When working with a large amount of cement, a problem inevitably arises associated with the rapid solidification of the composition. The joints of areas previously poured and covered with fresh mortar (working seams) are a weak point of the finished structure, and requires laborious processing, otherwise it is impossible to concrete reliably.
The ideal option is to either pour the mixture continuously or at short intervals so that it does not have time to harden. However, there are also special components that can be added. Their principle of action is to reduce the rate of connection of cement with water (hydration and hydrolysis).
Advantages of Using Supplements
Pros of using:
- Reduction of time and energy consumption for vibration;
- Preservation of workability;
- The possibility of concreting at an air temperature of up to + 30 °C due to an increase in the period of preservation of mobility;
- Obtaining a highly mobile mixture;
- Reduction of cement consumption;
- Exclusion of delamination;
- Reduced shrinkage;
- Increased strength;
- Improving the surface of the finished structure;
- More comfortable working conditions by reducing vibration noise.
Types of retarders for setting and hardening concrete
1. Chemical additives.
The first type is composed of one component. They are usually sold in powder form.
Nitrilotrimethylenephosphonic acid (NTF)
The agent does not cause oxidation of the reinforcement. NTF is suitable for all types of cement, but if the recommended dose is exceeded, the strength grade may decrease. The additive is also a plasticizer. This substance is added in an amount of 0.02-0.15% of the mass of cement.
It is sold in the form of a powder that is highly soluble in water. The substance is completely decomposed naturally, has water-retaining, plasticizing properties. Fall asleep in the amount of 0.05-0.25%.
Adding to the concrete solution allows: to reduce the vibration time or to do without it altogether, to reduce the cement consumption by 20%.
2. Ready-made formulations of several components.
They are produced and sold in finished form (powder or solution) by companies specializing in the manufacture and supply of construction chemicals:
SikaPlast 520 N.
Its basis is a unique polymer developed by the manufacturer Sika. Introduce in the amount of 0.2-1.5% of the mass of cement.
Retarder (supplier Promsnab from Kemerovo).
Does not contain components that are corrosive to the reinforcement. Reduces the setting speed by 2-8 times (depending on the dosage), incompatible with antifreeze additives.
Linamiks (Polyplast Company).
This is a whole series based on various chemical components.
Ready-made formulations can be purchased in bags, barrels, bottles or cans.
3. Waste from food production.
Certain types of food waste are safer to reduce the setting speed:
- The liquid obtained in the manufacture of cottage cheese or cheese.
- Its composition: whey proteins, lactose, milk fat.
- It has a strong retarding effect when added directly to the concrete mix, and at the same time is a plasticizer.
- Dosage: 1.5-3% by weight of cement.
Feed sugar molasses from molasses supplier malaysia.
- It is a thick dark viscous liquid, a waste of the sugar industry.
- Molasses replaces the plasticizer, it is not suitable for use in the manufacture of precast concrete structures.
- Recommended dosage: 0.05-0.3% by weight of cement.