastic or metal, rubber or anything else you can think of. Most commonly you would use this concrete to create an exposed aggregate where loose aggregate is imbedded into the top of partially cured concrete. Exposed aggregate with small coloured stones is very common and you likely have seen this before. Exposed aggregate with marbles and microchips is less common to be sure – but not any less possible.
With some basic practice you can learn to create incredible things such as statues, pool decks, artificial rocks, ponds, waterfalls and decorative art.