A Guide to Concrete Retarders: Types, Benefits, Uses, and Drawbacks

Concrete admixtures and retarders are popular materials used to enhance the mechanical properties of concrete and mortar. Nowadays, concrete retarders are highly preferred in hot weather to allow time to properly mix, transport, and place concrete wherever necessary.

Many construction chemical manufacturers provide concrete retarders but to get the best results it is always recommended by the experts to choose the best ones. Nevertheless, in this blog, we will explore all about concrete retarders including their mechanisms, types, benefits, and more.

What is a Concrete Retarder?

To give idea about the concrete retarders, it is additives that are added to cement-based mixtures like mortar or concrete to delay the setting time of the cement paste. These are commonly known as concrete retarders, which are water-soluble additives that get easily dissolved in water.

When you add the concrete retarder in the concrete mix can result in extending the setting time of the concrete by approximately up to one hour. It basically slows down the hardening in warm or hot weather to allow construction workers more time to mix, deliver and pour the concrete. In fact, concrete retarders reduce the pace of the process while conserving water.

Mechanism of Retardation

A concrete retarder is a type of admixture that temporarily stops the hydration process upon addition to the mixing water or on application to the surface of fresh concrete, thereby allowing additional time for the concrete to rest before it begins to harden.

The mechanism involved in such retarders depends on both the type of retarder and cement involved. It is worth noting that the retarder effects are temporary or for a short period of time, and after a certain period, its mechanism fades, and the watering goes back to normal.

Below are the four key ways retarders slow down the setting process:

1. Adsorption:

A retarding additive forms a protective coating on the surfaces of the cement particles. The barrier reduces access by water molecules to the unhydrated cement, hence it retards the hydration reactions. As a result, the cement paste thus remains workable for a longer time due to the insufficient hydration produced to initiate hardening. The retarder complex with the C3A of cement and comes out of solution, incorporating into the hydrating material.

2. Nucleation:

When water is added to it, the surfaces of cement particles release calcium and hydroxyl ions into the mix. When their concentration increases up to a certain critical amount, C2S and CS start crystallizing. In this process, the crystal nuclei of calcium hydroxide absorb the retarding admixture that delays further crystal growth until the point where the cement becomes supersaturated.

3. Complexation:

At the start of the process, calcium ions given out by the cement grains make some complex with other ions. It is easier to dissolve cement when these complex forms. In the liquid phase of the cement paste, during hydration with a retarding admixture, the concentrations of Ca²⁺, OH⁻, Si, Al, and Fe are increased. This buildup of calcium and hydroxyl ions interferes with the association between these ions and thus slows down the hydration process.

4. Precipitation:

During precipitation, the retarder interacts with the highly alkaline solution to form insoluble derivatives. The phenomenon resembles with adsorption. In a few minutes of mixing water with cement, the pH of the solution goes beyond 12. These insoluble compounds create protective coatings around the cement particles, which slows down the hydration process. The coating forms a diffusion barrier that restricts the ability of water to reach the cement particles effectively.

This is all about the mechanism of concrete retarders and now let’s check out the types of concrete retarders. 

Types of Concrete Retarders

There are broadly two categories of concrete retarders which are as follows:

1. Organic Retarder

• Phosphonates
• Sugars
• Lignosulphonates
• Hydroxycarboxylic acids and their salts

2. Inorganic Retarder

• Phosphonates
• Borates
• Salts of Pb, Zn, Cu, As, Sb

Now, let’s understand how retarding additives acts on the concrete’s properties.

How Retarding Additives Affect Concrete’s Properties?

1. Effect on Strength: When used with concrete, retarding additives decrease the initial compressive strength compared to non-treated concrete.
2. Effect on Durability: As retarding additive primarily slows down the setting time of the concrete, without affecting other properties of the concrete. Therefore, after curing retarded concrete shows the exact durability as the ordinary concrete.
3. Effect on Slump Loss: It is evident that the concrete treated with retarding additive shows great workability of the concrete by lowering slump loss.
4. Volume Deformation: Retarding admixtures has little effect on drying shrinkage but it may lead to an increase in plastic shrinkage.
5. Effect on Workability: The concrete workability is slightly affected by the retarding additives which led to a 60-100 mm more initial slump.
6. Effect on Air Entrainment: Most of the retarding additives do not accompany air, although some are. Particularly those based on Hydroxycarboxylic acid can reduce the air content.
7. Bleeding Risk: Whenever the concrete retarders are used in the concrete mixture, the risk of bleeding in the concrete grows.
8. Freeze-Thaw Cycles: The use of air-entraining admixtures often elevates the concrete’s resistance to freezing and thawing.
9. Heat of Hydration: Although retarding additives doesn’t eliminate the heat production of concrete. However, it delays the increase in peak temperature for the amount of time the concrete was retarded.

