Differences Between Slipform and Climbing Formwork

Slipform is a formwork system that rises in a controlled manner while concrete placement continues; climbing formwork, by contrast, is moved to the next pouring level after the concrete has gained sufficient strength. The fundamental difference between the two methods is whether production proceeds continuously or in lifts.

In tall reinforced-concrete structures, the right method is determined by evaluating height, geometry, concrete and reinforcement arrangement, site logistics, and construction schedule together. In projects where a long and repetitive reinforced-concrete shaft must be raised in a short time, slipform often ceases to be merely an alternative and becomes the method required by the structure.

What is slipform?

Slipform is a construction method in which the formwork moves upward in small and controlled steps by means of hydraulic jacks while concrete placement continues. Concrete is placed in layers from the upper part of the formwork; when it emerges from the bottom of the formwork, it must have reached a consistency and early-age strength sufficient to retain its own shape.

The dismantling, transporting, and re-erecting cycle performed after each pour stage does not exist in slipform. As a result, the shaft can be raised continuously with far fewer horizontal construction joints.

For this reason, slipform stands out especially in the following structures:

• Reinforced-concrete chimneys
• Single-cell or multi-cell reinforced-concrete silos
• Elevator, dispatch, and process towers
• Shafts and building cores
• Tall bridge and viaduct piers
• Long and repetitive vertical reinforced-concrete shafts

As height and repetitive production increase, the setup cost is spread over a larger volume of work, and the time advantage of continuous operation grows. In our separate article, we explain in more detail why slipform stands out in tall reinforced-concrete structures.

What geometries can be built with slipform?

Slipform is not a method limited only to circular structures with a constant diameter. When geometry, the formwork system, and the execution plan are designed together, different cross-sections can be constructed with slipform:

• Cylindrical and circular sections: Chimneys, tanks, shafts, and silo shells
• Conical sections: Reinforced-concrete chimneys whose diameter and wall thickness decrease as they rise
• Rectangular and box sections: Elevator towers, dispatch towers, and building cores
• Multi-cell sections: Groups of cells connected to each other by common walls
• Polygonal and special sections: Project-specific columns, cores, and industrial load-bearing elements
• Gradually changing sections: Expansions, contractions, and wall-thickness transitions for which an engineering solution is developed in advance

The Kaluga 8500 TPD Cement Plant project is one of the strongest examples of this variety. In the project, four cement silos each 24 meters in diameter and 70 meters in height, a raw meal silo, eight clinker distribution silos, a multi-cell silo, a rectangular elevator building, and triangular columns inside the raw meal silo were constructed with slipform. While total slipform work reached approximately 110.000 square meters, the works also continued during the winter months; on site, the temperature occasionally fell below -20 °C.

We explain in more detail the relationship between silo geometry, horizontal material pressures, and the construction method in our article on the construction of high-capacity reinforced-concrete silos.

Another example showing that a rectangular section is not an obstacle to slipform is the 83-meter-high Eti Bakır Siirt Madenköy Dispatch Tower. Although the structure, which has a large number of window openings, widens at approximately the 66th meter, it was completed using slipform through special formwork design and detailed engineering.

These examples show that applicability is determined less by the shape of the section than by the nature of the geometric change, detailed engineering, and execution experience.

What is climbing formwork?

In climbing formwork, the system remains stationary during concrete placement. After the concrete reaches the required early-age strength, the formwork is separated from the surface and moved to the next pouring level. The structure rises in predetermined lifts and pouring cycles.

Climbing formwork makes it possible to take measurements after each pour, readjust the formwork, and prepare reinforcement and embedded parts. In return, a separate cycle and a horizontal construction joint are created for each lift.

What types of climbing formwork are there?

SİBA’s climbing formwork applications can be considered in two main groups according to how the formwork unit is moved to the next level.

• Crane-lifted climbing formwork

The formwork and working platform are lifted to the next level by crane after the concrete has gained sufficient strength. It is an economical solution for low- and medium-height structures if sufficient crane capacity is available on site.

Columns of preheater buildings in cement plants are among the typical application areas of this method. Beam and slab connections, embedded parts, and the need for inspection after each pour make non-hydraulic climbing formwork more suitable in many cases.

• Hydraulic self-climbing formwork

The system rises with hydraulic cylinders by using anchors and rails on the structure. Formwork panels and platforms can be moved together; crane dependency is reduced. Concrete is still poured in lifts, and the formwork moves after the concrete has gained sufficient strength.

Hyperbolic cooling towers are highly specialized structures due to their large diameters, thin reinforced-concrete shells, and continuously changing curvatures over the height. Maintaining geometric tolerances at every elevation requires regular readjustment of the formwork surfaces and continuous measurement throughout production.

In these structures, hydraulic climbing formwork is not merely an alternative used instead of slipform; it is a controlled construction method that directly responds to the needs of hyperbolic geometry. The four hyperbolic cooling towers SİBA built at Afşin–Elbistan B Thermal Power Plant are important examples of this application.

The fact that the lifting system is hydraulic does not by itself make the method slipform. The distinguishing point is whether the formwork progresses continuously while concrete placement is ongoing or is moved to the next lift after the completed pour.

What is the difference between slipform and climbing formwork?

