What is Waterproofing Admixture for Concrete?
A waterproofing admixture is a specific type of admixture used in construction to prevent water from passing through hardened concrete when there is a pressure head. It is also known by other names such as water resisting admixture, permeability reducing admixture, or damp proofing admixture. This admixture is designed to reduce the permeability of concrete, making it more resistant to water penetration.
The use of a waterproofing admixture in construction is crucial in preventing damage caused by water infiltration. When water penetrates concrete, it can weaken the structure and cause it to deteriorate over time. This can lead to costly repairs or even the need for a complete replacement of the concrete structure. By adding a waterproofing admixture to the concrete mix, the concrete becomes less permeable and more resistant to water penetration, thereby reducing the risk of damage caused by water.
Overall, a waterproofing admixture is an essential component in the construction of durable and long-lasting structures that are able to withstand the effects of water infiltration. Its ability to reduce the permeability of concrete makes it an effective solution for preventing water damage, and it is widely used in various construction projects such as building foundations, retaining walls, and basements.
Requirement of Waterproofing Admixture for Concrete
Concrete is a widely used construction material, and water is an essential component of the concrete mixing process. From the initial mixing to the curing of concrete, water plays a vital role. However, once concrete gains its required strength, any water penetration can cause severe damage to the concrete. Corrosion of reinforcement and freeze-thaw damage are the two primary types of damage that can result from water infiltration in concrete.
After curing, the water content in concrete evaporates and leaves behind voids within the material. To create a durable concrete structure, it is recommended to use a low water-to-cement ratio. This can help reduce the porosity of the concrete. However, even with a minimal water-to-cement ratio, concrete cannot be entirely waterproof. This is because concrete is a porous material, and water can penetrate through its pores and micro-cracks due to capillary action.
To address this issue, there is a need for an admixture that can help control the porosity of concrete. Such an admixture can help reduce the potential for water penetration in concrete and, thus, minimize the risk of damage to the material. In summary, while water is an essential component of concrete construction, its presence can also pose a significant risk to the durability of concrete. To ensure long-lasting concrete structures, it is essential to use low water-to-cement ratios and admixtures that can help control the porosity of the material.
Functions of Waterproofing Admixtures
Permeability reducing concrete admixtures, also known as waterproofing admixtures, are used to improve the water resistance of concrete structures. These admixtures function by altering the properties of the concrete, specifically by reducing the size, number, and continuity of capillary pores within the concrete. Capillary pores are small, interconnected spaces within the concrete that allow for the passage of water through the material.
By reducing the size and number of these pores, permeability reducing admixtures effectively block the capillary pores of the concrete, preventing the absorption of water due to capillary action. Additionally, some waterproofing admixtures may also line the capillary pores with hydrophobic materials, further preventing the absorption of water into the pores.
It’s important to note that permeability reducing admixtures cannot completely prevent the movement of water through cracks in the concrete or through poorly compacted concrete. These factors are among the most common reasons for water leakage in concrete structures. However, by reducing the size and number of capillary pores and blocking their continuity, waterproofing admixtures can significantly improve the water resistance of concrete structures, helping to prevent damage from water infiltration.
Waterproofing concrete structures is a common requirement to prevent damage due to water penetration. While coatings, sealers, and membranes are popular options, they can be expensive and time-consuming to apply. A more efficient solution is to use a water-resisting admixture that can prevent the ingress of water into the concrete, thereby making it waterproof. The American Concrete Institute’s (ACI) Committee 212 provides guidance on the use of such admixtures in its ACI 212.3 Rev10 report, which is titled “Report on Chemical Admixtures for Concrete”. Chapter 15 of this report offers detailed information on permeability-reducing admixtures.
Materials Required to Prepare Waterproofing Admixtures
According to the ACI 212.3 Rev.10 report, there are several types of materials that can be used as waterproofing admixtures. One such type is hydrophobic or water-repellent chemicals, including oils and petroleum products. These chemicals work by creating a layer along the pores in concrete, thereby blocking the entry of water without filling the pores.
Another type of material that can be used as a waterproofing admixture is finely divided solid particles, in the form of inert or chemically active fillers. These particles act as densifiers and restrict the movement of water through the pores in the concrete.
Crystalline materials with hydrophilic properties can also be used as waterproofing admixtures. These materials work by increasing the density of calcium silicate hydrate and/or generating pore-blocking deposits that resist water penetration.
It is important to note that the ACI 212.3 Rev.10 report does not limit the use of materials for waterproofing admixtures to those mentioned above. Any material that is effective in blocking water penetration can be used as a single admixture or in combination with two or more other materials.
Dosage of Waterproofing Admixtures for Concrete:
The appropriate dosage for admixtures depends on the specific type of admixture being used and the desired level of performance for the concrete. Typically, hydrophobic admixtures are added in a proportion of around 2% by weight or volume of the concrete, while pore blocker types may require 5% or even more. It’s important to note that the percentage is based on the weight or volume of the concrete and not on the cement used.
Mechanism of Water Resisting Admixtures:
Water resisting admixtures are used to lower the porosity of concrete, which is a key factor in its ability to withstand water penetration. However, achieving lower porosity requires a reduction in the water content or water cement ratio. When the water cement ratio is lowered to less than 0.45, the porosity of concrete is significantly reduced. But if the water cement ratio is further reduced, the workability of concrete is adversely affected, making it difficult to achieve full compaction. This can result in shrinkage cracking, which can compromise the strength and durability of the structure.
To address this issue, water-reducing admixtures can be used. These admixtures are designed to reduce the amount of water required for a given volume of concrete without compromising its workability. By allowing for sufficient workability of the concrete, the water-reducing admixture can ensure that the concrete is fully compacted, reducing the risk of shrinkage cracking. This not only improves the strength and durability of the structure but also enhances its resistance to water penetration. Therefore, the use of water-resisting admixtures and water-reducing admixtures can help produce a more durable and long-lasting concrete structure.
When it is not possible to reduce the water cement ratio in concrete, there is an alternative method that can be used to improve its properties. This involves the use of pore blocking admixtures that are typically small in size, approximately 0.1 microns. These admixtures can be either reactive or unreactive, or insoluble polymer emulsions. During the hydration process of the concrete, these admixtures can settle in the pores and block them. This mechanism can help the concrete prevent further absorption of water and improve its overall durability.
Hydrophobic admixtures are another type of admixture that can be used to improve the properties of concrete. These admixtures are soluble with the concrete and react with the calcium in fresh concrete, forming a layer that is adsorbed by the surfaces of capillaries. This layer, after the process of hydration, can prevent the penetration of water into the pores of the concrete. However, it is important to note that the resistance of hydrophobic admixture is limited and depends on several factors such as the hydraulic head, the quality of the concrete, and the effectiveness of the admixture.
In conclusion, the use of pore blocking and hydrophobic admixtures are effective methods to improve the durability and water resistance of concrete. These admixtures can be used when it is not possible to reduce the water cement ratio and can help to prevent the absorption of water in the pores of the concrete. It is important to consider the limitations and factors that may affect the effectiveness of these admixtures when selecting the appropriate one for a particular application.