Calcium aluminate cement is a special cement with high performance and strength that is resistant against heat. Calcium aluminate cements differ from other cements, especially when compared to Portland cements, in chemical, physical and mineralogical terms. Calcium aluminate cements are used in concretes with resistance in high temperatures and refractory applications, in tunnels requiring cold weather and early age high strength, in road applications and field concretes. In this article written on Çimsa Blog, we will talk about pipe coating usage of calcium aluminate cement.
What is Calcium Aluminate Cement?
Binding materials are very important in the construction sector, and they are observed to be used in many different applications. Calcium aluminate cement (CAC) is one of the binding materials and contains calcium aluminate component. CAC is a special cement type used in high temperature applications. It is known that calcium aluminate cement has been successfully used in sewage and wastewater pipes for a long time. CAC is preferred in pipe coating applications due to its properties of fast strength gaining, high durability and chemical durability, high temperature resistance, etc. You can check out our other blog post titled Everything You Need to Know About Calcium Aluminate Cement’ for detailed information on CAC.
Where are Pipe Coatings Used, What are the Required Properties?
Pipelines are important infrastructure systems used to transfer wastewater, gas, petroleum, and chemical materials. Pipe coatings need to have properties such as durability, resistance against corrosive effects and strength. And at this point, the unique properties of calcium aluminate cement come into play.
What are the Properties Required to be Present in Pipe Coating Material?
High Durability
An indispensable quality that pipe coating materials have to have is high durability. Calcium aluminate cement is an ideal pipe coating material with high durability it provides. The strength of calcium aluminate cement is affected by various factors such as water/cement ratio, porosity and density of the application surface. For long-term durability, it is known that CAC is required to have under 12% porosity and under 40% water/cement ratio.
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Fast Strength Gaining
Pipelines require fast repair processes due to their locations. Calcium aluminate cement provides early high strength gaining ability in these applications thanks to its physical, chemical, and mineralogical properties. With this property, it allows for commissioning with 6 hours of early high strength and 24 hours of final strength gaining.
Chemical Durability
Pipes are being exposed to many different chemical substances and their effects due to the water structures they carry. Therefore, pipe coatings should be resistant against chemical effects.
Especially waters rich in sulphate negatively affects the pipe structure. Sulphate causes chemical reactions and wearing in the concrete in contact with it. This type of water can cause corrosion in the metals found in pipelines. The presence of calcium aluminate cement slows down sulphate penetration, thus preventing ettringite formation. Therefore, CAC is preferred in sulphate-dense environments.
Calcium aluminate cement also provides protection for pipe coatings in environments with chloride. Environments rich in chloride have an especially increasing effect on rusting. CAC significantly decreases chloride permeation ratio. Studies conducted showed that concrete without CAC with a chloride ratio of 3% in weight drops this ratio to 1% in concrete with CAC.
Acid Resistance
Acidic environments cause significant deformations in structures with all cement types including CAC. The resistance of concrete to acid is related with the cement amount that would neutralize acid attack. In acidic environments, the resistance of CAC mixture to acid is affected by acid’s pH value more than acid concentration. When pH value is over 4, AH3 compound released in the structure of calcium aluminate cement acts as a barrier against acids. When pH value is under 4, CAC was observed to decrease acid attacks more compared to Portland cement.
Biological Attacks
Biological attacks are especially bacterial in nature, and they are commonly seen in sewage pipes. As one of the most important issues that damage pipes, biological attacks lead to very significant repair costs if no measure is taken beforehand. The reason for biological attacks are acids produced by aerobic bacteria as waste. In sewage, anaerobic bacteria turn sulphate into sulfur. This sulfur is used by aerobic bacteria as nutrient. In turn, aerobic bacteria produce acid as waste. This situation which reduces pH level down to 2 cause serious damages on the pipes
It is possible to take measures against these attacks by making pipe coatings using calcium aluminate cement. CAC is proven to be more resistant to acid attacks compared to Portland cement.
Calcium Aluminate Cement’s Application on Pipe Coatings
Pipe prepared with CAC should be prepared by considering long-term strength. For this, attention should be paid to keeping the water/cement ratio below 0.4 (TS EN 14647). Proper mixing and vibration processes should be conducted in order to obtain a good quality CAC. Additionally, there is a risk of shrinkage crack formation during CAC application. This crack formation should be prevented by heating the concrete during curing. You can check out our other blog post Calcium Aluminate Cement: Points to Take into Consideration to learn more about points to consider while using CAC.
References
- https://cimsa.com.tr/formulhane/kalsiyum-aluminat/kalsiyum-aluminat-cimento-hakkinda-bilmeniz-gereken-her-sey/
- Ann, Ki & Cho, Chang-Geun. (2013). Corrosion Resistance of Calcium Aluminate Cement Concrete Exposed to a Chloride Environment. Materials. 7. 10.3390/ma7020887.
- https://www.researchgate.net/publication/262955184_Corrosion_Resistance_of_Calcium_Aluminate_Cement_Concrete_Exposed_to_a_Chloride_Environment
- Hewlett, P. C., & Liška, M. (2019). Lea’s chemistry of cement and concrete. Butterworth-Heinemann.
