Due to it’s strong fluidity, shotcrete is highly beneficial. When the homogeneous mix is applied pneumatically, it simply conforms with even rugged surfaces whereas maintaining the initial resistance to compression to offer good structural support from the beginning.
A family of chemical polymers like plasticizers and super-plasticizers are liable for the material’s fluidity. These are also called water reducers to minimize the total water-to-cement ratio, providing it a more ‘liquid’ consistency devoid of diluting the mix with water.
These additives are normally added all through the mixing process and allow the concrete mix to become yielding until application keeping its consistency unchanged.
Plasticizers and super-plasticizers provide a temporary dispersing effect, that produces a comprehensive hydration of each cement particle, making the fluidity of the mix better.
This mix is amalgamated with volcanic fly ash to form the type of hydraulic concrete, a fully hardy and weatherproof material along with extremely erosive salt water.
Plasticizers: first steps - First generation of plasticizers is known as Lignosulphonates. It belongs to a byproduct originated from wood processing that is frequently applied in recent times to form a workable mix with only basic raw materials.
These additives, known as Mid-Range Water Reducers [MRWR] affix themselves to the surface of a cement particle, that bears both positive and negative charges. Plasticizer polymers, which are negatively charged, neutralize the positive charges on the cement surface, transforming the entire surface completely negative.
It causes a physical effect that allows the negatively charged cement particles to keep away each other, providing a dispersing effect to develop better water infiltration. This mix can now function well devoid of adding more water, and allows for a cutback in the overall amount of water necessary, reducing the water-cement ratio by around 10%.
But these additives can defer the curing process, which may sequentially produce further complicacies. If curing is not done within a certain timeframe, a greater amount of hydrostatic pressure could amass in a formwork column over a long lasting period, causing the formwork to burst.
The second generation: Plasticizers 2.0: This type of plasticizer can significantly lessen the water-to-cement ratio of around 25%. Polysulfonates like naphthalene and melamine offer same type of working mechanism to the first generation of plasticizers, producing an electrical dispersing albeit of superior intensity.
These polymers conform to the cement particles, charging them negatively to form repulsion among related particles, allowing water to flow and hydrate the mix in an efficient manner.
This similar repulsion activity also activates major air occlusion, raising the workability of the mix but at the same time developing pockets of air that reduces its resistance and settle its structural integrity.
This type of polymer may also put other challenges, since it provides a very narrow window of ‘workability’: as soon as the cement is hydrated, it is likely to develop a crust-like byproduct that makes application complicated.
Super-plasticizers: the third generation - Super-plasticizers stands for the additives which bring huge benefits along with a water-to-cement ratio curtailment of around 40%.
Polycarboxylates alias High Range Water Reducers (HRWR) function on the base of sterical in spite of electrostatic repulsion. A major steric effect is steric hindrance for which a chemical reaction can’t occur. In this case it stops cement particles from agglomerating.
Polycarboxylates stands for complex co-polymers which are applied to satisfy several functions, and comprise of a negatively charged ‘backbone’ molecule with polymeric side chains.
Most of these additives can be amalgamated jointly, and blended with other types like air-entraining, accelerating and retarding additives