The construction industry continues to evolve with the adoption of advanced methods that improve speed, quality, and efficiency. One such method is the slipform construction technique, which is widely used for building vertical and horizontal concrete structures. In slipform construction, concrete is poured continuously into moving formwork. This allows construction to progress without joints, resulting in a uniform and monolithic structure while optimising labour, materials, and overall project costs.
In this blog, we explore the slipform construction technique in detail, including its core components, step-by-step construction process, different types of slipforming, along with its advantages and limitations.
What Is Slip Form Construction Method?
Slipform construction is a modern construction technique used for continuous vertical, horizontal, and other uniform cross-sectional design structures. It uses a self-supported or hydraulically lifted movable formwork system. The concrete pouring process greatly depends on the early setting characteristics of concrete and stops only when the required casting length is reached. The formwork rises in sync with the concrete setting, usually at 300 to 450 mm per hour, to ensure the material below is strong enough to support both its own weight and construction loads.
Slipform systems are often used to construct core walls, lift shafts, stair shafts, roadways, curbs, and barriers in building construction.
Key Components of a Slip Form System
The following are some of the important components of a slip form system:
Formwork
The slip form formwork system is the most essential component, made of wood, steel, or aluminium panels, based on the project’s location and requirements. These will help to withstand continuous movement and lateral pressure from fresh concrete. It involves inner and outer forms that bind together through adjustable yokes.
Yokes and Yoke Legs
Wales and yokes are horizontal and vertical supports that connect both internal and external forms firmly.
Hydraulic Jacks
These hydraulic jacks are used to raise the complete formwork in an upward or horizontal direction at a specific rate (30 to 45 cm per hour). This jacking system can be controlled electronically or manually.
Working Platforms
This component gives a safe surface for workers during pouring, reinforcement fixing, and finishing. This also includes space for materials, workers, and safety rails.
Control System
An integrated control system ensures uniform lifting and alignment throughout the process. Any uneven movement can result in cracks or distortions in the structure. The jacks can be controlled either manually or electronically (automated hydraulic control systems), allowing precise regulation of the lifting speed to synchronise with the concrete setting rate. This ensures the concrete forms quickly enough to hold shape but remains workable during placement.
The Slip Forming Process: Step-by-Step
Step 1: Foundation Preparation and Setup
Before starting the slip-forming process, a strong foundation or wall starter is built to support the slip-form rig. For steel structures, embedded plates and beams are welded during the foundation level. Vertical reinforcements are installed with appropriate lengths, and blockouts for elevator, mechanical, and electrical openings are formed prior to starting the slip form process. For silos or special structures, the slip form is set up to a specific height on the basis of the foundation design, and cranes lift reinforcements and embedded plates to the platform.
Step 2: Concrete Placement
Concrete is poured continuously into the formwork in layers commonly ranging from 100 to 250 mm. The mix must have a controlled slump value (commonly 50–80 mm) to balance workability and setting time, and vibrators are used for compaction. Real-time monitoring of concrete temperature and strength development is increasingly used to optimise timing and quality.
Step 3: Formwork Movement
Hydraulic jacks lift the shuttering incrementally (usually 10–25 mm per stroke), maintaining a controlled and uniform upward movement at a rate of about 300–450 mm per hour. Workers on the platform concurrently fix reinforcements, embed items, and pour fresh concrete. The process is continuous and seamless, eliminating the need for horizontal joints and reducing weak points.
Step 4: Curing and Finishing
As the formwork ascends, the exposed concrete surface will be cured utilising water sprays, curing compounds, or wet burlap. Minimal finishing is performed just after the concrete appears from the form. The process repeats until the structure is complete, with careful attention to curing and finishing for durability and aesthetics.
Types of Slip Forming
Generally, slip forming is classified into three main types on the basis of the direction and application: Vertical, horizontal, and Inclined slip forming
1. Vertical Slip Forming
This is the most commonly used type of slip formwork. Here, the formwork will be raised vertically through hydraulic jacks or other mechanical systems. As the formwork slowly rises, fresh concrete is continuously added at the top, and concrete at the bottom starts to harden. The rising speed of the formwork is controlled carefully so that by the time the concrete reaches the bottom of the form, it is strong enough to hold its shape without collapsing. It is used to build vertical structures, such as towers, cooling towers, chimneys, silos and core walls.
