Concrete admixtures are essential components used to enhance the properties of concrete mixes. This guide provides valuable insights into various types of concrete admixtures, their characteristics, European standards and applications.
Concrete Admixture Basics
Concrete admixtures are liquids or powders which are added to the concrete during mixing in small quantities. The dosage is usually defined based on the cement content (expressed as a percentage by weight of cement or %bwc).
Concrete admixtures have a significant impact on the fresh and/or hardened concrete properties. Admixtures can act chemically and/or physically on the cement hydration.
Concrete Admixtures Defined According to European Standards
According to EN 206, various types of concrete admixtures are defined with requirements described in EN 934-2. In the standard EN 934-2, the different product groups are defined and described below.
| Permitted Dosage | ≤ 5% by weight of the cement. (The effect of a higher dosage on the performance and durability of the concrete must be verified.) |
| Low Dosages | Admixture quantities < 0.2% of the cement are only allowed if they are dissolved in part of the mixing water.) |
If the total quantity of liquid admixture is > 3 L/m³ of concrete, their water quantity must be included in the w/c-ratio calculation.
If more than one admixture is added, their compatibility must be verified by specific testing.
Admixtures According to EN 934-2
| Water Reducing Admixture / Plasticizer | Admixture which permits a reduction in the water content of a given mix without affecting the consistence, or which increases the slump/flow without affecting the water content; or produces both effects simultaneously. | |
| High Range Water Reducer / Superplasticizer | Admixture which permits a high reduction in the water content of a given mix without affecting the consistence, or which increases the slump/flow considerably without affectingthe water content; or produces both effects simultaneously. | |
| Retarder and Water Reducing Admixture | Combines effects of a water reducing admixture (primary effect) and a retarder (secondary effect). | |
| Retarder and Superplasticizer | Combines effects of a superplasticizer (primary effect) and a retarder (secondary effect). | |
| Set Accelerator and Water Reducing Admixture | Combines effects of a water reducing admixture (primary effect) and a set accelerating admixture (secondary effect). |
| Viscosity Modifying Agent (stabilizer/water retaining admixture) | Reduces the loss of mixing water by reduction of bleeding of the fresh concrete. |
| Air-entraining Agent | Provides evenly distributed air voids system by introducing a specific quantity of small air bubbles during the mixing process which remain in the concrete after it hardens. |
| Set Accelerator | Reduces the time to initial set, with an increase in initial strength. |
| Hardening Accelerator | Accelerates the early strength development of the concrete, without or with minor influence on the setting time and plastic properties of freshly mixed concrete. |
| Retarder | Extends the time to initial set, with an extended workability time and retardation of early strength development. |
| Water Resisting Admixture | Reduces the capillary water absorption of hardened concrete. |
Additional Types of Concrete Admixtures Not Defined in European Regulations
| Shrinkage Reducing Admixtures | Reduces early age drying shrinkage of the concrete in order to prevent drying shrinkage cracks. |
| Pumping Aid | Admixture to improve the stability of the fresh concrete and easy pumping of concrete especially with application of difficult aggregates and unfavourable grading curves. |
| Corrosion Inhibiting Admixtures | Admixture producing a protective layer on the steel reinforcement in reinforced concrete. As a result start of corrosion is delayed and corrosion speed is decreased leading to extended durability. |
| Surface Improving Admixtures | Blowhole reducing admixture that significantly reduces the overall air void content in the fresh concrete for production of high quality fair-faced concrete. |
| Admixtures to Control Alkali-silica Reaction | Admixture allowing for control of alkali-silica reaction (ASR) in high-alkali concrete. Application minimizes deleterious expansions in concrete due to ASR and increases durability and life span of the concrete structure. |
Polycarboxylate Ether Technology
The major characteristic of polycarboxylate ether-based superplasticizer technology is its targeted polymer design to achieve specific concrete properties. The mode of action is based on the adsorption of the PCE onto the cement grain and dispersion of the particles by electrostatic repulsion and steric hindrance.
Characteristics that can be influenced are:
- Adsorption speed
- Water reduction with high initial liquefaction / workability
- Slump retention without retardation and subsequent fast strength development
- Early strength development with sufficient workability time
- Stickiness
- Stability / viscosity
Various combinations of these properties can be optimized.
Polymer Structure of PCE and How It Works
Polymer Structure PCE
The polymers consist of backbones with carboxyl groups and side chains.
- The first component – backbone with carboxyl groups – is responsible for the attainable water reduction / initial slump and mixing time respectively.
- The second one – side chains – determines the slump keeping capability of the superplasticizer, affected by an increasing number of side chains.
The crucial factor is the limited space for carboxyl groups and side chains along the backbone. Either a carboxyl group or side chain can be attached at a certain location.
Variations in those factors lead to three generic types of polymers:
- water reducing
- slump controlling
- slump retaining polymers
Mode of action: PCE
Adsorption of the polymer (backbone) on the cement grain.
Detail of the adsorption of the polymer (backbone) on the cement grain.
Improved workability due to steric hindrance.
Detail of improved workability due to steric hindrance.
Designing an Ideal PCE with Sika® ViscoCrete®
It is possible to design a PCE with a large number of carboxyl groups and consequently low number of side chains, leading to high water reduction and shorter slump life of the concrete (Water Reducing ViscoCrete® Polymer).
Another possibility is to have a large number of side chains resulting in lower water reduction and longer slump life. These type of PCE work by creating a certain depot effect which results in an extended slump retention (Slump Retaining ViscoCrete® Polymer).
The third possibility is to design PCE which are able to change their structure in concrete over time. This special behavior causes a delayed dispersion effect. Such kind of specifically designed polymer can be used for slump controlling (Slump Controlling ViscoCrete® Polymer).
The Sika® ViscoCrete® technology offers more than the possibility to design PCE polymers with specific properties. It enables combination of various polymers to exploit the potential of each one. This compatibility is a major advantage of Sika® ViscoCrete® technology: tailor made solutions can be developed and adapted to the performance of the concrete mix. Moreover, final products can be optimized regarding the local market requirements to yield the best cost-performance solution.
Sika® ViscoCrete® Product Technology
Sika Products
Here is a handy glossary of Sika concrete admixture product brands and their admixture type:
| Brand Name | Product Type |
|---|---|
| SikaControl® AER | Air-entrainer |
| Sika® Antisol® | Curing agent |
| SikaControl® SRA | Shrinkage reducer |
| SikaControl® ASR | Admixture to control alkali-silica reaction in concrete |
| Sika® FerroGard® | Corrosion inhibitor |
| SikaFiber® | Micro synthetic, macro synthetic or steel fiber |
| SikaFume® | Silica fume |
| Sika® Stabilizer Lightcrete | Foaming admixture |
| Sikament® | Superplasticizer |
| SikaPaver® | Compaction aid / anti-efflorescence admixture |
| SikaPlast® | Superplasticizer |
| Sika® Plastiment® | Plasticizer / water reducer |
| Sika® Plastocrete® | Plasticizer / water reducer |
| Sika® Stabilizer Pump | Pumping agent |
| SikaRapid® | Concrete accelerator |
| Sika® Rugasol® | Surface retarder |
| Sika® Separol® | Mold release agent |
| Sika® Sigunit® | Shotcrete accelerator |
| Sika® Stabilizer VMA | Viscosity modifying agent |
| SikaTard® | Concrete and Shotcrete retarder |
| Sika® ViscoCrete® | Superplasticizer |
| Sika ViscoFlow® | Workability enhancing admixture |
| SikaControl® WT | Water resisting admixture |
