Concrete plasticizers
You've probably heard of concrete plasticizers. Plasticizers help us liquefy the concrete mix for better compaction. Often we need the mix to be thin so that it can be transported with a mixer, for example, so that it flows where we need it to go and so that we can compact it as well as possible, i.e. get rid of air bubbles.
But why not just dilute the mixture with water?
The problem with water is basically that there will be no water in the final product. Concrete uses it for curing and any water beyond the requirements of the curing process is actually a detriment. The goal of plasticizers is to make the mix workable without the concrete losing quality by dilution.
The correct water ratio is one of the most important factors. The whole issue is referred to by concrete mixers as the Water Coefficient. It not only dilutes the mix, but is often pushed to the surface by the heavier aggregate. This displacement can also take some of the cement binder with it. This displacement of excess water is known among concrete workers as bleeding.
To illustrate, we use this phenomenon in the custom fabrication of bowls when the customer wishes to expose the pathways of water rising and exposing the aggregate.
So, in order to achieve the necessary plasticity of the mix without degrading it with too much water, we can use a plasticizer. This replaces a certain amount of water without risking the mixture becoming degraded. Depending on how much water the plasticizers replace, we call them
plasticizers that replace 5% to 15%
superplasticizers replacing 15% to 30%
hyperplasticizers replacing 30% or more
The Romans already added animal plasticizers such as blood, eggs or milk to Roman cement. This helped with the workability of the mix, but also for better adhesion and also frost resistance. Today, the three main types used in terms of chemistry are:
Lignisulfonates are natural substances that are extracted from wood. They are effective in reducing water consumption and improving the workability of concrete. Lignins are otherwise used, for example, in the softening of hard water and, interestingly, the oxidation of lignosulfonates from softwood trees can produce Vanillin, an artificial vanilla flavour!
Polycarboxylates are synthetic substances that are effective in reducing water consumption and improving the water tightness of concrete. They are also used in laundry detergents where they prevent washed out dirt from soiling washed clothes again.
Melamine resins are synthetic substances that are effective in reducing shrinkage and improving the frost resistance of concrete.Melamine is then made famous in the form of fibers that are very durable and non-flammable.
Plasticizers and superplasticizers can often be purchased at hobby houses, whereas hyperplasticizers must be ordered. It is important to read the method of use as some are added to the mixing water, others are poured into the mix. Like most additives, plasticizers should not be encountered with dry cement.