2. Horizontal Slip Forming
Here, the formwork moves horizontally (along the length of the structure). Concrete is continuously poured, vibrated, and compacted while the formwork slowly moves forward. The movement of the formwork allows the concrete to settle and take shape continuously, without stopping to rebuild forms for each section. This type of slip formwork is used to build horizontal structures, such as road pavements, bridge decks, and large concrete slabs.
3. Egg Shape Slip Form System
This is a specialised type of slip form construction technique used for constructing curved or irregularly shaped concrete structures, especially those with an egg-shaped or non-circular profile (commonly used in sewers, tunnels, and water infrastructure). Although it’s called a slip form system, its working principle is similar to a jump form; the formwork is moved upward in stages, but it is designed to handle complex curved geometries. When the structure’s circumference changes (e.g., the wall becomes wider or narrower), the system adjusts using a cantilever plate. This plate can be extended or removed to match the shape. This ensures the formwork fits perfectly as the diameter or shape transitions along the height.
4. Conical Form-work System
This is a specialized formwork system used to construct cones, tapered structures, or walls with changing thickness or shape. It is designed to automatically adjust its geometry as the structure changes from wide to narrow, or from angular to circular. These plates form the surface against which concrete is poured. They are connected using steel yoke frames (rigid support structures). Both types of plates have mechanisms that allow them to automatically adjust to the required shape as construction progresses. It is used to build structures of varying wall thickness, including tapering walls and structures whose formwork changes geometrically from angular to circular.
Advantages of the Slip Forming Technique
Continuous Construction: Due to the simultaneous placement of concrete and the movement of formworks, the site can make complete use of manpower and construction equipment without a major break.
Speed and Efficiency: In a slip form building, the formwork will be erected only once and will remain untouched until the completion of the entire structure, improving the construction speed and efficiency.
High Quality of Structure: The slip form construction method is designed specially to build the structure with great accuracy and quality. It helps to achieve essential compaction and a smooth surface finish in concrete work without cold joints or marks of forms.
Cost-Effective: Although builders need to make a large investment for the primary setup, it can save a lot of money in large projects.
Enhanced Safety and Accessibility: Since the formwork and workers do not need to move multiple times, the method offers safer working environments and allows continuous site activity.
Challenges and Limitations
Although the slip form construction technique offers many benefits, the builder also needs to consider the following major limitations:
Demands Continuous Operation: As slip forming must run day and night, any delay in the supply of concrete or equipment failure can cause defects or weak areas.
High Initial Setup Cost: The complete setup for slip-forming involves high initial charges and skilled labour to operate.
Mix Design Sensitivity: Concrete mix must have a proper workability and setting time; if not, slumping or cracking may occur.
Limited Flexibility: This technique is only suitable for structures with uniform cross-sectional designs, not for other designs with irregular structures.
Conclusion
Slip form construction is a proven construction technique that enables faster execution while maintaining dimensional accuracy and structural continuity. It is particularly suitable for structures with uniform or repetitive cross-sections, such as silos, chimneys, cores, and bridge piers. By allowing continuous concrete placement, slip forming minimizes construction joints and enhances the overall monolithic behavior of the structure. While it requires careful planning, skilled supervision, and uninterrupted operations, slip form construction remains an efficient and cost-effective solution for projects that demand consistent quality, speed, and structural integrity in modern civil engineering practice.
FAQs: Slip Form Construction Method
What is a slipform in construction?
Slipform construction is a modern construction technique used for continuous vertical, horizontal, and other uniform cross-sectional design structures.
What is the slip formwork technique?
Slip formwork uses a self-supported or hydraulically lifted moving formwork system that rises continuously as concrete is poured. The formwork typically climbs 300–450 mm per hour, matching the concrete’s early setting rate so the material below becomes strong enough to support its own weight and construction loads.
What is the difference between slipform and jumpform?
Slipform moves continuously, creating seamless tall structures, while jumpform moves in segments, suitable for multi-level buildings with joints. Slipform is ideal for uniform, high-rise structures; jumpform offers flexibility for varied designs.