The above-mentioned effects can be observed when the concrete retarders are added to the concrete mixture. However, the best concrete retarder doesn’t affect the concrete properties after the setting time effect. Keep reading to know the various uses of concrete retarders.

Uses of Concrete Retarder

There are various applications of concrete retarders to get the desired outcome in particular situations. The following are the uses of concrete retarder: 

• Concrete retarders are mostly used with concrete admixtures when temperatures are hot or warm.
• Builders, developers, or construction companies often use concrete retarders when they aim to build big buildings or infrastructure projects.
• In some situations, the retarder is used on the outer surface of the formwork to stop the matrix from hardening.
• In certain instances, the retarder is applied to the outer surface of the formwork to prevent the matrix from hardening. However, the remaining concrete part gets hard due to the non-application of the concrete retarder.
• Admixtures that delay the reaction rate are utilized during the grouting process in oil wells.

Now that you are aware of retarder additive uses, let’s have insights into the advantages of concrete retarders.

Benefits of Concrete Retarders

There are several advantages of concrete retarder which are as follows:

• By using the concrete retarding admixtures, the workability and cohesion ability of concrete can be preserved. Resulting in increasing the time requires to set.
• Concrete retarders can help lower the risks associated with long-distance transportation in hot weather by targeting the acceleration of the initial setting time caused due to high temperatures.
• Due to the concrete retarder’s properties, it slows down the hardening process between concrete pours and helps avoid the formation of cold joints in large construction projects.
• In certain situations, concrete retarders can be used to decrease segregation and bleeding when poor sand grading is inevitable.
• When the concrete setting time is delayed and the workability of concrete is increased then concrete retardants improve permeability.

Limitations of Concrete Retarder

Each material has its own set of advantages and disadvantages when applied. Let’s explore some of the limitations of using concrete retarders.

• It is possible to use water reducers along with concrete retarders, but careful monitoring of the curing process is essential to avert bleeding and cracks.
• In the case of gypsum, it can positively delay the setting time of concrete when the process is properly monitored and managed. If gypsum addition is not monitored then it could result in unwanted expansion and an indefinite delay in the concrete setting.
• It is possible that concrete retarders can have different effects on various types of cement at different concentrations.
• The appropriate dosage of retarding admixtures must be determined based on the cement’s water-cement ratio, cement content, and C3A concentration.

The best concrete retards are always used in many great construction projects, however, you should also choose a branded one to get the best results in the construction process. Let’s have a look at one of the top-quality dry mix raw materials that can be used with the concrete admixtures.

Introducing Sodium Gluconate by Sakshi Chem Sciences Pvt Ltd

Sodium Gluconate which is also known as Sodium Salt of Gluconic Acid which is a dry mix raw material, can be used as a setting time retarder. Our Sodium Gluconate is formulated under strictly controlled conditions through the fermentation of glucose. To give an idea about it, it is a white crystalline powder and easily soluble in water.

Our Sodium Gluconate is non-toxic, non-flammable, and non-corrosive. In short, Sodium Gluconate is an environment-friendly and biodegradable construction chemical. When it is added to cement, it inhibits hydration and slows down the setting time of the concrete mix.

Conclusion

To wrap up, a concrete retarder’s role is impressive in the construction industry as it delays the hydration process. It keeps the concrete workable and easier to handle for an extended period. Concrete retarders are specifically useful in hot and warm temperatures to allow time for workers to deliver, transport, and pour the concrete. However, it is very essential to buy this construction chemical from authorized and genuine manufacturers like Sakshi Chem Sciences Pvt Ltd. 

We are one of the leading construction chemical manufacturers in India offering 200+ construction chemicals to construction companies, developers, builders, and various clients. Our trained team offers the best consultation, customized quotations, and assistance on quality products. So, if you are also searching for the best quality construction chemicals then get in touch with us.

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