• Production pattern: Slipform moves continuously while concrete placement is ongoing. Climbing formwork, by contrast, is moved to the next level between completed concrete pours.

• Construction joints: In slipform, the number of horizontal construction joints is greatly reduced. In climbing formwork, a construction joint is formed between each lift and must be planned.

• Suitable structure types: Slipform stands out in long, continuous, and repetitive reinforced-concrete shafts. Climbing formwork is suitable for structures that progress in stages, include frequent connections, or require inspection after each pour.

• Geometry: Slipform can be applied in constant sections or sections that change in a pre-plannable way. Climbing formwork offers an advantage in geometries that require the formwork surfaces to be readjusted at each pouring level.

• Working pattern: Slipform requires uninterrupted and highly disciplined site organization. Climbing formwork proceeds with planned pouring cycles and allows controlled stoppages.

• Main advantage: The main advantage of slipform is speed and production continuity. Climbing formwork, on the other hand, provides geometric flexibility and the possibility of detailed control at every pouring stage.

Climbing formwork stands out in short rises and in structures that require control after each pour; slipform stands out in completing tall and continuous shafts with fewer construction joints. In very tall chimneys, high-capacity storage structures, and shafts, if the geometry is suitable, slipform is the method that should be preferred.

Why does slipform require a high level of execution discipline?

Once slipform starts, concrete, reinforcement, embedded parts, surveying, surface finishing, and material logistics proceed simultaneously. In most projects, execution is spread over 24 hours a day in shifts. A delay in concrete delivery, equipment failure, or reinforcement not being ready can affect the entire production. For this reason, supply, backup equipment, shift arrangements, measurements, and stoppage scenarios must be planned in advance.

Experience means not only operating the system; it also means being able to read the behavior of the concrete, formwork, reinforcement, and crew together and notice a deviation before it affects production.

How do concrete and reinforcement design affect slipform?

In slipform concrete, 28-day compressive strength alone is not sufficient. The concrete must place easily inside the formwork, fill the spaces between reinforcement bars, and reach enough early strength to retain its shape when it emerges from the bottom of the formwork.

Delayed setting can cause surface deterioration; excessively rapid setting can lead to sticking to the formwork and surface damage. Temperature, consistency, aggregate distribution, admixtures, and setting time must be monitored; the slipping rate must be adjusted according to the behavior of the concrete on site.

Reinforcement design is equally important. Lap splices, mechanical couplers, opening reinforcement, anchors, and embedded parts must be detailed so that the work crew can keep up with the formwork speed. Establishing a practical reinforcement arrangement without compromising structural safety is one of the fundamental conditions for achieving the target speed.

For this reason, the slipform system, the concrete mix design, and the reinforced-concrete design cannot be considered independently of one another.

How are different formwork systems used together in the same project?

Not every structure in an industrial facility requires the same formwork system. Maritza Iztok East 1 Thermal Power Plant shows this clearly. In the project, the large hyperbolic cooling tower was built with hydraulic climbing formwork, while the circular silos and two rectangular elevator towers were built with slipform.

Constructing the elevator towers with climbing formwork would have created a continuous tower crane requirement. SİBA developed a project-specific execution arrangement compatible with cranes operating from ground level so that these two structures could be built with slipform without installing a tower crane. This arrangement, which eliminated the need for a tower crane, was a special engineering solution developed for the geometry and logistical conditions of the Maritza Iztok site.

Resolving three different structure types on the same site according to their own needs shows that the right choice begins not with understanding the system, but with understanding the structure.

SİBA’s expertise in slipform, climbing, and special formwork systems includes developing the construction method together with geometry, reinforced-concrete design, site conditions, and construction schedule.

Conclusion

Slipform provides fewer construction joints, continuous production, and high vertical progress in tall, continuous, and repetitive reinforced-concrete shafts. This advantage is achieved through the right concrete and reinforcement design, project-specific formwork engineering, continuous measurement, and experienced site organization.

Climbing formwork, on the other hand, may be the more suitable solution in short rises, sudden geometry changes, and special structures such as hyperbolic cooling towers that require readjustment at every pouring level. Neither system has absolute superiority for every structure. SİBA’s approach is to determine which method is required in which part of the structure and to manage different systems within a common construction plan.

Frequently Asked Questions

In which structures is slipform used? It is used in reinforced-concrete chimneys, single-cell and multi-cell silos, towers, shafts, elevator structures, building cores, and tall bridge piers.

What is the main difference between slipform and climbing formwork? Slipform moves while concrete placement continues. Climbing formwork is moved to the next level after the concrete has gained sufficient strength.

Can slipform be used in conical and rectangular structures? Yes. With project-specific design, conical, rectangular, multi-cell, polygonal, and gradually changing sections can be executed.

Is slipform suitable for short structures? Not always. In projects where setup and organization costs cannot be spread over sufficient height, other systems may be more economical.

Why is slipform concrete specially designed? The concrete must be easy to place and must retain its shape when it emerges from the bottom of the formwork. Setting time and early-age strength must be compatible with the slipping rate.

Why does slipform require an experienced team? Concrete, reinforcement, surveying, the hydraulic system, and logistics are managed together within continuous production; an error in one operation can affect the entire system.