Recommendations for the Placement of Additives or Admixture in Concrete
The use of an admixture makes it possible to improve certain qualities of a mixture of mortar, concrete, or plaster. Additives are liquid or powder products that are added at the beginning, during, or at the end of mixing. An adjuvant should always be used in small quantities. Its percentage by weight relative to the cement is generally between 0.2% and 2%. The dosage should be carried out in strict accordance with the manufacturers’ guidelines.
The characteristics of concrete or a mortar that can be optimized by the use of an ad hoc admixture :
● Consistency;
● Setting time ;
● Sealing;
● Frost resistance;
● Mechanical resistance ;
● Impact resistance ;
● Abrasion resistance;
● Chemical resistance;
● Color and aesthetics;
The different types of concrete admixtures
There are many additive products to modify the properties of concrete, mortar, or plaster.
Plasticizers and superplasticizers
Plasticizer additives, formerly known as plasticizers, are the most widely used in the manufacture of concrete. Their role is as follows:
● Increase the compactness and strength of concrete;
● Facilitate its implementation;
● Increase its maneuverability and workability;
● Reduction of mixing water;
● Reduce segregation of concrete by acting as a binder.
The plasticizer consists of wood or corn derivative. More powerful, the superplasticizer is made up of a synthesis of molecules.
Areas of application of plasticizers and superplasticizers:
● Ready-mixed concrete;
● Concrete for building;
● Road concrete;
● Shotcrete;
● Concrete for works of art;
Accelerators or antifreezes
There are two types of accelerator adjuvants.
The hardening accelerator
It accelerates the hardening of concrete by increasing the speed of its rise in strength. It allows to :
● Strip the concrete elements in a shorter time;
● Avoid long exposure to freezing;
● Charge faster.
Areas of application of the hardening accelerator:
● Ready-mixed concrete;
● Short-term strength concrete;
● Rapid stripping concrete;
● Prestressed concrete.
The setting accelerator
This additive makes it possible to reduce the setting time of the concrete or to place it frost-free. Its fields of application are identical to those of the hardening accelerator. However, concrete applied in cold weather can be added.
Set retarders
This additive makes it possible to extend the setting time. Therefore, the concrete can be worked longer.
Application areas of the set retarder:
● Ready-mixed concrete;
● Pumped concrete;
● Continuously cast concrete;
● Concrete applied in hot weather;
Air entrainers
The addition of this type of product causes micro air bubbles in the concrete which improves its durability and its resistance in the event of freezing and thawing. This additive also facilitates the implementation of concrete.
Areas of application for air entrainers:
● Ready-mixed concrete;
● Structural concrete;
● Concrete that must resist freezing and thawing;
Mass water repellents
A mass water repellent reduces the permeability of concrete by absorbing water by capillarity, thus preventing rising dampness. Its tightness is thereby reinforced. It also reduces the appearance of efflorescences such as saltpeter, among others.
Fields of application of the mass water repellent:
● Ready-mixed concrete;
● Waterproof concrete in the mass;
● Radiated concrete;
● Concrete for water tank and cistern;
● Precast concrete (curb, paver, etc.)
Other existing adjuvants on the market
● Dye: dyes the concrete in the mass;
● Fibers: metallic to increase the mechanical resistance of the concrete and avoid cracks or plastic to limit surface shrinkage;
● Protective additives: protects fresh concrete and mortar against drying out (water evaporation), which is too rapid;
How to properly use admixtures for concrete, mortar, and coatings?
Any concrete additive should be used with care. Here are some tips to follow so that your mix of concrete, mortar, or coating is successful.
● Does the adjuvants very precisely. An underdose decreases the effectiveness, an overdose causes undesirable effects;
● Avoid mixing additives from different manufacturers;
● Store the products away from frost and direct sunlight;
● Respect the expiry date;
● Introduce the admixture into the mixer when the mixture is already well wetted
Need advice on choosing a concrete admixture?
The team at your nearest Concrete contractors Houston is at your service to answer your questions about the different types of additives and their use. To find out more, you can also contact us by phone or via our online form.
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