Sika Admixtures For Value Addition And For Improved Durability Of Concrete

Concrete is a very versatile and commonly used construction material worldwide. The main reasons for concrete being a popular choice as a construction material are its - availability, easy production, strength, workability, cost and durability. Concrete is normally specified by its strength and workability, but for important structures often durability parameters such as water permeability, chloride migration and length change are specified.

This article briefly mentions about three types of durability-increasing admixtures offered by Sika, which protect concrete from water-permeability, steel corrosion and drying-shrinkage cracking.

Sika WT-200 P (IN)
This is an integral crystalline permeability-reducing admixture for concrete.

Sika WT-200 P (IN) improves the durability of concrete by reducing the water absorption and water penetration in concrete. When added to concrete, the active ingredients of Sika WT-200 P (IN) react with water and cement particles in the concrete to form compounds, which increase the density of the calcium silicate hydrate gel, some of the reaction products also form precipitates (pore-blocking deposits) in the existing micro cracks and capillaries, hence reducing the water penetration. If hairline cracks are formed in concrete during its service life, the active ingredients present in Sika WT-200 P (IN) react with moisture and seal the crack, promoting crack healing.

By reducing the permeability of concrete, Sika WT-200 P (IN) prevents the entry of harmful contaminants in concrete including chlorides and overall improving the durability of the concrete.

Sika Ferrogard-901 (IN)
This is a liquid concrete admixture formulated to protect embedded reinforcing steel from corrosion, and to provide an effective means for extending the service life of concrete structures. In sound concrete, steel reinforcement is protected by the highly alkaline environment, which deposits a passivating layer of iron oxides around the steel. This passivating layer can be broken down by a number of destructive mechanisms, including carbonation and chloride penetration. Once the steel loses its protective layer, corrosion can begin to occur. Steel corrosion is an electrochemical process consisting of two partial reactions, one at the cathode and one at the anode. Sika FerroGard-901 (IN) is an active, dual purpose, bipolar inhibitor containing a combination of aminoaclohols, an organic and inorganic inhibitor. This protects both the anodic and cathodic parts of the corrosion cell. Due to its high vapour pressure, Sika FerroGard-901 (IN) penetrates through concrete to the steel reinforcement, where it is absorbed onto the surface. Sika FerroGard-901 (IN) forms a continuous protective film around the steel presenting a physical barrier to chlorides and other deleterious substances. Because of its high affinity to steel, Sika FerroGard-901 (IN) is also able to displace chloride ions from the metal surface to protect concrete from chloride induced corrosion.

Sika Control-40
This is a shrinkage-reducing admixture (SRA) used to prevent drying shrinkage cracking in concrete. Addition of Sika Control-40 to concrete typically reduces its drying-shrinkage by over 50%. Sika Control-40 also reduces the number of cracks formed in concrete, which reduces the ingress of contaminants into concrete, thus improving its durability. Shrinkage of concrete occurs in three basic modes: plastic-shrinkage, autogenous-shrinkage and drying shrinkage. Drying shrinkage is more detrimental in most of the concrete. One of the methods to reduce drying-shrinkage is use of SRAs. Drying-shrinkage cracking in concrete is caused when there is a loss of water from the capillary pores of hardened concrete. When the water evaporates from the capillary pores, the water menisci formed within the pores exerts pressure by pulling the walls of the concrete inwards, which leads to shrinkage cracks in the surrounding concrete. When Sika Control-40 is added to concrete, it reduces the surface tension of the water present in the capillary pores of concrete and prevents the formation of menisci which pulls the pore walls, thus minimizing drying-shrinkage cracking.

Dr. Ketan R Sompura
Head of R&D and Technical - Concrete,
Sika India Pvt. Ltd.
T: +91 22 6270 4038