Early Developments: Cement mortar lining (CML) for cast iron pipes was first introduced in the United States in the 1920s. The primary objective was to prevent internal corrosion and tuberculation in cast iron pipes, which were common in water distribution systems. The initial method involved manually applying a cement mortar coating to the interior of the pipes.
Adoption and Standardisation: As the benefits of CML became apparent, including extended pipe lifespan and improved hydraulic performance, the technique gained wider acceptance. By the 1940s, CML was widely used for new cast iron pipe installations and for rehabilitating existing pipelines. The American Water Works Association (AWWA) began to develop standards for CML, ensuring consistency and reliability in the application process.
Transition to Ductile Iron Pipes: In the 1950s, ductile iron pipes began to replace cast iron pipes due to their superior mechanical properties, including higher strength and flexibility. The cement mortar lining process was adapted for ductile iron pipes, maintaining the advantages of corrosion resistance and hydraulic efficiency. Over the following decades, CML became the standard internal coating for ductile iron pipes in water distribution systems worldwide.
Modern water supply and sewerage system. Underground pipeline works. Water supply and wastewater disposal of a residential city. Close-up of underground utilities. View from the big pipe
Stack of ductile iron pipes for water supply ready for transportation and logistics.
Process of Applying Cement Mortar Lining to Ductile Iron Pipes by Centrifugal Application
The centrifugal application process involves several detailed steps:
- Surface Preparation:
- Cleaning: The interior surface of the ductile iron pipe is thoroughly cleaned to remove any loose material, rust, or contaminants. This is typically done using abrasive cleaning.
- Inspection: The cleaned surface is inspected to ensure it is free of defects that could affect the adhesion of the cement mortar.
- Mixing Cement Mortar:
- Components: A precise mixture of cement, sand, and water is prepared. The specific ratio of these components depends on the type of cement used and the desired properties of the mortar.
- Consistency: The mixture is continuously stirred to maintain a uniform consistency and prevent setting before application.
- Centrifugal Application:
- Machine Setup: The pipe is mounted on a centrifugal machine, which is designed to spin the pipe at a controlled speed.
- Application: The cement mortar is fed into the pipe while it spins. The centrifugal force generated by the spinning action forces the mortar to spread evenly along the interior surface of the pipe.
- Uniformity: The speed of rotation and the rate of mortar feeding are carefully controlled to ensure a uniform lining thickness, typically around 3 to 4 mm, depending on the pipe’s diameter.
- Curing:
- Initial Set: After application, the pipe is allowed to rotate at a slower speed to ensure the mortar sets evenly without sagging.
- Curing Methods: The lined pipe is then cured to achieve the desired strength. Curing methods can include air curing, where the mortar is exposed to air, or water curing, where the interior is kept moist to facilitate hydration.
- Inspection: After curing, the lining is inspected for uniformity and any defects are repaired.
Autogenous Healing of Cement Mortar Linings
Autogenous healing is a natural process where minor cracks in the cement mortar lining self-repair over time. This occurs because the cement in the mortar continues to hydrate, even after the initial curing period. The ongoing hydration process produces calcium silicate hydrate, which fills in small cracks and voids, restoring the integrity of the lining.
Hazen Williams’ C Value of Cement Mortar Lined Ductile Iron Pipes According to AWWA
The Hazen Williams’ C value for cement mortar lined ductile iron pipes, as specified by the American Water Works Association (AWWA), is typically 140. This value represents the pipe’s hydraulic efficiency, with higher values indicating lower friction losses and better flow characteristics.
Establishment of Hazen Williams’ C Value by AWWA
The AWWA established the C value of 140 through a combination of laboratory testing and field data collection. Extensive tests measured flow rates and pressure drops in pipelines with cement mortar linings, leading to the conclusion that a C value of 140 accurately reflects the reduced friction and enhanced flow properties of these pipes.
Advantages of a High Hazen Williams’ C Value
- Increased Flow Capacity: A higher C value means lower frictional resistance, allowing for greater flow capacity compared to pipes with lower C values.
- Energy Efficiency: Reduced frictional resistance translates to lower energy requirements for pumping water through the pipes, leading to decreased operational costs.
- Extended Lifespan: Maintaining a high C value helps preserve the internal diameter of the pipes, reducing the likelihood of blockages and extending the service life of the pipeline.
Evaluating Hazen Williams’ C Value under Field Conditions
The Hazen Williams’ C value can be evaluated in the field by measuring the actual flow rate and pressure drop in a pipeline. This involves the following steps:
- Flow Measurement: Measure the flow rate of water through the pipeline using flow meters.
- Pressure Measurement: Measure the pressure at different points along the pipeline.
- Calculation: Use the Hazen Williams equation to calculate the C value based on the measured flow rate, pressure drop, and the internal diameter of the pipe.
Applications of Different Types of Cements for Cement Mortar Lining
1. Ordinary Portland Cement (OPC): Suitable for general water supply applications, providing adequate strength and durability.
Case Study:
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- Project: Berlin Water Supply Project, Germany.
- Details: DN 600, K9 ductile iron pipes, 15 km. in length, commissioned in 2016.
- Outcome: Successfully provided corrosion resistance and maintained hydraulic efficiency.
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2. Blast Furnace Slag Cement: Ideal for environments with moderate sulphate exposure and where reduced heat of hydration is needed.
Case Study:
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- Project: Riyadh Sewer Line Project, Saudi Arabia.
- Details: DN 700, K9 ductile iron pipes, 12 km. in length, commissioned in 2014.
- Outcome: Enhanced durability in a moderately sulphate-rich environment.
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3. Sulphate Resisting Cement (SRC): Used in highly aggressive environments with high sulphate concentrations.
Case Study:
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- Project: Barcelona Coastal Water Distribution, Spain.
- Details: DN 500, K9 ductile iron pipes, 18 km. in length, commissioned in 2017.
- Outcome: Improved resistance to sulphate attack, ensuring long-term serviceability.
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4. High Alumina Cement (HAC): Applied in environments requiring rapid strength development and high resistance to chemical and abrasive attack.
Case Study:
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- Project: Dubai Industrial Effluent Discharge, UAE.
- Details: DN 450, K9 ductile iron pipes, 10 km. in length, commissioned in 2015.
- Outcome: Quick strength development and superior chemical and abrasion resistance.
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These case studies from Europe and the Middle East highlight the practical applications of various types of cements in providing durable and efficient linings for ductile iron pipes under diverse environmental conditions.